Simulation of Solar Powered Absorption Cooling System for Buildings in Pakistan

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1 Simulation of Solar Powered Absorption Cooling System for Buildings in Pakistan A thesis submitted to The University of Manchester for the Degree of Doctor of Philosophy in the Faculty of Engineering and Physical Sciences 2016 Muhammad Asim School of Mechanical, Aerospace and Civil Engineering University of Manchester 1

2 Table of Contents Abstract... 7 Declaration... 8 Copyright Statement... 9 Acknowledgement List of Publications List of Tables List of Figures Abbreviations and Symbols Chapter 1: Introduction Background Energy World Energy Pakistan and Energy Electricity Generation History Current Status and Future Plans Impact of the Energy Crisis Conclusion Aims and Objective Structure of the Thesis Chapter 2: Renewable Energy Resources in Pakistan Introduction Renewable Energy Potential Wind Energy Hydroelectric Energy Solar Energy Solar Energy Systems and Pakistan Current Status of Solar Energy Application Photovoltaics Solar Thermal Institutional Infrastructure Pakistan Council for Renewable Energy Technologies Alternative Energy Development Board (AEDB) Educational Institutes Pakistan Engineering Council (PEC)

3 2.6 Doctoral Research on Solar Energy Potential in Pakistan Conclusion Chapter 3: Pakistan s Climate and Buildings Energy Introduction Geography of Pakistan Population Climate of Pakistan Temperature and Humidity Heat Index and Pakistan Thermal Extremes in Pakistan Comfort Temperature Standard Comfort Temperature Adaptive Thermal Comfort Building Energy in Pakistan Energy Efficient Buildings: Building Energy Code of Pakistan Benefits of Introducing Building Energy Code in Pakistan Case Study of Energy Efficiency Improvement in Existing Houses in Pakistan Results of the Case Study Findings on the Basis of Energy Efficient Housing Reports Conclusion Chapter 4: Solar Cooling Systems Introduction Solar Electric Cooling Solar Thermal Cooling History of Solar Thermal Cooling Systems Development World Solar Thermal Cooling Status 2014 and IEA Road Map Solar Thermal Cooling Systems Solar Thermal Collectors Stationary Collectors: Concentrating Solar Power (CSP) Comparison of Thermal Collectors Thermal Cooling Systems Absorption System Adsorption System

4 4.5.3 Solid and Liquid Desiccant Cooling System Ejector System Solar Cooling for Hot Climates Solar Cooling System Research for Pakistan and India Conclusion Chapter 5: Methodology Introduction Experimental Study Limitations of Experimental Study Simulation Study Limitations of Simulation Study Solar Energy System Simulation Programs WATSUN Polysun f-chart Method and Program Building Energy Simulation Programs Energy Plus Integrated Environment Solutions (IES) Virtual Environment (VE) TRNSYS TRNSYS Validity Meteorological Data for Simulation Program Weather Data Types Pakistan Weather Data Conclusion Methodology Weather Data Chapter 6: Building Model and Simulation Introduction Building Model TRNSYS Simulation Studio The Building s Initial Parameters Zones Thermal and Material Properties Building Model Initial Simulation Results Internal Gains and Infiltration Addition Building Model Modification

5 6.5.2 Modified Building Model Results Building Envelope Conduction Solar Cooling System Initial Parameters Calculations Chiller Cooling Capacity Solar Collector Calculation Cooling Systems Reference Model Solar Cooling System Simulation Solar Cooling Process Evacuated Tube Collector Hot Water Storage Tank Absorption Chiller Cooling Coil Cooling Tower Pumps Fan Pipes Weather Data Reading and Processing Controllers Solar Cooling Simulation System Conclusion Chapter 7: Results and Discussion Introduction Evacuated Collector Energy Yield Evacuated Tube Collector Efficiency Room Cooling Load Room Air Temperature Storage Tank Heat Loss Storage Tank Internal Energy Change Pipe Heat Loss The Solar Cooling System s Electrical Energy Consumption Cooling Tower Absorption Chiller Validation of Simulated Results Simulation Tool Validation Simulation Inputs Validation

6 Simulation Results Validation Parametric Analysis Collector Area and Flow Storage Tank Volume: Chilled Water Outlet Temperature Conclusion Chapter 8: Conclusions and Recommendations Summary General Discussion Main Finding: Feasibility of Solar Thermal Cooling of a Building in Pakistan Building Model and Energy Methodology Solar Cooling System and Operational Parameters System Optimisation Results Validation and Sensitivity Analysis Conclusions and Recommendations Addition to Knowledge Conclusions Recommendations Energy and Solar Energy Data Building Energy and Efficiency Solar Thermal Cooling Further Studies Building Energy and Efficiency Solar Cooling System References 222 Appendices 243 Appendix A: Annual and Monthly Maximum Average Temperature and Relative Humidity for District Cities of Pakistan Appendix B: World and Pakistan Solar Energy Maps with Solar Insolation for District Cities of Pakistan Appendix C: Equipment Operation Parameters Appendix D: System Heat Balance

7 Abstract This research investigates the potential of a solar powered cooling system for single family houses in Pakistan. The system comprises water heating evacuated tube solar collectors, a hot water storage tank, and an absorption chiller. A literature review was carried out covering: Energy situation, climate, and renewable energy potential in Pakistan; Energy and thermal comfort in buildings, particularly for hot climates; Solar collectors and solar cooling systems, particularly for hot climates; Dynamic thermal simulation and weather data for solar energy systems and buildings. It was found that Pakistan is short of energy and that there is a great need to cool buildings. Renewable energy cooling systems are, therefore, of interest. The system described above was selected, as it was found that solar energy is abundant in Pakistan when cooling is required; thermal systems can be more economical than photovoltaics for hot climates and suitable components (collectors, absorption chillers, etc.) are commercially available. The TRNSYS dynamic thermal simulation program was selected as the main research tool, as it has been tested for solar energy and building applications by many researchers and suitable experimental facilities were not available. A simple typical building in Pakistan with a solar cooling system was simulated. Optimum values for key parameters were found by repeated simulations. It was concluded that the system would be able to provide cooling when required without an auxiliary heat source, and that an evacuated tube collector with a gross area of 12 m 2, a collector flow rate of 165 kg/h, and a storage tank volume of 2 m 3 would provide satisfactory performance for a 3.52 kw absorption chiller integrated with 42m 3 single room. The results were in good agreement with published results from other researchers. Sensitivity analysis was carried out for the collector area, collector flow rate and storage tank size. It was found that varying the collector area had the largest effect on system performance, followed by varying the storage tank volume. Varying the collector flow rate had the smallest effect. It is recommended that solar cooling systems should be considered for Pakistan, and that further research should be carried out into reducing building cooling loads, using surplus heat for other loads, improving the performance of the proposed solar cooling system, and comparing it with other systems such as photovoltaics. 7

8 Declaration No portion of the work referred to in the thesis has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning. 8

9 Copyright Statement i. The author of this thesis (including any appendices and/or schedules to this thesis) owns certain copyright or related rights in it (the Copyright ) and s/he has given The University of Manchester certain rights to use such Copyright, including for administrative purposes. ii. Copies of this thesis, either in full or in extracts and whether in hard or electronic copy, may be made only in accordance with the Copyright, Designs and Patents Act 1988 (as amended) and regulations issued under it or, where appropriate, in accordance with licensing agreements which the University has from time to time. This page must form part of any such copies made. iii. The ownership of certain Copyright, patents, designs, trademarks and other intellectual property (the Intellectual Property ) and any reproductions of copyright works in the thesis, for example graphs and tables ( Reproductions ), which may be described in this thesis, may not be owned by the author and may be owned by third parties. Such Intellectual Property and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property and/or Reproductions. iv. Further information on the conditions under which disclosure, publication and commercialisation of this thesis, the Copyright and any Intellectual Property and/or Reproductions described in it may take place is available in the University IP Policy (see in any relevant Thesis restriction declarations deposited in the University Library, The University Library s regulations (see and in The University s policy on Presentation of Theses. 9

10 Acknowledgement All praises to Almighty Allah who bestowed upon me the capabilities to complete this work. I extend my sincerest thanks to my praise worthy supervisor Dr. Jonathan Dewsbury for his precious time, valuable guidance, continuous support, constructive criticism, motivations and incredible encouragements. Finally, I am grateful to all of my family members who always support and pray for my success. It is all because of their encouragements, prayers and support that enabled a successful completion of this endeavor. I would also like to thank all of my colleagues and friends for their continuous support. Last but not least I am thankful to the University of Engineering and Technology, Lahore, Pakistan for supporting me financially to carry on this research work 10

11 List of Publications 1. Muhammad Asim, Jonathan Dewsbury, Safwan Kanan,. TRNSYS Simulation of a Solar Cooling System for the Hot Climate of Pakistan in SHC 2015, International Conference on Solar Heating and Cooling for Buildings and Industry December, 2015, Turkey: Elsevier. (No publication details) 2. Safwan Kanan, Jonathan Dewsbury, Gregory F.Lane-Serff, Muhammad Asim,. The Effect of Ground Conditions under a Solar Pond on the Performance of a Solar Air- Conditioning System. in SHC 2015, International Conference on Solar Heating and Cooling for Buildings and Industry December Turkey: Elsevier. (No Publication details) 3. Safwan Kanan, Muhammad Asim, Rohan Kumar. A Simple Salt Gradient Solar Pond Model for Lahore.Technical Journal, UET Taxila Pakistan, (Accepted, No Publication details) 11

12 List of Tables Table 1-1: Latest details of future electricity generation projects by fuel type Table 2-1: Hydroelectric energy potential in Pakistan Table 2-2: Solar energy application and types of collector used Table 3-1: Heat Index and its effects Table 3-2: Climate zones of Pakistan for comfortable temperature Table 3-3: Designed indoor (T d ) globe temperature for selected cities Table 3-4: Potential energy conservation areas Table 4-1: History of solar thermal cooling development Table 5-1: Comparison of differences between experimental & TRNSYS simulation data 128 Table 6-1: Properties of materials assigned to walls and roof surfaces Table 6-2: Room envelope heat conduction calculations Table 6-3: COP of absorption chillers Table 6-4: Pumps power and flow rates Table 6-5: Pipes size and flow rates Table 6-6: Collector pump controller inputs Table 7-1: Comparison of simulated vs published results.197 Table 7-2: Summary of parameters used by researcher for parametric analysis 202 Table 7-3: Sensitivity of storage tank volume on tank heat loss and internal energy and collector efficiency

13 List of Figures Figure 1-1: Global energy source consumption growth % from 2012 to Figure 1-2: Global energy source consumption growth from Figure 1-3: World primary energy demand projection Figure 1-4: Pakistan s primary energy consumption by fuel Figure 1-5: Electricity generation by fuel type Figure 1-6: Electricity demand and supply Figure 1-7: Electricity consumption by economic groups Figure 1-8: Activities most affected by power outage Figure 2-1: Wind energy potential of Pakistan Figure 2-2: Solar energy spectrum distribution Figure 2-3: Solar energy balance on earth Figure 2-4: Solar insolation over Pakistan Figure 2-5: PV and solar thermal power systems power range and global irradiation Figure 2-6: Regions of world appropriate for solar thermal power plants Figure 3-1: Geography of Pakistan Figure 3-2: Administrative areas of Pakistan Figure 3-3: Area distribution of Pakistan Figure 3-4: Population distribution of Pakistan Figure 3-5: Population density in Figure 3-6: Pakistan annual mean daily temperature Figure 3-7: Pakistan normal mean heat index distribution Figure 3-8: Areas of moderate and severe heat wave frequency in South Asia Figure 3-9: ASHRAE standard comfort temperature zone Figure 3-10: Acceptable temperature ranges for naturally conditioned spaces ASHRAE 55 rev Figure 3-11: 30 years average monthly mean daily temperatures Figure 3-12: Climate zone map of Pakistan.68 Figure 3-13: Outside air and inside temperature with solution comparison during day time..71 Figure 3-14: Comparison of outside air and inside temperature with solutions at midnight...72 Figure 3-15: Initial cost of different solutions Figure 3-16: 10 years cost of different solutions Figure 4-1: Schematic overview of solar electric cooling system

14 Figure 4-2: Schematic diagram of vapour compression refrigeration system Figure 4-3: Solar light spectrum used in a PV system Figure 4-4: Overview of thermal cooling system Figure 4-5: Solar energy collector s application Figure 4-6: Types of solar thermal collectors Figure 4-7: Construction of flat plate collector Figure 4-8: Schematic diagram of compound parabolic collector Figure 4-9: Schematic diagram of evacuated tube collector Figure 4-10: Linear Fresnel reflector (Left) & compact linear Fresnel reflector (Right) Figure 4-11: Schematic overview of power tower (central receiver system) Figure 4-12: Schematic of a parabolic trough collector Figure 4-13: Parabolic trough collector tracking mechanism Figure 4-14: Schematic of a parabolic dish Figure 4-15: Yearly thermal performance of stationary and tracking collectors Figure 4-16: Schematic overview of solar absorption cooling system Figure 4-17: Schematic diagram of solar adsorption system Figure 4-18: Desiccant cooling process Figure 4-19: Principle of desiccant cooling Figure 4-20: An illustration of solar assisted solid desiccant cooling system Figure 4-21: A Solar assisted liquid desiccant cooling system Figure 4-22: Schematic view of solar ejector cooling system Figure 5-1: Building model and low zero carbon technologies analysis Figure 5-2: Model diagram in TRNSYS simulation studio view Figure 5-3: TRNSYS simulation result plot overview Figure 5-4: TRNBuild wall and windows types and area selection Figure 5-5: TRNBuild wall type manager with construction materials Figure 5-6: Climatic comparison between Lahore and Amritsar Figure 5-7: Amritsar daily mean temperature (EPW vs WMO) Figure 5-8: Lahore temperature comparison (WMO vs TMY2) Figure 5-9: Pakistan s cities maximum average temperature from TMY Figure 5-10: Pakistan s cities average relative humidity from TMY Figure 5-11: Pakistan s cities average global horizontal radiation from TMY Figure 6-1: Typical single storey house in urban Punjab Figure 6-2: Typical single storey house in rural Punjab

15 Figure 6-3: Model building location.141 Figure 6-4: Trnsys-3d two zone (room) model back and top views Figure 6-5: Trnsys-3d two zone (room) model front view Figure 6-6: Import of Tnsys3d model into simulation studio step Figure 6-7: Import of Trnsys3d model step Figure 6-8: After import of Tnsys3d model final window in simulation studio Figure 6-9: Parameters for heat transfer co-efficients Figure 6-10: Standard and user defined inputs Figure 6-11: Building outputs Figure 6-12: Room1volume, surface and areas calculated by TRNSYS Figure 6-13: Properties of material assigned to external roofs Figure 6-14: Properties of windows assigned Figure 6-15: Radiation and geometry modes Figure 6-16: Initial result, room 1 and room2 air temperatures Figure 6-17: Ambient and room 1 temperature comparison Figure 6-18: Ambient and room 2 temperature comparison Figure 6-19: Room1 air temperature with initial gain, infiltration, and ventilation Figure 6-20: ASHRAE standard materials assigned to walls, roof and floor Figure 6-21: ASHRAE standard properties of windows Figure 6-22: Room 1 temperature after assigning walls and windows materials Figure 6-23: Solar cooling system Figure 6-24: Evacuated tube collector TYPE 71 efficiency curve for I =1000 W/m Figure 6-25: Collector solar data input Figure 6-26: Operation of hot water storage tank Figure 6-27: Tank inlet and outlet connections Figure 6-28: Absorption chiller input and out connections Figure 6-29: Cooling coil connections Figure 6-30: Auxiliary cooler connections Figure 6-31: Pumps connection Figure 6-32: Fan connections Figure 6-33: Pipes connections Figure 6-34: Weather data processor connections Figure 6-35: Collector pump controller connection Figure 6-36: Room air fan controller connections

16 Figure 6-37: Complete process diagram of solar cooling system Figure 7-1: Solar collector monthly yield (kwh) Figure 7-2: Collector monthly and annual efficiency (%) Figure 7-3: Room monthly cooling load and solar energy availability (kwh) Figure 7-4: Ambient (Blue) and room (Red) temperature comparison ( C) Figure 7-5: Tank heat loss (kwh) Figure 7-6: Tank heat loss as percentage of energy collected (%) Figure 7-7: Ambient and tank temperature with solar radiation available in July-August 190 Figure 7-8: Tank internal energy change (kwh) Figure 7-9: Pipes heat loss to and from ambient air (kwh) Figure 7-10: Monthly Electrical Energy Load (kwh) Figure 7-11: Auxiliary cooler heat rejected (kwh) Figure 7-12: Chiller actual and rated COP Figure 7-13: Chilled water outlet temperature with the TRNSYS provided data file Figure 7-14: Chilled water outlet temperature with referenced data file Figure 7-15: Energy balance of solar cooling system Figure 7-16: Annual input and output energy distribution.200 Figure 7-17: Sensitivity of collector area and annual energy collected and efficiency.204 Figure 7-18: Sensitivity of collector flow rate and annual energy collected and efficiency..204 Figure 7-19: Variation of maximum chilled water temperature and number of hours above set point with collector area.206 Figure 7-20: Variation of maximum chilled water temperature and number of hours above set point with tank storage volume..207 Figure 7-21: Sensitivity of storage tank volume and maximum chilled water temperature and number of hours above set point

17 Abbreviations and Symbols $ Dollar Pound Sterling Coefficient of Transmittance Euro µm Micro metre 3D Three Dimensional A Area ACH Air changes per hour AEDB Alternative Energy Development Board ASHRAE American Society of Heating Refrigerating and Air-Conditioning Engineers a-si Amorphous Silicon a-sic Amorphous Silicon Carbide a-sige Amorphous Silicon Germanium a-sin Amorphous Silicon-Nitride BECP Building Energy Code of Pakistan BEE Bureau of Energy Efficiency (India) BLAST Building Load Analysis And System Thermodynamics BP British Petroleum CDA Capital development Authority (Islamabad) CdS Cadmium Sulphide CdTe Cadmium Telluride CH4 Methane gas CIBSE Chartered Institution for Building Services Engineers CIGS Copper Indium Gallium Selenide CIS Copper Indium Selenide CLFR Compact Linear Fresnel Reflectors CNG Compressed Natural Gas CO 2 Carbon dioxide Coll. Collector COP Coefficient of Performance C P Specific Heat at Constant Pressure CPC Compound Parabolic Collectors CPV Concentrating Photo Voltaic CRS Central Receiver System c-si Crystalline Silicon CSP Concentrating Solar Power CSU Colorado State University 17

18 CTZ California Climate Zones Cu 2 S Cuprous sulphide CuInSe 2 Copper Indium Diselenide CWEC Canadian Weather for Energy Calculation DC Direct current DDY Design Day Data DHW Domestic hot water DNI Direct Normal Irradiation DOE Department of Energy (US) DSG Direct Steam Generation DSSC Dye-sensitised solar cell E East ECBC Energy conservation building code(india) EME College of Electrical and Mechanical Engineering (Pakistan) ENERCON National Energy Conservation Centre (Pakistan) EPW Energy Plus Weather ESTIF European Solar Thermal Industry Federation ETC Evacuated Tube Collectors ETP Energy Technology Prospective FATA Federally Administrated Tribal Area FPC Flat Plate Collector GaAs Gallium Arsenide GBP British Pound Sterling Gt Giga ton GUI Graphic User Interface g-value Solar energy transmittance of transparent material (glass) (%) GW Giga Watt GWh Giga watt hour GW p Giga Watt Peak GW th Giga Watt Thermal H 2 O Water HI Heat Index hr Hour HVAC Heating Ventilation and Air Conditioning HW Heat Wave HX Heat exchanger I Incident solar Insolation IAM Incidence Angle Modifiers ID Identification IEA International Energy Agency IES Integrated Environment Solution 18

19 In ISO I T IWEC J k K kg kj km KPK KSK kw kw C kwh LED LEED LFR LiBr LPG m m 2 m 3 MENR m h MJ m L Mt MW MWh MW P N N 2 O NASA NCDC NED NEPRA NESPAK NGO NH 3 Inlet International organisation for standardisation Total incident solar Insolation International Weather for Energy Calculation Joule Kilo Kelvin Kilo gram Kilo joule Kilo metre Khyber Pakhtun Khwa (Pakistan) Kala Shah Kaku (Lahore) Kilo Watt Kilo Watt cooling Kilo Watt Hour Light Emitting Diode Leadership in Energy and Environmental Design Linear Fresnel Reflectors Lithium Bromide Liquefied Petroleum Gas Mass flow rate / metre Square metre Cubic metre Ministry of energy and natural resources (Turkey) Fluid flow rate to and from heat source Mega Joule Fluid flow rate to and from load source Mega ton (metric) Mega Watt Mega Watt Hour Mega Watt Peak North Nitrous Oxide National Aeronautics and Space Administration National Climatic Data Centre Nadirshaw Edulji Dinshaw (Pakistan) National Electric Power Regulatory Authority (Pakistan) National Engineering Services Pakistan Non-Governmental Organisation Ammonia 19

20 NIST nm NOAA NO x NREL NSRDB NUST OCA Out Pa PCAT PCRET PCSIR PEC PMD PMISP PMV PPD PSVEP PV Qc Qe Qg Q S Qu RC R-value SHGC SHS SO x SRCC SSE SWH Ta Tamb T c Tc T d TEG T env TESS National Institute of silicon Technology (Pakistan) Nano metre National Oceanic and Atmospheric Administration Nitrogen Oxides National Renewable Energy Laboratory National solar radiation date base (US) National University of Science and Technology (Islamabad) Optical Coupling Agent Outlet Pascal Pakistan council for appropriate technologies Pakistan Council for Renewable Energy Technologies Pakistan Council for Scientific and Industrial Research Pakistan Engineering Council Pakistan Meteorological Department Prime Minister s Initiative for Solar Power (Pakistan) Predicted mean vote Predicted percentage of dissatisfaction Parliamentarian Village Electrification Program (Pakistan) Photo Voltaic Condenser heat rate Evaporator heat rate Generator heat rate Solar energy incident on panel Useful heat energy rate Reinforced Concrete Thermal resistance of insulator Solar Heat Gain Coefficient Solar Home System Sulphur Oxides Solar Rating and Certification Commission Surface meteorology and solar energy (NASA) Solar Water Heating Air temperature Ambient temperature Comfortable Temperature Collector temperature Design Indoor Temperature Tri-Ethylene Glycol Environment temperature Thermal Energy Systems Specialists 20

21 T g T H T i T IN TiO 2 T L T MAX TMY T O T OLT TR T r TRNSYS TRY TWh TWh th UAE UET UK UN UNEP USA USAID USD U-value VE W w WMO w PV w T γ I γ o ΔT ΔT H ΔT L η cool ηsol.cool θc μc-si Indoor Globe Temperature Upper Input temperature Indoor Temperature Temperature for high limit monitoring Titanium Dioxide Lower Input temperature Maximum Input temperature Typical Meteorological Year Operative temperature Outdoor Long Term Temperature Ton of Refrigeration Mean radiant temperature TRaNsient SYstem Simulation Test reference year Tera Watt Hour Terra Watt Hour Thermal United Arab Emirates University of Engineering and Technology (Pakistan) United Kingdom United Nation United Nation Environment Program United states of America United States Agency for International Development United States Dollar Overall heat transfer co-efficient (W/m 2.K) Virtual Environment Watt Work rate World Meteorological Organization Photo voltaic work rate Total work rate Input control function Output control function Change in Temperature Upper dead band temperature difference Lower dead band temperature difference Cooling efficiency Solar cooling efficiency Acceptance Angle Microcrystalline Silicon 21

22 Chapter 1: Introduction 1.1 Background Titled Solar Cooling, although this study has been done for the climatic conditions of Lahore, Pakistan, it is expected that the results will also be useful for other countries in the south Asia region which have similar climate and building construction styles. The main aim of this work (as explained in more detail in later sections of this chapter) is to investigate the potential and operational feasibility of a solar cooling system for buildings in the context of Pakistan s climate and location. The thermal performance of a solar collector, solar energy availability, building cooling load profile with existing construction materials and performance of an absorption chiller were investigated. This chapter gives brief information about world energy consumption and a background to the energy crisis in Pakistan, current status and future electricity generation plans to overcome the energy crisis through the contribution of renewable energy in primary energy consumption. The future electricity demand and impact of the energy crisis on domestic users is also presented. At the end of the chapter, detailed aims and objectives, as well as the structure of the thesis, are given. 1.2 Energy Energy is an important commodity for continued human development and economic growth. The availability of sufficient, affordable energy is a vital key to eradicating poverty, improving human welfare and raising living standards worldwide. Historically, fossil fuels have been the main source of energy supply and have contributed a major part in fulfilling human energy demands. Renewable energy sources have also been important for humans from early times. For example, biomass has been used for heating and cooking, and wind energy for transport and, later, for electricity production [1, 2]. The current sources of energy, with a major contribution from fossil fuels, have three main concerns: depletion of resources, environmental impacts and the security of energy supply. The increasing demand and limited reserves have led to the exploration of alternative sources of energy. The continuous consumption of fossil fuels has had various impacts on the natural environment. The global implications include global warming and local impacts, such as an effect on human health and the ecology. Onshore oil and gas drilling, exploration and 22

23 % Change production waste (fluids and solids) have contaminated the surroundings. Coal mining and exploration has resulted in land degradation through mine fires and the impact of mining on forest areas is of particular concern. Nuclear energy is linked to real threats of radioactive emissions and is also of concern due to its possible association with military use, the impact of mining nuclear fuel and nuclear waste hazards. Renewable energy sources (biomass, solar, wind, geothermal and hydropower) are cleaner energy sources. Renewable energy sources have the potential to provide energy with zero or almost zero emissions of air pollutants and greenhouse gases [1, 2]. 1.3 World Energy The BP Statistical Review of World Energy 2014 reveals that the world s primary energy consumption grew by 2.3% in 2013 compared to the previous year. As such, the global oil, gas, and coal reserves at the end of 2013 are predicted to last 53.3, 55.1 and 113 years, respectively, at current production rates. The affirmed reserves are quantities that geological and engineering information indicate, with reasonable certainty, can be recovered in the future. The global consumption growth rate (%) from year 2012 to 2013, of oil, gas and other sources is shown in Figure 1-1[3] Global energy source consumption growth rate from 2012 to oil Gas Coal Nuclear Hydel Renewables Figure 1-1: Global energy source consumption growth % from 2012 to 2013 [3] Figure 1-1 shows that renewables are growing annually at a higher rate than other fuels. Renewables now account for 2.7% of global energy consumption, up from 0.8% a decade ago[3]. 23

24 Annual average growth (%) According to BP s Energy Outlook 2035, published in January 2014, world primary energy demand is expected to increase by 41% from 2012 to 2035, with an annual average growth rate of 1.5%. The major consumer is expected to be the residential sector, in the form of electricity consumption. Global CO 2 emissions from energy use are growing at 1.1% annually and are expected to double from 1990 to 2035[4]. The projected global annual average consumption growth rate (%) of different fuels from is shown in Figure 1-2. Figure 1-2 shows that, by 2035, the annual growth rate of renewables will be higher than all other fuels. 7 Global energy source consumption average growth rate projection oil Gas Coal Nuclear Hydel Renewables Figure 1-2: Global energy source consumption growth from [4] According to the International Energy Agency s (IEA) World Energy Outlook 2013, world energy demand will increase by 33% by 2035 with reference to year There will be an increase in energy source consumption of oil by 13%, coal by 17%, natural gas by 48%, nuclear by 66% and renewables by 77%. In the buildings sector, energy use will grow at an average rate of 1% per year till 2035 and households will account for almost 60% of the increase in energy demand. The increase will be in the form of electricity used for lighting, space heating and cooling[5]. Energy-related CO 2 emission rise will be 20% by 2035, and most increase in energy will be in electricity demand. About half of the net increase in electricity will be generated by renewables and the total share of renewables in electricity generation will be about 30% by The share of renewables in primary energy will be increased to 18% by 2035 under the new policies scenario, as shown in Figure 1-3[5]. 24

25 Energy Demand (TWh) World primary energy demand Other Renewables Bioenegy Hydro Nuclear Gas Oil Coal New Policies 2035 Current Policies 2035 Figure 1-3: World primary energy demand projection [5] Although this is a significant proportion, it will take many years for renewables to surpass the proportion of fossil-based energy under current policy. The new policies scenario takes account of policy commitments to reduce greenhouse gas emissions. Solar energy is an emerging source of energy with worldwide potential. It is seen to have the potential to contribute a major proportion of renewable energy sources in the future. Solar energy is not a new idea and has been implemented effectively for many years. Solar energy applications, like domestic hot water and space heating, have proven economic and useful compared to conventional energy systems for these purposes [6]. Solar energy has many benefits: it cannot be monopolised by a few countries, as with fossil fuels, for example. It has no conversion processes producing emissions and can be easily integrated into buildings. Solar energy could be the largest source of energy by 2050 [6]. 1.4 Pakistan and Energy The availability of energy in any country is linked with its economic and social strength. Pakistan is an energy-deficient country, wherein the majority of the population has no provision of basic energy facilities such as electricity and gas [2]. Pakistan is also facing 25

26 serious threats due to global warming. Under the United Nations Environment Program (UNEP) [2], Pakistan s thousand kilometre-long coasts are classified as particularly vulnerable to the effects of sea level rise. According to BP s Statistical Energy Review 2014, the primary energy consumption of Pakistan during 2013 was TWh, whereas for the UK it was 2360 TWh for the same duration. Pakistan s CO 2 emission was Mt in The CO 2 emission was tonnes per capita in 2010 [3]. The primary energy consumption per capita was 5.60 MWh in 2011, whereas, in developed countries like the UK, it was MWh for the same period [7]. Pakistan s CO 2 emission of electricity generation and transmission is kg/kWh and kg/kWh, respectively. Electricity consumed emissions are g/kWh and g/kWh for CH 4 and N 2 O, respectively[8]. The primary energy consumption by source for year is shown in Figure 1-2. It is clear that most of the energy consumed is from fossil fuels and the contribution of renewables other than hydroelectric is negligible (less than 0.05% of total)[3]. Biomass consumption is excluded, because reliable statistics of its use are not available. Pakistan's primary energy consumption by fuel (2013) GAS OIL HYDRO ELECTRIC COAL NUCLEAR 6% 2% 10% 32% 50% Figure 1-4: Pakistan s primary energy consumption by fuel 2013[3]. Figure 1-4 shows that most of the primary energy is shared by oil, coal, and natural gas, but Pakistan has few reserves of fossil fuel. Pakistan had oil and natural gas reserves of 342 million barrels and 803 billion m 3, respectively, as of the end of December These reserves will last for 15 and 27 years respectively under the current production rate[9]. Oil, coal, and gas are imported to meet requirements and, during the year , 66% oil and 26

27 45% coal of total consumption were imported. The natural gas domestic production is 66% of total consumption and different plans are proposed for the import of natural gas to meet demand [10] Electricity Generation History At independence in 1947, Pakistan had 60MW of electricity generation capacity. Electricity supply has fallen short of demand due to rapid industrialisation, population growth, and urbanisation. The supply is often unable to meet demand due to poor governance, weak institutions, incompatible power tariffs and poor load management and future planning. The national grid system still supplies electricity to only 65% of the total population. The electricity supply system is not reliable to maintain a consistent supply to the consumers[11]. The first major electricity shortage crisis was triggered in 1994, when the country was facing a shortage of 2000 MW between peak demand and supply. Under the new power policy in 1994, an attractive incentive was given to electricity generation companies to overcome the demand and supply gap. This policy was successful and the country s generation was more than demand till the end of 2006[12]. In 2005, the planning commission of Pakistan announced a plan vision for 2030 with key targets for future energy of the country. Considering energy as a key factor for the development and sustainability of the country, a detailed plan was made to make Pakistan self-sufficient in power and reduce its dependence on a single source, especially imported fossil fuels. This was the first policy to utilise renewable energy technologies (other than hydroelectric power) in Pakistan to provide an energy mix in the national energy supply system. It was estimated to add a minimum of 9,700 MW (5%) of total electricity generation capacity from renewables (hydroelectric, wind and solar) by 2030 [13, 14]. The current power policy was announced in 2013, aiming to develop highly efficient power generation, transmission, and distribution in a sustainable and economical manner. Special consideration was given to renewable energy utilisation and wind and solar energy-based electricity generation projects were initiated: 3432 MW of wind power projects are planned to be completed by the end of 2016; 341MW P of solar energy projects are planned to be completed by the end of 2015 and hydroelectric power projects of total capacity 3514 MW are planned to be completed by the end of 2017 [15]. 27

28 1.4.2 Current Status and Future Plans According to BP s Statistical Energy Review 2014, Pakistan s total electricity generation was TWh in 2006 and TWh in 2013 [3]. More than 30% of the population do not have access to electricity[5]. Due to poor implementation of energy policy, poor management and distribution losses, Pakistan is in a situation where electricity demand has been greater than supply since 2007[12]. In Pakistan, electricity transmission and distribution losses are very high, ranging from 9.5% to 34.3%. It is less in urban areas and higher, due to electricity theft and nonpayments of bills, in Sindh, Balochistan and FATA areas [11, 16]. The electricity generation growth rate was less than the growth rate of consumption in the last decade. This demand and supply gap was about 1912 MW in 2007 and 6518MW in 2012, equivalent to 29% of total demand in summer peak hours[17]. This gap resulted in power supply cuts of about 8-10 hours and hours per day in the winter and summer seasons, respectively [5, 15, 18]. The electricity power generation by fuel type in Pakistan is shown in Figure 1-5[19]. Electricity generation by fuel type (2015) Nuclear 3% Wind 1% Hydroelectric 33% Fossil fuels 63% Figure 1-5: Electricity generation by fuel type 2015[19] The details of electricity generation future projects are shown in Table

29 Table 1-1: Latest details of future electricity generation projects by fuel type [19] Completion Year Fuel Capacity (MW) Gas 3147 Oil 425 Solar 1000 Hydroelectric 4222 Coal 7560 Nuclear 600 Wind 650 Total/ Fossil fuels 17604/11132 Figure 1-5 shows that, currently, most of the electricity is generated by fossil fuels and the contribution of renewables is considerably less, other than hydroelectric. Table 1-1 shows the future electricity generation projects, including wind, solar and hydroelectric. By the year 2018, the contribution of renewables will be sizeable, but the major contribution will still be by fossil fuels. According to the National Electric Power Regulatory Authority (NEPRA) 2014 report, under current policy and planning, the projected electricity peak demand and supply in Pakistan to year 2019 is shown in Figure 1-6[20]. Actual ( ) and projected ( ) electricity peak demand and supply Supply (MW) Demand (MW) Figure 1-6: Electricity demand and supply [20] 29

30 Figure 1-6 shows that demand is continuing to exceed supply, despite supply being approximately double from 2012 to The annual average growth rate of electricity consumption is 14.5%, which has been more than supply since 2007 [20] Impact of the Energy Crisis In Pakistan, the domestic sector is the major consumer of electricity and the current crisis has a direct impact on domestic consumers. Electricity consumption share by different sectors in the country for year is shown in Figure 1-7. Electricity consumption by economic group Others, 5.5% Public Lighting, 0.5% Agriculture, 11.4% Domestic, 46.9% Industrial, 28.9% Commercial, 6.7% Figure 1-7: Electricity consumption by economic groups [16] The supply of natural gas also falls in the winter season, causing an energy shortage for domestic heating and cooking facilities. Natural gas supplies also fall short due to use in Compressed Natural Gas (CNG) based motor vehicles, urea production, power generation, and textile industry consumption. In the summer season, energy demand increases, mainly due to air conditioning, household appliances (refrigeration and deep freezers) and tube wells (irrigation water for rice crop) [11]. The deficiency of energy supply has affected not only people s psychology and health, but it has also severely damaged economic activities across the country[21]. High level stress and 30

31 sleep deprivation among people are also observed in the population, as their daily schedule is heavily influenced by planned power outage. An increase in the crime rate is also associated with planned and unplanned power outage. The other impacts include closure of healthcare facilities and other services, which disrupts the everyday life of millions [21]. A study carried out in 2013 showed that the overall power outage cost to urban areas domestic consumers alone was estimated at GBP 1.30 billion per annum. The most affected households belong to the income group from GBP per month; those have no other alternative supply system. This group constitutes 57% of the country total urban population. The activities most disturbed by power outage, according to Pasha s classification, are shown in Figure 1-8[17]. Activities most affected by power outage Cooling/Heating 2% 2% Studies (home work )of childern 8% Preparation for work/school 25% Regular household work(cooking,cleaning) 13% water shortage income generating activities (home based) Social activities 15% 18% Entertainment, Leisure 17% Figure1-8: Activities most affected by power outage [17] The most important activity affected is the heating /cooling used to maintain comfort inside buildings. This is basic facility which is required most of the time inside buildings to live in. The study has shown that a high percentage (42%) of households do not have alternate or self-generation facilities. The annual average power outage cost per residential consumer is 207 in terms of direct spoilage and adjustment costs. The average outage cost per kwh for a residential consumer is Residential customers average expenditure on electricity jumped from 5% to 16% of total annual expenses after 2007, compromising basic necessities. 31

32 The worst time of the year for power outage is summer and on Sundays, Mondays and Fridays. About 29% of consumers showed willingness to pay above the current tariff, to obtain a more reliable electricity supply[17]. Recent study shows that solar cooling systems in hot climates (Riyadh and Jakarta) can make a significant contribution to reducing primary energy consumption. A solar energy-based cooling system can reduce primary non-renewable energy consumption and CO 2 emissions by 30-79%, with a solar fraction of 22-80%. [22]. In European climates (Germany and Spain), the use of solar thermal and solar electric systems can save 40-60% of primary energy consumption [23]. Mateus and Oliviera [24] established that for single family house, solar integrated system with 20-80% solar fraction is more economical and profit able than conventional ones for south European locations. According to European Solar Thermal Industry Federation (ESTIF) report on solar thermal markets in Europe, trends, and market statistics 2014, single family houses are currently largest market sector using thermal equipment. In European region the share of single family houses is 40-46% and for multi-family houses its 27-29% [25]. 1.6 Conclusion Energy demand is increasing globally, including in Pakistan. Most of the energy resources are based on fossil fuels. These fuels are damaging the environment and causing global warming. To meet the energy demand without any or with minimum environmental damage and, to address the issue of limited fossil fuel resources, policies have been recommended to increase the share of renewable energy resources for clean and sustainable development. Pakistan has also faced an energy crisis over the last few years and it is highly likely this crisis will continue for years to come unless it is addressed properly. One of the major reasons of the energy crisis is dependency on fossil fuels and its imports, as domestic production is considerably less than requirements. In the past, no major project and plan has been executed to reduce the dependency on fossil fuels by using alternative resources to deal with the energy crisis. In Pakistan the use of renewables for the primary energy and electricity generation is negligible, except for hydroelectric power generation. To address the current energy crisis 32

33 and meet future energy demands, renewables will be a suitable option. The use of renewables is clean and could provide a long-term solution to Pakistan s energy issues, along meet the global goal of decreasing CO 2 emissions. The energy statistics data showed that the use of solar energy is negligible in Pakistan s primary energy mix. There is a need for long-term and consistent plans and policies to meet the country s energy requirements, along with promotion of clean renewables, especially solar energy. The potential of solar energy and its usage in Pakistan is described in detail in Chapter 2. The domestic sector is the major consumer of electricity and the electricity crisis has a direct impact on domestic consumers. Electricity shortage has a major effect on comfort (heating/cooling) in buildings. It is the worst in summer, when cooling is required due to the high ambient temperature. There is need for a system which works to provide cooling and heating during summer and winter. Solar energy-based systems are a reliable way of meeting energy demand for lighting, cooling, and heating and help to reduce CO 2 emission and dependency on imported fuels[26] as the potential of solar energy is highest than any other source of energy (Section 2.2). 1.7 Aims and Objective The aim of this research is to investigate the potential of a solar powered cooling system and the feasibility of achieving comfort in buildings in Pakistan. The objectives of this work are to: Investigate the energy scenario of Pakistan with respect to the electricity crisis, future energy plans, and the potential and current status of renewable energy resources application. Carry out a detailed study of Pakistan s solar energy potential, the annual and monthly average solar insolation values for main cities and its current status of application. Study climatic conditions, comfort temperatures, building energy consumption and codes and possible techniques for improved efficiency in current building designs. Carry out a literature review of photovoltaic systems, solar thermal systems and heatdriven, low-energy cooling systems. 33

34 Design and analyse the building 3D model with current construction materials in Pakistan and the simulation of a solar powered cooling system using suitable simulation program. Examine the simulation results, validation of input data, calculations, and results of the solar cooling system with overall recommendations of solar cooling system effectiveness to achieve building comfort in Pakistan. 1.8 Structure of the Thesis The thesis has eight chapters and begins with an introduction, chapter 1, providing an overview of world energy and a detailed analysis of current and future electricity demand and generation in Pakistan. In addition, the generation based on different fuel types and effect of current energy shortage crisis is also presented. Finally, aims and objectives of this research are given. Chapter 2 is about renewable energy resources in Pakistan. Renewables potential and the application of solar energy in specific are presented. Institutional infrastructure for promotion of renewables is also reviewed. Status and the application suitability of solar energy systems in Pakistan are presented. In chapter 3, climate and building energy use in Pakistan is investigated in detail. The mean maximum temperature, thermal extremes, seasonal distribution, and comfort conditions are examined. The current building energy code of Pakistan is analysed in terms of energy efficiency. A United Nations project for energy efficiency improvement for existing houses in Pakistan is also discussed and a conclusion is drawn from that project s findings. In chapter 4, solar energy cooling systems are reviewed. Efficiency, types, and the current status of PV systems and IEA future targets are analysed. Solar thermal collector systems are described in detail and different cooling systems suitable for solar thermal energy application are described. A summary of application of solar cooling system in hot climates is also presented. Status of solar cooling system in Pakistan is also reviewed. In chapter 5, a detailed literature about experimental and simulation studies of solar cooling system are presented. Solar energy systems and building energy simulation programs are 34

35 reviewed. Program suitable for a solar cooling system integrated with a building model is studied in detail. A conclusion is drawn for the selection of a suitable simulation program. Weather data types are reviewed and suitability of each data type with the different energy simulation program is discussed. Weather data files available for Pakistan cities are also analysed and data are selected to model typical weather in summer. A conclusion is drawn for the selection of data to be used in the simulation. Chapter 6 is about the building model, a description of solar cooling components and operating parameters. Initial simulation results and modifications in building materials are also presented. Mathematical calculations for operating parameters of the solar cooling system are carried out and used to estimate simulation initial parameters. In chapter 7, the final results of simulations, carried out for a typical building model with a solar cooling system, are given. All the results are discussed in detail with results validation and parametric sensitivity analysis. A conclusion is drawn regarding the feasibility aspect of solar cooling in Pakistan. Chapter 8 is the final chapter, results are summarised and conclusions, general discussions with recommendations, are presented. The possible scope of further work, which will be valuable to carry out, is expressed. 35

36 Chapter 2: Renewable Energy Resources in Pakistan 2.1 Introduction In chapter 1 it was shown that fossil fuels (oil, coal, and natural gas) are a major source for primary energy consumption in Pakistan. This is causing environmental damage due to emissions of carbon dioxide and other gases promoting global warming and disturbing climatic conditions. Energy demand and prices are consistently rising and volatility has caused a severe energy crisis in Pakistan. Many techniques and technologies are used to convert renewable energy into a useable energy form for environmental and climate protection. At present, the use of renewable technologies in Pakistan is small as compared to other sources of energy. Only hydroelectric energy is being used, whose relative share is decreasing in primary energy. There is a need to increase the use of renewable and sustainable energy resources like solar, wind and hydroelectric energy resources in Pakistan. Pakistan is enriched with renewable energy resources; an overview of the potential of renewables for current and future use in Pakistan is described in the following sections. Related to this research, solar energy will be discussed in detail. 2.2 Renewable Energy Potential Pakistan has sufficient potential for wind, hydroelectric and solar energy to meet the country s present and future energy demands [2, 27]. At present the share of renewables is very low (except in the case of hydroelectric energy) compared to the use of fossil fuel based energy systems. The Pakistan government is making an effort to promote renewable energy to increase the share of renewable energy in the country s energy mix [2, 28]. For residential applications at a micro level in remote or undeveloped areas, the viable and sustainable options are off-grid hydroelectric, solar and wind power systems. These options are sufficient for electricity and cooking needs and would help to reduce de-forestation [29] Wind Energy In Pakistan the potential areas for wind energy are very limited as shown in Figure 2-1. Pakistan is rich in wind energy only in the coastal areas of Sindh, Balochistan and some Northern areas. One part of the coastal area in Sindh is only 60 km wide and 170 km long and 36

37 has the potential for about 60,000 MW of capacity. The annual average wind speed of this corridor is from 5.9 to 7.1 m/s. Most of the remote villages in coastal area can have electricity through micro wind turbines. The first wind energy project with 6 MW of capacity was installed in 2009 and the installed capacity is now 106 MW [28, 30]. According to the Alternative Energy Development Board (AEDB), 5 wind farms with a total power capacity of MW are operational and 9 farms with 479 MW of capacity are under construction. Fourteen projects 814 MW of capacity are in the process of being planned and there are no details of the completion time for these projects [30]. Figure 2-1: Wind energy potential of Pakistan [27] Wind energy associated environmental issues such as noise, effects on animals, deforestation and soil erosion and visual impact cause concerns about utilising it. Variation in wind speed and inconsistent power output are considered drawbacks for the promotion of wind energy [31]. 37

38 In Pakistan, the availability of wind energy is less during the 8 months from September to April. Capacity from the available wind is significantly low, with an annual average of being quoted by AEDB for Pakistan [2]. The data presented above for wind energy shows that wind energy is limited to a small area of the country. The annual available capacity is much less and its contribution to meet the peak demand would not be dependable. Wind energy cannot be the main source of electricity generation Hydroelectric Energy Pakistan has identified a potential of about 60,000 MW of hydroelectric power, which can be harvested. About 86% of this hydropower potential is still untapped. The total installed capacity by the end of June 2014 was only 7097 MW. In 1960 the share of hydroelectric was 70% of the total electricity generation capacity whereas it was only 30% in The cost of hydroelectric electricity generation is lower and it is the cheapest source of energy than any other source in Pakistan[28]. The availability of hydroelectric energy depends on seasonal variation. It also depends upon reservoir levels and in flow and out flow from reservoirs [28]. According to an economic survey of Pakistan , ninety-seven micro hydroelectric projects with a total capacity of 758 MW are being planned for different locations around the country; feasibility studies and construction are being carried out. The micro hydropower projects with a capacity of about 110 MW, have been operating in different parts of the country [32]. Hydroelectric energy projects could be a source for future clean energy. High initial costs, the length of time to build dams and environment damage linked with hydroelectric energy have raised concerns about the implementation of such projects. The main hydroelectric energy sites in Pakistan lie in earthquake danger zones and since 2005 earthquake investment risks have discouraged national and international investors from initiating large capacity projects for hydroelectric energy. The Indus water treaty with India has involved a lot of risks and delays in project initiation. The hydro politics (rift among provinces) in Pakistan regarding construction of larger hydroelectric power based dams is also a major hurdle in addition to new capacities [33]. The hydroelectric energy potential of Pakistan is shown in Table

39 Description Table 2-1: Hydroelectric energy potential in Pakistan [34] Project Under Implementation Public Sector (MW) Private Sector (MW) Province Level Federal Level Projects with Feasibility Study Completed (MW) Projects with Raw Sites (MW) Total Resources (MW) Total The data for hydroelectric energy shows that sufficient potential for clean and cheap energy exists. The potential could provide sustainable energy to meet future demands. High initial costs, political rifts, the Indus water treaty with India, security risks and environmental issues are major concerns when considering harnessing hydroelectric energy potential Solar Energy Solar energy is the most abundant renewable energy resource on earth and it is available for use in its direct (solar radiation) and indirect (wind, biomass, hydro, ocean) forms. The energy radiated by the sun is around 5% ultraviolet light, 43% visible light and 52% infra-red light as shown in Figure 2-2 [35]. The solar radiation spectrum spans a wide range of wavelengths, and resembles black body radiation at 5500K. Figure 2-2: Solar energy spectrum distribution [35] 39

40 The black body radiation spectrum is shown by a black solid line in Figure 2-2.Most shorter wavelength (nm) ultraviolet radiation is absorbed in the atmosphere. Water vapour and carbon dioxide absorbs longer wavelength energy while dust particles scatter more radiation, dispersing some of it back into space. Clouds also reflect radiation into space [36]. The energy balance of the earth, based on the incoming solar radiation, is explained in Figure 2-3. Figure 2-3: Solar energy balance on earth [36] Considering all these factors, around 52% of the incoming radiation energy, 700 Million TWh annually, reaches the earth s surface as solar radiation [37]. The global annual energy consumption in 2014 is approximately Million TWh which is only a small fraction (0.02%) of the solar energy availability [38]. Sunlight reaches Earth s surface directly and indirectly by numerous reflections and deviations in atmosphere. On clear days, direct irradiance represents % of the solar energy reaching the earth s surface whereas, on a cloudy or foggy day, the direct component is zero. The indirect or diffused radiations are received on earth after its direction has been changed by scattering the atmosphere. The direct component of solar irradiance is of the 40

41 greatest interest for high temperature solar thermal systems because it can be concentrated on small areas using mirrors or lenses, whereas diffuse components cannot be. For concentrating solar rays, clear sky is required, which is usually in semi-arid areas or regions with hot climates [39, 40]. Solar energy systems can be used anywhere on the earth but some regions are better than others. Pakistan is richer with solar energy than other renewable energy sources. The available estimated solar energy potential of Pakistan is about 2900GW [the source is not clear whether it is average or peak available capacity[41]. Solar energy can provide a power supply all over the country even in remote areas. Solar energy available in Pakistan is sufficient for use all year in summer and winter seasons for both cooling and heating with small and large scale applications. A comparison of solar and wind energy prospects indicates that solar energy has an advantage over wind energy for a number of reasons including potential, availability and acceptability by locals. Solar energy is much more economical than wind energy for Pakistan [2]. Pakistan can take advantage of using solar energy technologies. This energy source has wide and uniform distribution, throughout the country. Detailed solar energy maps of Pakistan and the world are shown in Appendix A. A solar energy map of Pakistan is shown in Figure 2-4. The mean global insolation on a horizontal surface in Pakistan is about 4-6 kwh/m 2 day with enough sunshine hours (10-12) required for harnessing solar energy. The south western part, from Baluchistan, is richer in solar energy with annual average global insolation of kwh/m 2 /day with annual average daily sunshine hours of 8-10 hours. These are favourable conditions for photovoltaic and solar thermal applications. The global insolation for district cities in Pakistan is listed in Appendix A [42]. Sukhera et al.[43, 44] Raja and Twidell [45-47] and Muneer et al. [48] analysed measured solar radiation data of five main cities of Pakistan. The annual average solar insolation is 19MJ/m 2 /day (5.26kWh/m 2 /day). The annual average solar energy map of Pakistan is shown in Figure

42 Figure 2-4: Solar insolation over Pakistan [49] Solar energy data shows that solar energy is abundant in Pakistan. The available energy is suitable for applications in both solar PV and solar thermal systems. There is no political or legal or climatic issue linked with solar energy usage. It can be used both for off grid or grid connected energy supplies as well. It is suitable both for micro and large scale energy generation. 2.3 Solar Energy Systems and Pakistan The application of solar energy systems (photovoltaic and solar thermal systems) depends on system capacity and available solar irradiation in that area. The relationship between solar irradiation range and solar power system application selection is shown in Figures 2-5 and 2-6. The areas where both technologies can be used overlap in a narrow range. Photovoltaic operation covers a wide range from less than one watt to several megawatts. Photovoltaics can be used as standalone as well as grid-connected systems [50]. 42

43 Figure 2-5: PV and solar thermal power systems power range and global irradiation [50] Solar thermal systems are used in high irradiation areas. There are areas in which one of the two technologies should be preferred over the other for technical and economic reasons. Figure 2-6: Regions of world appropriate for solar thermal power plants [51] 43

44 Considering Figures 2-5 and 2-6, it is clear that Pakistan lies in an area of high potential for both photovoltaic and solar thermal technologies. The annual average global irradiation varies from kwh/m 2 in most of the country. Research work in the field of PV and solar thermal applications can help the country to overcome the current power crisis and use clean energy sources. A list of application for solar energy technologies and the solar energy systems used is shown in Table 2-2. Table 2-2: Solar energy application and types of collector used [37] Application System Collector Solar Water Heating Thermosyphon system Passive Flat Plate Integrated collector storage Passive Compound Parabolic Direct circulation Active Flat Plate, Compound Parabolic, Evacuated Tube Indirect water heating systems Active Flat Plate, Compound Parabolic, Evacuated Tube Air systems Active Flat Plate Space Heating And Cooling Space heating & service hot water Active Flat Plate, Compound Parabolic, Evacuated Tube Air systems Active Flat Plate Water systems Active Flat Plate, Compound Parabolic, Evacuated Tube Heat pump systems Active Flat Plate, Compound Parabolic, Evacuated Tube Absorption systems Active Flat Plate, Compound Parabolic, Evacuated Tube Desiccant cooling Active Flat Plate, Compound Parabolic, Evacuated Tube Adsorption units Active Flat Plate, Compound Parabolic, Evacuated Tube Industrial Process Heat Industrial air & water systems Active Flat Plate, Compound Parabolic, Evacuated Tube Steam generation systems Active Parabolic Troughs, Linear Fresnel Reflector Solar Desalination Multi stage flash Active Flat Plate, Compound Parabolic, Evacuated Tube Multiple effect boiling Active Flat Plate, Compound Parabolic, Evacuated Tube Solar Thermal Power Systems Parabolic trough collector systems Active Parabolic Troughs Parabolic tower systems Active Solar Towers Parabolic dish systems Active Parabolic Dish Solar furnaces Active Solar Towers, Parabolic Dish As Pakistan receives high levels of solar radiation, all these technologies can potentially be applied to use solar energy. 44

45 2.4 Current Status of Solar Energy Application Pakistan has a huge potential for photovoltaic and solar thermal applications, but there is no solar thermal power plant or any specific industrial or commercial application of these technologies. In recent years under the new power policy 2013, there has been a trend towards the use of PV systems for domestic and commercial electricity generation. The first PV system electricity generation project of 1000MW P was initiated in 2013 and the 1 st phase of 100MW P has been completed and is in operation. The details of solar energy applications in Pakistan are summarised here Photovoltaics Photovoltaic systems generate electricity directly. They are suitable for small and large electricity generation projects. The areas of Baluchistan and Sindh (especially Thar Desert) are most suitable for photovoltaic energy generation due to their high levels of solar radiation[52]. Balochistan is the largest area province with the least population density of about 22 people per square kilometre and most inhabitants live in rural areas as scattered tribes. Most of these villages and areas are still to be electrified. The houses here require watts of power for lighting purposes. Transmission and distribution lines are difficult and not economical for these low power scattered populations in hilly areas. Off-grid or local power generation through solar PV systems is a possible solution as conventional fuels are also costly to transport into these areas [52]. In the early 1980s, the government installed eighteen photovoltaic systems for the electrification of remote village areas in different parts of the country[52]. Due to improper operation and maintenance, these systems failed to produce the desired output. Similarly, the public health department installed twenty solar water pumps in Northern areas and Balochistan but these pumps did not perform well due to a lack of operation and maintenance knowledge and trained, skilled operators. Currently solar photovoltaic energy technologies are used in the country only for rural telephone exchanges, highways, and motorways emergency telephones. In late 2005, Solar Energy International and the National University of Sciences and Technology (NUST) were jointly awarded a USAID project to provide solar pumping systems for drinking water supplies in six villages in the Federally Administrated Tribal Areas (FATA) in the Northwest of Pakistan [52]. 45

46 In April 2012, the government allowed duty free import of all types of PV based system. Both private and public sectors are financially contributing towards implementation and promotion of clean energy photovoltaic systems in the country. Many companies are involved in both trading and manufacturing photovoltaic based home appliances including lamps, battery chargers, lights and torches [52]. According to the Pakistan economic survey , about 65 MW P of electricity is generated by PV systems. Approximately 793 MW P from Grid solar PV power plants are under development and in different phases of planning. Under the Prime Minister s directive on solar electricity, a supply programme for 3,000 homes in 400 villages across the country has been started [32]. Solar PV technology use in Pakistan is being promoted on a small and large scale. The first stage for a 1000MW P solar PV electricity generation plant is operational and some other projects are under construction. The use of solar PV is increasing but it is very small compared to the potential that can be harnessed Solar Thermal Solar thermal technology converts solar energy into heat energy and is used for many applications in heat exchange processes. These technologies are simple, economical and hazard free. The applications are cooking, heating, cooling and steam for electricity generation for domestic, commercial, and industrial purposes. The use or application of solar thermal energy technologies in the Pakistan is reviewed here Solar Cooker A number of public and Non-Government Organisations (NGOs) are actively participating in the promotion of solar cookers. Both box and concentrator type cookers are in use in the Northern and North West Mountain areas of the country. The use of solar cookers can be increased to save precious forest wood used for cooking. 67% of the total population is living in rural areas and the estimated consumption of biomass energy is 27% of their total energy consumption. The biomass is mainly firewood and crop residues [52]. 46

47 Solar Water Heater Solar water heating is very popular and a commonly used solar thermal application but in Pakistan, its use is very limited. It is used only in the Northern areas during the winter season due to a shortage of supply of natural gas and Liquefied Petroleum Gas (LPG). In the past few years, due to the crisis in electricity throughout year and shortage in the natural gas supply during the winter season, the use of solar water heaters is increasing throughout the country for domestic hot water in the winter season [52]. According to the Pakistan economic survey , approximately 16,715 units of solar water heaters are in use in Northern areas, Balochistan, North Punjab and Khyber Pakhtun Khwa (KPK) [32] Solar Dryers Solar energy can be effective in drying agricultural products especially fruits and grains. It can produce a clean, high quality taste and quick drying and cost economic products. Solar dryers are in use to dry fruits and preserve fruits for off-season use. Both public and NGOs are actively participating in promoting solar dryers in all parts of the country [52] Solar Desalination A large part of the population in the country, especially in Balochistan, Sindh, and south Punjab has no clean drinkable water facilities. The available water is polluted or, saline due to a high concentration of sodium chloride. This saline water is not suitable for drinking, cooking, and washing. Solar energy can be effective and economical for desalination of this polluted and saline water. Solar desalination technologies are very simple, low cost, and easy to use for people with little technical training. The government has installed two plants with a production capacity of 23 m 3 / day, which converts sea water into sweet water in Gawadar city. Some other projects are still under consideration for implementation in Sindh [52]. 2.5 Institutional Infrastructure In Pakistan most of the research and development work is carried out by public sector organisations. Public sector organisations, which were and are involved in research regarding solar energy applications, are described here. 47

48 2.5.1 Pakistan Council for Renewable Energy Technologies The Pakistan Council for Renewable Energy Technologies (PCRET) was established in 2001 as a result of the merger of National Institute of Silicon Technology (NIST) and the Pakistan Council for Appropriate Technologies (PCAT). The aim was to have more effective and beneficial results for renewable technology research. The selected renewable sources were micro hydropower generation, wind energy, biogas, photovoltaic and solar thermal technologies. This organisation contributed to the application of different renewable technologies. With regard to solar energy, the achievements were as follow [52]: 100 kw electricity for 500 houses, mosques, schools and 265 street/garden lights through use of a 300 Solar PV system Installation of 21 solar dryers with a total capacity of 5230 kg/day Completed pilot scale production of solar cells Testing laboratory for PV and solar thermal appliances Alternative Energy Development Board (AEDB) The Alternative Energy Development Board (AEDB) deals with alternative energy resources, which include wind, micro wind, micro hydro, solar photovoltaic, solar thermal, bio-diesel, biomass and energy from waste and fuel cells. AEDB, with the assistance of the World Bank, will convert 100,000 agricultural water pumps for irrigation to run off solar energy within the next five years. There are 1,100,000 water pumps across the country of which 250,000 electric pumps share, on average, 3000 MW peak electric loads during the day. The World Bank has approved a pilot project under which initially 25 water pumps will run off solar energy [52, 53]. According to the Economic survey of Pakistan , about 1,429 units of a solar water pumping system are working in the country both for agriculture and community drinking water systems [32] Educational Institutes The educational institutes of Pakistan have made only a limited contribution to research, development, and application of renewable energy technologies. So far there are no special courses that have been started by universities, technical and vocational training institutes regarding renewable energy technologies. For solar thermal and photovoltaic energy, the activity in different institutes is minor. At present, the College of Electrical and Mechanical Engineering (EME), the National University of Science and Technology (NUST) Rawalpindi 48

49 is carrying out research on solar thermal power generation and solar thermal devices for heating purposes. The Nadirshaw Edulji Dinshaw (NED) University of Engineering and Technology, Karachi, has research facilities for solar thermal and photovoltaic energy with funding for research in this area. The University of Engineering and Technology (UET) Lahore has established a centre for energy research and development both at Lahore and Kala Shah Kaku (KSK) campus [54-58] Pakistan Engineering Council (PEC) Under the clean energy initiative an on grid solar power generation system with a capacity of 100 kw P will be installed under grant aid from the Government of Japan at the PEC head office building at Islamabad. This will be the first of its kind in the country and will be an example to prove an effective measure to overcome energy shortages. The government of Pakistan under the Prime Minister s Initiative for Solar Power (PMISP) has approved a grant of GBP 0.50 Million for PEC. Under this project, PEC is installing 0.50 to 5.0 kw P standalone solar power systems at various engineering universities, commercial areas, and religious places [53]. 2.6 Doctoral Research on Solar Energy Potential in Pakistan In 1992, Raja [45] completed doctoral research on Assessment of solar radiation in Pakistan. Mean monthly maps of distribution of daily global, diffuse, and direct solar insolation for Pakistan were presented, using measured data for five cities and sunshine hours data of thirty seven other stations. The solar insolation measured data was from (except Quetta ) and the sunshine hour s duration was from years until The global solar insolation was calculated from sunshine duration using Angstrom type insolation-sunshine relation. It was found that the annual mean daily global solar insolation in the major parts of the country from 16.0 to 21.5 MJ/m 2 /day (4.4 to 6.0 kwh/m 2 /day) with mean of 19.0 MJ/m 2 /day (5.26 kwh/m 2 /day). It was also reported that all five station have mean daily insolation more than 10.0 MJ/m 2 /day (2.77 kwh/m 2 /day) with at 85% probability. Raja also presented data for distribution of monthly mean daily diffuse and direct (beam) solar insolation for Pakistan. It was reported that measured data for diffused insolation was available for one city (Quetta) of three year duration ( ) and for other cities it was predicted using empirical relationships. The direct insolation for 40 stations was computed by the difference of global and diffuse insolation. 49

50 The main limitation of Raja s work is that the country s solar energy potential is estimated on the basis of five stations measured data. For solar energy applications, long term solar data from high resolution satellite data or measured data for more cities would provide confidence for design and operation. In 2012, Shah [59] completed doctoral research on the Analysis of solar energy production, utilisation, and management for facilitating sustainable development in and around the deserts of Pakistan. It was established that available solar energy potential utilisation could provide socioeconomic development and benefits (fresh water, electricity) to the population in desert areas of Pakistan. The daily solar energy potential of 90,000 km 2 of desert would be, on average, about 30-65GW/m 2 [59-61] of electricity. It was concluded that an area of 60 km 2 would be sufficient to meet energy demand for the daily needs for water and electricity for 500 persons village [62]. It was concluded that 0.70 kg per person per day of CO 2 emissions could be avoided if a solar power generation process were used instead of fossil fuels [59]. It has also been found that solar assisted water desalination for coastal areas of Pakistan is feasible and potential utilisation could contribute to the development of a 1,046 km long coastal area with a population of more than 10 million [63]. Pakistan s solar energy potential is sufficient for solar PV and thermal application as shown in Figure 2-6 and Appendix B. There is a need to improve the data on solar energy availability, principally by collecting data for more locations. Doctoral and academic research into solar cooling systems in Pakistan and India will be described in Section Conclusion Renewables are the source of clean and sustainable energy resources. Use of renewables can help to meet the global goals for control of carbon emissions and global warming. Pakistan has sufficient potential in renewables which could provide clean and sustainable energy to meet the current and future energy demands. In the past and at the moment only hydroelectric energy and biomass are extensively used; wind and solar energy need to be promoted. As presented in Section 1.4, in Pakistan the amount of renewables for primary energy consumption is very low compared to the potential. 50

51 Solar energy is the largest available renewable source of energy. The use of solar energy is much less than its availability. It could provide clean energy amounting to many times more than world energy consumption (0.154 Million TWh for year 2013) for years if it could capture only 1% of the total available 700 Million TWh. Solar energy has several advantages over wind, biomass, and hydroelectric energy. Environmental and political problems are linked with the promotion of these other renewable technologies in Pakistan. The solar energy potential covers almost all of the country and the technology can be used on a large scale, which would be economically viable and with the same standards of service and maintenance. Pakistan lies in a location with annual solar insolation of kWh/m 2. This insolation is suitable for micro to mega solar energy generation by all types of solar PV and solar thermal systems. Pakistan is suitable for application of all types of PV and solar thermal technologies for heating, cooling, power generation and industrial applications. Public and private sector partnership along with special incentives can promote the application of solar energy technologies. The application of solar energy systems can help in the improvement of social and economic values in remote areas of Sindh, Punjab, and Balochistan. Solar energy is widely available in all areas of Pakistan. It is the only undisputed and short and long term solution to the current crisis which is a source of green and clean energy. The use of solar at a micro scale at the domestic level could help to meet demand for daily energy consumption both for lighting and hot water. Institutional level infrastructure (technical training) is available in the country which could contribute a lot to the promotion of solar energy based domestic appliances. The institutional contribution is much less compared to its potential. The benefit of solar energy use would be apparent throughout the country s population both in urban and rural areas. It would help to develop remote areas in all provinces and facilitate the extremely dense populated cities. Solar energy can be the best alternative to both electricity and natural gas shortages for domestic use both for heating and cooling applications (Section 1.5). 51

52 Chapter 3: Pakistan s Climate and Buildings Energy 3.1 Introduction In chapter 1, world energy data shows that the predicted annual average growth in energy consumption in the buildings sector will be 1% till 2035 and major consumption will be for lighting and space cooling due to increases in population and urbanisation. Pakistan energy data shows that 54% of total electricity is being consumed by the domestic and commercial sectors. The climatic conditions in Pakistan are hot and sunny for most of the year. The major energy consumption in buildings is for cooling systems in summer. In this chapter geography, population, climatic conditions, comfort temperature, thermal extremes, and building energy in Pakistan will be described in detail. All these parameters are important in comfort, cooling system design and cooling demand in the future. 3.2 Geography of Pakistan Pakistan lies in South Asia between latitude 24 N to 38 N and longitude 61 E to 78 E and the total area is 796,096 km 2. The neighbouring countries are China in the north, India in the east, Afghanistan and Iran in the west and the Arabian Sea to the south. It has a varied landscape with flat Indus and Punjab rich plains, deserts and the Plateau of Balochistan in the west and mountains in the north and North West as shown in Figure 3-1.The economy is agriculture based, and the total arable land in the country is about 28% of the total area. About 80% of the cultivated land is irrigated through the world s largest irrigation system linked with five main rivers [64]. 52

53 Figure 3-1: Geography of Pakistan [65] Pakistan is divided into seven main administrative areas, which are Punjab, Sindh, Balochistan, Khyber Pakhtun Khwa (KPK, formally North West Frontier Province) Federally Administrated Tribal Areas (FATA), Gilgit Baltistan, and Jammu & Kashmir. These administrative areas are shown in Figure 3-2. Figure 3-2: Administrative areas of Pakistan [66] 53

54 The area and population distribution for each administrative unit is shown in Figures 3-3 and 3-4 respectively. 1% 3% 8% Pakistan's area distribution 23% Punjab Sindh Khyber Pakhtunkhwa Balochistan 40% 16% Azad Kashmir FATA 9% Gilgit Baltistan Figure 3-3: Area distribution of Pakistan [67] Pakistan's population distribution (2010) 5% 2% 2% 1% Punjab Sindh 14% Khyber Pakhtunkhwa Balochistan Azad Kashmir 23% 53% FATA Gilgit Baltistan Figure 3-4: Population distribution of Pakistan [67] The above Figures 3-3 and 3-4 show that about 76% of the total population lives in the Punjab and Sindh provinces, although these provinces constitute only 39% of the total land area. Balochistan and KPK cover 49% of the area of the country but the population share is 19%. The other administrative areas have less than 12% of the land area and 5% of the total population. 54

55 3.2.1 Population Pakistan is one of the most populated countries in the world. Since 2003 it has been ranked as number 6 most populated country in the world [5]. The population density is increasing continuously. The population density of the provinces and country in 2010 is shown in Figure Pakistan population density per km Punjab Sindh Khyber Pakhtunkhwa Balochistan Azad Kashmir FATA Gilgit Baltistan Pakistan Figure 3-5: Population density in 2010 [68] According to the Pakistan Bureau of Statistics, the country population has reached more than 184 million. It is estimated that Pakistan s population will be about and million by 2030 and 2050 respectively [69]. In 2013, about 33% of the total population was living in urban areas and this number was expected to rise to 50% by Presently cities suffer from a housing deficit of about 3 million units and 50% of the current urban population lives in slums. There will be an increase in demand for houses and electricity for lighting and cooling systems [70]. 3.3 Climate of Pakistan Climate plays an important role in building design, energy demand, heating and cooling system requirements, and operational hours for these systems. There are different climatic conditions in the different parts of the country. Ambient temperature and relative humidity are important for cooling load calculation and they are described here as climatic conditions 55

56 [71]. The climate of Pakistan is generally arid with hot summers and cool or cold winters with wide variations between extremes of temperature at given locations [72] Temperature and Humidity On the basis of temperature experienced, the country is divided into three main seasons: summer, monsoon, and winter. The summer season lasts from April to June and monsoon from mid-june to mid-september. In southern and eastern areas the temperature is highest and decreases towards the north and west, and reaches a minimum in the northern and western parts. In the summer season the average temperature in the north is below 15 C whereas in the south it is more than 35 C. About 80% of the population of the country lives in climatic condition with hot summer seasons and requires cooling systems for comfort [73]. The mean minimum and maximum temperatures for all major district cities of Pakistan are shown in Appendix B [42]. The annual mean daily temperature of the country from years 1971 to 2000 is shown in Figure 3-6. Figure 3-6: Pakistan annual mean daily temperature [74] 56

57 The annual average relative humidity for most of the areas of the Pakistan is from 40% to 70%. It is higher than 70% at the Makran coast and lower than 40% in south-eastern Balochistan, and in the extreme north [73].The annual average relative humidity for district cities in Pakistan is shown in Appendix B [42]. 3.4 Heat Index and Pakistan Most of the areas in Pakistan have hot weather conditions in the summer. Continuous high temperatures and high relative humidity for long periods become a significant hazard and pose a health risk. Different climate models projections show that global air temperature will increase in the future due to long wave s radiative effects of increasing greenhouse gases, especially CO 2 emissions (These gases absorbs and re-emit the long wave infrared radiation emitted by earth thus increasing the atmospheric temperature). The heat-related damage and casualties are likely to increase due to global warming effects and increasing heat waves during summer seasons. Cooling systems are required to create comfort inside buildings [75, 76]. The heat index [75] is a measure of stress caused to humans by increases in humidity and temperature. As the moisture increases, the ability of the human body to release heat through evaporation decreases which creates stress and discomfort, heat stroke or even death to humans. The heat index is a simplified relationship between ambient temperature and relative humidity versus apparent temperature. The Heat Index (HI) Equation (1) is: [77] HI = T R TR x10-3 T R T 2 R TR x10-6 T 2 R 2 (1) Where T= Ambient dry bulb temperature ( F) R= Relative Humidity (%) The above Equation (1) is applicable when air temperature and humidity are above 26 C and 39% respectively. A relation of different heat index temperature ranges and their effects on humans is shown in Table

58 Heat Index Table 3-1: Heat Index and its effects [75, 78] Health effects C Fatigue possible with prolonged exposure and/or physical activity C Heat cramp and heat exhaustion possible with prolonged exposure and/or physical activity C Heat cramp or heat exhaustion likely & heat stroke possible with prolonged exposure and/or physical activity. > 54 C Heatstroke highly likely with continuous exposure. In Pakistan the heat index and its possible effects start in summer from May to September. The heat index range from C is tolerable for the people of Pakistan. The normal heat index for summer seasons based on recorded real time data of mean monthly maximum temperatures and relative humidity from in Pakistan is shown in Figure 3-7. Figure 3-7: Pakistan normal mean heat index distribution [75] Figure 3-7 shows that most of the areas of the eastern side (Punjab and Sindh) and south eastern Balochistan are in danger and the extreme danger zones of the heat index, which poses serious threats to health. Buildings in these areas require cooling system for health as well as comfort. The analysis of recorded weather data shows that there is an increase in temperature and humidity causing a rise in the heat index and for the summer season the heat index is increased by 3 C. For this period in the country, on average the increase in humidity 58

59 is 6.2% and the increase in maximum temperature is 0.25 C. The summer season has been prolonged while winters have become shorter in Pakistan [75]. 3.5 Thermal Extremes in Pakistan Heat waves (HW) are the by-product of climate extremes. These are now more frequent and intense during summer in most parts of the world. Recent studies[79-83] on heat waves reported a risk of more intense and frequent heat waves in the near future. A heat wave is defined as very high temperatures over a sustained number of days [84]. Heat wave-related causalities are increasing and in 2003 more than 70,000 were recorded in Europe [85, 86]. Heat waves are the most prominent cause of weather-related human mortality in the U.S. and Europe [87]. Asia is not far behind in terms of the impact of prolonged spells of heat waves. The hottest summer in China for the last fifty years was recorded in Shanghai in 2003 when the mortality rate was at its maximum due to cardiovascular and respiratory disorders [88]. Heat waves generally develop during pre-summer (March/April) and pre-monsoon (May/June) in Pakistan. Heat wave conditions have been frequent during pre-summer after the 1990 s due to climate change [84]. The country weather data from shows there has been an increase of 0.47 C in the annual mean daily temperature with an average of C per decade [64]. The frequency of continuous hot days and hot nights has increased annually since 1960, and on average there has been an increase of 20 days of continuous hot days from 1960 to 2003 (hot day or hot night is defined by temperatures exceeding 10% of average day or night temperatures in the given climate for that region or season). Similarly, the frequency of hot nights per year has increased by 23 nights for the same period. The frequency of cold days and nights has decreased significantly since 1960 (cold days or cold nights are defined as those with temperatures 10% below the average day or night temperatures for the given climate for that region or season). On average the number of cold days has decreased by 9.7 days and the number of cold nights by 13 from 1960 to 2003 [71]. Heat waves with temperatures between 40 C and 45 C and durations of 5 and 7 consecutive days have been increasing in all regions of Pakistan from 1961 to There is an increase in the spell of 10 consecutive days at temperatures of more than 40 C in the Punjab, Sindh, and Balochistan regions. The heat wave periods with temperatures of more than 45 C for 10 consecutive days has increased in the Punjab, Sindh, Balochistan, and Khyber Pakhtun Khwa. The moderate and severe thermal extremes for temperatures between 40 C and 45 C have 59

60 increased more for 5 and 7 days than for 10 consecutive days. The area of moderate and severe heat wave frequency in South Asia is shown in Figure 3-8 [84]. Figure 3-8: Areas of moderate and severe heat wave frequency in South Asia [84] It is expected that continuous increases in temperatures may make heat waves more frequent and intense than they are at present. Severe damage to people s lives is expected, unless adaptation measures are taken to mitigate heat-related discomfort [84]. 3.6 Comfort Temperature Standard Comfort Temperature Comfort temperature, is a temperature at which people feel on average neither cool nor warm. It can vary with varying ambient or climatic conditions. The main factors which influence thermal comfort and determine heat gain and loss are metabolic rate, clothing insulation, air temperature, mean radiant temperature, air speed, and relative humidity. The American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) standard -55 defines the acceptable standard comfort temperatures and is shown in Figure 3-9 [89]. Figure 3-9 shows the ASRAE standard comfort temperature is C and relative humidity is %. 60

61 Figure 3-9: ASHRAE standard comfort temperature zone [89] Operative temperature (To), is uniform temperature of an imaginary black enclosure in which occupants would exchange the same amount of heat by radiation plus convection as in the actual non-uniform environment. The empirical relation is expressed as Equation 2 [90, 91]. To= (Ta + Tr ) / 2 (2) Where, Ta= Air temperature of surroundings ( C) Tr = Mean Radiant Temperature ( C) The mean radiant temperature (Tr) is the uniform surface temperature of an imaginary black enclose in which an occupant would exchange the same amount of radiant heat as in the actual non-uniform space. The empirical relationship is expressed as Equation 3 [90]. Tr = Tg v a (Tg-Ta) (3) Where, Tg = Globe temperature ( C) v a = Air velocity (m/s) 61

62 Globe temperature (Tg) is a value, which is measured directly by globe thermometer at thermal equilibrium with the environment, when heat gain by radiation is equal to heat loss by convection [91] ISO 7730 International standard ISO 7730 is used to predict the thermal sensation and degree of discomfort of peoples exposed to a moderate thermal environment. It is also used to specify acceptable thermal comfort conditions. It is based on two techniques: Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) [92, 93]. PMV is an environmental index commonly used to specify thermal comfort conditions in moderate thermal environments. It predicts the mean value of votes of large groups of people on the ISO thermal sensation seven point scale from +3 to -3 from hot to cold respectively. The comfort zone is specified by PMV between to [92, 94]. The PPD index establishes a quantitative prediction of the number of thermally dissatisfied persons. It predicts the percentage of a large group of peoples likely to feel too hot or too cold in a given environment as in the PMV scale. The PMV value is used to calculate PPD in terms of percentage of dissatisfaction [92, 94] Limitations of ISO 7730 Laboratory studies have often supported the validity of ISO 7730 whereas field studies have not. The standard is also criticised for a lack of theoretical validity [93]. The ISO 7730 standard does not adequately describe comfort conditions for tropical and hot climates. Air temperatures above 30 C and air velocities of more than 1m/s are common in buildings in tropical countries. Many field studies have found that occupants can be comfortable at temperatures over 30 C if fans are in use, even though the PMV is over 2. PMV over estimates discomfort in hot conditions and under estimates it in cold conditions [95, 96]. Francis and Edward investigated and found errors incurred through the use of ISO It is found that for annexe E, linear interpolation can generate small errors. A correction factor was proposed as, without correction, relative humidity can lead to errors of up to 20% of comfort span at 30% relative humidity for low activity levels [94] Adaptive Thermal Comfort People have a natural tendency to adapt to changing conditions in their environment. This tendency is expressed in the adaptive thermal comfort approach. The adaptive thermal 62

63 comfort approach is based on findings of surveys on thermal comfort conducted in the field. Analysis of international field studies shows that peoples adapt to temperatures they experience and are comfortable over a greater range of temperatures other than predictions of ISO 7730 and ASHRAE standard temperatures. For the air-conditioned building the comfort temperature is different from that in naturally ventilated buildings [97, 98]. The adaptive approach is used to estimate the indoor temperature at which building occupants are more likely feel comfortable. Most occupants are comfortable with +/-2 C of the comfort temperature [32]. Acceptable operative temperature ranges for naturally conditioned spaces according to ASHRAE 55rev-2003, for different climatic areas is shown in Figure 3-10 [99]. Figure 3-10 Acceptable temperature ranges for naturally conditioned spaces ASHRAE 55 rev [99] Figure 3-10 shows that for naturally conditioned spaces (no mechanical cooling) people are adapted to higher temperatures than the ASHRAE standard comfort zone. For New Delhi the range is between 26 C to 30 C, when the mean monthly outdoor temperature is between 33 C and 35 C. These conditions are also applicable to Lahore as the climatic conditions of New Delhi and Lahore are similar. For a period of 30 years, recorded data for mean monthly temperature for both Lahore and New Delhi is shown in Figure The mean monthly 63

64 Temperature (ᵒC) temperature in Lahore is slightly lower than in Delhi from February to June. The acceptable comfortable temperature for Lahore will be in the same range as for New Delhi. 40 Lahore vs New Delhi nean daily temperature Lahore New Delhi January February March April May June July August September October November December Figure 3-11: 30 years average monthly mean daily temperatures [100] In Pakistan two thermal comfort surveys were conducted to find out adaptive comfortable temperatures in Pakistan by Nicol et al. [97, 101, 102]. One was longitudinal, conducted in summer and winter, and the other was transverse conducted each month over the year. The results were close and it was established that there is a relationship between outdoor conditions and indoor comfort in line with adaptive thermal comfort. For comfortable temperature observations in Pakistan, the country is divided into five climatic zones, which are shown in Table 3-2 [97]. Table 3-2: Climate zones of Pakistan for comfortable temperatures [97] Climate zone Representative city Monthly mean outdoor temperature range ( C) Zone I: Tropical Coastland Karachi Zone II: Subtropical Continental, Lowland arid Multan, Lahore Zone III: Subtropical Continental, Highland Semiarid / Sub-humid Quetta Zone IV: Subtropical Continental, Lowlands / Sub-humid Islamabad, Peshawar Zone V:Subtropical Continental, Highland humid Gilgit, Saidu Sharif Most of the population (more than 60%) in Pakistan lives in climatic zone II, which needs cooling systems in the summer for comfort inside buildings. 64

65 Nicol used Equation (4) to calculate design indoor temperature (T d ) or set point for airconditioned buildings in Pakistan, from records of monthly mean outdoor long term temperatures T OLT [97, 103]. T d = To LT (4) The calculated indoor or set point temperature (T d ) for selected cities in Pakistan is shown in Table 3-3. Month Table 3-3: Designed indoor (T d ) temperature for selected cities [97, 101] City Gilgit Islamabad Karachi Lahore Multan Peshawar Quetta Saidu Sharif January February March April May June July August September October November December Annual average The annual average adopted indoor set point temperature is higher than the ASHRAE standard of 26ºC in summer and 21ºC in winter. This data will help to use passive or low energy solutions and also reduce cooling load when designing cooling systems. 3.7 Building Energy in Pakistan According to the IEA, during 2011, global final energy consumption in all buildings is 33,610 TWh and expected increase to up to 42,915 TWh by Currently buildings share 29% of total electricity consumption and this figure will increase to 38% in Currently space heating and cooling contribute about 60% of total energy consumption in buildings. The IEA suggests the possibility of saving 3% of total energy consumption by improving energy efficiency in buildings and making a major contribution by reduction in electricity consumption [5]. 65

66 In Section 1.5, it is shown that in Pakistan about 54% of total electricity is consumed in domestic and commercial buildings. Pakistan has increasing demand for air conditioning systems due to the rising heat index and thermal extremes as discussed in Sections 3.4 and 3.5. Energy demand in buildings is increasing by 15% per annum; high energy use also leads to more carbon emissions due to combustion of fossil fuels to meet the energy demands [104]. The ongoing energy crisis has added difficulties in maintaining comfort inside the buildings as discussed in Section Energy Efficient Buildings: The present buildings in Pakistan have the following problems [105]: Poor comfort in peak summer and winter seasons High cooling and heating loads Poor energy efficiency The current buildings in Pakistan have the potential for increasing energy efficiency and about 50% of energy demand can be saved through comprehensive measures [105]. Energy can be saved in existing buildings by insulation of the building envelope (walls, roof and ground floor), glazing of windows, installation of energy efficient heating and cooling systems, annual service of appliances, installation of temperature controllers and thermostats. Effective use of day light in building has multiple benefits including occupants feeling comfortable, more productivity at work, improved aesthetics and energy saving compared to inefficient buildings [106]. Turkey has successfully implemented energy efficiency policy for buildings and achieved electricity reduction by about 25-30% in buildings. The policy was prepared and implemented in 2004, by the Ministry of Energy and Natural Resources (MENR) with the help of internal donors [107]. In India, the Bureau of Energy Efficiency (BEE) was established in 2001 and has implemented an Energy Conservation Building Code (ECBC) in 2007 and aims to achieve energy savings of 25-30% in different buildings [5, 108]. The estimated potential of energy savings in Pakistan s buildings is described in Section This estimated potential is higher than actually achieved by Turkish building energy policy implementation as there is no building energy code in practice in general. 66

67 3.7.2 Building Energy Code of Pakistan In Pakistan for energy efficiency in buildings, the Ministry of Environment has updated the 1986 Building Energy Code of Pakistan (BECP) in 2008 with the support of the National Engineering Services Pakistan (NESPAK) under contract with the National Energy Conservation Centre (ENERCON). This code was implemented by the Pakistan Engineering Council (PEC) in February 2014 for buildings with a total connected energy load of 100kW or greater, 900m 2 of conditioned space or greater or unconditioned space of 1200m 2 or greater. The purpose of this code is to provide minimum requirements for energy efficient design and construction of buildings in Pakistan [109]. It is mainly focussed on: a) New buildings and their systems b) New systems and equipment in existing buildings This code is not applicable to a) Buildings using no electricity or fossil fuels b) Equipment and portions of building systems that use energy primarily for manufacturing industry and processes A critical analysis of this energy code, bearing in mind energy efficiency and cooling systems, in the context of solar cooling is carried out and presented here. Section IV of the code, describes mandatory requirements for building energy usage but does not provide guidance on improving energy efficiency in existing buildings and systems. There is no description for building materials application for energy efficiency or passive heating, cooling and natural ventilation systems, although the majority of the population lives in rural areas having no mechanical systems for building comfort [110]. Section V of the code describes heating, ventilating and air conditioning requirements. Mandatory requirements for natural and mechanical ventilation, equipment minimum efficiencies, temperature and humidity controls are described. An air leakage limit is mentioned but no procedure is mentioned for how it varies in winter and summer with comfortable conditions. For natural ventilation, it is not mentioned which section of the national building code of Pakistan and ASHRAE should be followed. Mechanical cooling systems of more than 28 kw must have automatic control systems, whereas most of the domestic and commercial systems are less than this in capacity. The set point for summer and winter should not be less than 25ºC or more than 21ºC respectively. Temperature and humidity ranges for restaurants, office building, museums and communication centres and 67

68 airport terminals are prescribed, but for schools, domestic buildings, hospitals, mosques and other public services buildings they are not described [110]. Section XIV of the code describes the climate zones of Pakistan and temperature ranges measured in these climate regions. The climate zone of Pakistan in the building energy code map is not in accordance with tabulated zones in the code. The correct climate zone map in accordance with Table 3-2 climatic zones of Pakistan is shown in Figure Figure 3-12: Climate zone map of Pakistan [110] The building energy code does not cover all types of buildings and equipment efficiency standards but still has the potential to reduce building energy consumption, which is discussed in the next section Benefits of Introducing Building Energy Code in Pakistan ENERCON presented a study on the benefits of implementing the energy code in buildings. It is estimated that implementation of the code can save about 29% on overall energy use in buildings. Using an energy code standard for building envelopes of U-value for walls and windows can save 56% and 38% of energy usage respectively. It is also estimated that with 68

69 changes in window to wall ratios from 0.38 to 0.33, about kWh of energy can be saved on average [111]. Currently air conditioning systems represent 25% of total electricity consumption in buildings. By implementing the energy code about 18% of the total air conditioning systems electricity consumption could be saved. The energy code recommends that using a summer temperature set point of not less than 25ºC can save 35%, using solar cooling can save 25% and using occupancy sensors can save 15% of total energy consumption in buildings [111]. Some other areas for potential savings are shown in Table 3-4. Table 3-4: Potential energy conservation areas [105] Conservation Areas Saving Potential (%) Overall lighting 29 High efficiency lighting (LEDs) 72 Fluorescent tube ballasts 83 Lamp fixtures 50 Printers 19 Heaters 17 Copiers 10 Fans 5 Computers 2 The overall potential for 29% of savings is in line with the Turkish energy efficiency policy, which saved 25-30% on energy use in buildings. This saving potential is just an estimate as no experimental evidence has been described by ENERCON. 3.8 Case Study of Energy Efficiency Improvement in Existing Houses in Pakistan In 2010, UN-HABITAT (United Nation Settlement Programme) in partnership with the Ministry of Environment, National Energy Conservation Centre (ENERCON) and Capital Development Authority (CDA), demonstrated and tested measures to improve the thermal performance of housing with Reinforced Concrete (RC) flat roofs [112]. This project s phase one had three steps as explained below: 69

70 Roof Preparation The roofs were prepared and repaired for leakage removal, water proofing with bituminous coating and plain cement concrete (1:2:4) toppings. Thermal Improvements Three techniques were used to improve the thermal performance of RC slab roofs which were: insulative techniques, reflective surface techniques and radiant barrier techniques. Insulative material reduces heat transfer between objects of different temperatures. The reflective surface bounces back the incident light and a radiant barrier inhibits heat transfer by thermal radiation. Performance Criterion The thermal performance was monitored for 20 days in the month of July 2010 during the summer season. The thermal comfort level was set below 34 C. This temperature was set as a target to reduce the room temperature below it Results of the Case Study During daytime with peak ambient temperatures, the highly effective materials are paperboard false ceilings (radiative) and jumbolon extruded polystyrene (insulative) respectively. They reduced room temperature on average by 4 C as compared to rooms with no solution. Three reflective and four insulative materials also showed good effectiveness in temperature reduction in the range of C. The other solutions, three radiative, two reflective and five insulative, gave average efficiency as shown in Figure 3-13 [112]. 70

71 42 Temperature comparison at day Out Side AirTemperature at 3 PM With Solution Inside Room Temperature Figure 3-13: Outside air and inside temperature with solution comparison during day time [112] The performance of the material at midnight is shown in Figure All the materials reduced the room temperature as compared to rooms with no solutions; the most effective materials were paperboard false ceilings (radiative) and jumbolon extruded polystyrene (insulative) and smart concrete tiles (insulative) respectively. The reduction in room temperature was about 4.7 C. The other materials gave a temperature reduction of C [112]. 71

72 38.0 Temperature comparison at night outside air temperature at mid night with solution inside room temperature Figure 3-14: Comparison of outside air and inside temperature with solutions at midnight [112] The initial cost analysis shows that reflective materials are cheaper, insulative materials are expensive and radiative barrier materials are in between. For initial cost per square metre the lime wash, weather sheet paint, and enamel paints are the cheapest ( ). For initial cost per square metre, Alnoor tiles, Munawar AC tiles, and smart concrete tiles are the most expensive ( ). The initial cost of all materials is shown in Figure 3-15 [112]. 72

73 COST/SQ. MTR GBP ( ) COST /SQ. MTR GBP ( ) Initial cost of solution 8 6. Reflective Material. Radiative barrier material. Insulative material Figure 3-15: Initial cost of different solutions [112] The 10 year cost analysis of these materials showed mixed results. Two reflective, two insulative and four radiative barrier materials have 10 year cost ranges of per square metre. The 10 year costs of these solutions is shown in Figure 3-16 [112] Reflective. Radiative barier. Insulative 10 years cost of solution Figure 3-16: 10 years cost of different solutions [112] 73

74 3.8.2 Findings on the Basis of Energy Efficient Housing Reports All the solutions improved comfort and indoor temperature decreased by 2-4 C on average. This improvement in passive building cooling measures helps to reduce electricity consumption and saves on CO 2 emissions. This decrease in cooling load is favorable for any cooling system especially for application in solar cooling systems. Paperboard false ceilings are cheapest for both initial and 10-year costs and highly efficient in reducing indoor temperature both at day and midnight. They are highly recommended to improve thermal comfort and reduce cooling loads in summer. In current and new buildings, this material and solar cooling systems can both help to provide sustainable cooling systems for comfort in summer. Some solutions/techniques are equally effective both in summer and winter seasons for improved infiltration and leakages. These techniques are more effective in areas with hot summers and cold winters. Such solutions include Jumbolon (polystyrene), brick tiles with stabilised mud, insulating paper board, stabilised mud, mud with thermopole and thermopole false ceilings. Some new materials, specifically insulative (polystyrene, insulating paper board, smart concrete tiles and Munawar tiles), are more efficient in reducing cooling load and add aesthetics to the inside of rooms. None of the solutions provide comfortable indoor conditions during hot weather as occur in the summer in Pakistan. 3.9 Conclusion Punjab and Sindh are the most populated provinces of Pakistan. The population of the two provinces is more than 75% of the country s population. The climate of Pakistan is mostly hot and dry. Most of the areas have hot summers with a mean daily maximum temperature of more than 34 C and they require cooling systems for comfort. The annual average relative humidity for most of the areas is from 40% to 70%. In the past four decades there is an average increase of 3 C in the heat index. There is an increase in the frequency of thermal extremes of temperature values of more than 40 C and 45 C. This high temperature climatic zone is mostly in the Punjab and Sindh regions which are home to majority of the country s population. 74

75 The ASHRAE standard comfort temperature is about 26 C. The comfort zone specified by PMV is between to The ISO 7730 standard does not adequately describe comfort conditions for tropical and hot climates when air temperature is above 30 C and air velocities of more than 1m/s. For New Delhi (Lahore) ASHRAE adaptive comfort temperature range is between 26 C to 30 C, when the mean monthly outdoor temperature is between 33 C and 35 C. Similar temperature range was obtained by Nicol et al. [97, 101, 102] adaptive thermal comfort in Pakistan. Use of an adaptive comfort temperature as a set point compared to an ASHRAE standard temperature can help to reduce the building cooling load and improve the efficiency of cooling systems. In Pakistan there is overall potential for 29% of savings in building energy. The Turkish building energy efficiency code s success shows that after the application of building energy codes and standards in Pakistan s buildings the following benefits may be achieved: Decreased cooling and heating loads Improved energy efficiency Comfortable livings Improved and healthier life styles Improved productivity The case study of the building thermal performance improvement project showed a potential for improving existing buildings for comfort in summer with the application of a few techniques. With nominal expense using insulative and other techniques a lower cooling load and electricity consumption reduction could be achieved in existing buildings. As discussed in Chapter 1, the energy crisis and very hot climate in the summer are adding hardships to the lives of the majority of the population and the most significant factor is the absence of cooling systems during power cut periods. Long term and sustainable clean energy systems should be introduced to solve the energy crisis and create comfort conditions during the summer. 75

76 Chapter 4: Solar Cooling Systems 4.1 Introduction In the previous chapters, the literature has discussed in detail of energy demand, electricity crisis, and the effects of energy crises, solar energy potential, climate, and building energy in Pakistan. The literature showed there is demand for sustainable energy system which can provide comfort in buildings, especially during the hot summer season. Solar energy is widely available in most areas of the country, and its application can provide sustainable, clean energy. As cooling demand increases in line with increases in solar radiation intensity increases, solar cooling could provide a logical solution. This research s aim is to investigate the potential of a solar energy powered cooling system for the climate of Pakistan. Solar energy is already widely used as an energy source for cooling [ ]. Solar cooling technologies are mainly categorised into passive solar and active solar systems based on the process of capturing, converting, and distributing solar energy. Active solar technologies are photovoltaic and solar thermal systems [118]. A variety of solar cooling technologies have been developed and many are already available in the market [119, 120]. Passive solar techniques include orienting a building towards the Sun, selecting materials with favourable thermal properties for heat gain or designing light dispersing properties and spaces for natural ventilation to provide cooling effects [121]. This research is carried out using an active solar technique for cooling in buildings. Active solar cooling can be achieved by integrating photovoltaic (solar electric) or solar thermal with the cooling generation system [117, 122]. The efficiency of the thermal collector improves as the ambient temperature increases whereas the solar PV modules efficiency reduces [120, 123]. The economic study shows that solar thermal cooling is more viable than solar electric cooling in hot climates and annual costs are location dependent. So, for Pakistan, hot climate solar thermal will be preferable. The solar thermal cooling system specific cost per kwh of cooling in Spanish locations is between 0.13 and 0.30 /kwh. In hot climates like Jakarta and Riyadh, the specific costs are as low as 0.09 to 0.15 /kwh[22]. Solar thermal cooling has better compatibility with supply and demand, with cheap storage compared to solar electric cooling. The investment cost of both solar electric and solar 76

77 thermal cooling systems is similar[124]. The average CO 2 emission saving for solar cooling in European region is 226kg/kW C per year by saving on the consumption of primary energy [24]. 4.2 Solar Electric Cooling In solar electric cooling systems, photovoltaic (PV) panels are mostly used to power conventional vapour compression based cooling machines [ ]. A Stirling refrigerator can also be connected to PV panels for cooling. The COP of Stirling refrigerators is less than that of a vapour compression cooling system [ ]. The main components of solar electric cooling are PV panels, a direct current (DC) motor and vapour compression chiller, cooling tower, chilled water pump, condenser water pump, and air handling unit, as shown in Figure 4-1. The PV panels are sized to provide necessary electric power to motor, driving the compression chiller. When the PV panels cannot supply the required power due to weather conditions or at night, a power regulator is used to draw auxiliary power from the grid connected supply system. The power regulator is capable of tracking the maximum power from solar panels and minimises the use of power from a grid connection [117, 118, 120, 131]. Figure 4-1: Schematic overview of solar electric cooling system [132] The vapour compression cycle consists of four components which are used to remove heat from a lower temperature (cold reservoir) to higher temperature (hot reservoir) space. These components include the evaporator, compressor, condenser, and expansion valve as shown in Figure 4-1[132]. 77

78 These components are connected in a close loop as the refrigerant is continuously circulated to all of the components. The operation of the vapour compression system is shown in Figure 4-2.The refrigerant starts from stage 1, with a low temperature and pressure at inlet to the compressor. The refrigerant exits the compressor with a high temperature and pressure in a gas phase. The super-heated refrigerant enters the condenser at stage 2 and exchanges heat to a lower temperature secondary fluid. The refrigerant exits the condenser as liquid at stage 3 and enters the expansion valve. In the expansion valve, the pressure of liquid is decreased through a throttling effect and the sudden decrease in pressure reduces the temperature of refrigerant[133]. Figure 4-2: Schematic diagram of vapour compression refrigeration system[133] The refrigerant exits the expansion valve as a mixture of liquid and gas, with a low temperature and pressure at stage 4. After stage 4, the refrigerant enters the evaporator and absorbs the heat from the primary fluid. The refrigerant exits the evaporator at a slightly higher temperature in the gas phase [ ]. The co-efficient of the performance (COP) of the refrigeration system is defined as the cooling power (Q e ), divided by work in w, as expressed in Equation 1. 78

79 COP = η cool = Q e / w (1) The primary fluid is usually indoor air, or water which then cools the air through a cooling coil. Similarly, the secondary fluid is usually outdoor air or water which then rejects heat to the ambient air through a cooling tower [118, 132]. PV modules are devices which convert sunlight directly into electricity without any intermediate systems [134]. PV cells are normally semiconductors and produce direct current, details of the types and efficiency of solar cells will be discussed in the next section. The main disadvantage of PV systems is their low efficiency. The power produced (w PV ) by a PV panel is calculated by using the efficiency of the PV panel (η PV ) and solar energy incident on the panel (Q S ) as shown in Equation 2 [119, 132]. w PV = η PV Q S (2) And Q S = I A (3) Where I = Incident solar Insolation (W/m 2 ) A= Area of PV collector (m 2 ) The overall efficiency of solar electric cooling system is expressed in Equation 4. η sol.cool = η PV η cool = Q e / Q S (4) In solar electric system compressors, power consumption (w) should be provided by the PV panels. The total area (A) of the solar PV panels can be calculated to cover the total daily power consumption (w T ) of the compressor by using total daily solar radiation (I T ) and daily total PV power production (W PV ) T [135, 136]. A = w T / η PV. I T (5) The PV system is suitable for small sized refrigeration systems used for medical or food applications in remote areas, with no conventional energy resources and a high level of solar radiation [120, 137]. Solar tracking systems can be used to obtain maximum power from sunrise to sunset time [135].Solar electric vapour compression cooling systems are limited and few systems are available in literature [138]. 79

80 4.3 Solar Thermal Cooling Solar thermal systems produce heat energy gained from solar radiation through the heating of a fluid circulated through a collector. Solar thermal systems are able to exploit both direct and diffused radiation, and therefore can be installed anywhere [120, 139]. The use of solar thermal energy for cooling in hot and sunny climates is a promising application of solar thermal collectors in buildings. The main advantage is that in solar air conditioning applications, cooling loads and solar gains occur at about the same time in summer. Solar cooling has the potential to significantly reduce electricity consumption, contribute to fossil fuel energy saving and electrical peak load reduction. Solar thermal cooling can help in achieving carbon emission reduction and promoting clean and environmentally friendly refrigerants used in thermal cooling systems compared to conventional vapour compression cooling systems [140]. The solar cooling technology has not been widely applied and needs more research and development to achieve competitive levels of reliability and cost with conventional cooling technologies [120, 141]. Solar thermal systems can use more incoming solar radiation than PV systems. When a solar light strikes with a PV system, about 35% of the total incident spectrum (Ultraviolet to Yellow) can be utilised to generate electricity and rest spectrum of about 65% (Orange to Infrared) is converted to heat, as shown in Figure 4-3 [40]. Solar light spectrum used in PV system ULTRAVOILET 10% VOILET 5% BLUE 5% INFRARED 45% Converted to heat ~65% useful in a Si based PV ~35% GREEN 10% YELLOW 5% RED 15% ORANGE 5% Figure 4-3 Solar light spectrum used in a PV system[40] As the solar thermal system converts solar energy to heat energy, collectors have no such limitation. A solar thermal collector can absorb over 95% of the incoming radiation spectrum 80

81 depending on the absorbing materials [40]. Due to losses and inefficiencies, not all absorbed energy is converted to useful energy. The collection efficiency of commercially available solar thermal collectors is more than double compared to PV systems [142, 143] History of Solar Thermal Cooling Systems Development The application of solar thermal system for cooling is about five decades old. A summary of important developments in solar thermal cooling systems is described in Table 4-1. Table 4-1: History of solar thermal cooling development Year Development Of Solar Thermal Cooling System First Study of the use of solar thermal energy for cooling purpose [144] First commercial single effect absorption chiller for solar cooling [145] First simulation of a solar heating and cooling system [146] First TRNSYS simulation of solar processes and its application [147] Experimental study of a hybrid solar air condition system [148, 149] Experimental study of home heating and cooling with flat plate collector [150] Experimental study of a Yazaki solar cooling system for solar house one [151] Design of a residential solar heating & cooling system using the evacuated tube collector [152] Development of a double effect absorption chiller for solar assisted cooling [153] Development and test of solar Rankine cycle heating and cooling systems [154] Fortran-based modelling and simulation of a solar absorption cooling system [155] Development of a solar cooling absorption chiller with 5-10kW capacity [156] Experimental study of a solar liquid adsorption cooling system [157] Study of the performance improvement of a solar cooling unit [158] Experimental studies of a solar air conditioning system with a partitioned hot water storage tank [159] Grossman established triple & double effects are better than single effect solar powered chillers [160] R114 replaced by R142b in solar ejector system for better efficiency and environmental effect [161] Simulation & optimization of LiBr solar absorption cooling system with evacuated tube collector [162] Investigation of liquid desiccant system for solar air conditioning [163] Simulation study of solar LiBr-H 2 O absorption cooling system with parabolic trough collector [164] Study of an air-cooled LiBr-H 2 O absorption chiller cooling system in extremely hot weather [165] Experimental investigation of solar absorption cooling system without backup in tropical climate [166] Study of alternative designs for 24-h operating solar powered absorption refrigeration technology [167] Study of solar cooling systems utilising concentrating solar collectors [168] Experimental comparison of two solar driven air cooled LiBr-H 2 O absorption chillers [169] A theoretical & experimental study of the solar ejector cooling system with R236fa carried out [170] Design of solar ejector cooling system for a COP of 0.32 [171] Techno-economic review of solar cooling technologies based on location-specific data [172]. 81

82 4.3.2 World Solar Thermal Cooling Status 2014 and IEA Road Map 2050 The global solar cooling market grew at an average annual rate of about 40% from 2004 to About 1,200 systems of different types and sizes were installed worldwide by 2014 and most of these systems are in Europe (75%). The use of solar cooling is rising in many regions with sunny, dry climates, including Australia, India, the Mediterranean islands, and the Middle East. The availability of small (less than 20 kw) cooling kits for residential use has increased for the residential sector in Central Europe [173]. One of the market drivers for solar cooling is the potential to reduce peak electricity demand, particularly in countries with significant cooling needs. The cost of solar cooling kits continues to fall, declining by 45 55% (depending on system size) over the period [173]. Solar cooling could avoid the need for additional electricity transmission capacity caused by higher peak loads from the rapidly increasing cooling demand in many parts of the world [174]. According to the IEA 2050 roadmap, up to 2050, solar thermal energy use for cooling could contribute to 417 TWh th per year. The installed capacity of more than 1000 GW th for cooling will account for nearly 17% of energy use for cooling in 2050 [174] Solar Thermal Cooling Systems A solar thermal cooling system consists of four basic components: a thermal collector, thermal storage, thermal chiller, and heat exchanging system to exchange heat with a conditioned space [117, 120]. An overview of solar thermal cooling system is shown in Figure 4-4.The other components normally required are a hot water pump, auxiliary heater, chilled water pump, cooling tower, condenser water pump, and air handling unit [5, 6]. 82

83 Figure 4-4: Overview of thermal cooling system[123] The types of solar thermal collectors and thermal cooling systems are discussed in detail here as these are important components of a solar thermal cooling system. 4.4 Solar Thermal Collectors Solar thermal collectors are heat-exchanging devices that transform solar radiation into internal energy in a fluid (air or water). The collected solar energy is carried away by circulating fluid either directly to hot water or space conditioning equipment or to a thermal energy storage system for use at night and or in cloudy days [175]. On the basis of temperature spectrum application, solar collectors are divided into three categories, as shown in Figure 4-5 [176]. Low temperature (Domestic Hot Water) Medium temperature (Solar Heating and Cooling of Buildings) High temperature (Industrial Process Heating and Electricity generation) 83

84 Figure 4-5: Solar energy collector s application [176] There are two basic types of solar collectors; stationary and concentrating, as shown in Figure 4-6. Stationary collectors have same area and do not track solar radiation whereas concentrating collectors have concave reflective surfaces to intercept and focus the solar radiation to a small area for an increased solar energy flux [37, 177]. Figure 4-6: Types of solar thermal collectors [178] Normally, concentrating collectors are used for power generation rather than solar heating or cooling. These collectors will be covered in the review of collectors for the purpose of comparison Stationary Collectors: These collectors are normally permanently fixed in a position and do not track the sun. Three collectors fall into this category; 84

85 a) Flat Plate Collector (FPC) b) Compound Parabolic Collectors (CPC) c) Evacuated Tube Collectors (ETC) Flat Plate Collectors (FPC) A typical flat-plate solar collector is shown in Figure 4-7. When solar radiation passes through a transparent cover and impinges on the black absorber surface, a large portion of the incoming energy is absorbed by the plate and is transferred to a transport medium in fluid tubes for storage or direct use [141, 177]. Figure 4-7: Construction of flat plate collector [37] The underside of the absorber plate and the side of casing are well insulated to reduce conduction losses. The liquid tubes are connected at both ends by large diameter header tubes. A transparent cover used to reduce convection losses from the absorber plate through the restraint of a stagnant air layer between the absorber plate and glass. It also reduces radiation losses from the collector [141, 177]. FPC s are available in a wide range of designs and materials. These are the most used type of collector. The major purpose is to collect more solar energy with a lower cost. These are normally used for low temperature applications of up to 80 C. FPC is usually fixed in position, oriented directly towards the equator, facing south in the Northern hemisphere and north in the Southern Hemisphere. The optimum tilt angle of the collector is equal to the latitude of the location with angle variations of (10 15) more or less [37, 177]. 85

86 Compound Parabolic Collectors (CPC) CPC s have the capability of reflecting nearly all of incident radiation to the absorber. The necessity of moving the collector to accommodate the changing solar orientation is reduced by using a trough with two sections of parabolic sides facing each other, as shown in Figure 4-8. CPC s accept incoming radiation over a relatively wide range of angles. Due to multiple internal reflections, the incident radiation within the collector acceptance angle (θc) is directed to the absorber surface at the bottom of collector. The shown reflector has a lower portion which is circular (AB and AC) and the upper portions (BD and CE) are parabolic. The upper part of the collector truncated to increase the radiation passage to the absorber. CPC s are usually covered with glass to avoid dust and other materials from entering the collector [37, 177]. Figure 4-8: Schematic diagram of compound parabolic collector [37] The orientation of a CPC collector is relative to its acceptance angle. The collector can be oriented along its long axis in either a north-south or east -west direction and its aperture tilted directly towards the equator at an angle equal to the local latitude. When oriented along the north-south direction, the collector must track the sun by turning its axis continuously. As the acceptance angle is wide along its long axis, the seasonal tilt adjustment is not required. When oriented with its long axis along the east-west direction, a little seasonal tilt adjustment is required. For stationary CPC collectors, the minimum acceptance angle is 47 in order to cover the declination of the sun from summer to winter. In practice, bigger angles are used to enable the collector to collect diffuse radiation with a lower concentration ratio [37, 177]. 86

87 CPC collectors are useful for sunny and warm climates. For higher temperature applications, a tracking CPC can be used. These are not favourable for cold, cloudy, and windy days [37, 177] Evacuated Tube Collectors (ETC) Evacuated tube collectors are highly efficient in circumstances where there is a lower radiation and a higher difference between the absorber and ambient temperature. Evacuated tubes collectors are more expensive than glazed flat plate collectors. Evacuated tube collectors use glass tubes with a vacuum. This vacuum works as insulation, reducing heat loss from the collector and thus increasing the efficiency of the collector. Some ETCs use liquidvapour phase change materials for efficient heat transfer [37, 177]. Figure 4-9: Schematic diagram of evacuated tube collector [37] The sealed copper pipe is attached to black copper fins that fill the tube (absorber plate). The heat pipe contains a small amount of fluid (e.g. methanol) that undergoes an evaporating condensing cycle. In this cycle, solar heat evaporates the liquid and the vapour travels to the heat sink region where it condenses and releases its latent heat. The condensed fluid returns back to the solar collector and the process are repeated. These tubes are connected to a heat exchanger (manifold), as shown in Figure 4-9. Water or glycol flows through the manifold and picks up the heat from the tubes. The heated liquid is stored or heats the load, directly or through a heat exchanger [37, 177]. 87

88 4.4.2 Concentrating Solar Power (CSP) In concentrating collectors, solar energy is optically concentrated before it is transformed into heat. Concentration is obtained by the reflection or refraction of solar radiation by use of mirrors or lens. This reflected or refracted radiation is concentrated in a focal area, thus increasing the energy flux per unit area in receiver. CSP systems are designed to produce medium ( C) to high high-temperature ( C) heat for electricity generation or for the co-generation of electricity and heat[179]. These systems are capable of exploiting only Direct Normal Irradiation (DNI), which is the energy received directly from the Sun (not scattered by the atmosphere) on a surface tracked perpendicular to the Sun s rays. Arid or semi-arid areas with strong sunshine and clear skies are suitable for CSP application [39]. CSP are of following four types; a) Linear Fresnel Reflectors b) Power Towers (Central Receiver Systems) c) Parabolic Troughs d) Parabolic Dish Linear Fresnel Reflectors: (Line Focus, Fixed Receiver) Linear Fresnel Reflectors (LFR) are curved trough systems made by using long rows of flat or curved mirrors to reflect the solar rays onto a downward facing linear, fixed receiver as shown in Figure The receiver can attain temperature of up to 250 C.The main advantage of the LFR system is its simple design of flexibly bent mirrors and fix receivers with low-cost direct steam generation. LFR plants have low efficiency in the conversion of solar energy to electricity [37, 177, 179, 180]. Giorgio Francia was the pioneer in developing both a linear and two-axis tracking Fresnel reflector system in 60s. For higher temperatures, he used two-axis tracking as modern optics and coatings were not available [177]. 88

89 Figure 4-10: Linear fresnel reflector (Left) & compact linear fresnel reflector (Right) [37] The difficulty with LFR is that in order to avoid shading and blocking between adjacent reflectors, the space needs to be increased between reflectors. The most recent design is for Compact Linear Fresnel Reflectors (CLFR), two parallel receivers for each row of mirrors as shown in Figure The classical LFR system has only one receiver and there is no choice of the direction and orientation of reflector. The interleaved arrangement minimises beam blocking by adjacent reflectors and allows high reflector density and low tower height [37, 177, 180] Solar Towers (Point Focus, Fixed Receiver) Solar towers are also known as Central Receiver Systems (CRS). Large numbers of small reflectors called heliostats are used to concentrate the solar rays on a central receiver placed on top of a fixed tower, as shown in Figure Each heliostat has a m 2 area of reflective surface. Some new commercial tower plants use Direct Steam Generation (DSG) system in receivers, in which slightly concave mirror segments on the heliostats directed rays into the cavity of a steam generator to produce high pressure and temperature steam. The heat energy absorbed by the receiver is transferred to be circulated for use. The main advantages of central receivers are: [177, 179] It minimises the thermal energy transportation as it collects solar energy optically and transfers it to a single receiver. The concentration ratio of is achieved and has high efficiency, both in energy collection and in electricity conversion. 89

90 Figure 4-11: Schematic overview of power tower (central receiver system) [37] In addition, the concept is highly flexible with a wide variety of heliostats, receivers, transfer fluids, and power blocks. The average solar flux impinging on the receiver values from 200 to 1000 kw/m 2. This high flux helps to achieve high temperatures of more than 1500 C. The heat transfer and storage fluid may be water /steam, molten sodium or molten nitrate salt (sodium nitrate / potassium nitrate) [37, 177, 180] Parabolic Troughs (Line Focus, Mobile Receiver) This system has light structures and low cost technology for process heat applications of up to 400 C. A parabolic trough system consists of parallel rows of mirrors (reflectors) curved in one dimension to focus the solar radiation on a linear receiver, as shown in Figure The mirror array can be more than 100m long with the curved surface at 5-6m across. A linear tube is placed along the focal line to form an external surface receiver. Stainless steel pipes (absorber tubes) with a selective coating serve as heat collectors. The coating allows pipes to absorb high levels of solar radiation while emitting much less radiation. A glass cover tube is placed around the receiver tube to reduce the convective heat loss. The tube may be evacuated to further reduce convective heat loss. The disadvantage of a glass cover tube is that the reflected light from the concentrator must pass through glass to reach absorber, adding a transmittance loss. The glass envelope has an antireflective coating to improve transmissivity [37, 177, 179, 180]. The reflectors move in tandem with the Sun as it crosses the sky. It is sufficient to use single axis tracking of the Sun and thus a long collectors module is produced. The collector can be oriented in an east west direction, tracking the sun from north to south or oriented in a northsouth direction and tracking the sun from east to west. Over a period of year, a horizontal 90

91 north south, trough field usually collects slightly more energy than a horizontal east-west one. However, the north-south field collects a lot of energy in the summer and much less in the winter. The east-west field collects more energy in winter than a north-south field and less in the summer, providing a more constant annual output. Therefore, the choice of orientation usually depends on the application and energy needed during summer or winter [37, 177, 179, 180]. Figure 4-12: Schematic of a parabolic trough collector [37] The tracking mechanism of a parabolic trough collector is shown in Figure The tracking system must be reliable and able to follow the Sun with certain degree of accuracy and it returns to its original position at the end of the day or at night. The tracking mechanism is also used to protect collectors from hazardous environmental working conditions such as wind gusts, overheating, and the failure of the thermal fluid flow system, by turning the collector out of focus. The tracking mechanism has two categories: mechanical and electrical/electronic. The electronic system is more reliable and accurate in tracking [37, 177]. 91

92 Figure 4-13: Parabolic trough collector tracking mechanism [37] All parabolic trough plants currently in commercial operation rely on synthetic oil as the fluid for heat transfer from the collector pipes to the heat exchangers, where water is preheated, evaporated, and then superheated. The superheated steam runs a turbine, which drives the generator to produce electricity. After condensation, water returns to the heat exchangers. Parabolic troughs are the most mature system among CSP technologies and mostly used in all commercial plants. A recent development in parabolic troughs collectors is the design and manufacture of the Euro trough with a lightweight structure to achieve cost effective solar power [37, 177, 180] Parabolic Dish Collectors (Point Focus, Mobile Receiver) Parabolic dishes concentrate on the solar radiation at a focal point above the centre of the dish. The entire apparatus tracks the Sun in two axes, with the dish and receiver moving in tandem, as shown in Figure Most dishes have an independent engine/generator (Stirling machine or micro turbine) at the focal point. Dishes have the highest solar to electric conversion efficiency over any other CSP system. The salient features of dishes make it competitive with PV modules, and other CSP technologies. A parabolic system can achieve temperatures in excess of 1000 C [37, 177, 179, 180]. The salient features of parabolic dishes are; [177] They always pointing towards the Sun, these are the most efficient of all collectors. 92

93 The concentration ratios are in the range of , making it more efficient in solar energy absorption and power conversion systems. These have modular collector and receiver units that can function independently or as part of a large system. Figure 4-14: Schematic of a parabolic dish [37] Parabolic dishes are limited in size (tens of kw or smaller) and each produces electricity independently, which means that hundreds or thousands would need to be co-located for large-scale production [37, 180] Comparison of Thermal Collectors For solar thermal cooling, most concentrating collectors are expected to be too expensive as an input thermal energy system for building integrated solar cooling system. The high cost is mainly due to the complexity of the tracking system [123]. However, tracking can provide a significant increase in energy output. A 10-year comparison of stationary and tracking solar collectors is shown in Figure The stationary collector was tilted at 40 at Askov, Denmark. The annual energy output of the single axis vertical and horizontal tracking is about 7% and 55% more than the stationary collector. The two axis tracking collector has about 75% more energy output compared to the stationary collector [181]. 93

94 Annual energy output (kwh/m 2.year) Thermal performance of collectors Stationary Vertical Tracking Horizontal Tracking vertical+horiz ontal Tracking Figure 4-15: 10 year thermal performance of stationary and tracking collectors [181] A thermal cooling system operates with an input heat at a temperature of between 60 C and 100 C, so a high temperature output of concentrating collectors is not required. For solar thermal cooling, both flat plate and evacuated tube collectors are used [123]. Evacuated tube collectors are preferred over flat plate collectors due to the higher thermal efficiency and to produce higher temperature output [182, 183]. Higher efficiency at low incidence angles making them more suitable for daylong performance [177, 183]. Flat plate collectors are the most used collectors in solar cooling installations. Although Evacuated tube collectors are expensive, they need less collector area compared to flat plate collectors. The average collector area for a flat plate collector is 4.6m 2 /kw C, whereas for an evacuated tube collector it is 2.5m 2 /kw C [132, 184]. 4.5 Thermal Cooling Systems Thermal cooling systems are driven by heat, instead of electric power to run the compressor in a conventional vapour compression cooling system [132]. Thermal cooling systems are always preferred when a large amount of waste heat energy is available. To couple with a renewable energy system, such as solar thermal energy, these cooling systems are used for solar assisted cooling and air-conditioning [185]. 94

95 In thermal cooling systems, sorption technology is used. In this technology, the cooling effect is obtained by physical or chemical changes between a pair of substances (the sorbate and the sorbent). The sorption system is classified into open and closed sorption systems. The open sorption system includes a solid and liquid desiccant system whereas absorption and adsorption systems are closed sorption systems [117, 120, 132]. There are of four main types of thermal cooling systems, which are: Absorption system Adsorption system Solid and Liquid desiccant dehumidifiers Ejector system Absorption System Absorption is a process in which two substances in different states are mixed into each other. These two different states form a solution called a mixture. This process is reversible and can occur by the addition or removal of heat. The first absorption system was introduced in 1895 [117, 120, 132]. Absorption system-based machines are the most commonly used thermal driven cooling systems in solar cooling installations. In absorption systems, an absorbent, on the lowpressure side, absorbs an evaporating refrigerant. The two most used combinations of fluids include lithium bromide-water (LiBr H 2 O), where water is the refrigerant and ammoniawater (NH 3 H 2 O) systems, where ammonia is the refrigerant. The first pair is used for building cooling and the second for low temperature applications [37, 117, 120, 132]. 95

96 Figure 4-16: Schematic overview of solar absorption cooling system[120] In the absorption refrigeration system, low pressure refrigerant vapour from the evaporator is dissolved in the absorbent in the absorber, as shown in Figure Then, the solution is pumped to a high pressure with an ordinary liquid pump. The addition of heat in the generator is used to separate the refrigerant from the solution. In this way, the refrigerant vapour is compressed with less mechanical energy than the vapour compression systems demand. The weak solution is then returned to the absorber through a heat exchanger to recover heat. The remainder of the system consists of similar components to a vapour compression system (a condenser, expansion valve, and evaporator [37, 120, 185]. The LiBr H 2 O system operates at a generator temperature in the range of C with water used as a coolant in the absorber and condenser. The limitation of the LiBr H 2 O systems is that their evaporator cannot operate at temperatures much below 5 C since the refrigerant is water vapour. Commercially available absorption chillers for air conditioning applications usually operate with a solution of LiBr H 2 O and use steam or hot water as the heat source [37, 117, 132]. The single effect absorption chillers are mainly used for building cooling loads, where chilled water is required at 6 7 C. The COP of single effect absorption system varies from 0.60 to This variation is due to the heat source and the cooling water temperature. Single effect chillers can operate with hot water temperatures ranging from about 65 to 150 C [37, 117, 120, 132]. 96

97 The double effect absorption chiller has two stages of generation to separate the refrigerant from the absorbent. The temperature of the heat source needed to drive the high-stage generator is essentially higher, and is in the range of C. Double effect chillers have a higher COP of about The triple effect machines can have a COP of about 1.70 [37, 117, 120, 132]. Absorption systems can use flat plate or evacuated tube collectors for single and double effect machines, and evacuated tube or concentrated parabolic collectors for triple effects cases [132]. From the literature, it is established that LiBr H 2 O absorption systems are a mature technology and have a good perspective for energy efficient cooling in buildings [124] Adsorption System Adsorption technology was first used for cooling systems in the early 1990s. The adsorption process is surface phenomenon whereas absorption is a volumetric phenomenon [117, 120]. In adsorption systems, a solid (the adsorbent) and gas (the refrigerant) interact with each other. The adsorbents are porous solids, and can reversibly adsorb large volumes of a vapour. This interaction can be chemical or physical and depends upon adsorption forces. In chemical adsorption, there is an exchange of electrons which occurs between solids and gas. In physical adsorption, molecules of a refrigerant come to fix to the surface of the absorbent [37, 117, 120, 132, 185]. Solar adsorption s practical application in the field of refrigeration is relatively recent. The concentration of adsorbate vapours in a solid adsorbent is a function of the temperature of the mixture (adsorbent and adsorbate), and the vapour pressure of the latter. Under constant pressure conditions, it is possible to adsorb or desorb the adsorbate by varying the temperature of the mixture. This forms the basis of the application of this phenomenon in the solar-powered adsorption refrigeration, as shown in Figure 4-17 [37, 117, 120]. A number of different solid adsorption pairs, such as activated carbon ammonia, zeolite water, zeolite methanol, activated carbon methanol, and silica gel-water are used. The efficiency of adsorption systems is low. Many systems integrate the adsorbent bed and the solar collector together by packing the adsorbent in the collector. For continuous operation, two adsorption cycles are combined and such systems can have a COP of 0.60 [37, 117, 120, 132, 185]. 97

98 Figure 4-17: Schematic diagram of solar adsorption system[95] The activated carbon methanol working pair was found to perform the best. Complete physical property data is available for a few potential working pairs, but the optimum performance remains still unknown. The advantages of adsorption system include: no danger of damage due to high temperatures, environmentally friendly materials use, less usage of electricity and low maintenance costs. The disadvantages are: a lower COP than absorption systems, higher initial costs, and requiring a high vacuum tightness of the container [37, 117, 120, 132] Solid and Liquid Desiccant Cooling System A desiccant cooling system is the combination of evaporative cooling and dehumidification. These are best suitable for application where humidity is low. These are open sorption cooling systems as water is used as a refrigerant in direct contact with the ambient air. The desiccants are natural or synthetic substances capable of absorbing or desorbing water vapour due to difference of water vapour pressure between the surrounding air and desiccant surface [117, 132, 185]. The driving force for the desiccant process is the difference in vapour pressure between the air and the desiccant surface. When the water vapour pressure on the desiccant surface is 98

99 lower than air, water is absorbed by the desiccant. When the water is absorbed, the vapour pressure in the desiccant is equal to that in the air, as shown in Figure Figure 4-18: Desiccant cooling process [186] To allow for the repeated use of the desiccant, regeneration is required. This is accomplished by heating the desiccant to increase its water vapour pressure. The heat required for regeneration is supplied at a low temperature ( C). Both solid and liquid desiccant materials are used. These include lithium chloride, tri-ethylene glycol, silica gels, aluminium silicates (zeolite), aluminium oxides, lithium bromide solution, and lithium chloride solution with water [117, 186]. A desiccant cooling system comprises of three components; regeneration heat source, the dehumidifier (desiccant material), and the cooling unit as shown in Figure 4-19 [186, 187]. Figure 4-19: Principle of desiccant cooling [186] 99

100 Solid Desiccant System A solid desiccant cooling system uses rotating wheels made of silica gel, zeolite, or lithium chloride as sorption materials. Figure 4-20 illustrates a solar-driven solid desiccant cooling system. The system has two, slowly revolving wheels and several other components between the two air streams and a conditioned space. The return air from the conditioned space first goes through a direct evaporative cooler and enters the heat exchange wheel with a reduced temperature (A-B). It cools down a segment of the heat exchange wheel when it passes through (B-C) and is heated as it does so. This warm air stream is further heated to an elevated temperature by the solar heat in the heating-coil (C-D). The heating-coil has a temperature of between 50 C to 75 C. The resulting hot air regenerates the desiccant wheel and is rejected to ambient (D-E). On the other side, fresh ambient air enters the regenerated part of the desiccant wheel (1-2). Dry and hot air comes out of the wheel as the result of dehumidification. This air is cooled down by the heat exchange wheel (2-3). Depending on the temperature level, it is directly supplied to the conditioned space or further cooled in an after cooler (3-4). If no after cooler is used, the cooling effect is created only by the heat exchange wheel that was previously cooled by the humid return air at point B on the other side. The temperature at point 3, T 3, cannot be lower than T B, which in turn is a function of the return air condition at point A, as shown in Figure 4-20 [117, 119, 132, 185]. Figure 4-20: An illustration of solar assisted solid desiccant cooling system [119] 100

101 This system allows a saving of up to 50% of primary energy compared to the vapour compression system and is environment friendly. However, further improvements in the efficiency of this system are required [132] Liquid Desiccant System In the liquid desiccant cooling system, dehydration is obtained by absorption. The desiccant wheel is replaced by a dehumidifier and regenerator. The air is cooled down by spraying an absorbent solution into the air. Generally, the solution consists of water and lithium chloride or calcium chloride. The liquid desiccant assisted air conditioning can achieve up to 40% of energy savings with regards to the traditional air conditioning system and savings become even greater when regeneration energy is drawn from waste heat, solar energy or any other free energy sources. Liquid desiccant can also store a large amount of energy by storing concentrated solutions. This storage can make it a more promising future cooling system with solar energy [117, 119, 132, 185]. In a liquid desiccant cooling system, the liquid desiccant circulates between an absorber and a regenerator in the same way as in an absorption system. The main difference is that the equilibrium temperature of a liquid desiccant is determined not by the total pressure but by the partial pressure of water in the humid air to which the solution is exposed. A typical liquid desiccant system is shown in Figure In the dehumidifier, the concentrated solution is sprayed at point A over the cooling coil at point B, while ambient or returns air at point 1 is blown across the stream. The solution absorbs moisture from the air and simultaneously cools down by the cooling coil. The results of this process are the cool dry air at point 2 and the diluted solution at point C. An after cooler at point 3, cools down this air stream further to the lower temperature, as shown in Figure 4-21 [117, 119, 132]. 101

102 Figure 4-21: A Solar assisted liquid desiccant cooling system [119] In the regenerator, the diluted solution from the dehumidifier sprayed over the heating coil at point E, connected to solar collectors and the ambient air at point 4, is blown across the solution stream. Some water is taken away from the diluted solution by the air while the diluted solution is heated up by the heating coil E. The result is a concentrated solution collected at point F and the hot humid air is rejected to the ambient at point 5. A recuperative heat exchanger preheats the cool diluted solution from the dehumidifier using the waste heat of the hot concentrated solution from the regenerator, resulting in a higher COP [119]. The liquid desiccants have an advantage because of their operational flexibility and capability of absorbing pollutants, and bacteria, and being regenerated at relatively low temperatures. Other advantages are high energy storage and the ability to continuously pass a large volume of air through a close system. The disadvantages of liquid desiccant cooling systems include less dehumidification in humid climates, a relatively larger size, and heavier and reduced efficiency due to air leaks [117, 119, 132, 140]. A study of a hybrid cooling system, conventional electrical and desiccant cooling systems in four different locations worldwide (Hamburg, Chicago, Sao Paulo, and Singapore), showed that the solar cooling system is not yet economically viable [124, 188]. 102

103 4.5.4 Ejector System A solar ejector cooling system is a low grade thermal energy driven technology. The ejector is a thermally driven compressor that operates on a vapour compression refrigeration cycle. The generator and ejector take the place of the electric compressor; it uses heat rather than electricity to produce the compression effect in a vapour compression system. A solar ejector system is shown in figure 4-22 [132]. Figure 4-22: Schematic view of solar ejector cooling system [132] The ejector cycle start from the generator exit, where the refrigerant is in a superheated state. Under these conditions, the internal geometry of the ejector sucks the evaporator vapour for its compression at an intermediate pressure. The working fluid enters the condenser and it is cooled down to a saturated liquid state. After the condenser fluid is divided into two streams; the first stream is pumped to the evaporator generator. The other stream is passed through an expansion valve, to create a cooling effect and then enters the evaporator. In the evaporator it exchanges heat for space cooling [117, 185]. Ejectors have been used in evacuating air from low-pressure steam condensers. An ejector in this application acts as a vacuum pump, driven by low pressure steam. Efficiency was not as important as reliability. It was a small step to form a vapour compression heat pump using an ejector as a heat driven compressor. Steam-driven ejector heat pumps became common in air conditioning, particularly in hotels and ships during the early 20th century. Ejector systems were found to be low cost, very reliable and maintenance free. The main advantages are the absence of moving parts, being smaller in size, having lower initial costs, and the simplicity in design. They also consume less electricity compared to other refrigeration systems. The 103

104 main disadvantage of the ejector is its low COP compared to other cooling systems. The COP of ejector systems is in range of , which is much lower than vapour compression or absorption systems. Due to low COP, ejector systems use is not preferred [132, 140]. From the literature presented on solar thermal cooling systems, it is observed that absorption cooling systems are most commonly used in all of the installations. Single effect absorption systems can be used with both flat plate and evacuated tube collectors. As presented in Section 4.4.3, evacuated tube collectors are more efficient and require less space than the flat plate collectors, therefore in this research, the absorption cooling system with an evacuated tube collector will be investigated for the feasibility of a solar cooling system for the climate of Pakistan. 4.6 Solar Cooling for Hot Climates Locations across the world with minimum annual solar insolation of 2000 kwh/m 2 and a location between 40 north and south latitude are considered suitable and favourable for the installation of solar thermal system applications. The suitable locations include Australia, Africa, Europe (Mediterranean countries), China, Russian federation, Middle East, India, Pakistan, Iran, South and Central America and USA (South-Western) [140]. In hot climates, air conditioning in buildings is increasing and conventionally provided by electric driven cooling systems. To reduce the load on an electrical network during peak loading time, thermal driven cooling systems powered by solar energy can be used [22]. Many researchers have investigated solar cooling systems for hot climates. As early as the 1960s Chinnapa [144] and Tablor [189], concluded from experimental studies that flat plate collectors could be used to drive heat-operated cooling systems. In the 1970s, Ward et al. [149, 152, ], studied the operations of a solar cooling system installed at a CSU solar house in the USA. Muneer [194], Uppal [195], presented a feasibility and design study of a solar cooling system for Libya. The collector tilt angle for maximum energy output and capacity of the absorption chiller was proposed. Ayyash [196], and Homoud et al. [197] presented feasibility and experimental studies of solar vapour absorption cooling systems with a flat plate collector for Kuwait. It was found that the COP of the cooling system and the saving in electricity consumption was 0.60 and 25-40% respectively. 104

105 Yueng at al. [198] and Fong et al. [118] presented experimental and comparative studies for solar-powered cooling systems for Hong Kong. The experimental absorption system, with a flat plate collector showed an annual efficiency of 7.8%, with an average solar fraction of 55%. The later compared the performance of five different cooling systems for buildings. On the basis of a year-long operation, for the best total primary energy consumption, the order of solar systems is; solar electric compression refrigeration, solar absorption refrigeration, solar, adsorption refrigeration, solar solid desiccant cooling and solar mechanical compression refrigeration. For solar collectors, the primary energy consumption of the evacuated tube collector is 29.2% less than the flat plate collector for absorption refrigeration. For the same area, the evacuated tube collector collected 81% more energy than the flat plate collector during a one-year operation. It is concluded that a solar absorption cooling system (either with a flat plate or with evacuated tube collectors) can save 15.6% to 48.3% in annual energy compared to conventional electric compression systems. Sorour [199], Elsafty [200], and Schwerdt [201], investigated the feasibility, economic and experimental studies of a solar cooling system for Egypt. It is found that solar cooling systems with both flat plate and evacuated tube collectors can provide sufficient energy for operation. The economic study showed that the total cost of a double effect vapour absorption system is 45% and 37% lower than a single effect and vapour compression cooling system, respectively. The experimental study for the adsorption system showed that the COP of the system in the summer was 0.25 to The thermal efficiency of the CPC collectors was observed from 50-65%. Izquirdo et al. [202], Syed et al. [203] and Martinez et al. [204], presented experimental and test results of designed, solar absorption cooling systems for Spain. Solar cooling systems with flat plate collectors and hot water storage systems showed a COP from 0.34 to The specific collector area was from m 2 /kw C. Balghouthi et al. [205, 206], presented a feasibility and optimisation study of the solar cooling system for Tunisia. A system consists of 11kW LiBr-H 2 O absorption chiller with 30m 2 flat plate collector tilted at 35 with a 0.80m 3 hot water storage tank, was proposed. Pongtornkulpanich et al. [207], presented an experimental study of a 35.2kW LiBr-H 2 O single-effect absorption cooling system in Thailand. The evacuated tube collector of area 72m 2 provided an 81% solar fraction. Kim [165] studied the performance of an air cooled Libr-H 2 O absorption chiller in extremely hot weather at 35 C and 50 C ambient temperature. It is observed that at 50 C, the COP of the direct and indirect air cooled chiller was decreased to 81.6% and 75% and the cooling power also decreased by 37.5% and 35.6% respectively 105

106 compared to 35 C. It is established that the direct air cooled chiller design is better in terms of energy efficiency. Alili et al. [208, 209], optimised and proposed a solar cooling system for Abu Dhabi. The optimisation carried out for a 10kW absorption system with evacuated tube collectors of area 3.4m 2 /kw C and it was established that it could save up to 35% in energy compared to conventional electric compression systems. Another model was proposed of the same capacity, with an evacuated tube collector specific area 6m 2 /kw C and a hot water storage tank with a specific volume of 0.1m 3 /kw C. The proposed system can save 47% in primary energy and 12 metric ton/year of CO 2 emission. Ssebataya et al. [210], investigated the performance of a solar cooling system in UAE conditions. A 35.2kW solar absorption system with a 128m 2 evacuated tube collector and 1m 3 hot water storage was used to cool 96.75m 2 floor areas with 22 C indoor set point. The COP of the cooling system was observed from 0.60 to Tsoutsos et al. [211], proposed the design of a solar absorption cooling system for a Greek hospital. The performance of the system in four different cities in Greece was analysed. 500m 2 solar collectors provided 74.23% solar fraction with 15m 3 hot water storage. The efficiency of the solar cooling system was highest in the most southern locations. Praene et al. [212], carried out simulation and experimental investigations of a solar absorption cooling system in Reunion Island. A solar-driven 30kW LiBr-H 2 O single effect absorption chiller with 90m 2 double glazed flat collectors and 1.5m 3 hot water storage was investigated. The room temperature set point was 25 C and a 100% cooling load was provided by the solar cooling system. It was concluded that the solar assisted cooling system could save CO 2 emission of 0.23kg /kw C compared to a conventional electric compression system. Ayadi et al. [213], presented a performance assessment for a solar cooling system for office buildings in Italy. A 17.6kW absorption chiller with flat plate collectors of a 61.6m 2 absorber area, and 5m 3 hot and 1m 3 cold water storage was installed. The thermal efficiency of the collector was 30% to 40% and the absorption chiller COP was Fasfous et al. [214], studied the potential of utilising solar cooling in the University of Jordan. The analysis was performed using an 8kW solar cooling system. A flat plate collector with an area of 40m 2, and 2.3m 3 hot water storage tanks was used and provided a 15-25% solar fraction. The economic analysis showed the system pay back is assumed 24 years and concluded that the solar cooling system is not feasible with the proposed system. 106

107 Eicker et al. [22, 124], studied the energy and economic performance of solar cooling systems worldwide. Six different locations were selected and it was found that the evacuated tube collectors can reduce the collector area by 50% compared to flat plate collectors. It is found that both solar electric and thermal cooling can reduce primary energy consumption by 21-70% depending on location, building standard and internal load conditions. Solar thermal systems showed a better match to the demand and supply compared to the solar PV electric system. It is established that in hot regions, solar cooling costs are quite comparable with conventional cooling costs. It is found that in the hot climates of Jakarta and Riyadh, the specific costs are as low as 0.09 to 0.15 /kwh. The solar cooling systems can save CO 2 emissions from 30-79%. Assilzadeh et al. [162] simulated and optimised a 3.5kW solar absorption cooling system for Malaysia, Sim [215] modelled and simulated 4.5kW solar thermal cooling system for Qatar, Sharkawy et al. [216] investigated the potential application of a solar cooling system for Egypt and Saudi Arabia, Ozgoren et al. [217] investigated the performance of a 3.5kW solar absorption cooling system for Turkey and Mazloumi [164], simulated 17.5kW solar absorption cooling system for Iran. The results of these studies are similar to the literature presented earlier. The literature of studies presented above are both simulation and experimental. The literature showed that in most of the studies flat plate collector is used, however, it was also established evacuated tube collector uses less than half area for same energy output compared to flat plate collector [22, 124, 198]. It was also established that vapour absorption cooling system is most widely used and has higher COP than other cooling systems[118]. The building integrated systems have successfully maintained the selected set point for room temperature[210, 212]. It was also found that energy consumption and CO 2 emission saving by all solar cooling systems is significant [22, 118, 124, 208, 209]. It was also proved that for hot climates solar thermal cooling system performance is better than solar electric cooling system[22, 124]. These studies presented differ in many aspects as performance indicators vary by location. The literature presented is for different climatic conditions worldwide with different solar energy potential. The systems and results are different for; collector area ( m 2 ), collector type (Flat plate or evacuated tube), collector efficiency (7.8-65%), collector tilt (at 107

108 location latitude), collector specific area (1.5-6m 2 /kw C ), hot water storage tank volume (0.8-15m 3 ), water storage type (hot-cold),chiller type (absorption or others), Chiller capacity ( kW), chiller COP ( ), building integration and room set point (22-25ᵒC), solar fraction (15-81%), electrical energy saving ( %) and cooling tower types (wet or air cooled) and comparison of different mode of operations and different systems. All these studies were beneficial for the selection of different components for current research. This include selection of type of collector, type of storage tank, type of chiller, mode of operation of chiller (single or double), cooling tower type (dry or wet) and other operational parameters for these components. The detailed justification for each of these components is given in Chapter 6. The data of these studies is also used for results validation and parametric analysis as no experimental data for Pakistan and neighbouring country is available for solar powered absorption cooling system Solar Cooling System Research for Pakistan and India Little literature is available on the doctoral, and academic published research on solar cooling systems in Pakistan and India. Most of the research work carried out is on solar desiccant cooling systems. Khalid at al. [54, 55], presented a study of a solar assisted hybrid desiccant cooling system for the climate of Pakistan. Khalid et al. [218], presented an experimental and simulation study of a solar assisted pre-cooled hybrid desiccant cooling system for Pakistan. The experiments were performed on a gas fired pre-cooled hybrid solid desiccant cooling system test rig for highly humid Karachi weather. The TRNSYS model of the same system was validated by experimental results. Both experimental and simulation results were in good agreement with each other and other research studies. The experimental data were used as input for the TRNSYS model. The economic assessment of the system showed a payback period of 14 years. Gupta et al. [219] carried out research on an open cycle 10.5kW desiccant solar air conditioner-concept, design and cycle analysis. Bansal et al. [220] carried out experimental study of performance testing and evaluation of solid desiccant solar cooling unit in Delhi. The system had very low cooling capacity of 1.5kWh/day. The theoretical and experimental COP of the system was and It was concluded that for Delhi climatic condition the unit needs to be re-designed. Jani et al.[221] simulated solar assisted solid desiccant 108

109 cooling systems using TRNSYS. The system was designed for 60kW cooling load with inside set point condition at 50% RH and 25ᵒC. It was observed that system in recirculation mode showed higher COP than in ventilation mode. Mittal et al.[222] investigated modelling and simulation of a solar absorption cooling system for India. The performance of 10.5kW solar driven LiBr-H 2 O absorption cooling system with flat plate collector was investigated. It is found that system performance was highest at 80ᵒC temperature from the storage tank. Kumar[223] in 1990, completed doctoral research on Thermal design and performance evaluation of vapour absorption/adsorption solar space conditioning systems. It was concluded that open cycle absorption cooling system with solution storage option is feasible for continuous air-conditioning in India [224]. A comparative study with methanol- LiBr.ZnBr 2, methanol- LiI.ZnBr 2 and H 2 O-LiBr mixtures has also been undertaken. It was found that the COP of the methanol-lii.znbr 2 and methanol-libr.znbr 2 mixtures are almost the same, while for the H 2 O-LiBr mixture, the COP is slightly higher than other mixtures [225]. It is also concluded that double absorption solar cooling systems are better in performance than conventional systems [226]. It was found that a desiccant cycle is more efficient under high latent heat load and higher ambient humidity conditions and uses less energy compared to conventional vapour compression cooling systems[227]. Habib et al.[228] simulated a solar heat driven adsorption chiller for Indian city of Durgapur. The result showed that this chiller is capable of providing cooling throughout the year under the climatic condition of studies location. The literature also showed that combination of different collectors and cooling system from 30kW to 350kW capacity, solar powered cooling systems are in operation in India [229]. The detail of operational parameters and other specification is not available. The literature presented showed that most of the research was carried out on desiccant and adsorption cooling system for hot and humid climatic conditions [ ]. This limitation (hot humid climate) creates a need and potential of solar powered cooling system for hot and dry climatic conditions for the current research, as the climatic condition of Lahore is hot and dry. Mittal et al.[222], Kumar [223], and Habib et al.[228] studied systems suitable for hot dry climates (absorption and adsorption); their work shows that these systems are capable of providing cooling using solar energy. The current research is detailed analysis of solar powered cooling system with building integration as their work does not provide details and validation. 109

110 4.7 Conclusion Cooling systems share a major part of total energy consumption in buildings through electricity. Solar energy-based cooling systems can significantly reduce the grid consumption of fossil fuel-based generated electricity and help to reduce CO 2 emissions. Solar cooling systems can help to promote environmentally friendly refrigerants. The main advantage of solar cooling is that maximum solar energy is available when the cooling load is required in the summer. The use of solar cooling systems is increasing in line with clean energy goals and under IEA policy and solar cooling will contribute to 17% of total energy use in cooling by Solar electric systems are suitable for small size refrigeration or in remote areas with no grid supply. The application of solar electric cooling systems is limited and only a few systems are available in the literature. Solar PV systems can only use about 35% of the spectrum of incident solar light. Solar electric systems have showed lower performance in hot climates as the efficiency of solar to electric conversion is reduced by an increase in ambient temperature. Solar thermal cooling systems use and development started in the 60s. Different techniques have been developed as being suitable to solar energy availability and output capacity. Solar thermal systems work efficiently in high ambient temperatures and use about 95% of the spectrum of incident solar radiation. Concentrating solar collectors are normally used for electricity generation only. CSP systems are designed to produce medium ( C) to high ( C) temperature heat for electricity generation or for the co-generation of electricity and heat. Flat plate collectors are the most used collectors in solar cooling installations. Evacuated tube collectors have high efficiency with low radiation and have a wide range of applications compared to other stationary collectors. Although evacuated tube collectors are expensive, but they need less specific collector area compared to flat plate collectors. The average collector area for flat plate collectors is 4.6m 2 /kw C whereas for evacuated tube collectors its 2.5m 2 /kw C. For this research, the solar cooling evacuated tube collector will be used for hot water to be used in the cooling system. 110

111 Four types of cooling systems are being used for solar thermal cooling. From the literature it is established that the absorption system is the most efficient, mature and widely used due to its commercial availability. Single, double, and triple effect absorption systems have been developed for applications and efficiency range. For this research, a single effect vapour absorption cooling system will be used. The use of desiccants and adsorption systems is new for solar cooling and research is ongoing to improve process efficiency. An ejector system-based cooling technique is not new but it is not favourable as compared with compression and absorption systems due to lower efficiency. Research is being carried out on ejector systems for efficiency improvement with different refrigerants and effective use for solar cooling. Despite its attractiveness, solar thermal cooling technology is still in the development stage. Most installations currently in operation showed differences in the collector area per kilowatt of cooling capacity. The general range of collector area for thermal cooling system is between 2m 2 to 10m 2 per kw C. For hot climates, solar cooling is economical compared to conventional compression cooling using electricity. For Pakistan s climatic conditions, the experimental and simulated solar assisted desiccant cooling system showed feasibility of the system operation to meet the cooling loads in summer. 111

112 Chapter 5: Methodology 5.1 Introduction A detailed literature review for solar cooling systems has been presented in chapter 4. Types of solar cooling systems, solar collectors, and thermal cooling systems were described. This chapter is about the methodology available and adopted for research into building integrated solar thermal cooling systems for Pakistan s climatic conditions. The proper sizing of a solar cooling system is a complex task which includes both predictable (collector and other component performance characteristics) and unpredictable (temperature and humidity) components. The system can be used either as a standalone system or with conventional air conditioning [211, 230]. To evaluate the feasibility and performance of a solar cooling system two widely-used techniques are the manufacturing of a prototype and experimental evaluation, and dynamic simulation. In this chapter a detail of literature is presented about experimental and simulation studies for solar cooling systems and meteorological data types are explained. The selected technique with details is presented in the next sections. The problem in designing a new solar cooling facility is that there are no standard specifications and configurations to follow due to variation in climatic conditions and building characteristics. Every case is a specific, and detailed study (optimisation) is required to achieve maximum efficiency of the system. Different tools and systems are used by researchers for solar cooling system studies worldwide [231]. The solar cooling system can be designed and evaluated by two possible criteria. One criterion is where solar cooling system contributes according to its capacity and providing a share of total cooling demand. The second criterion is where solar cooling system provides total cooling demand with solar energy. a system based on the first criterion can produce the most cooling energy from a given system. The second criteria based system is more complex to obtain an optimum configuration as there is the need to meet the total cooling demand. Such systems are best for thermal comfort in small scale facilities for domestic applications [231]. This research is aimed to evaluate performance of a building integrated solar powered absorption cooling system. The goal is to use the solar energy to meet the whole cooling 112

113 demand of the selected building with actual construction materials and standards used in Pakistan. The building energy in Pakistan has been described in the Sections 3.7 and 3.8. The principal techniques available for the study of solar cooling systems are by experiment or by dynamic simulation. As described in Section 4.8.1, there is no experimental or installed solar absorption cooling system facility in Pakistan; dynamic simulation will therefore be the adopted methodology for this research. For dynamic simulation of a building integrated solar absorption cooling system, a realistic 3D building model with actual building construction (construction standards, materials, glazing fraction, size, etc.) will be chosen and the solar powered cooling system will be sized so that it can maintain room temperature level at the required set point all the time. To evaluate building cooling load, internal gains by persons and equipment will be considered. The selected solar absorption cooling system will be optimised for the most efficient configuration and operation parameters. The optimisation will consider all the main system variables (collector area, tilt and energy gain, storage tank volume, pump, and fan flowrate) and the criteria for most efficient will be the least collector area with maximum energy gain, storage tank volume with minimum heat loss and fan flow to maintain room set point temperature. The results of the dynamic simulation will be validated by published results, and the more important system parameters will be analysed through parametric analysis of the system to evaluate the effect of these parameters on whole system performance. The detailed methodology with system design and results will be presented in next chapters. 5.2 Experimental Study An experiment can be characterised as an investigative activity that involves intervening in a system in order to see how the properties of interest in the system change. Experiments play a central role in scientific practice and are considered to have a more direct relationship with the object of study, contributing to establishing a valid reference about real systems. It is well established that experiments are designed to test and validate hypotheses. Field experiments have an advantage over laboratory experiments as they take place in natural conditions, but the choice of type of experiment depends on the type of experiment outcomes. Field experiments are more realistic, but there may be many uncontrolled variables that affect the results. Laboratory experiments allow known variables to be controlled [232]. 113

114 More than 1,000 solar thermal cooling systems have been installed worldwide. The available literature shows that often hybrid systems with free cooling support are installed and evaluated [124]. Most installations in operation are part of demonstration projects and most of the systems are in European countries [204]. The first experimental study of solar cooling systems was carried out by Chinnappa in 1962 using a flat plate collector [144]. The first design and construction of a residential solar cooling and heating system was presented in 1975 by Ward et al. [190]. Some other researchers also presented experimental results for different solar cooling systems in the late 1970s and early 1980s [ , 191, 192]. The first experimental study using an evacuated tube collector for solar heating and cooling was presented by Ward et al. in 1979 and some other researchers in later years [152, 193, 233]. In the 1980s many experimental studies were presented with different designs and arrangements for solar cooling systems [154, ]. In the 1990s studies were presented to show the performance of some existing systems and some newly installed absorption and adsorption cooling systems in different locations worldwide [158, 197, 198, 202, 220, ]. In the 2000s experimental work was carried out with all four types of solar cooling systems, hot and cold water storage, all stationary collectors and both stand alone and fossil fuel heat energy back up [159, 163, 203, 207, ]. Some studies were carried out to analyse the performance of stratified storage tank use in solar cooling systems [250, 251]. In the late 2000s and after 2010 experimental studies were fewer in number as most of the studies were carried out as dynamic simulations [169, 201, 214, ]. Some experimental studies were performed to verify and validate different simulation results. [169, 204, 212, 213, 255, ]. All the experimental studies were carried to evaluate the potential of solar cooling systems, the economics, the parametric analysis, the efficiency of solar thermal collectors and cooling systems for a specific location. Most of the systems were building integrated and to be used for both heating and cooling purposes. In Pakistan research on the application of solar energy cooling systems is limited. As presented in Section 4.8.1, one solar assisted desiccant cooling experimental set up and the TRNSYS simulation program is available at NED University Karachi (Pakistan). The experimental results are limited to a humid area as the climate of Karachi is different from the typical climate of the rest of the country [55, 218]. In first year of research, contacts were made consistently with Dr. Khalid (the author of the above references) for equipment specification and possible experimental work on solar cooling, but no answer was received. 114

115 The application of solar thermal systems for cooling is not setup or available for experimental work at the present author s university in Lahore. In the early months of the second year of study, contact was made to try to establish the use of experimental facilities at UAE University Al-Ain, but due to time limitations, the experimental set up could not be arranged so a simulation option was selected as suitable simulation program was available at the University of Manchester Limitations of Experimental Study Experimental studies provide opportunity to identify cause and effect relations. One major limitation of experimental study is that experiments are conducted in a particular environment and results may be hard to generalise except field and natural experiments [267]. Another limitation is that the environment is likely to affect the results, but perfect controlled conditions are generally not possible. The experimental research may be able to tell that one method, design, etc. is better than other, but may not able to explain the reason [268]. The experimental studies carried out on solar cooling have described, collector area, collector type, collector tilt, collector yield and efficiency, storage type and volume, chiller type and capacity, chiller COP, solar fraction, Solar COP and Electrical COP. The most common used equipment is flat plate and evacuated tube collector, hot water storage and vapour absorption chiller. Use of other collector types, cold water storage, stratified tank, other types of cooling systems and parametric study of the systems is limited. The studies of solar cooling systems mentioned in previous section have several limitations. The duration of the studies was limited to few hours or days only in most of the research and only few have been carried out for a season or year [159, 166, 198, 233, 234]. All the studies are based on components temperatures and the heat balance of the whole solar thermal cooling system is not presented in details from heat input to the heat rejection at each component or system level [212, 213, 245, 253, 264]. The room temperature set point and relative humidity of the building integrated systems have not been described, in all of the studies. Only building conditioned area is described no information is provided about the building construction materials, windows, door, and orientation [201, 214, 220, 234, 240, 247, 269]. 115

116 The experimental studies described the size and type of hot and cold water storage but no detail is provided about heat loss /gain from these tank and average temperature [193, 220, 234, 240, 241, 244, 247]. The solar energy collectors type, area and tilt is described but no detail is provided about collector efficiency curve, flow control, pump capacity and effect of tilt on collector energy yield [253, 260]. Most of the studies are without building integration and studies with integration have no description about cooling coil and fan specification [201, 214, 220, 234, 240, 247, 269]. Most of the studies have solar fraction less than 50% and no study was carried out about 100% solar fraction [159, 163, 203, 207, 214, , 260]. The experimental studies results do not enable us to predict performance of the proposed system of the current research. 5.3 Simulation Study Simulation is the production of a computer model for a system and it complements a physical experiment. Simulations are numerical experiments and give system performance information similar to physical experiments. These are relatively quick, inexpensive, and produce information on the effect of design variables and system performance. Simulation can be used for exploring new conditions not present in particular real world settings. Using cost data and economic analysis, simulation results can be used to find economical systems. Simulation is a powerful tool for research, development and design of systems [40, 270]. Computer modelling of thermal systems has many advantages. It is effective for parametric studies and helps to investigate the effects of system variables on performance. A wide range of climatic data can be used to determine the effects of weather on design. It eliminates the expense of building prototypes, and provides complete understanding of system operations. It makes it easy to optimise systems and output estimation [40, 141, 230]. The use of simulation for study of solar processes has been used since the late 1960s [40]. The first simulation study was carried out by Sheridan et al. in 1967 for solar water heaters [271]. Many other researchers carried out simulation for different solar heating and solar cooling systems in the late 1960s and early 1970s [146, ]. The first simulation study on design and optimised systems for residential heating and cooling by solar energy was carried out in 1974 [278]. The first simulation study for hybrid solar air conditioning was 116

117 presented in 1976 [148]. In the 1980s many studies were carried out for simulation of solar cooling systems and thermal performance and economics were analysed [155, 279]. In the 1990s feasibility studies, design optimisation, modelling and technical assessment of solar cooling systems was simulated [199, 280, 281]. In the 2000s most of the simulation research was carried out on solar cooling systems based on absorption, for which integrated systems were built with different collectors, energy and carbon emission saving with solar cooling systems [24, 162, 164, 205, 206, ]. Some studies were carried out to compare simulation results with actual installation data [287, 288]. After 2010 most of the simulation studies were on design, performance, optimisation, and sensitivity analysis of solar cooling systems and comparisons of different solar cooling systems [22, 23, 118, 178, 188, 204, , 215, 265, ]. Simulation studies are nearly as old as the experimental studies for solar thermal heating and cooling systems[40]. After 2000, most of the literature available about solar thermal cooling systems relates to simulation of solar cooling systems more than experimental studies. The literature referred shows that TRNSYS is the most widely used simulation program. The literature presented above described collector area and yield, collector tilt, collector flow, storage tank type, heat loss, and capacity, pumps power and flow, type of cooling tower, chiller type, capacity and COP, results validation and sensitivity analysis of the system, building geometry, materials, heat gains and infiltration. Some other advantages of the simulation studies include the comparison of different building materials, change of locations worldwide, different cooling systems, collector s type change, storage types, and other parametric variation in the system operation. The literature showed that solar cooling system simulation studies are flexible, detailed, and can help to study different and maximum efficient system design for any location worldwide. However, none of the studies in the literature cover the proposed system for Pakistan Limitations of Simulation Study Simulations are powerful tools for system design and analysis but there are some limits in simulation use. It is easy to make mistake by assuming incorrect values for system parameters, and neglecting important factors. A high level of skill and scientific judgement is required for useful results. Physical problems such as leaks, plugged or restricted pipes, scale 117

118 on heat exchangers, failure of controllers, poor installation of collectors and poor insulation cannot easy modelled or accounted [40, 141]. Simulations programs deal only with thermal process but mechanical and other factors can also affect the thermal performance of solar systems. There is no substitute to carefully conducted experiments. A combination of simulation and practical experiment can lead to better understanding of the system [141]. 5.4 Solar Energy System Simulation Programs Simulation programs should ideally offer computational speed, low cost and ease of use. Over the years many programs have been developed for modelling and simulation of solar energy systems. The most popular programs are WATSUN, Polysun, f-chart, and TRNSYS. TRNSYS is used for both solar energy and building energy systems so its details are presented in Section WATSUN Watsun simulates active solar systems and was developed by the Watsun simulation laboratory at the University of Waterloo, Canada in the early 1970s. It models two kinds of systems: solar water heating systems without storage and solar water heating with storage. It combines collection, storage, and load information with the hourly weather data for a location. Both hourly and monthly reports include data about solar radiation, energy collected, load, and auxiliary energy. It can calculate long-term performance and economic analysis to assess the costs and profits of the solar heating system [141, 230]. WATSUN uses TMY weather data with hourly values for global radiation on a horizontal surface, dry bulb temperature, wind speed, and relative humidity. It uses a synthetic weather generator WATGEN, which uses monthly average values and generates hourly data for a given location. The user defines one input file called simulation data files and Watsun generates three output files: a listing file, an hourly data file, and a monthly data file. The systems that can be modelled include domestic hot water, pool systems, and industrial process heating. The program models each component in the system, such as the collector, pipes and tanks [141, 230]. The program was validated by developers against the TRNSYS program using several test cases. The comparisons were very favourable; differences in predictions for yearly energy delivered were less than 1.2% in all configurations tested [311]. 118

119 WATSUN was not used for this research because it cannot simulate solar cooling systems and building energy together at once Polysun This program provides dynamic annual simulations of solar thermal systems and helps optimisation of the system. The basic systems that can be simulated include: domestic hot water, space heating, swimming pools, process heating, and cooling. It provides simulation with a dynamic time step from 1 second to 1 hour. Worldwide meteorological data for 6,300 locations are available. Polysun has a claimed accuracy within 5-10% variation. It is a program with economic viability and ecological balance, which includes emissions of the eight most significant greenhouse gases. The emissions for a solar integrated system and the conventional fuels can be compared [141, 230]. Polysun was not used for this research because it cannot simulate building integrated solar thermal cooling systems and building energy f-chart Method and Program The f-chart method provides a mean for estimating the annual thermal performance of active heating systems common in residential applications, using air, or liquid as a working fluid. The f-chart is used to estimate the fraction of a total heating load that can be provided by a solar system. The f-chart was developed by Klein et al. [147, 312] and Beckman et al. [313]. The primary design variable is the collector area and the secondary variables are the collector type, storage capacity, fluid flow rates, and load and collector heat exchanger sizes. This method correlates the results of many hundreds of thermal performances of solar heating system simulations performed on TRNSYS, in which the simulation conditions were varied with practical system designs. The resulting correlations give f, the fraction of the monthly load supplied by solar energy as a function of two dimensionless parameters. One is related to the ratio of collector losses to heating load, and the other to the ratio of absorbed solar radiation to heat loads. The f-chart system was developed for three standard system configurations: liquid and air systems for space and hot water heating, and systems for service hot water only [141, 230]. 119

120 The f-chart program was developed by the developers of TRNSYS and the model is intended only for solar heating systems. This program can be used to estimate performance for all stationary solar collectors, and one or two axis tracking concentrated collectors. This program, however, does not provide the flexibility of detailed simulation and performance investigation in the same way that TRNSYS does[230]. f-chart was not used for this research because it cannot simulate solar cooling systems and building energy. Also it cannot be used for detailed simulation of solar thermal systems as it is used to simulate fractions only. 5.5 Building Energy Simulation Programs Building energy system simulation programs can calculate the behaviour of building thermal control systems and the resultant impact on energy use, peak energy demand, equipment sizing and occupant comfort as well as providing performance details. An energy efficient and effective design, detailed analysis of building energy demand, energy savings, and supply technologies can be tested and optimised by such programs. Many building energy simulation programs for evaluation of energy efficiency, renewable energy, and sustainability are developed. Here the popular programs that are commonly used for simulation of energy systems in buildings are the only ones discussed Energy Plus Energy plus is an energy analysis and thermal load simulation program. Energy Plus is derived from both the Building Loads Analysis and System Thermodynamics (BLAST) and DOE 2 programs and was released in BLAST and DOE 2 both were developed for building energy and load simulation after the energy crisis of the early 1970s, when it was realised that building energy consumption is a major component of American energy consumption. The programs were used by design-engineers and architects to design and size heating, ventilation and air-conditioning (HVAC) equipment and for equipment life cycling cost analyses and energy performance optimisation. Energy Plus comprises completely new, modular, structured code written in Fortran 90 [314, 315]. Using this program, the user can define building envelopes, a building s physical make-up, and related mechanical systems. It can calculate heating and cooling loads necessary to maintain thermal control set points, conditions throughout a secondary HVAC system, coil 120

121 loads, and energy consumption of equipment as well as verifying that simulation is in accordance with actual building operation. Some of the main features of the Energy Plus program are [314, 315]. Sub-hourly, user-definable time steps. Text based weather input and output files. Heat balance based solutions. Atmospheric pollution calculations. Energy Plus is used to simulate many buildings and HVAC design options directly or indirectly through links to other programs to calculate thermal loads and energy consumption on a specific design day or for a certain period [314, 315]. Many researchers have used Energy Plus for modelling and simulation of building energy performance and improving building energy models [ ]. The most important limitation of Energy Plus for the present research is that it lacks solar collector models although it does have models for absorption chillers and storage tanks. Users can create their own collector model through codes but it might be a lot of work to validate it and link it correctly to the main program Integrated Environment Solutions (IES) Virtual Environment (VE) IES-VE is used for building and system design. It creates a 3D building model with data such as materials, constructions, internal heat gains, systems, and controls. IES-VE is used to build a model and collects information on building geometry, occupancy, climate and installed equipment [325]. IES-VE is used to design low energy and high performance systems. Energy and carbon analyses are carried out under the tool Apache Simulation. This is a central simulation processer that assesses thermal performance, simulates solar gain on surfaces, surface temperatures, and radiant exchanges. Building and room-level annual, monthly, hourly, subhourly and up to one minute time step analysis is possible. It contains an extensive database of global weather. It calculates sensible and latent gains from lights, natural ventilation, mechanical ventilation and infiltration [325]. 121

122 In IES-VE three tools are used for HVAC calculations; Apache HVAC, Apache Loads, and Apache Calc. Apache HVAC simulate system prototypes and models and the system library contains a variety of model systems. Apache Loads simulates heat loss and gains, heating and cooling loads using the ASHRAE heat balance method. It can simulate the cooling load for buildings and zones and peak cooling loads. Apache calc. simulates heat gains to calculate the cooling load for a selected day and month with chartered institution of building services engineer (CIBSE) guidance. It can simulate climate, daylight, natural resource availability, energy and carbon with low/zero carbon technologies as shown in Figure 5-1 [325]. Figure 5-1: Building model and low zero carbon technologies analysis [325] Many researchers have used the IES-VE tool to simulate building design, construction materials, daylight characteristics, solar shading, low energy buildings, and occupant s behaviour [ ]. Like Energy Plus, the main problem with IES for this research is its lack of solar energy system models. Also, the user cannot create any model and add it to the IES TRNSYS TRaNsient SYstem Simulation (TRNSYS) is a widely used, thermal process dynamic simulation program. It was originally developed for solar energy applications, and can now be used for a wider variety of thermal processes. TRNSYS was developed at the University of Wisconsin by the members of the solar energy laboratory and the first version was released in 1977 [40]. TRNSYS can be used for simulation of solar PV, solar heating and cooling and building energy. It has the capability to interconnect system components in any desired manner, solving differential equations and information output. Given OUTPUT from one component is used as an INPUT to other components [336]. Each component has a unique TYPE number, and components from the standard library of TRNSYS were validated. In the 122

123 volume4- Mathematical reference of TRNSYS, reference to validation of each TYPE is included [337]. The components in TRNSYS include solar collectors, heating and cooling loads, thermostats, absorption chillers, fans, hot water storage, heat pumps and many more. TRNSYS provides an error of less than 10% between simulation results and actual operating systems; details of TRNSYS accuracy are described in Section The simulation time step can be as short as 1/1000 of an hour (3.6s) and can be helpful for detailed instantaneous micro analysis. The short time step (less than one hour) can be useful as it may be necessary for computational stability in the simulation and it can be used to simulate the dynamic response of the systems that respond faster in seconds or minutes [147, 312, 313, 338]. In addition to the main TRNSYS components, an engineering consulting company specialising in the modelling and analysis of innovative energy systems and buildings, Thermal Energy System Specialists (TESS), developed libraries of components for use with TRNSYS. The TESS library includes more than 500 TRNSYS components [230]. Numerous applications for the program are mentioned in the literature and described in Section 5.3. Some typical examples are for the modelling of a thermosiphon system [339, 340], modelling and performance evaluation of solar DHW systems [341], investigation of the effect of load profile [342], modelling of industrial process heat applications [343] and modelling and simulation of a lithium bromide absorption system [284] Interface TRNSYS operates in a graphic interface environment called Simulation Studio. In this environment, icons of ready-made components are dragged and dropped from a list and connected together according to the real system configuration [230]. The standard library includes approximately 150 models ranging from photovoltaic panels, multizone buildings, solar collectors, storage tanks, weather data processors and HVAC equipment [344]. The interface is shown in Figure 5-2. Each component of the system requires a set of inputs (from other components or data files) and a set of constants parameters, specified by the user. Each component has its own set of output parameters, which can be saved in a file, plotted, or used as input for other components. 123

124 Figure 5-2: Model diagram in TRNSYS simulation studio view [344] Output values can be seen on an online plotter as the simulation progresses. A typical output plot is shown in Figure 5-3. The project area also contains a weather processing component, printers, and plotters through which output data are viewed or saved to data files [230, 344]. 124

125 Figure 5-3: TRNSYS simulation result plot overview [344] TRNSYS has some built-in and supported tools which are described here TRNBuild In version 17, TRNSYS includes Trnsys3d, a plug-in for Sketch Up that allows multizone buildings to be drawn and imports the geometry directly from the Sketch Up interface into TRNSYS. TRNBuild is an interface for creating and editing all of the non-geometry information required by the TRNSYS building model. It allows extensive flexibility in editing wall and layer material properties, creating ventilation and infiltration profiles, adding gains, defining radiant ceilings and floors, and positioning occupants for comfort calculations [344]. A TRNBuild interface for the model materials is shown in Figures 5-4 and

126 Figure 5-4: TRNBuild wall and windows types and area selection [344] Figure 5-5: TRNBuild wall type manager with construction materials [344] Weather Data TRNSYS contains a variety of weather data with different weather data types. The main types available are TMY, TMY2 and TMY3 (for US), EPW, CWEC, IWEC and Meteonorm for all the major cities of the world. A detail of these weather types is presented in section 5.6. In TRNYS for Pakistan TMY2 weather data is available for the five major cities Karachi, Lahore, Peshawar, Multan, and Quetta. The climatic conditions are different for all the cities. 126

127 A detailed monthly average minimum, maximum dry bulb temperature and monthly average humidity ratio is shown in Appendix B and discussed in the weather data Section TRNSYS Validity Mitchell et al. [345] compared the measured and TRNSYS simulated performance of solar energy systems for CSU house I, for three different time periods. It found that simulated energy data was in agreement with measured data. The agreement was generally within 2ºC. It has also been recommended that simulation models can be used to predict long term system performance. For different components the difference between measured and TRNSYS simulated data was between 0.7% and 7% [40]. Beckman et al. [346] described TRNSYS as the most complete solar energy system modelling and simulation program. Kalogirou et al. [339] performed TRNSYS modelling and validation of a thermosiphon solar water system. It was found that the mean deviation between TRNSYS predicted and actual experimental values was 4.7%. Monfet et al. [347] performed TRNSYS simulation for large heating and cooling plants and calibration with monitored data. It was found that there was a good agreement between the simulated and monitored data with less than 8% variation. Hang et al. [348] conducted a TRNSYS study of the optimisation method for a solar assisted double effect absorption system installed in USA and the results showed that the actual system result was in excellent agreement with the physical model in TRNSYS. Ayompe et al. [265] validated the TRSNSY model for a forced solar water heating system with a flat plate and evacuated tube collectors for three representative days of weather conditions in Ireland. The results showed that the model overestimated the heat collected by 7.4% and 12.4% for a flat plate and the evacuated tube collectors respectively. Martinez et al. [204] investigated the TRNSYS design and test results for a low capacity solar cooling system in Spain. It was observed that the level of agreement between experimental and simulated values was high. The difference between experimental and simulation parameters was between 2% and 5.50%. Ssembatya et al. [210] carried out TRNSYS simulation studies on the performance of solar cooling systems in UAE conditions. It was observed that, overall, the trends for experimental values were close to TRNSYS simulation. Almeida et al. [337, 349] performed dynamic testing of systems using TRNSYS. It was observed that comparison of simulation and measured system energy yield showed very good agreement with a +/-3 % variation. Banister et al. [350] validated a multi-mode single tank TRNSYS model with experimental data. The 127

128 agreement between simulation and experiment was found to be very strong, with typical differences in tank temperatures of less than 1ºC. He et al. [351] studied low temperature solar thermal cooling system application in China. The comparison between four days of TRNSYS simulated and measured data for heat gain using a collector and system COP, showed that the measured data was 7% and 5% higher than simulated data respectively. Bava et al. [352] carried out a TRNSYS simulation of a solar collector array with two types of solar collectors. It was found that simulated energy transferred in one year from collectors was only 1.2% higher than the measured energy amount. The simulated collector s outlet temperatures were in good agreement with measured ones. Eicker et al. [353] simulated heat rejection and primary energy efficiency for solar driven absorption cooling systems. Palacin et al. [354] also observed the variation to be in the range of 1-7%. The comparison between the simulated and experimental systems showed a variation of between 1% and 4%. A summary of the above described work is shown is Table 5-1. Table 5-1: Comparison of differences between experimental and TRNSYS simulation data Author Parameters Difference between Experimental and TRNSYS simulation (%) Mitchel et al Collected and Delivered energy, Auxiliary energy, Air heated heat flow Kalogirou et al Hot water tank initial and final temperatures 4.7 Monfet et al Chilled water temperature, Condenser water temperature, Pumps, Chiller and cooling tower electricity consumption, COP of chiller, Ayompe et al Heat energy collected Martinez et al Collector and storage tank outlet temperature Almedia et al Energy yield, (+/-3.0) He et al Collector yield, Total cooling energy, Auxiliary energy demand, Collector efficiency, System COP, Average room temperature and Solar fraction Bava et al Collector energy collected 1.2 Eicker et al Collector energy, Evaporator and generator power, 1-4 Palacin et al Collector energy, Evaporator and generator energy, Electrical energy 1-7 The above Table 5-1 shows that the variation in TRNSYS results from measured data for solar thermal systems is less than 10%. The TRNSYS simulation proved reasonably accurate for solar thermal systems modelling. T. He at el. s work was on solar thermal cooling systems similar to those in this research. The comparison was for four days of data and it can be expected that the annual average comparison will show the variation to be lower. As Bava et al.[352] observed that the annual average variation between simulated and measured data was 1.2%, whereas the seasonal variation was higher at +7% (Jun-Dec) and -8% (Jan-May). 128

129 Antoni et al. [355] validated the TRNSYS simulation solar combi+ system model with measured data. The simulated results for storage fluid temperatures and heat transfer rates were in good agreement with a difference of less than 2%. Keizer et al. [356] used TRNSYS as a tool for long term fault detection in solar thermal systems. The average variation between simulated and measured solar yield was up to 5 %. 5.6 Meteorological Data for Simulation Program Weather conditions and loads are factors that affect cooling system performance. Loads are dependent on weather for heating and cooling in buildings, and also other factors which are not related to weather. Meteorological data, including ambient temperature, solar radiation and wind speed, wind direction and relative humidity are measured at the weather recording station around the world [357, 358] Weather Data Types For simulation of solar cooling systems, weather data with the important parameters and derived data is used. All simulations in this research are performed with real meteorological data and it is important to select a suitable data set [357]. The data set type depends upon the simulation program to be used. To compare the full range of system performance, it is best to use a full year of data or a full season of data if the process is seasonal [358]. Klein [312] developed the concept of a design year for first time, which helped to create different types of weather data for building energy calculations. The available data sets differ according to the process by which they are compiled, the amount and type of data presented. A brief description of some important weather data sets are presented here Test Reference Year (TRY) The earliest hourly weather data set specifically designed for use in building energy simulation is the Test Reference Year (TRY) derived from measured data at the National Climatic Data Centre (NCDC). The data was available for 60 locations in the US for the period from The limitations of the TRY were the exclusion of solar radiation and extreme high or low temperatures [358]. 129

130 Typical Metrological Year (TMY) Hall et al. s [359] detailed study of 23 years of data for solar radiation at 26 stations in the US and resulted in the generation of typical meteorological year data for those and others locations. This TMY data was used to simulate heating systems and added data which was not available with TRY [357]. A TMY is a data set for hourly values of meteorological elements and solar radiation for a period of one year. It consists of typical months of real weather data selected from different years and combined to form a data set of a year of typical weather. It provides hourly data for meteorological elements that contribute to performance comparisons for different types for single or multiple locations. It is not a good indicator for predicting the system parameters for the next one or five years as selected data is data for a typical month. It is useful to represent typical conditions judged for a longer period such as 30 years. It is not useful to design systems and their components to fulfil extreme weather conditions for a location as it represents typical conditions instead of extreme conditions. A typical meteorological year is classified into three categories [360, 361]. TMY: This consists of data sets derived from the NCDC of National Oceanic and Atmospheric Administration (NOAA) with measured data for 26 US locations from years TMY 2: This consists of data sets derived from years , from the National Solar Radiation Data Base (NSRDB) of US National Renewable Energy Laboratory for 239 stations. TMY3: This consists of data sets derived from years , from the NSRDB of the US National Renewable Energy Laboratory for 1,020 stations worldwide. The TMY, TMY2 and TMY3 data sets cannot be used interchangeably due to differences in time (local versus solar), formats, data types and units [357, 360, 361]. Schmitt et al. [362] have developed algorithms to generate weather data for extreme conditions International Weather for Energy Calculations (IWEC): IWEC was generated as a result of the ASHRAE research project RP-1015 for the ASHRAE technical committee. The purpose was to represent more typical weather than a single representative year could give. These files contain typical weather data suitable for use in 130

131 building energy simulation software for 227 locations outside Canada and the US. Data for all locations is available in an energy plus weather format [358, 363, 364]. All files of IWEC data are derived from 18 years ( ) of DATASAV3 hourly weather data originally archived in the US, at the National Climatic Data Centre (NCDC). The solar radiation data is estimated on an hourly basis from earth-sun geometry and hourly weather elements particularly cloud amount data [311, 363]. Like TMY files the IWEC files are typical years that normally avoid extreme conditions. Sizing of heating, ventilation, and air conditioning systems that require the consideration of extreme conditions cannot use the IWEC files Energy Plus Weather (EPW): Energy plus weather (EPW) data is generated by the United States Department of Energy. EPW is compiled from TMY, TMY2, TMY3, and other international data sets. This format data is now available on the Energy Plus website for more than 2,100 locations; 1,042 locations in the US, 71 in Canada and more than 1,000 locations in another 100 countries throughout the world [363]. The EPW format has generalised weather data for use in energy simulation programs. The data includes dry bulb, dew point temperature, relative humidity, station pressure, solar radiation (global, extra-terrestrial, horizontal, direct and diffuse) illuminance, wind direction and speed and cloud cover [363]. Each EPW file is named using an ISO standard three-letter country code, followed by the location name, World Meteorological Organization (WMO) and the source format such as California Climate Zones 2 (CTZ2), Canadian Weather for Energy Calculations (CWEC) [363]. There are three files associated with each location: energy plus weather files (EPW), a summary report on data (STAT) and a compressed file (zip) which contains the EPW, STAT and Design Day Data (DDY) files for the location [363] Pakistan Weather Data Official weather data for Pakistan is recorded and maintained by the Pakistan Meteorological Department (PMD). It is a scientific and public service department managed by the Ministry 131

132 TEMPERATURE (ᵒC) of Defence to provide meteorological data services. Data available is not in any of the standards described in the previous section, which can be used for building energy simulation programs. The available data is for a few weather stations and contains ambient temperature, wind speed, and humidity only. NASA SSE provides complete satellite data for any location across the world with parameters for solar energy calculations. In Appendices A and B, the annual and monthly daily mean maximum temperature, humidity ratio and solar insolation on a horizontal surface for Pakistan district cities is derived from NASA surface meteorology and solar energy (SSE). In a solar cooling simulation program, two important weather data sets used are energy plus weather (EPW) and typical meteorological year (TMY). For Pakistan the details of availability of these two types of data set are described here EPW Weather Data for Pakistan The available EPW data is only for one city - Karachi. Karachi is a coastal city with a hot and humid climate. The population density in coastal areas is much lower than in other climatic regions apart from Karachi city, which is the most populous city in Pakistan. For this research Lahore city has been selected as its climate represents typical conditions in the country. Lahore is the second most populous city in Pakistan and more than 50% of the population of Pakistan lives in climatic conditions similar to those in Lahore [68]. For Lahore EPW data is not available but it is available for the nearest Indian city, Amritsar, which is about 40 kilometres away from Lahore with similar climatic conditions. Comparison from the WMO provided 30 years of typical weather data for both cities and is shown in Figure LAHORE MEAN MAXIMUM AMRITSAR MEAN MAXIMUM LAHORE MEAN MINIMUM AMRITSAR MEAN MINIMUM JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Figure 5-6: Climatic comparison between Lahore and Amritsar [100] 132

133 TEMPERATURE (ᵒC) Figure 5-6 shows that the maximum average temperature is similar for both cities (blue and green). This is important as this research is based on cooling systems, required in hot climatic conditions during the summer season from April to September. The EPW data for Amritsar, India is available at the energy plus weather data official website. The data is obtained from the site and read through the program Climate Consultant 5.5 [365]. A comparison between EPW and WMO data is carried out for Amritsar. This comparison clearly shows a difference of 4-6ºC on average maximum and minimum temperatures as shown in Figure 5-7. The discrepancy implies that EPW data for Amritsar may be unsuitable for Lahore. A detailed study would be required to explain the discrepancy and thereby, perhaps, show whether the Amritsar EPW data is suitable for the present research MEAN MAXIMUM(WMO) MEAN MAXIMUM(EPW) MEAN MINIMUM(WMO) MEAN MINIMUM(EPW) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Figure 5-7: Amritsar daily mean temperature (EPW vs WMO) [100, 363] TMY2 Data for Pakistan As there is variation in EPW and WMO typical weather data for Amritsar, some other data types for Pakistan cities was sought. It was discovered that TRNSYS contains TMY2 weather data files for five main cities in Pakistan along with 1,036 cities worldwide. This weather data is provided by METEONORM [344]. The data is for the years and was obtained from about 7,400 stations worldwide. This data contains mean air temperature, humidity, sun shine duration and solar radiation [358]. 133

134 TEMPERATURE( C) TEMEPRATURE (ᵒC) For Lahore, a comparison between WMO data and TMY2 data is carried out and it shows a minor (less than 1ºC on average) variation in the data values for both sets. This comparison is shown in Figure 5-8. The good agreement between the two data sets gives confidence that the TMY2 data can be used to perform valid simulation MEAN MINIMUM(TMY) MEAN MINIMUM(WMO) MEAN MAXIMUM(TMY) MEAN MAXIMUM(WMO) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Figure 5-8: Lahore temperature comparison (WMO vs TMY2) [100, 344] A comparison of TRNSYS available TMY2 data of global horizontal radiation, mean maximum dry bulb temperature and relative humidity for the five major cities was carried out to analyse the climatic conditions in these cities and is shown in Figures 5-9, 5-10, and LAHORE MULTAN KARACHI QUETTA PESHAWAR JAN FEB MAR APR MAY JUNE JUL AUG SEP OCT NOV DEC Figure 5-9: Pakistan s cities maximum average temperature from TMY2[366] 134

135 GLOBAL HORIZONTAL RADIATION (w/m2) RELATIVE HUMIDITY (%) LAHORE MULTAN KARACHI QUETTA PESHAWAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Figure 5-10: Pakistan s cities average relative humidity from TMY2 [366] 350 LAHORE MULTAN KARACHI QUETTA PESHAWAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Figure 5-11: Pakistan s cities average global horizontal radiation from TMY2[366] The analysis of the data shows that Lahore, Multan, and Peshawar have very similar climatic conditions. So data for Lahore is suitable for use as typical weather data for Pakistan. Quetta s climate is different, characterised by low temperatures and humidity both in summer and winter. Karachi s climate is not typical for Pakistan due to high humidity in April, May, and June. Karachi also has low solar radiation, is the lowest of all the cities in summer and the highest in winter which is not suitable to represent typical conditions for solar cooling applications. Also, the annual average solar insolation for Quetta and Karachi is higher than other cities as shown in Appendix A. 135

136 5.7 Conclusion Methodology To evaluate the feasibility and performance of a solar cooling system widely used techniques are experimental evaluation or the dynamic simulation. Experiments play central role in scientific studies and are considered a direct relationship with real systems. Field experiments have advantage over laboratory experiments as they take place in natural conditions. More than 1000 solar cooling systems are installed worldwide and most are in European countries. First experimental study of solar cooling system was carried out in 1962 and after mid 2000s the number of experimental studies is limited compared to dynamic simulation studies. The history of simulation studies is as old as experimental studies. For this research an experimental system is not available in Lahore, so the adopted methodology will be dynamic simulation. From among the available dynamic simulation programs, TRNSYS was selected as the most suitable for this research. It is a comprehensive program used for simulation of both solar energy and building energy systems. A 3D building model can easily be created using Sketchup and building materials and geometry (walls and windows) can be assigned in Trnsys3d. It simulates both solar PV and thermal systems in details. It can integrate buildings with solar and cooling components and contains more than 500 models of different components. The TRNSYS library contains a variety of components for detailed and real system simulations. These component s parameters are from tested data components from Thermal Energy Systems Specialists (TESS). The outputs from each component can be plotted both in graphical and excel data formats. This can be easy to use for heat balance and other calculations. TRNSYS supports all types of weather data formats and it contains weather data for all main cities in the world. For Pakistan, TMY2 data is available for five cities. The literature presented for use of different simulation programs shows that TRNSYS is the most widely used for solar energy cooling (also heating) system worldwide. The literature available for use of other programs is limited. Many researchers have validated TRNSYS simulation results with the experimental results and established that TRNSYS results are in good agreement with experiments. The accuracy of TRNSYS is high, within 10% variation from experimental results. For solar energy collected, chilled water temperature, chiller COP and storage tank temperature simulations TRNSYS results are 4%, 3%, 3%, and 3.5% 136

137 different from experimental data on average. For solar cooling system simulation this variation is less than 5% on average, which means TRNSYS can be used to perform solar cooling system with confidence. The sequence of the methodology used for this research will begin with the creation of building model for part of a typical single family house in Pakistan. The building model will be imported in TRNSYS and will be assigned typical materials, heat gains, and inside operational conditions to calculate the cooling load. According to the cooling load a solar thermal cooling system will be designed and connected to the building model to maintain the desired set point during the peak summer time. An important system performance criterion is that it will be designed to meet the cooling load without an auxiliary energy source, other than electricity for pumps; fan etc. the system design will be optimised by trial and error to minimise the component sizes while maintaining the desired performance. The final results will be drawn for the optimised system and validated by previous published results. A parametric analysis will be carried out in TRNSYS for the most important parameters for the solar thermal cooling system and sensitivity of the system performance to these parameters will be examined. Finally, overall conclusions will be drawn Weather Data Weather data is a key input for solar cooling systems and building energy simulation as system design and operation depends on climatic conditions and variation. For simulation of solar energy systems different weather data types have been developed from the measured data across the world. The most important data types are TMY, EPW, and IWEC. EPW weather data is comprehensive data derived from various other weather data set. Unfortunately, for Pakistan this type data is available only for Karachi, which is not representative of the typical climate in Pakistan due to high humidity and less solar insolation during the summer season. Lahore is the city of most interest for this research, as its climate is typical of where more than 50% of the population lives. EPW weather data is available for the Indian city of Amritsar, which has a similar climate to that of Lahore. Therefore, Amritsar data was selected and analysed but there is difference of 4-6ºC on average in the temperatures for 137

138 Amritsar between EPW and WMO data. This difference makes it unsuitable to use this (Amritsar) EPW weather data as an input for simulation without a detailed study to explain the discrepancy. TMY2 data is useful for long term predictions of solar and building energy systems.tmy2 data for five main cities in Pakistan are available in TRNSYS. The available TMY2 data represent climate zones for all areas of the country. The climatic conditions of Karachi and Quetta are different and limited to these areas only although the solar energy availability of these cities is higher than other cities. Lahore, Multan and Peshawar data show that these cities have about similar climatic conditions. The mean daily temperatures show that during the summer season from April to September, these areas require cooling systems to maintain comfort during times of peak temperature. The calculations and simulation of results will, therefore, be performed using the TMY2 weather data for Lahore, as typical for Pakistan. 138

139 Chapter 6: Building Model and Simulation 6.1 Introduction In Pakistan most areas experience hot summer seasons with high ambient temperatures as described in Section 3.3. In cities during the summer, people spend more time indoors so buildings should be made comfortable for hot weather conditions. Most residential buildings are 1-2 storeys, with fired bricks walls and flat reinforced concrete (RC) slab roofs [97, 367] and most of the houses have 2-4 rooms [368]. These RC roofs retain heat absorbed in the daytime and emit it during the night affecting comfort in buildings, when all family members are in. This is worst for congested areas and houses with cooling systems (fans, coolers, and air conditioners) combined with poor ventilation, making sleeping difficult, affecting people s comfort and health [112]. Rooms are uncomfortable during the peak summer season (also in winter) due to many hours of electricity cuts (gas in winter) although cooling (also heating) systems are in place [112]. For simulation of building cooling load in the climatic conditions of Lahore, a simple twozone building was selected as TRNSYS TYPE 56 required a minimum of two thermal zones. This model was based on a common, typical construction design and materials of single storey houses in Lahore, Punjab (the largest area with more than 50% of the total population) [67] and other areas[97]. The model used in the research is an actual existing building with current building materials and dimensions. The details of typical construction materials used in different cities of Pakistan are described in Appendix C [97]. The selected single storey model house was similar to that selected by the UN energy efficient housing project in Pakistan, both in terms of construction material and size as described in Section 3.8. Typical single storey houses in urban and rural Punjab are shown in Figures 6-1 and

140 Figure 6-1: Typical single storey house in urban Punjab[369] Figure 6-2: Typical single storey house in rural Punjab [370] 6.2 Building Model TRNSYS supported Sketchup (Google Sketchup) was used to model an existing building near Lahore airport and the location is shown in Figure 6-3. It s a newly built (2010) house with a concrete roof and double bricks walls. The model used 3D building geometry for a space to be used for solar thermal cooling simulation. The model created was imported to TRNSYS for integration with solar thermal cooling system simulation and analysis. The Trnsys3d plug-in was used to add the geometric information into the building model, which was necessary for detailed energy calculations. Sketchup zones are different fromtrnsys3d zones. In Sketchup, interior walls separate one zone from another. In Trnsys3d zones are divided by the dynamic flow of energy which is indicated by infiltration, shades, solar gain, and other energy-based parameters. The designed model is a two-zone building with zones separated by a wall in Sketchup and by different energy flow in Trnsys3d. 140

141 Figure 6-3: Model building location The selected building consisted of two room/zones (rooms are representing zones) having the same volume, door and windows areas with doors and windows at different locations in both. Room1 has one window and one door, whereas Room 2 had two doors and one window. This is a typical construction with a drawing room with a door on the street side and courtyard side and a bedroom with one door on the courtyard side. The average room size in urban and rural areas is from 20-70m 3 with 1-2 windows [371] and the model used these measurements for analysis. A two zone simple model drawn in Sketchup with Trnsys-3d plug-in was created and its description and view are shown in Figures 6-4 and 6-5. Some others parameters are as follows: Floor area = 14m 2 Zone volume (V) = 42 m 3 Location: N, E, Proportion of window area in external wall = 10% Window area: 1.5m 2 141

142 Figure 6-4: Trnsys-3d two zone (room) model back and top views Figure 6-5: Trnsys-3d two zone (room) model front view 142

143 6.3 TRNSYS Simulation Studio The 3D building model created in Sketchup was imported to the TRNSYS simulation studio. The simulation studio is the main simulation engine of TRNSYS with graphical plotting and output with spreadsheet facilities. TRNSYS components are called Types and each Type is assigned a number; for the building model, Type56 was used. The systematic import of 3D building models to simulation studio is shown in Figures 6-6 and 6-7. Figure 6-6: Import of the Trnsys3d model into the simulation studio step-1 Figure 6-7: Import of the Trnsys3d model into the simulation studio step-2 143

144 In the above Figures 6-6 and 6-7, the building rotation was set to a default value of zero and the location was set to Lahore, Pakistan by selecting TMY2 weather data for Lahore available in TRNSYS weather data. Figure 6-8: After import of Trnsys3d model, the final window in the simulation studio The screen after the import of the building model and components are shown in Figure 6-8. During the import, TRNSYS calculates the volume of zones, number of surfaces, view factor to sky calculation, sorting of zones/air nodes and surfaces. It generates a *.BUI file and opens it in TRNBuild and *_b17_idf (this file can be used to go back from TRNBuild to Trnsys3d GUI) with the same order of zones and surface numbers. All Building-related materials, geometry and thermal properties are viewed and modified in the TRNSYS plug-in called TRNBuild. TRNBuild opens independently or by right clicking on building Type 56 using edit building The Building s Initial Parameters In TRNBuild, building materials, thermal calculation parameters and the model construction, with details of walls and windows for zones, are assigned according to selected standards. In TRNBuild American/ASHRAE, French, German, Japanese, Spanish and TESS standard 144

145 libraries are available and American/ASHRAE is selected as a default standard. The initial values for building materials, thermal comfort and other parameters were used from TRNBuild pre-defined default values selected within the American/ASHRAE standard. The details of some default and initial parameters used in the simulation are described here. In TRNBuild the settings menu is used to set up some general settings for the simulation. These basics settings include data files location, selected standard libraries, import and export model applications, TRNSYS input data files, and some other parameters required for the TRNSYS program applications for simulation. The other important building settings in TRNBuild are the project settings which include building orientations and miscellaneous settings. The orientations menu shows the orientation of building surfaces. Each orientation is described by direction (N, S, E, W or H), Azimuth angle of orientation (0-South, 90-West, 180-North and 270-South) and slope of orientation (0-Horizontal, 90-Vertical and 180- Facing down). When the initial building rotation is set (shown in Figure 6-7) the orientations are assigned to the model surfaces by the TRSNYS program. The miscellaneous settings include properties, inputs and outputs. The properties are material thermal properties; some are general properties and others are parameters for internal calculation of heat transfer co-efficients as shown in Figure 6-9. Heat transfer co-efficients depend heavily on the temperature difference between surface and fluid and direction of heat flow. TRNBuild automatically selects default values for properties during the model import. For thermal calculations, the general values used are: air density (1.204kg/m 3 ), air specific heat (1.012kJ/kg.K) and air pressure (101325Pa), water vaporisation heat (2454kJ/kg), Stefan Boltzmann constant (5.67e -8 W/m 2 K 4 ) and approximate average surface temperature (293.15K). 145

146 Figure 6-9: Parameters for heat transfer co-efficients The miscellaneous settings include inputs and outputs other than properties. TRNBuild calculates and creates standard inputs during the Trnsys3d model import. The inputs can be added and removed unless related to building description. Most of the inputs used are from weather data and building location as shown in Figure Figure 6-10: Standard and user defined inputs Outputs are the last step in the building description and the desired parameters are defined to be plotted from the simulation results. Outputs can be added and deleted as required simulation result parameters for analysis. The Outputs window for Type56 in TRNBuild is shown in Figure The default outputs are zone air temperature and sensible heat (positive for cooling and negative for heating). 146

147 Figure 6-11: Building outputs Zones Thermal and Material Properties The zones window contains all information for thermal zones in the building model. A thermal zone may have more than one air node. The air nodes can move within a zone for multi air nodes zones. The Zones window describes an air node s regime data, walls, windows and optional building equipment and operation specifications including infiltration, ventilation, cooling, heating, gains and comfort and geometry modes as shown in Figure Regime Data Regime data includes volume of air node, total thermal capacitance kj/k (standard is 1.2 zone volume), initial temperature, initial relative humidity and humidity model for air nodes. The zone initial temperature and initial relative humidity used were 20 C and 50% respectively. In the case of the building model, TRNBuild takes a zero value for capacitance as its default. For initial simulation all default parameters are used. Walls For the building model, TRNBuild calculates parameters and assigns materials including wall type, wall area, wall category (external, internal, adjacent and boundary) surface number and 147

148 wall gain. TRNBuild contains a library according to the selected standard for walls and a new wall type can be defined. It also calculates total wall thickness and standard u-value according to wall material. The summary of walls is shown in Figure Figure 6-12: Room1 volume, surface and areas calculated by TRNSYS Similarly, for wall layer, a standard library is available and the user can define a new layer. New layer definition has four category options that are: massive (normal construction), mass less (to neglect thermal mass), active (concrete core cooling and heating) and chilled ceiling (chilled ceiling panel). In addition to wall constructions the co-efficient of solar absorptance is also required as shown in Figure It depends upon properties of wall finish and the standard value for each surface is available in the library. TRNBuild uses default values automatically and changes are possible if required. Finally, the convective heat transfer co-efficient of the wall required and standard vales are: inside - 11kJ/h m 2 K and outside - 64kJ/h m 2 K. 148

149 Figure 6-13: Properties of material assigned to external roofs The properties of materials used for an external roof are shown in Figure The detailed description of other wall types and materials is as follows. By default TRNBuild assigned standard materials to the adjacent wall (partition between zones) front/inside with three materials layers (plasterboard, fiberglass and plasterboard) with a total thickness of 0.090m and u-value of 0.508W/m 2 K. The external wall was assigned with three material layers (plasterboard, ASHRAE fiberglass and ASHRAE wooden sidings) with a total thickness of 0.087m and a u-value of 0.510W/m 2 K.The solar absorptance of all walls is 0.6 for both sides. The long wave emission coefficient of all walls is 0.90 for both sides. Windows In TRNBuild, windows can be defined for external and adjacent walls. Windows can be added, edited or deleted depending upon the geometry mode settings. The specifications for windows geometry and materials include windows type, area, category, surface number, gain, orientation and shading device. The TRNBuild standard and default setting for windows is shown in Figure

150 Figure 6-14: Properties of windows assigned When the *.BUI file is written during model transfer, the windows area is automatically subtracted from the wall area by considering it an extra surface with area. This window can be assigned different materials, glazing, frame and optional properties of shading devices including convective heat transfer co-efficients for a window (glazing + frame) as shown in Figure TRNBuild contains a standard library for windows according to the available standards. In the library, each type is assigned with an ID number, u-value, g-value, convective heat transfer coefficient, frame properties and optional properties of shading devices. The selected default settings for windows are shown in Figure Infiltration Airflow into the zone from outside is specified by infiltration. In TRNBuild, infiltration is optional and it can be a constant value, an input or scheduled value. The infiltration is defined in terms of number of air changes per hour (ACH). By default, infiltration is off for the initial simulation parameter. Ventilation Airflow from external heating or cooling equipment into the zone is specified by ventilation. In TRNBuild, ventilation is optional and it can be defined by airflow (air change rate or mass flow rate), temperature of airflow (outside or other) and humidity of airflow (relative or 150

151 absolute humidity and outside or other). By default, ventilation is off and the user can create different types of ventilation. For initial simulation default parameters are used. Heating Heating requirements and heating control in any zone are defined by heating type. Using heating in a zone is optional and by default it is off. Heating control is defined by set temperature, heating power (unlimited or limited) and humidification (off or on with relative or absolute humidity). For initial simulation default parameters are used. Cooling Cooling requirements and cooling control in any zone is defined by cooling type. Use of cooling in the zone is optional and, by default, it is off. Cooling control is defined by set temperature, cooling power (unlimited or limited) and humidification (off or on with relative or absolute humidity). For initial simulation default parameters are used. Gains Internal gains including persons, electrical devices and lighting are defined by gains. Gains are optional and by default, they are off. A person s activity gains are defined according to the ISO 7730 standard. Use of computer and artificial lighting is optional. Gains are from a standard library and the user defines other gains which are available according to selected standards. For initial simulation default parameters are used (no gain at all). Comfort Thermal comfort calculations are based on the ISO 7730 standard. Specification of comfort is optional and by default the comfort setting is off. The user can define the comfort type based on clothing factor, metabolic rate, external work and relative air velocity. The internal calculation based on comfort is calculated by a simple model (based on area weighted mean surface temperature) or a detailed model (based on view factor of reference point). For initial simulation default parameters are used, which is that no comfort standard is used. Schedule TRNBuild offers a scheduling system for infiltration, cooling, heating, ventilation, gains and comfort. The schedule types are, day-night, and light, set off, use, weekend, workday and 151

152 work light. Frequency is daily or weekly with any start stop times during the 24 hour duration. For initial simulation no schedule is used. Geometry and Radiation Modes Radiation modes of thermal zones are for direct and diffuse shortwave and long wave radiation distribution within zones. The available options are beam radiation and diffuse radiation distribution with standard and detailed models, and long wave radiation exchange with a zone offering standard, simple and detailed models as shown in Figure Figure 6-15: Radiation and geometry modes TRNBuild supports different levels of geometric surface information for each zone. Geometry modes use manual, mixed and 3D data. If the geometry mode is set to manual data for all three dimensions will be deleted. Detailed models for radiation mode selections work only if geometry is set to 3D data. For the initial simulation 3D data is used when 3D model is imported into TRNSYS. 6.4 Building Model Initial Simulation Results After the model import in TRNSYS with all the default settings and parameters selected as initial parameters for the building model with Lahore TMY2 data, a simulation was executed and initial results were obtained. The TRNBuild default building model outputs were zone air temperatures and sensible heat required for the zone (positive for cooling and negative for 152

153 heating). For initial results only zone temperatures were plotted to study the room s temperatures with (American/ASHRAE) TRNBuild pre-selected default parameters. For better plot results, temperature ranges were set from 0 C to 55 C and sensible heat ranges were set from zero to 5000 kj/hr. The default simulation time-step was one hour and the total duration was 8760 hours for a year (365 days). For the purpose of simplicity only the room s temperatures were plotted to observe the inside air temperature with default materials and others parameters. The initial results are shown in Figures 6-16, 6-17 and Figure 6-16: Initial results, room1 and room2 air temperatures Figure 6-17: Ambient and room 1 temperature comparison 153

154 Figure 6-18: Ambient and room 2 temperature comparison Figure 6-16 shows that both rooms have very high temperatures in the summer season with a peak temperature of more than 45 C which is higher than the ASHRAE standard comfort temperature. It also shows there is a need for a cooling system for comfort, which is realistic for Pakistan weather conditions. The pattern and range of temperature for both rooms is similar. Figures 6-17 and 6-18 show the comparison between room 1 and room 2 temperatures with the ambient temperatures respectively. It is clear that both rooms have temperatures higher than ambient temperature both in summer and winter seasons. For the current research concern is with temperatures in the summer season as research relates to cooling load for comfort temperatures in the summer season. Default (initial) building properties were assigned by TRNSYS to both rooms. For simplicity and reference, all the modifications and changes were made in room 1 only. The reference was there, so that it was possible to check (as an aid to trace errors) if the results detected something was wrong while modifying room 1. The cooling system was designed for room 1 and could be multiplied for a multi-rooms building Internal Gains and Infiltration Addition The first change made in the building parameters was the addition of internal gains, infiltration and ventilation to room 1 as the TRNSYS default settings do not use any gain or infiltration. This addition made the simulation results more realistic and estimated the maximum room temperature and cooling load with gains and losses. Internal gain used the 154

155 default ISO 7730 standard with the presence of one person with light activity from 4 pm to 9am and a 100 W/m 2 incandescent lamp and one TV/computer of power 140W as the internal gains. Infiltration was set according to the LEED standard as 0.2 (ACH) and ventilation as 2.0 (ACH) with ambient temperature and humidity [372]. The simulation results after addition of gains and losses showed an increase in room 1 air temperature, which is shown in Figure Figure 6-19: Room1 air temperature with internal gain, infiltration, and ventilation Figure 6-19 shows an increase in room air temperature due to an increase in internal heat gain and infiltration of ambient air. The peak temperature during the summer is more than 50 C. Ventilation is heat input to the room in the middle of the day when ambient temperature is high and heat removal is at night when the ambient temperature is lower, which lowers the room temperature. The initial results showed that there is a need to modify building construction materials and operating parameters to improve building comfort levels and minimise the cooling load before designing a cooling system to maintain the standard comfort conditions inside the room. 155

156 6.5 Building Model Modification Construction Materials Walls Room 1 was assigned actual construction materials from the TRNBuild library according to the ASHRAE Standard to make the model more realistic according to constructions commonly used in Pakistan as described in Sections 6.1 and 6.2. The construction included reinforced cement and concrete for roof and floor, and solid brick walls. In TRNBuild, normally the roof is considered as a roof surface with external conditions and the floor as a roof surface with boundary conditions. Boundary condition is the temperature of a node to which surface back is connected through pure resistance. For a simple model, the roof and floor are both simulated as a roof with external conditions. The library for walls and roof materials is the same. The detailed properties of three materials assigned to walls, roof and floor are shown in Table 6-1. The composition of the wtype115 and wtype11 are different, although both are heavy concrete. Table 6-1: Properties of materials assigned to walls and roof surfaces Surface Library No. Type Description External Roof 25 wtype mm heavy weight concrete External Floor 11 wtype mm heavy weight concrete External/Adjacent Wall 64 wtype 20 Solid brick wall (200mm) Solar absorptance of wall Convective heat transfer coefficient of wall Front:0.60 and back:0.60 Front:11 kj/h.m 2 K back: 60kJ/h.m 2 K Others wall parameters include solar absorptance and convective heat transfer co-efficients of the wall for the front and back sides. Solar absorptance and connective heat transfer coefficients are the same for all the walls and roof surfaces. The thermal capacitance of the room was set to a standard value which is 1.2 times room volume and is 54.60kJ/K. The summary of material assigned to walls, roof and floor surfaces is shown in Figure

157 Figure 6-20: ASHRAE standard materials assigned to walls, roof and floor Windows Windows ID-1001 was selected from the ASHRAE library as an external window 1. It is a single glaze window, which is the most commonly used window type in Pakistan (author s own observation). All the properties were according to the ASHRAE standard and selected window properties and other parameters are shown with details in Figure The u-value and g-value of TRNBuild default windows (ID: 6001, u-value 2.89W/m 2.K, g-value 0.789) are less than the selected single glazed window. Figure 6-21: ASHRAE standard properties of window ID

158 Gains Room cooling or heating load was based on room envelope conduction and internal heat gains. The gains were set for occupancy according to the ISO7730 standard with light activities of 170W (75W sensible heat 95W latent heat) total heat and, a computer with 50W of power and artificial lighting with a total heat gain of 19 W/m 2. These were updated according to the best energy efficient available equipment and were different to the default described in Section Modified Building Model Results After assigning materials to walls, roof, floor and windows, simulation results for zone 1 (room 1) air temperature were derived to observe the effect of assigning commonly used materials in Pakistan. The results showed a decrease in the room 1 air temperature in comparison to previously assigned TRNBuild default materials. This decrease in temperature occurs both in summer and winter. This indicates a decrease in energy transfers from the outside to the inside of the room. The room peak temperature during summer decreased to less than 43 C as shown in Figure Figure 6-22: Room 1 temperature after assigning walls and windows materials Further modification required is integration of the cooling system with the building. The building materials and internal gains used were the same and the final results were plotted for standard room comfort conditions. 158

159 6.5.3 Building Envelope Conduction TRNBuild is lacking only in defining the doors created in the Trnsys3d model. It considers doors to be parts of walls. The area of doors is included in the wall area. If the difference between doors and walls is important, doors may be modeled as windows. For actual assigned materials, the heat conduction through walls, roof, floor and door was carried out in detail to compare the heat conduction effect from doors. The heat conduction of actual materials is shown in Table 6-2. The U-value for floor was higher than for roof in spite of being thicker, because of the difference in composition of both materials. Similar construction materials with a U-value ( W/m 2 K) were used by Montero et al. [302] for solar assisted cooling systems for the climate of Guayaquil, Ecuador. The thermal conductivity of wood across the grain, yellow pine, timber =0.147 W/m.K [373]. The normal thickness of a door according to (Indian standard) IS = m [374]. The heat loss co-efficient for the door = 2.45 W/m 2 K. Table 6-2: Room envelope heat conduction calculations Surface Area (m 2 ) U-Value (W/m 2 K) Heat loss UA (W/K) Front wall Back wall Adjacent wall Side wall Roof Floor Window Door Total If the door is considered part of the wall (the U value is 2.09 W/m 2 K instead of wood 2.45W/m 2 K) the total UA value decreases by 0.72W/K ( ) or about 14% only. Therefore, neglecting the door and considering it as part of the wall did not have a large effect on the results. 159

160 6.6 Solar Cooling System Initial Parameters Calculations Chiller Cooling Capacity In the previous sections, the conditioned zone was not comfortable. Therefore, to make it suitable for the comfort of residents in the summer a cooling system needed to be designed. To start the TRNSYS simulation for a solar cooling system an estimation of initial parameters was required for all components of the solar cooling system. In this section some calculations are performed to get initial parameters to start the simulation. The selected building model was an existing building with typical construction with two rooms each with a space volume of 42m 3. An air-conditioning unit about 3.52kW (1 Ton of refrigeration) capacity was expected to be sufficient for comfort during the peak summer season for the room with a volume of 42m 3. Estimated installed capacity = 3.52 kw ~12660 kj/hr. The TRNSYS default value for the Type107 chiller gives a difference between the hot water inlet and the outlet temperature from the chiller at 46 C but for low temperature heat sources, such as solar collectors, it is assumed to be 33 C. The standard COP for absorption chillers is shown in Table 6-3. Table 6-3: COP of absorption chillers [375] Chiller Type Heating Source C.O.P Range Single effect Hot water or steam 0.60 to 0.75 Double effect Hot water or steam 1.19 to 1.35 Double effect Direct fired 1.07 to 1.18 COP of chiller = 0.60 (lower as a conservative estimate) The COP of a chiller is expressed as Equation 1. COP = Q e Q g (1) Q e = 3520 W So, Q g = = 5867W~21100 kj/hr The hot water flow rate (m) from the tank to the chiller was estimated from Equation 2. Q g = m C P (ΔT) (2) 160

161 5867 = m m = kg/sec ~ 153kg/hr Where, C P is the specific heat capacity of water and it is 4190 J/kg.K Solar Collector Calculation Solar energy availability varies each month due to seasonal changes. For the solar collector initial parameters, from the summer season a month was selected with the highest solar energy availability to meet the cooling load of the building. All the calculations were made for a single day, and then the simulation was run to optimise the system for one day (24 hr) then for the whole year (8760 hrs). According to NASA, SSE data as shown in Appendix A, the month of May has the maximum daily average insolation incident in Lahore on a horizontal collector and is measured at approximately, 7.34 kwh/m 2 [42]. Assuming May 15 th (day number 135, hours ) to be a clear day with no clouds and with 14 hours of bright sunshine day length, the average incident radiation received per square metre during each hour would be: = 0.524kW/m 2 = 524 W/m 2 This means that the total incident energy rate available on the surface of a collector with an area of 1m 2, would be 524W. The efficiency of an evacuated tube collector ranges from 50% to 85% [376]. Supposing the mean efficiency of the evacuated tube collector is 67% (a conservative value). The energy absorbed at the collector and water flow rate would be as follows. The energy rate absorbed/available from collector = = 351 W/ m 2 ~ 1264 kj/hr. m 2 So, 1m 2 area of evacuated tube collector could produce a maximum energy rate = 351 W/ m 2 Assuming there is no heat loss from the collector outlet to the tank storage and the tank to the absorption chiller, the energy output required from the collector would be equal to Qg calculated from Equation 1: 161

162 Q coll.out = Q g = 5867 W The area of the collector would be = required energy output energy available per unit area = ~17 m 2 Zambolin et al. [377] did experimental work on the performance of a flat plate and an evacuated tube collector for a single day, showing the difference between the collector inlet and the outlet temperature to be 30 C. The water flow rate for a collector can be calculated from Equation 3. Q coll.out = m C P (ΔT) (3) 5867 = m m = kg/sec ~ 168 kg/hr This is approximately the same as the flow rate from the tank to the chiller, because ΔT is about the same. Theoretically, 5.867kW (21100 kj/hr) of heat energy is required by a chiller generator for 3.52kW (3520W) refrigeration cooling output. The energy supplied by a solar collector to a storage tank is 5.967kW (21481kJ/hr). This is sufficient heat energy to run the cooling system by assuming zero tank heat losses at the start of the simulation. Later on in the optimisation process the tank and pipes losses were introduced Cooling Systems Reference Model In the above basic calculation, parameters were referenced from the literature mentioned. Some other parameters were referenced from the literature are described here. Eicker et al. [353] analysed heat rejection and primary energy efficiency of solar driven absorption systems. They analysed an 18kW solar cooling absorption system installed at the Solar Next Company in Rimsting, Germany. The solar cooling system had hot and chilled water storage, flat plate and evacuated tube collectors, a wet cooling system (dry cooling is also possible) with fan coils for the distribution of cooling air. 162

163 All the electrical loads of the chiller, fan, pumps and cooling system were referenced from [353], adjusted in proportion to the rated cooling capacity. All other parameters were either TRNSYS standards or optimised values according to the system energy balance. For a TYPE 71 collector, the collector test reports representative data is available on the web from testing institutes. The evacuated tube collector model CALDORIS was selected from different available models due to a nominal flow rate of 180 kg/hr as most suitable. It is manufactured by Caldoris Polska Sp.Zo.o and tested for performance and quality in accordance with the EN :2006 standard. The efficiency a 0 (0.769) and loss coefficients a 1 (2.52 W/m 2 K), a 2 (0.0106W/m 2 K 2 ) were selected from this tested model [378]. 6.7 Solar Cooling System Simulation Different types of component are available in TRNSYS to simulate solar cooling systems. As described in Section 4.4.3, the evacuated tube collectors are more efficient than flat plate collectors. Also absorption chillers are the most commonly used chillers. For the simulation both of these two components were selected. For small capacity and low temperature heat input applications a dry cooler is a better choice than a wet cooler [353]. To store heat for load after sunset and the smooth operation of the chiller, a hot water storage tank was selected [379] Solar Cooling Process A simplified summary and process flow diagram involved in the simulated solar cooling system is shown in Figure 6-23 and explained here. It should be noted that the lines in the diagram represent logical connections in the simulation rather than physical pipes etc. The process of solar cooling starts from the solar heat collection through an evacuated tube collector Type71. The cold water from a stratified water storage tank Type4a bottom is pumped to the collector and hot water returns to the top of the storage tank. The collector pump Type3d is controlled by a timer controller (not shown) and turns on during the day when energy is available. The controller working parameters are described in Section The hot water from the top of the tank is pumped to the chiller Type107 and returns to the bottom of the storage tank through a pump Type3d

164 The chiller absorbs heat from the cooling coil Type697 by circulating chilled water through a pump Type3d-4. The returned chilled water from the cooling coil exchanges heat with the absorption solution inside the chiller. The absorption solution is cooled by cooling water from the auxiliary dry cooler Type1246. Figure 6-23: Solar cooling system The hot cooling water from the chiller is circulated by a pump Type3d-3 to the auxiliary cooler Type1246. It is a dry cooler and cools hot water by exchanging heat with ambient air. The cooled water is returned to the chiller to absorb heat from the absorption solution. The chilled water in the cooling coil Type697 exchanges heat with the air coming from the fan Type112b. The fan takes air from the building Type56 which is cooled down through a cooling coil and returned to the building. The fan is controlled by the controller Type108 (not shown) which monitors the inside temperature of the building. As the temperature goes above the set point the fan turns on. The detailed description of the controller is in Section The components used for the simulation of solar energy collection, storage and cooling systems integrated with the building are described here with some important operating parameters. The details of all components, parameters, and inputs are shown in Appendix C. 164

165 Collector efficiency Evacuated Tube Collector An evacuated tube solar collector of TYPE 71 is used for TRNSYS simulation. It is a TRNSYS TESS standard collector with experimental data validation [344]. The loss coefficients a 1 and a 2 used are from the collector (SPF No.C1586: CALDORIS-58-30) as a reference [378]. This reference collector model is selected as the nominal flow rate is in the same range as this research design (Section 6.6.2). The collector s efficiency depends on the collector inlet or average or outlet temperature (Tc). In Type 71 input parameters, one (1) is for the collector efficiency parameters given as a function of the inlet temperature. Two (2) is for a function of the collector mean temperature and three (3) is for a function of the collector outlet temperature. In this research, two (2) is used as a collector average temperature (Tm) for collector efficiency calculations. The efficiency of a collector is written as Equation 4. Collector efficiency = a 0 [a 1 (Tc-Tamb)/I] [a 2 (Tc-Tamb) 2 /I] (4). The efficiency of the collector type with the selected a 0 (0.769), a 1 (2.52W/m 2 K) and a 2 ( W/m 2 K 2 ) and I=1000 W/m 2, using Equation 4, is shown in Figure % 80% 70% 60% 50% 40% 30% 20% 10% 0% Tm-Ta Figure 6-24: Evacuated tube collector TYPE 71 efficiency curve for I=1000 W/m 2 The Solar Ratings and Certification Commission (SRCC) define the efficiency of an evacuated tube collector using the same equations as for a flat plate; the main difference (from a modelling point of view) is in the treatment of Incidence Angle Modifiers (IAM). Type71 reads a text file containing a list of transversal and longitudinal IAM s. IAM is the 165

166 variance in output performance of a solar collector as the angle of the sun changes in relation to the surface of the collector. Transversal IAM measures change the performance of the collector as the angle of the sun changes at right angles to the collector tube axis. Longitudinal IAM measures change in performance as the angle of the sun changes along the collector tube axis. The default number of IAM s in TRNSYS is 5 and the optimised number for maximum energy yield and efficiency results is also 5. The reference values used for TYPE 71 are shown in Appendix C. Figure 6-24 shows that collector efficiency decreases as the difference between a collector s mean temperature and ambient air temperature increases. The higher the difference the higher the heat loss to ambient will be. For a temperature difference of 30ºC the efficiency of a solar collector is about 67%, which is higher than the initially selected collector efficiency of 60% in Section Simulation Parameters The inputs to the collector Type71 simulation model are fluid properties, flow rate and weather data. Collector inlet fluid temperature and flow is the outlet of a storage tank cold side. The flow is controlled by a controller, which cuts off flow if fluid temperature difference between inlet and outlet is less than 2 C. The operation of the controller is explained in Section The collector slope is zero (lying flat on the roof) and other input data is shown in Figure

167 Figure 6-25: Collector solar data input Collector Outputs The collector gave three outputs which were outlet temperature, outlet flow rate, and useful energy gain. The outlet temperature is at the exit of the array and the outlet flow is the same as the inlet flow rate. The rate of useful energy gain by the solar collector fluid was calculated by Equation 5. Qu = m C P (T coll.out T coll.in ) (5) Hot Water Storage Tank The hot water storage tank Type 4a was used to simulate the thermal storage tank in TRNSYS. It is a stratified storage tank with fixed inlets and uniform losses with an auxiliary heating system. The stratified tank delivers water at a slightly higher temperature than an unstratified tank [357]. This is a simple stratified tank suitable only as a storage tank without auxiliary heating. The tank volume is 2m 3 with a total height of 1m and an area of 2m 2 and a diameter of 1.6m. This volume is sufficient to provide energy for 24 hour operation of an absorption chiller with about 12 hour back up. Tank Type4a includes two auxiliary heating elements and auxiliary heating elements are not used in this simulation so their maximum heating capacity is set to zero. 167

168 Figure 6-26: Operation of hot water storage tank Fluid is hot on the top side and cools down as it moves downwards and is cold at the bottom of the tank. The tank is divided into ten equal heights (each 0.10m). It was assumed that losses from each tank node are equal. The hot water from the collector enters the tank top and leaves from the top to the chiller. The cold side water enters at the bottom of the tank returning from the chiller and leaves the tank bottom for the inlet to the collector as shown in Figure 6-26, where, m h and m L are the fluid flow rates to and from the heating side and load side respectively and the temperature difference from top to bottom is about 10 C. Inputs and Outputs The inputs to the tank are the hot side inlet (collector outlet) fluid flow rate and temperature and cold side (Chiller outlet) fluid flow rate and temperature. The ambient/environment temperature is an input for heat loss calculations. The input and output connections for hot a water storage tank are shown in Figure For storage tank heat loss calculation it is assumed that the tank is well insulated with minimum heat loss. For storage tank with fiber glass insulation of thickness 0.050m [380] and R-value 6m 2 K/W, the tank average heat loss co-efficient is about 0.167W/m 2.K [381]. The boiling point temperature of the fluid in the storage tank is set to 100 C. When the tank temperature reaches the boiling temperature, venting of steam occurs to keep the fluid at boiling temperature. The venting is assumed to occur with negligible loss of mass. 168

169 Figure 6-27: Tank inlet and outlet connections The tank outputs include the fluid flow rate, temperature to the heating source (collector inlet), energy rate, fluid flow rate, and temperature to load (chiller inlet). Internal energy change (kj), auxiliary heating rate, energy rate from the heating source (collector), tank thermal losses rate, average tank temperature, and temperature of any specified node are also outputs from the storage tank Absorption Chiller A hot water fired single effect absorption chiller Type 107 is used in TRNSYS simulation. Type107 uses a normalised catalogue data, lookup approach to model a single-effect hot water fired absorption chiller. Hot water-fired indicates that the energy supplied to the machine generator comes from a hot water stream. Because the data files are normalised, it can operate for a variable set of inlet fluid temperatures, cooling capacities and outlet chilled water temperatures. The chiller capacity is set at 3.52kW with COP of 0.60 as described in Section The chiller cooling water inlet temperature is from a cooling tower and the chilled water set point is at 7 C. Many parameters are linked with the TRNSYS library supplied data file. These include a number of hot water temperatures, a number of cooling water steps, a number of chilled water set points and a number of design load fractions. The TRNSYS default values were used for all these four parameters as they are parameters tested by the Thermal Energy System Specialists (TESS). 169

170 The specific heat capacity for hot water, cooling water and chilled water is 4.190kJ/kg.K. The auxiliary electrical power required by an absorption chiller to operate a solution pump and refrigerant pumps is set to 0.061kW. This parameter is taken from a reference absorption chiller model [353]. Figure 6-28: Absorption chiller input and out connections Inputs and Outputs The TRNSYS default and selected set-point temperature for the chilled water stream is set to 7 C, which is the design temperature for commercially available chillers [297, 382]. If the chiller has the capacity to meet the current load, it will modulate to meet the load and a chilled water stream will leave at this temperature. Inputs to a chiller are hot water flow rate and temperature from a storage tank, cooling water flow rate and temperature from a cooling tower and chilled water flow rate and temperature returned from a cooling coil. The chilled water flow rate was set to 250 kg/hr and the inlet hot water from the tank hot temperature with a flow set to 150 kg/hr in accordance with chiller performance. For the cooling water from the cooling tower, the flow was set to 800 kg/hr. All these flowrates are used to maintain to a chiller set of 7 C. 170

171 Outputs from the chiller are hot water flow, temperature return to the storage tank, cooling water flow, temperature to the cooling tower and chilled water flow, as well as temperature to the cooling coil. Hot, cooling, and chilled water energies and electrical energy required are also outputs from the chiller simulation. The chiller input and output connections for a chiller Type107 are shown in Figure Cooling Coil A conventional cooling coil model Type697 is used in TRNSYS to model building air cooling through chilled water from a chiller. This component models a cooling coil where air cools down as it passes across a coil containing a cooler fluid (typically water). This model relies on user-provided external data files that contain the performance of the coil as a function of the entering air and fluid conditions. Type697 models a simple air-cooling device that removes energy from an air stream according to performance data found in a combination of three external data files and based upon the flow rates and inlet conditions of the air stream and a liquid stream. In Type697, three data files are required. The first provides water temperature correction factor performance data. The second provides correction factor data for the performance based on varying air temperatures while the third provides correction factor data for the performance based on varying airflow rates. The default values are used for all these three parameters as they are parameters tested by the TESS and shown in Appendix C. At each time step, Type697 performs a call to the TRNSYS psychrometric routine in order to obtain air properties for the inlet air stream not specified by the user among the component s inputs. 171

172 Figure 6-29: Cooling coil connections Inputs and Outputs The Type 697 model works on two types of humidity modes used for inlet air. These modes are both for an absolute humidity ratio and the percentage of relative humidity. Some parameters are linked with the TRNSYS library and supplied in three data files. These are the number for water flow rates, the number for water temperatures, the number for air flows, the number for dry bulb temperatures, and the number for wet bulb temperatures. The rated volumetric flow rate for air is input from a fan. The total cooling capacity is 2.5kW and the sensible cooling capacity is 2.0kW. These settings are in accordance with chiller performance to maintain room temperature below the set point. For the Type 697, the TRNSYS default ratio of total cooling capacity to sensible cooling capacity is The inputs to the coil are chilled fluid flow and temperature from the chiller, as well as airflow, temperature, pressure and percentage of relative humidity from a building through a fan Type112b. Inlet air pressure is 1 atm and the air-side pressure drop is set to zero. The outputs include outlet fluid flow and temperature back to the chiller, outlet airflow, temperature and pressure and percentage of relative humidity to the building. The total heat transfer rate, sensible heat transfer, fluid heat transfer, condensate temperature, and flow are outputs from a coil. Input and output connections for the cooling coil Type 697 are shown in Figure

173 6.7.6 Cooling Tower The air-cooled cooling tower Type1246 is used to model an external proportionally controlled fluid cooler. Type1246 is a low-temperature heat-distributing unit such as radiators, convectors, and finned-tube units. This unit transfers heat through a combination of radiation and convection without a fan. Figure 6-30: Auxiliary cooler connections The rated capacity of the cooler is set to 5.83kW and the heat capacity of fluid is 4.190kJ/kg.K. The inputs to the auxiliary coolers are fluid flow and temperature from the chiller, heat loss coefficient and the temperature of the environment. The control function controls the on/off operation of the cooler. The loss coefficient (UA) for the fluid cooler during operation is set to zero. The outputs are outlet fluid flow and temperature to the chiller, cooling rate, thermal losses and useful cooling rate. The input and output connections of the auxiliary cooler Type1246 are shown in Figure Pumps For water flow simulation in TRNSYS, pump Type 3d was selected. This is a simple, single speed and constant flow pump with only inputs of fluid flow and pump electrical power. The TRNSYS library contains multiple pump types which are complex and meet different criteria. This pump model computes a constant mass flow rate using a variable control function, which must have a value of 1 or 0. The pump will be on when it is 1 and off when it is 0. A user-specified portion of the pump power is converted to fluid thermal energy. This 173

174 component sets the flow rate for the rest of the components in the flow loop by multiplying the maximum flow rate from the control signal. All the four pumps used for water flow from the solar collector to the storage tank, the storage tank to the absorption chiller, the absorption chiller to the cooling coil and from the absorption chiller to the auxiliary cooler are Type3d pumps as shown in Figure Figure 6-31: Pump connections The inputs to the pumps are fluid maximum flow rate, fluid temperature and control signal. The outputs are outlet fluid temperature, fluid flow rate and pump power consumption. These inputs and outputs are common parameters for all pumps used. The flow rate and power consumption [353] for all the pumps are shown in Table 6-4. Table 6-4: Pumps, powers and flow rates Pump Connection Maximum Power (W) Maximum Flow (kg/hr) Type3d Tank-Collector Type 3d-2 Tank-Chiller Type 3d-3 Chiller-Cooler Type 3d-4 Chiller-Coil Chiller Solution pump Fan TRNSYS Type112b was selected to model a fan to transfer air from building Type56 to cooling coil Type697. It is a simple, single speed fan with relative humidity inputs. The humidity mode for the cooling coils Type697 is relative humidity so Type12b was selected. Type112b models a fan which spins at a single speed and maintains a constant mass flow rate 174

175 of air. As with most pumps and fans in TRNSYS, Type112b takes mass flow rate as an input. Type112b sets the downstream flow rate based on its rated flow rate parameter and the current value of its control signal input which must have a value of 1 or 0. Figure 6-32: Fan connections The inputs to the fan are humidity mode, rated flow rate, rated power, motor efficiency and motor heat loss fraction. The selected humidity mode is 2, which is a percentage of relative humidity and the air flow rate is 300kg/hr (~ 250m 3 /hr) sufficient to maintain room temperature below a set point. The rated power is 23W and the default standard motor efficiency and heat loss fraction were selected. The default standard motor efficiency is 0.90 and the motor heat loss fraction is zero. The fan inlet air temperature and percentage of relative humidity is room 1 air temperature and percentage of relative humidity. The input control signal to the fan is the output from the thermostat Type108. The fan is OFF when the control signal value is 0 and the fan is ON if the control signal value is 1. The fan outputs are outlet air temperature, pressure, flow rate, humidity ratio, and percentage of relative humidity, power consumption, and air heat transfer. The outlet air temperature, flow rate, and percentage of relative humidity are input to the cooling coil Type 697. Fan input and output connections are shown in Figure

176 6.7.9 Pipes To simulate pipe connections between components Type31 pipe was selected. This component models the thermal behaviour of fluid flow in a pipe and thermal losses are also considered for realistic operation. The pipe connections are used between the storage tank Type4a and pumptype3d, solar collector Type71 and storage tank Type4a, chiller Type107 and auxiliary cooler Type1246 and between the chiller Type107 and cooling coil Type 697. The simplified layout of pipe connections is shown in Figure Figure 6-33: Pipe connections Inputs and Outputs As the same type of pipe is used, all inputs and outputs are the same except for pipe diameter and length, fluid temperature and flow rate. The pipe diameters were selected from the TRNSYS default standard sizes to sizes with optimal losses and fluid flow. The lengths of pipes were estimated from the room dimensions. The heat loss co-efficient for pipes is used as for the storage tank, namely 0.167W/m 2.K [381]. Fluid density and specific heat capacity value are 1000kg/m 3 and kj/ kg.k. The same ambient temperature is used for the pipes which is output from weather data for thermal losses of the pipes. The outputs included fluid outlet temperature and flow, environment losses, change in internal energy, average temperature, and rate of change of internal energy. The outlet temperature and flow were input for the components these pipes are connected to. Only environment losses were considered for heat balance calculations. Input parameters used for the pipes are shown in Table

177 Table 6-5: Pipe sizes and flow rate Pipe Connection Diameter(m) Length (m) Maximum Flow (kg/hr) Collector supply Collector-Tank Type 31 Tank-Pump Type 31-2 Chiller-Cooler Type 31-3 Chiller-Coil Weather Data Reading and Processing For weather data reading and processing TRNSYS Type15 was used. This component can read data at regular time intervals from an external weather data file, interpolating the data (including solar radiation for tilted surfaces) at time steps of less than one hour, and this data output is used in other TRNSYS components. This component reads weather data files in the following formats: Typical Meteorological Year all formats (.TMY), (.TMY2) and (.TMY3), International Weather for Energy Calculations (IWEC) format, Canadian Weather for Energy Calculations (CWEC) format, Energy Plus format (.EPW), Meteonorm files for TRNSYS (.TM2) and German 2004 and 2010 TRY formats. The connections for weather data Type15 output are shown in Figure Figure 6-34: Weather data processor connections 177

178 Controllers Two different types of controller were used for the current TRNSYS simulation. Controller Type2d was used to control the collector pump flow into the collector from the storage tank. Controller Type108 (thermostat) was used to control the fan air flow from room 1 to the cooling coil. Controller Type108 (thermostat) cannot be used with other components, as a simulation error occurs when it is connected with a chiller. Controller Type2d monitors and compares three parameters whereas Type 108 monitors only two parameters Collector Pump Flow Controller A differential controller with hysteresis for Type2d was selected for the collector pump flow control. This ON/OFF differential controller generates a control function γ ο. The value of this control function is either 0 or 1. The new value of γ 0 is dependent on whether γ i = 0 or 1. If γ i = 0 then it will compare the difference (T H - T L ) with ΔT L. If γ i = 1 then it will compare the difference (T H - T L ) with ΔT H. It will use either ΔT H or ΔT L for comparison. The controller settings are shown in Table 6-6. The controller is normally used with γ 0 connected to γ i giving a hysteresis effect. For safety considerations, a high limit cut-out is included with the Type2d controller. Regardless of the dead band conditions, the control function is set to zero if the high limit condition is exceeded. This controller is not restricted to sensing temperatures, even though temperature notation is used. Table 6-6: Collector pump controller inputs Input Symbol Value Upper input value T H Collector outlet temperature (T coll.out ) Lower input value T L Collector inlet temperature (T coll.in ) Monitoring value T IN Tank average temperature Input control function 1 Upper dead band ΔT H 4 Lower dead band ΔT L 2 High cut limit Tmax

179 Where, ΔT H = Upper dead band temperature difference ΔT L =Lower dead band temperature difference T H = Upper input temperature = Collector outlet temperature (ᵒC) T IN = Temperature for high limit monitoring = Collector inlet temperature (ᵒC) T L =Lower input temperature (ᵒC) T MAX =Maximum input temperature (ᵒC) γ I =Input control function γ o = Output control function Mathematically, the control function is expressed as follows: IF THE CONTROLLER WAS PREVIOUSLY ON If γ i = 1 and ΔT L (T H - T L ), γ o = 1 If γ i = 1 and ΔT L > (T H - T L ), γ o = 0 IF THE CONTROLLER WAS PREVIOUSLY OFF If γ i = 0 and ΔT H (T H - T L ), γ o = 1 If γ i = 0 and ΔT H > (T H - T L ), γ o = 0 However, the control function is set to zero, regardless of the upper and lower dead band conditions, if T IN > T MAX. This situation is often found in hot water systems where the pump is not allowed to run if the tank temperature is above some prescribed limit. In this simulation 100ºC is the high cut limit. Inputs and Outputs The inputs for the collector pumps controller are shown in Table 6-6 and connections are shown in Figure For this simulation, the controller s initial value was selected as 1, meaning the pump is ON at the start of the simulation. The pump will remain ON as long as the temperature difference in the collector outlet and inlet water temperature is more than or equal to 2 and the pump will turn OFF when the difference (T H - T L ) is less than 2. The pump will remain OFF until the difference (T H - T L ) is more than

180 Figure 6-35: Collector pump controller connection Fan Controller Room thermostat Type 108 was selected for the current simulation in TRNSYS. This is the only thermostat controller in the TRNSYS library. Type108 is a five stage room thermostat modeled to give five output ON/OFF control functions that can be used to control a system with a two stage heating system, an auxiliary heater and a two-stage cooling system. The controller commands first stage cooling at moderately high room temperatures and second stage cooling at room temperatures higher than the 1 st stage. First stage heating starts at a low room temperature, second stage heating at a lower room temperature, and auxiliary heating at an even lower room temperature. There is an option to disable first stage heating during the second stage, disable both first and second stage heating during auxiliary heating, and disable first stage cooling during second stage cooling. Inputs and Outputs In the simulation only first stage cooling is used and no second stage cooling and no heating (both first and second stage) are required at all. First stage cooling is set to ON when second stage cooling is ON as only first stage cooling is always used. The first stage cooling input is a set point in such a way that the system maintains room temperature at less than 26 C. The second stage cooling set point is 30 C (which will never be reached and second stage cooling is not available) and the monitoring temperature is the room 1 air temperature inside building Type56. The fan controller connections are shown in Figure

181 Figure 6-36: Room air fan controller connections The first stage heating was set to be off in the second and third stage and the second stage to be off in the third stage. The first and second stage heating and auxiliary heating were set to 10 C which was not achieved during the simulation 8760 hours. Therefore, heating is always off all the time of simulation. The controller outputs are control signals for first, second and third stage heating and control signals for first and second stage cooling. The first stage cooling signal is used to give a signal to a fan for air flow control. 6.8 Solar Cooling Simulation System The solar cooling components and operation sequence was described in Section The complete final solar cooling system with all its components is shown in Figure This includes some printers and plotters to get output graphs and an excel data sheet for energy calculations and heat balance. It also shows the complete layout of connections of all components and flow sequences. The red lines shown represent the hot water flow cycle, the blue lines represent the chilled water cycle, the green line represents cooling water, and sky blue lines represent the ambient temperature connections. The red dotted lines are for representation of control signals from the controller to the equipment. The remaining black lines are the output data from the system to the online plotter and printers. 181

182 Figure 6-37: Complete process diagram of the solar cooling system 6.9 Conclusion The model building used is a typical single family house in Pakistan. The 3D model was created in Sketchup and imported to TRNSYS for simulation. The simulation studio is the main simulation engine of TRNSYS program with graphical plotting and output with spreadsheet facilities. TRNBuild is used to assign building model materials and thermal properties. The model initial results with Lahore weather conditions and ASHRAE standard materials showed the room temperature is higher than 40 C without any internal gain and with internal gains it is higher than 40 C in summer season. Building materials were changed to make the model more realistic by replacing ASHRAE standard materials with referenced actual materials. The results with actual materials showed the room temperature was still higher than 40 C and the building needs a cooling system to maintain comfort in summer. Solar cooling system s initial parameters were calculated for a typical cooling capacity (3.52kW). Referenced and standard data is used to estimate the initial parameters. 182

183 Details of solar thermal cooling system components and operating parameters are described. All the components input and output parameters details are described, with the sequence of system operation. 183

184 Chapter 7: Results and Discussion 7.1 Introduction In the previous chapter 6, key operational parameters are described to estimate the collector energy output, collector water flow, collector area, and hot water flow to the chiller. All the components were connected in the TRNSYS model and operated for realistic parameters (referenced from literature). The cooling system was operated to maintain a standard comfortable temperature inside the room during the summer season. The system parameters were optimised on the basis of the TRNSYS simulation results. This optimisation was achieved on the basis of several hundred simulations by trial and error using repeated simulations.. The final results, after the system optimisation, are presented and discussed here in detail. The results of the numerical analysis are validated by previously published results. A parametric analysis is performed to study the effect of collector area, flow rate, and storage tank volume on the system performance. 7.2 Evacuated Collector Energy Yield The TRNSYS simulation output includes the collector heat gain (i.e. yield) and energy available (incident solar radiation). The final gross collector s area is 12m 2 to meet the building cooling load. Figure 7-1 shows the energy collected and available monthly from the collector. As expected, the energy available is greater in mid-summer and least in mid-winter. This is because the collector tilt is zero, in order to maximise the energy available in the summer when cooling is required and the sun is approximately overhead at noon. Also, as expected, the yield is greatest in mid-summer and least in mid-winter. In winter there is less energy available, heat loss from the collector is greater due to the lower ambient temperature, and less heat is required as the building does not need cooling and the heat from the collector only keeps the system hot so it will be able to operate when required. 184

185 Collector area (gross) = 12m 2 Solar energy available and collected (kwh) Energy Collected Energy available Figure7-1: Solar collector monthly yield (kwh) 7.3 Evacuated Tube Collector Efficiency The monthly and annual average collector efficiency is shown in Figure 7-2. Some key results are described here. Collector efficiency is maximum (86%) in the month of July and minimum (18%) in January, and the annual average efficiency is 61%. This general pattern is as would be expected from the energy available and collected (Figure7-1). The calculated maximum efficiency for the collector is slightly greater than the value of the maximum efficiency parameters a 0 in the month of July. This can be accounted for by the fact that the incident angle modifier values are more than 1 for some angles. 185

186 100% Evacuated tube collector efficiency 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Figure 7-2: Collector monthly and annual efficiency (%) 7.4 Room Cooling Load Room load is calculated from the heat removed from the room air which passes through the cooling coil. A thermostat controller Type108 is used to control air flow from a fan into the room to maintain the room temperature below 26 C [297] and all the parameters of the room, fan and cooling coil are explained in Chapter 6 and in Appendix C. The monthly room load is shown in Figure 7-3; this load is only for cooling, not for heating. As expected, the room cooling load is greater in mid-summer and least (zero) in the middle of winter. The room cooling load is higher in the months when the solar energy availability is also high; this is an advantage for a solar energy based cooling system. 186

187 2500 Total room load (kwh) room load solar energy available at collector Figure 7-3: Room monthly cooling load and solar energy availability (kwh) 7.5 Room Air Temperature For comfort, the room temperature is maintained by the fan air controlled by an on-off thermostat. The system is sized so that the room temperature is always under thermostatic control (less than 26 C) during the summer season. The room temperature and ambient temperature for the whole year are shown in Figure 7-4. The number of hours shown on the x-axis is the number of hours at approximately one monthly interval, from January to December. The system maintains the room temperature below the ambient temperature throughout the summer season. The maximum room temperature is between C in the months of April, May, June, July, August, and September ( hours). 187

188 Figure 7-4: Ambient (Blue) and room (Red) temperature comparison ( C) In the winter, although there is no heating in the simulation, the minimum room temperature is always above 11 C, and higher than the ambient temperature that is between 4-7 C. 7.6 Storage Tank Heat Loss A stratified hot water tank is used for storage of thermal energy obtained from the collector. The monthly heat losses for the tank are shown in Figure 7-5 and some findings are described here. The heat loss depends upon the temperature difference between the tank water and the ambient air temperature (which TRNSYS takes as the outside air temperature) and it is clear from Figure 7-5 that heat loss is maximum in winter and lowest in summer, as would be expected. 188

189 600 Tank heat loss (kwh) TANK HEAT LOSS January February March April May June July August September October November December Figure 7-5: Tank heat loss (kwh) Tank heat loss is low during the cooling season (May to October) and highest in winter season when cooling is not required and the temperature difference between the tank and ambient temperature is higher. The tank heat loss as percentage of energy collected is shown in Figure % 175% Tank heat loss to energy collected (%) 155% 135% 115% 95% 75% 55% 35% 15% -5% Figure7-6:Tank heat loss as percentage of energy collected 189

190 From June to August (between hrs), there is some heat absorbed by the tank instead of heat loss. This is due to monsoon season with some rainy cloudy days. The tank cools down on these days due to less solar radiation and tank temperature increases again when solar energy is available as shown in Figure 7-7. Figure 7-7:Ambient and tank temperature with solar radiation available in July-August Tank heat loss is also linked with tank volume; less volume leads to less heat loss as shown in Table Storage Tank Internal Energy Change The tank s internal energy is the energy contained in the tank in relation to some reference condition. The change in internal energy is the difference between the total energy added and the total energy removed from the tank. The internal energy change is an output parameter from the tank. The tank s internal energy change at the start of the simulation and at the end of each month is shown in Figure 7-8. The result shows that the tank s internal energy change is positive (heat gain) in spring and early summer and negative (heat loss) in autumn and winter. 190

191 Monthly net change in internal energy (kwh) NET INTERNAL ENERGY CHANGE Figure 7-8: Tank internal energy change (kwh) The maximum monthly changes in internal energy are +76 kwh in May and -97 kwh in January. The annual net change in internal energy is -100 kwh, which means the tank lost more energy than it gained due to winter season operation. These energy changes are equivalent to changes of 32.6 C, 41.6 C, and 42.9 C respectively in the mean tank temperature. The internal energy changes will be affected by the tank temperature at the start of the simulation, which was set to 50 C for all simulations. 7.8 Pipe Heat Loss Pipes are used in the simulation for water flow between different components. The pipes loss is heat transferred to and from pipes due to temperature difference with the ambient outside air in TRNSYS. The monthly heat loss for pipes is shown in Figure 7-9. Some pipes carry hot water, while some carry chilled water. The overall pipe heat loss is the net figure when some pipes have lost heat and some have gained heat. Pipe heat loss patterns are similar to tank heat loss. Heat loss is higher in the winter season and negative (i.e. heat gain) in the summer season. The annual net heat loss from all pipes is 114 kwh. 191

192 50 Pipes to air heat loss (kwh) PIPES TO AIR HEAT LOSS Figure 7-9: Pipe heat loss to and from ambient air (kwh) 7.9 The Solar Cooling System s Electrical Energy Consumption Electrical energy is required to run the pumps for water flow between components, fan air flow and chiller solution pump. The monthly total electrical energy consumption is shown in Figure The electrical energy supply is almost constant as all the pumps are ON continuously except the collector pump and the air fan. In January, February and December the fan is off when the room temperature is lower than the thermostat control temperature range (21-26 C). The solar collector water pump works only when solar energy is available during the day time. There is a small variation from month to month due to the different number of days in each month. The total annual electrical energy consumption for the solar cooling system is 1575 kwh and the total cooling load is 7291 kwh. Electrical energy represents about 21% of the total cooling load. In practice, the electrical energy consumption could be reduced by additional control as only the fan and collector pump are controlled and other equipment is always on for the sake of simplicity in the simulation 192

193 160 Monthly electrical energy consumption (kwh) Monthly electrical energy Load Figure 7-10: Monthly electrical energy load (kwh) The maximum electrical energy consumption (137 kwh per month) is during the summer season. The lowest energy supply (114 kwh per month) is in February due to the lowest number of days compared to other months and the fan is off for the first two weeks and restarts when room temperature is in range of thermostat control Cooling Tower An air cooled dry cooler is used for the simulation of cooling water for the chiller. The operating parameters are described in Chapter 6 and in Appendix C. The heat rejected by the cooler is simulation output and shown in Figure The heat rejected by the cooler is equal to the heat input from the tank hot water to the chiller, heat absorbed from the air in the room, and the electrical energy input into the system. The annual total heat energy rejected from the cooler is 19,836 kwh. The maximum heat rejected (3,122 kwh) is in the month of June against its total capacity of 4,200 kwh. The minimum heat rejection (48 kwh) is in January which is the heat input from the electrical energy of the pumps. 193

194 3500 Cooling tower heat rejected (kwh) Figure 7-11: Cooling tower heat rejected (kwh) 7.11 Absorption Chiller A hot water operated absorption chiller with a rated cooling capacity of 3.52 kw is used. The performance of the chiller is shown in Figure Chiller COP ACTUAL RATED Figure 7-12: Chiller actual and rated COP 194

195 The chiller performed at a rated COP (0.60) only from May to August during the peak summer season. It is 0.59 in April, September, and October. In March and November the COP is 0.58 and In December, January and February it is very much less as cooling is not required in these months. The reason for the COP being less than 0.60 is that the chiller is always on even when cooling is not required. The COP of the absorption chiller is same during cooling season as expected and calculated in Chapter 6. The maximum cooling load is 1165 kwh in June whereas the cooling capacity is 2535 kwh. This difference is more than 50% due to variation in heat supply and hot water temperature to the chiller as there is no backup heat source is installed. The over size of the absorption chiller will increase the economics of the system. The cooling load of the room is already explained in the room load Section Validation of Simulated Results Validation is the act of comparing some data with reference data and drawing conclusions from this comparison. Although most models are based on physical laws and material properties, modellers needs some experimental data to test the model s predictions. The comparison is used to establish confidence that the model can be used to predict performance where experimental data does not exist. In the comparison, the model can be evaluated by system parametric analysis. An advantage of simulation is the ability to perform parameter optimisation, which is difficult to do through experiments; however, a validated model allows optimisation with confidence at minimal cost [383]. Anand et al. [384] carried out the first presented study for validation methodology for solar heating and cooling systems and proposed a four level validation methodology. The first level includes: use of measured system parameters (component data) and measured weather data for simulation, to gain confidence in a known system under known conditions. Level two validation deals with performance prediction accuracy when the input data used represent a particular system. Level three includes the parametric variability for system performance to establish the model validity for the field system which is yet to be installed. Level four is the verification of simulation results from level three using field performance data. 195

196 The system variables they compared were: energy provided by solar, solar fraction, energy supplied by auxiliary and collection efficiency. They proposed that variation of +/-10 % between simulated and measured results for any program is satisfactory for the validation of solar heating and cooling [384]. Thacker et al. [385] presented a study on concepts of modelling and validation. In this it is established that it is desirable for a model to be accurate to within 10%. Bales [386] states that a TRNSYS simulation for a heat exchanger with variation of more than 20% is unacceptable. Kaplan et al. [387] recommend that for simulation of HVAC systems the maximum allowable difference between the simulated and measured data should be 15-25% (on a monthly basis) and 25-35% (on a daily basis), whereas for seasonal and annual periods the simulated outputs should be within 25% and 10% respectively of the measured amounts Simulation Tool Validation Many researchers have validated TRNSYS model simulation results with experimental/measured results. For the current research TRNSYS has been used as the simulation tool. The validation and accuracy of TRNSYS is described in Section and it shows maximum variation between simulation and experimental/measured data of less than 10%. The variation is in the acceptable range as described by the above references [ ], therefore it can be established that the methodology for the current research is valid and accurate enough to simulate a solar cooling system Simulation Inputs Validation According to Anand et al. [384] for validation of solar heating and cooling system, use of the measured data inputs and measured weather data provide a confidence in the known system under known conditions. For this research all of the input parameters of the solar cooling system are from measured and validated literature data as described in Section 6.6. The building model in section and 6.5 is also an actual existing building. There are neither hypothetical or assumed data used nor any which is not from any previous research work Simulation Results Validation In the literature experimental and simulated data for a solar thermal absorption cooling system with kW capacity is limited. Only four published references [162, 215, 217, 260] are available for this capacity range for climatic conditions in Malaysia, Qatar, UK, and Turkey. None are available for Pakistan. 196

197 The results from the current simulation are, therefore, compared with these and other published data for solar cooling systems of various sizes installed around the world. Priority was given to comparison with the above mention similar capacity systems and, where parameter data is mentioned, other literature is used. The current results are in close agreement with these published results. The detail of this comparison is presented in Table 7-1. Table 7-1 Comparison of simulated vs published results Parameter Current simulation Published results Reference Collector efficiency (%) 61 60, 63 Collector specific area (m 2 /kwc) Rosiek et al. [248] Ayompe et al.[265] European commission SACE [388] Slope of collector (ᵒ) for maximum energy yield in summer 0 0 NASA, SSE[42] Collector monthly yield (kwh/m 2 ) Blackman et al. [310] Collector flow (kg/h) Ssembatya et al. [210] Collector outlet temperature ( C) Agyenim et al. [260] Tank volume specific volume (m 3 /kwc) Agyenim et al. [260] Tank volume to collector area (l/m 2 ) Agyenim et al. [260] Storage tank heat loss co-efficient 0.20W/m 2 K 0.83W/m 2 K Shirazi et al. [389] Chilled water outlet temperature ( C) Chiller COP , 0.60 Chiller electrical power (kwh/kwc) Room temperature set point ( C) 26 24, 25.5 Solar fraction (%) , 83 Solar COP (COP th * η coll ) European commission SACE[388] Agyenim et al. [260] Rosiek at al. [248] European commission SACE [388] Sim [215] Fong et al. [390] Assilzadeh et al. [162] Fong et al. [390] European commission SACE [388] Total electrical energy consumption to total cooling produced (%) 21% 24% Rosiek at al. [248] Chiller operation hours /day (hrs) , 9 Agyenim et al. [260] Sim [215] System COP (Thermal +Electrical) Agyenim et al. [260] Electrical COP Agyenim et al. [260] Hot water storage capacity (hrs) 12 2 Sim [215] Annual energy balance difference (%) Thomas and Andre [391] 197

198 The comparison between simulated and published parameters shows good agreement with each other. The exception is only in tank volume and solar fraction which is higher in the current simulation for two reasons: i) the simulated system works as a standalone system without any fossil fuel backup and ii) the chiller is operated continuously. The systems studied previously by researchers were not standalone and operated for fewer hours Chiller Parameters Validation TRNSYS, Type107 is used to model a hot water operated absorption chiller which uses an external performance data file to simulate chiller performance. The results presented so far are based on chiller operation using the TRNSYS provided chiller data file. The chilled water outlet temperature data file for TRNSYS is shown in Figure7-13. Figure 7-13: Chilled water outlet temperature with the TRNSYS provided data file Reference [392] details the performance of an actual 17.6kW cooling capacity hot water operated chiller. This data was used to generate a chiller data file which was used in the TRNSYS simulation. The actual chiller data file is shown in Appendix C. The simulated chilled water outlet temperature, by using the reference data file, is shown in Figure

199 Figure 7-14: Chilled water outlet temperature with referenced data file From Figures 7-13 and 7-14 it is observed that there is a good agreement between TRNSYS and referenced data based chiller performance. There are minor differences in the chilled water outlet temperature during summer and spring time, which is in total for 12 hours higher than set point. However, this variation has not had any effect on the inside air temperature of the building, which was below the set point in both cases at all times Energy Balance for the Solar Cooling System The model solar cooling system integrated with the building includes many components with energy loss and gain associated with each component. The energy inputs are cooling delivered to the room, solar energy absorbed by the solar collector, heat gains by the heat storage tank and pipes and electricity used by the pumps, chiller, and fan. The main energy losses are heat rejected at the cooling tower and heat losses from the storage tank and pipes. The solar cooling system simulation is validated by the energy balance of the system. The total monthly energy input and output for the system is shown in Figure The total monthly input and output increase and decrease together as would be expected from the 199

200 variation of solar energy available and the cooling load. However, they are not quite equal. The details of monthly energy input and output are in Appendix D System energy balance (kwh) Total input Total output Figure 7-15: Energy balance of solar cooling system The distribution of the annual input and output for the solar cooling system energy is shown in Figure Input output energy distribution (kwh) Tank Heat Loss Pipes Heat Loss Cooler Heat Rejection Heat from Room 5000 Electrical Energy Collector gain 0 Input Output Figure 7-16: Annual input and output energy distribution 200

201 Major input energy is from the collector (59%) and the room cooling load (34%), which is 93% of the total input. Major output energy is the heat rejected by the cooling tower, which is about 93% of the total output (it is only coincidence that 93% occurs twice here). The total annual energy input to the system is kwh and the total energy output is kwh. Annual energy input is more than output and the system surplus energy is 148 kwh. In the simulation, the only energy storage in the solar cooling system is in the tank. The difference between energy input and output should, therefore, correspond to the change in the tank s internal energy. The tank output data showed an annual net change in internal energy, namely a decrease of 100 kwh. Thus the total discrepancy is = 248 kwh, which is 1.15% of the total energy input. This discrepancy shows that there are some minor energy losses in the simulation which were not accounted for. A similar energy balance discrepancy was described by Thomas and Andre [391] in the range of 90kWh to 370kWh due to the storage tank. TRNSYS technical support was contacted to assist and it was confirmed that no system is present to investigate such discrepancies. However, technical support described heat balance as a way of simulation validity. As the energy balance discrepancy is well within the range generally regarded as an acceptable error (Section 7.12), and it could not be explained despite exhaustive investigation, it was decided to accept it Parametric Analysis Saltelli et al. [393] defined the objective of parametric sensitivity analysis of a model to investigate how a given model (numerical or otherwise) depends on its input factors. This analysis is important in verification and validation of a simulation model. The characteristics of a solar thermal system are the combination of variables acting together with a changing pattern due to solar radiation variation. For operational parameter optimisation, it is necessary to make rational choices between parameters such as collector area, fluid flow rate and storage volume. The preference for operational parameter is not sufficient; the effect on system performance must be judged quantitatively so that it can be compared with the cost effect. Parametric studies refers to the investigation of performance parameters such as collector area, flow rate and storage tank volume [394]. 201

202 Parametric analysis of a solar thermal system is carried out by few researchers. The summary of available important studies is shown in Table7-2 and described here. Table 7-2: Summary of parameters used by researcher for parametric analysis Parameters Researchers Collector area Tank volume Collector flow Other parameters Saltelli et al. Lunde Calise Hang et al. Villar et al. Sim Ssembatya et al. Arsalis He et al. Shirazi et al. Lunde [394] describes that the important parameters for parametric analysis are collector area, storage capacity, collector orientation and collector type. Venegas et al. [264] carried out parametric analysis for solar absorption of a cooling system and observed that a major effect on solar COP, cooling energy produced and duration of cooling production, is due to radiation. Calise [297] carried out a parametric sensitivity analysis for a solar heating and cooling system for the collector area, collector outlet temperature and tank volume to solar collector area for different European cities. Hang et al. [395] carried out a parametric sensitivity analysis for solar fraction with the change in storage tank to collector area ratio for a solar cooling system. Villar et al. [300] carried out a sensitivity analysis for storage tank volume, collector area and slope, chiller COP and solar energy collected for a solar absorption cooling system in different configurations. Sim [215] performed a parametric sensitivity analysis for collector slope and area, storage tank volume and effectiveness of a heat exchanger for a solar cooling system. Praene et al. [396] carried out a parametric sensitivity analysis to optimise a solar absorption cooling system for distance between collector and hot water storage tank, chiller and collector inlet temperature. Ssembatya et al. [210] did a parametric analysis for collector area, water flow rate and slope with chiller inlet temperature to improve solar fraction for a solar cooling system. Arsalis [397] performed a 202

203 parametric study for collector area and tilt angle and storage tank volume for a solar heating and cooling system. He et al. [351] carried out a parametric analysis of heat storage tank volume for solar yield. Shirazi et al. [389] performed a parametric analysis for storage tank to collector area ratio, collector specific area on primary energy saving, collector area and heat storage tank volume on a solar assisted heating and cooling absorption system. From the above referenced literature, it is clear that the parameters most commonly regarded as important are storage tank volume, collector area and collector water flow rate. For the current research work these three most common parameters were selected for parametric sensitivity analysis and results were observed annually. It is reasonable to assume that the chiller, cooling coil, cooling tower and their associated pipes, pumps and fans would be sized for the building's design cooling load. The details of the parametric analysis for the collector area, collector flow and storage tank volume are described here. During the parametric analysis it was observed that when the room temperature increases above the thermostat upper limit (26 C), the simulation stops working (controller stuck error from TRNSYS) due to significantly less heat input compared to cooling load. However, for optimised parameters simulation works normally and no error was observed Collector Area and Flow Collector area directly affects the solar energy gained. The collector area and flow rate are varied and the change in collector energy gain and efficiency is observed. The results are shown in Figure 7-17.Figure 7-17 shows that increasing the collector area increases both, energy collected and collector efficiency for same flow. With a change of area from 6m 2 to 12m 2, the annual energy collected varies from 9.7 MWh to MWh and the collector efficiency from 54% to 61%. The reason is collector efficiency increases as the collector outlet temperature decreases with increase in area keeping constant flow. The evacuated tube collector efficiency with collector and ambient temperature difference is shown in Figure For a collector area less than 6m 2, the simulation also stops working (mathematical error from TRNSYS) as the heat input is significantly less than the cooling load during summer season. 203

204 Efficiency (%) Energy (MWh) Efficiency (%) Energy (MWh) 62 Collector area Collector efficiency (%) Energy collected (MWh) Area (m 2 ) 8 Figure 7-17: Sensitivity of collector area and annual energy collected and efficiency The change in collector flow rate effect on collector energy gain and collector efficiency is shown in Figure Collector efficiency (%) Energy collected (MWh) Collector Flow Mass flowrate (kg/h) Figure 7-18: Sensitivity of collector flow rate and annual energy collected and efficiency Figure 7-18 shows that increasing the collector flow slightly increases the energy yield and efficiency. The change of flow rate from 40 to 165 (kg/h), changes the annual energy collected from 12.30MWh to 12.66MWh and collector average efficiency from 58.5 to 61% respectively. The reason is as the flow increases the collector outlet temperature decreases for constant area, which increases efficiency. 204

205 Storage Tank Volume: A change in heat energy storage tank volume and its effect on annual tank heat loss, collector efficiency, and change in internal change is shown in Table 7-3. Table 7-3 shows that increasing the storage tank volume increases the tank heat loss reduces collector efficiency and increases the tank internal energy change. As with less volume surface area is less, the heat loss is lower from the tank. Whereas, lower volume results in less thermal storage and tank water temperature will be lower so with lower collector input water temperature and increase collector efficiency. Table 7-3: Sensitivity of storage tank volume on tank heat loss and internal energy and collector efficiency Tank volume (m 3 ) Tank heat loss (kwh) Collector efficiency (%) Chilled Water Outlet Temperature The simulated chilled water outlet temperature is a key system variable, because it only rises above its set point if the chiller is unable to meet load due to lower heat energy input. The simulated room temperature does not respond so clearly or quickly because of varying room heat gains, thermostat settings, and room thermal capacity. The simulation also stops working when the room temperature is above the thermostat upper limit (error message from TRNSYS). 205

206 Hours Temperature (C) Maximum Chilled water temperature Maximum Chilled water temperature Number of hours temperature above setpoint Collector area (m 2 ) 6 Figure 7-19: Variation of maximum chilled water temperature and number of hours above set point with collector area The effect of collector area on maximum chilled water outlet temperature and number of hours during the year when chilled water outlet temperature is above set point (7 C) is shown in Figure From Figure 7-19 it is clear that both the maximum chilled water temperature and number of hours when the chilled water temperature is above the set point, increases with a decrease in collector area. The effect of collector flow rate on the maximum chilled water outlet temperature and number of hours during the year when the chilled water outlet temperature is above set point (7 C) is shown in Figure

207 Hours Temperature (C) Maximum chilled water temperature Number of hours temperature above setpoint Maximum chilled water temperature Collector Flow (kg/h) Figure 7-20: Variation of maximum chilled water temperature and number of hours above set point with tank storage volume From Figure7-20 it is clear that both the maximum chilled water temperature and number of hours when the chilled water temperature is above the set point, increases with a decrease in collector flow rate. Chilled water temperature and number of hours when it is above set point remains the same when the collector water flow rate is decreased from 65kg/h to 40kg/h. The effect of hot water storage volume on maximum chilled water outlet temperature and number of hours during the year when the chilled water outlet temperature is above set point (7 C) is shown in Figure Figure7-21 shows that both the maximum chilled water temperature and the number of hours when the chilled water temperature is above the set point, increases with a decrease in storage tank volume. 207

208 Hours Temperature(C) Maximum chilled water temperature Number of hours temperature above setpoint Maximum Chilled water temperature Storage tank Volume (m 3 ) 6 Figure 7-21: Sensitivity of storage tank volume and maximum chilled water temperature and number of hours above set point It was concluded that an evacuated tube collector area of 12 m 2, collector flow rate of 165 kg/h and storage tank volume of 2m 3 would provide satisfactory performance of 3.52kW absorption chiller. These values were used for the final results described in Sections 7.2 to Conclusion A solar thermal cooling system integrated with a building model for one room of a single family house in Pakistan was simulated to maintain a comfortable room temperature. The house was of standard construction and did not include any measures to reduce the cooling load. The values of three key design variables (collector area, collector flow rate and storage tank volume) were initially found through simplified calculations and then optimised by trial and error using repeated simulations. The optimum values were the minimum values which enabled the system to maintain the required room temperature throughout the cooling season, with no auxiliary heat input in addition to the solar collector. It was found that the optimised values were close to the initial values. 208

209 For the optimised system: The required collector area (gross), flow rate, and storage tank size were respectively 12 m 2, 165 kg/h and 2 m 3. The annual electricity consumption for the system was 21% of the cooling load, but this could be reduced by improved controls. The annual heat loss from the storage tank was % of the total energy collected and most of this was in winter. The simulation results showed good agreement with published results from other researchers. The energy balance of the system showed a small discrepancy (approximately 1%) between the annual energy input and output, which was in the same range as reported by other researchers. A parametric analysis was performed on the collector area, collector flow rate and storage tank volume. It was found that varying the collector area had the largest effect on system performance, followed by varying the storage tank volume. Varying the collector flow rate had the smallest effect. The overall results showed that Pakistan s climate has a potential for solar powered thermal space cooling systems. It is feasible to use a solar thermal powered cooling system to meet the space cooling load for a single family house in the summer season. 209

210 Chapter 8: Conclusions and Recommendations 8.1 Summary The use of solar energy for cooling purposes is an attractive prospect; the key factor for this application is the availability of solar energy for a specific location and climate and suitable cooling technology. Currently, flat plate or evacuated tube collectors with absorption cooling technology could be used for solar cooling systems, as an alternative to fossil fuel based conventional electrical powered cooling systems. For hot climates like Pakistan, a solar cooling system could be a sustainable, clean, and viable system to meet cooling energy demand. 8.2 General Discussion Main Finding: Feasibility of Solar Thermal Cooling of a Building in Pakistan The results showed that solar thermal cooling for a typical existing building in Pakistan is feasible; the main aim of this research was to test whether this was so. The designed solar cooling system successfully maintained the room temperature below 26 C throughout the year without any backup heat source. The final system configuration and equipment sizes are comparable to previous published work and are shown in Chapter 7. The final solar powered cooling system for a 42m 3 room with 100% solar fraction consists of 12m 2 (gross area) of evacuated tube collectors lying horizontally, a 2m 3 hot water storage tank and a 3.52kW capacity absorption chiller. It was noted that published simulated and experimental studies generally mention collector aperture area, which is less than gross area. Strength of this research is that all the building dimensions, materials, heat gains, solar thermal cooling equipment operation parameters are based on published or actual data. None of the input parameters are assumed or hypothetical, which helps to ensure the validity of the research as described in Chapter 7. The major limitation of this research is that it is a theoretical study carried out with one building model and one solar thermal cooling system. Different building models, solar collectors, and thermal cooling systems are possible. A variant mentioned by most researchers is that the system cost and component sizes can be reduced by adding a backup heat source. A designer of a real system would need to consider the advantages and disadvantages (e.g. capital cost, running costs, and availability) of a system with or without possible backup heat sources before choosing the most suitable configuration. 210

211 8.2.2 Building Model and Energy One of the research objectives was to gather information needed to construct a suitable building model for the simulation work, including information on building constructions, building energy efficiency and indoor comfort conditions in Pakistan; these are discussed in Chapters 3 and 5. It was observed that in previous studies of solar cooling, no detail is provided about the building dimensions, thermal properties, or internal heat gains. Building energy efficiency is key factor for cooling system design and performance but is not mentioned by many researchers when reporting research into solar thermal cooling systems. An advantage of the current research is that all these details are provided. Existing buildings in Pakistan are generally not energy-efficient. As the building model in this research was intended to represent a typical existing building, there is scope for reducing the heat gains and cooling equipment sizes by improving the thermal properties of the building. The UN-habitat program [112] showed that there is potential for this in existing buildings. Future research work can be carried out to improve building energy efficiency, thermal comfort and cooling system sizes Methodology As suitable experimental facilities were not available, it was decided to investigate the feasibility and performance of the solar thermal cooling system by simulation. TRNSYS software was selected for this; details are presented in Chapter 5. Many researchers have validated TRNSYS simulation results with experimental results for solar thermal systems and established that it is a suitable tool for such simulations. Another advantage is that TRNSYS contains suitable typical weather data for Pakistan, which is not conveniently available from any other source. The main limitation of using simulation for this research is that no experimental data is available for Pakistan for comparison and validation. To test the validity of the simulation results, they were compared with published results from other researchers and a chiller performance data file was created to validate the chiller operation. It was found that all the results agreed well with those from other researchers and Validation is described in Chapter Solar Cooling System and Operational Parameters The details of solar cooling systems and operational parameters are described in Chapter 4 and 6 respectively. The selected components are well tested by other researchers, and data is available for operation and results validation. The selected components have relatively high 211

212 thermal efficiency and low heat losses compared to others in similar categories. A limitation is that comparisons cannot be drawn for different components for Pakistan climatic conditions; future work could be carried out for this. The component sizes for the solar energy collection and building cooling systems were estimated by simple mathematical calculation using reference data as described in Chapter 6. It was decided to investigate the feasibility of a system with no auxiliary heat source, as electricity outage hours are high as mentioned in Chapter 1. Having no backup heat source requires increased sizes of some components, which would increase some costs and energy losses. On the other hand, the costs and energy losses associated with a backup heat source are avoided. Solar electricity generation and storage using photovoltaic panels and batteries is now a well proven technology, and the electrical energy consumption of a solar thermal cooling system should be comparatively low. It was therefore decided not to investigate the supply of solar photovoltaic electricity for operating the solar cooling system's pumps, fan, and controls. The system's thermal losses and electricity consumption in the simulation results are higher than they would need to be in reality, as most of the simulated components operated continuously even when cooling was not required (for convenience in constructing the simulation model). The COP of the absorption chiller was also set to a lower conservative value (0.60) rather than the manufacturer's rated value (0.70), which led to a higher energy input, larger collector area and larger storage tank. Most previous studies have used a higher COP; however, with these limitations the results of this research are better than those found by other researchers in terms of specific sizes and efficiencies, as described in Chapter 7. Most researchers have set the collector tilt angle to the location latitude; in this research the collector tilt is set to zero, as this maximises the available energy during the hottest summer months at the location of interest (Lahore). It was observed that none of the researchers have mentioned Incident Angle Modifiers (IAMs), which are important parameters for evacuated tube collector operation. IAMs were incorporated into the collector model in this research, and were found to increase the collector efficiency. Other important system parameters which are not available in the cited literature but are provided here include the building cooling fan and coil capacities and operational parameters, and the hot water storage tank and pipes heat loss coefficients and insulation details. 212

213 8.2.5 System Optimisation Chapter 6 presents the calculations for the solar thermal cooling system initial parameters, which were used to start the simulation work. Initial parameter value calculations are not available from other authors. When the simulation was configured so that it operated successfully with all the components connected, it was run for different durations (one month, six months, and one year) with different time steps (one hour, 30 minutes, 15 minutes and 5 minutes). It was found that 15 minutes time step and one year continuous operation yielded satisfactorily detailed and stable results. Advantages of this research are that the system behaviour during a whole year was analysed, whereas in all experimental and simulation studies by other researchers the operation duration is limited to few hours, days, weeks or months only, and that different time steps and durations have been tested, whereas other researchers have used only single time step (mostly one hour) and duration for their results. System parameters were changed by trial and error for repeated simulations to find optimum parameter values, as presented in Chapter 7. A limitation of this methodology was the time taken, as there is no specific standard for solar cooling systems to guide the choice of parameter values. To obtain the final results hundreds of different combinations were simulated and analysed to find the best configuration. During simulation it was noted that a higher hot water storage temperature gave better chiller performance but reduced the collector efficiency. Most researchers have not mentioned this relationship in their publications. It was observed that the values of some parameters (e.g. collector flow and chiller capacity) were almost unchanged from the initial estimates to the final optimised values. This means that simple calculations can be used to obtain good estimates of some required parameters Results Validation and Sensitivity Analysis All the results are in good agreement with the published results, as described in Chapter 7. The hot water storage tank size is larger than reported by other researchers, which is because in this research the system operates continuously and meets the entire cooling load. The results are more detailed than those provided by previous researchers. A detailed chiller performance data sheet was constructed to validate chiller operation, which was performed 213

214 before only by two researchers. The number of parameters validated (more than 10) is more than considered by previous researchers. Energy balances were constructed as part of the validation, and showed that energy inputs and outputs were equal within less than 1%. This is within the acceptable range reported by other researchers. An energy balance of the whole system was constructed, which has not been reported by any other researcher. A sensitivity analysis was carried out for the effect of selected parameters of the solar energy system (collector flow, collector area and storage tank volume) on the system performance. These were chosen because they were expected to have the largest effect. This analysis showed that their order of importance was firstly collector area, then storage tank volume, and finally collector flow rate. Few researchers have performed sensitivity analysis on solar thermal cooling systems; their results are similar to those found here. The system performance measure used in this analysis was the chilled water outlet temperature, as it was found that this was maintained at its set point in the simulation provided the chiller was not overloaded and had sufficient heat available. Room temperature was a less useful measure of performance, as this was affected by room heat gains and losses, and control action. For experimental studies, on the other hand, researchers have used chiller inlet hot water temperature as a solar energy system performance criterion, as this can be changed with a backup heat source Conclusions and Recommendations The conclusions mentioned above and described in more detail in Section 8.3 are validated, and can provide confidence to designers for the application of solar thermal cooling systems in Pakistan. However, the simulation results are limited to one combination of system components, and do not provide system selection or design guidelines. Further research is required to study different combinations of systems and components to select the most suitable ones for Pakistan's conditions. The recommendations of the research are described in Section 8.4. The most important are related to Pakistan's energy crisis, the importance of building energy and comfort, solar powered cooling systems, and alternative and sustainable energy sources. The main advantage of implementation of these recommendations is that these would not only help to overcome the energy shortage but also provide an alternative, sustainable, and reliable energy 214

215 source. The limitation will be that the cost of the proposed system may be higher, and subsidies and supportive plans may be required for implementation as mentioned by some researchers. There is a need for sincere commitment and persistent policies, which will probably be difficult to maintain in view of the history of energy management in Pakistan Addition to Knowledge This research is the first study of a building integrated solar absorption cooling system for Pakistan or India. Continuous operation without a backup heat source is also an advance on previous knowledge, worldwide and in the region, as most studies have been for a few hours or days operation and with a backup heat source. More detailed results than other similar research, and detailed validation of the simulation at each step, are prominent features of this research. The results can be applied to existing buildings, but this research also shows that existing buildings are not energy-efficient and there is potential for improvement. Details of solar collector incident angle modifiers, storage tank and pipes heat losses, and the system energy balance are also additions to previous available knowledge. 8.3 Conclusions The research presented here demonstrates that cooling through a single-effect absorption chiller connected to a solar collector with a hot water storage tank can maintain room comfort for the climate in Pakistan. The first objective was to analyse energy scenarios, supply and demand, and the renewable energy potential in Pakistan. The literature on Pakistan s energy data showed that the primary source of energy is fossil fuels and the use of renewables is negligible except in the case of hydroelectric energy [3]. The domestic sector is badly impacted upon by energy crises and building indoor comfort is often not achievable in the hot summer season due to power cuts [17]. The future demand and supply data showed that the country will be energy deficient in meeting the demand until 2019 [20]. It is concluded that there is a need for an alternative and sustainable source to meet energy demand in the country. It is important that a newlydeveloped system can save electricity and help meet domestic sector comfort demands. The second objective was to review renewable resources, specifically solar energy. In Pakistan, the resource potential of about 60GW from each hydroelectric and wind energy 215

216 source has been identified [27, 28]. The wind energy potential is mainly limited to relatively small coastal areas, while political rifts and environmental issues are significant hurdles in the utilisation of hydroelectricity[33]. The solar energy potential of Pakistan is greater than that of any other renewable source with a daily average insolation of 4-6kWh/m 2 /day and 8-10 sunshine hours/day all over the country [49]. Pakistan is suitable for the application of all types of solar energy technologies as there is no political or environmental problem with solar energy as with wind and hydroelectric power. This potential could provide sustainable energy for current and future demand. The third objective was to study climatic conditions, indoor comfort conditions and their relationship to the building energy code of Pakistan. The climate of Pakistan is generally arid with hot summers and relatively cold winters. About 80% of population (total 184 million) [69], in the country lives in climatic condition with hot summer season, required cooling systems for comfort. Extreme high temperatures have increased in frequency and severity in the past decades and this is increasing energy demand for cooling [84]. Energy demand in buildings is increased by 15% per annum in Pakistan [104]. There is a negligible application of building energy codes and most buildings are energy inefficient. There is the overall potential to save about 30% of energy in buildings by applying building energy codes and other measures [111]. Simple radiative, insulative, and reflective materials can decrease the room temperature in the summer season and reduce a building s cooling energy demand [112]. The fourth objective was a literature review of solar cooling systems and especially solar cooling in hot climates, and this was aimed at identifying the current state of knowledge about solar cooling system technology relevant to the climate of Pakistan. Solar thermal cooling application started in the early 1960s and more than 1,200 systems have been installed worldwide [173]. In hot climates such as Pakistan, solar thermal is preferable to solar electric cooling both in terms of efficiency and load compatibility [24]. The climate of Pakistan is favourable for solar cooling applications as the greatest cooling loads and solar energy availability occur at about the same time in summer. Stationary collectors, flat plate and evacuated tube, are most commonly used for solar cooling applications as they are much cheaper than concentrating (tracking) collectors, and can generate sufficiently high 216

217 temperatures for solar cooling. Evacuated tube collectors are preferred over flat plate collectors due to their higher thermal efficiency and higher temperature output [183]. The average area required for a flat plate collector is 4.6m 2 /kw C, whereas for an evacuated tube collector it is 2.5m 2 /kw C [184]. An absorption cooling system is more efficient than other thermal cooling systems [132]. The fifth objective of the research was the selection of a suitable analysis methodology. TRNSYS is a comprehensive computer program which is widely used for dynamic simulation of building integrated solar energy systems. The accuracy of TRSNSY for solar energy systems has been tested by many researchers and found to be within +/- 10% variation of experimental data [336]. Weather data is a key input for solar cooling systems and building energy simulation. Suitable typical weather data (TMY2) for five cities in Pakistan is provided with TRNSYS [361]. A building model was created to simulate part of a typical house in Pakistan with actual dimensions and construction materials. The last objective was to perform a simulation, analyse the results and produce recommendations. The simulation was performed for a solar powered cooling system with an evacuated tube collector, hot water storage tank, absorption chiller, and dry cooler. The simulation was performed in the TRNSYS environment and the system operated continuously for 1 year (8,760 hours).the simulations results showed that a final optimum system for a 42m 3 room consists of 12m 2 (gross area) of evacuated tube collectors lying horizontally with 2m 3 of hot water storage tank for 3.52kW absorption chiller capacity. It is concluded from the simulation of the system that, on an annual basis without a backup heat source, 100% of the heat input demand can be covered with solar energy and the system can meet the building cooling loads. The component model of the absorption chiller needs a specific data sheet for its performance description. An actual chiller performance data sheet was constructed specifically for the current research [392]. The results showed a very good agreement of chiller performance between TRNSYS default chiller data and actual data. The accuracy of the model was investigated by validating the results with published and standard parameters. All the inputs are referenced to increase the model validity and 217

218 accuracy. All the results are in good agreement with the published results. A sensitivity analysis was carried out for the effect of selected parameters on collector flow, collector area and storage tank volume on the chilled water outlet temperature. This showed that the order of importance of these parameters for system performance was, firstly, the collector area, then the storage tank volume and, finally, the collector flow rate. 8.4 Recommendations Energy and Solar Energy Data There should be one agency which should publish authentic and accurate energy statistics data for research and other use. Similarly, CO 2 and other greenhouse gases emission and country population data for Pakistan are not available from any public agency of the country [69]. The available data is years old and need verified up to date from public agency. The theft, transmission, and distribution losses and less recovery of bills are main contributor of current crisis which need to be overcome with better policies and management as done in many developed countries. The renewable energy resource (Solar, wind and hydroelectric energy) should be utilised to help meet current and future energy demand. The future energy projects plans should target the use of these green energy resources with countable share in energy mix. The use of solar energy based products can help to meet basic needs for light and other utilities. The use of off grid PV systems in the remote areas of Balochistan, KPK, Sindh, and south Punjab can provide electricity in areas which are not connected to national grid system due to low population density. There should be comprehensive solar energy potential mapping for the country as Raja s work is confined to five cities[46]. The reliable and long term data are mandatory for successful solar energy system design and operation Building Energy and Efficiency Buildings in Pakistan are not energy efficient due to a lack of the application of any building energy code and standard. The building sector is a major consumer of electricity in the country; energy savings in buildings would reduce electricity demand and improve the comfort of buildings in the summer [111]. 218

219 New building codes (as in Turkey) should be introduced for energy efficient buildings in Pakistan to improve energy efficiency in existing buildings. The materials and techniques used by UN-HABITAT for improving energy efficiency of existing buildings have improved the comfort inside. The best material was paper board in term of cost and comfort [112]. This material should be used in current building to reduce cooling load and increase comfort. The building simulation results showed the use of double glazed windows in place of currently used single glazed windows or steel shutters can improve comfort, infiltration and heat gains and losses in buildings Solar Thermal Cooling Solar absorption cooling systems can be a sustainable and green solution as cooling demand for the building and solar radiation intensity take place more or less at the same time. It is recommended to promote use of these systems for cooling in Pakistan. The simulation results showed that in the proposed solar thermal cooling system, heat energy collected is not used in winter months. This excess energy can be used for domestic hot water in winter season when there is shortage of natural gas supply. 8.5 Further Studies Building Energy and Efficiency The research work on building energy, efficiency, and efficient building materials in Pakistan is limited. Building heating and cooling load with current materials should be investigated in details for all five climatic regions of Pakistan. The results for a typical building are specific and depend upon building geometry, construction material and the cooling system in use. The cooling load also depends upon human occupancy and activities. Cooling is required only in the summer and the simulation was carried out for a year. The results may be further split into summer and winter seasons for separate analysis of cooling and heating output for future research. Further work could be carried out to identify the energy efficient building materials with the minimum heat gains and cooling load for the all the climatic regions of Pakistan. 219

220 The current research was carried out for ASHRAE standard thermal comfort condition. Further research can be carried out for adopted thermal conditions for each climatic region of Pakistan for small sizes of cooling systems and economics Solar Cooling System In the current research, only two components were controlled and operated and only when required. All other components (chiller, fan, cooling tower, and cooling coil) were working continuously. Further research could be carried out to improve the system control so it includes realistic controls for pumps and the chiller to reduce the electricity consumption. Further research work could be carried out to investigate the effect of different types of collectors and cooling systems on system efficiency and energy consumption for the climate of Pakistan. This research is carried out using vapour absorption cooling system for Lahore climate. Further research can be carried out by using different cooling system in all climatic regions to establish the most suitable technology for each region. Further research can be carried out by using backup heat source and optimise the share of solar energy in the total energy supply with minimum collector and storage sizes. Further research can be carried out for hybrid solar thermal heating and cooling system for different climatic regions of Pakistan in combination with wind, micro hydroelectric and geo thermal energy. An experimental setup can be to assess the performance of actual solar cooling system and can be optimised using the TRNSYS results and the performance of both systems can be compared. In this research the tilt angle of the solar collector was fixed to zero. Further research can be carried out for monthly, seasonal, and annual tilt angle for maximum energy yield of collector. This work was performed for a solar thermal cooling system with grid supplied electricity. Further research could be carried out by providing solar PV based electrical energy for a standalone and self-sufficient solar powered cooling system. 220

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243 Appendices Appendix A: Annual and Monthly Maximum Average Temperature and Relative Humidity for District Cities of Pakistan 243

244 22 Year Monthly & Annual Average Maximum Temperature Degree Centigrade (at 10 m from surface) for District cities of Pakistan Sr.No City Latitude Longitude Elevation Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec Annual 1 Mirpur khas Nawabshah /Sanghar/Shahdadkot/Nosheroferoz Sukkur / Larkana/ Shikarpur/khairpur Umar kot Hyderabad / Jamshoro Tharparker Badin Dadu Ghotki Rahim yar khan Karachi city / Thatta Bahawalpur Multan / Muzaffargarh Jafarabad /Nasirabad /Jhal Magsi Okara /Sahiwal /Vehari /Pakpatan Kech (Turbat) Jhang /Rajanpur /Toba Tek Singh Awaran Bhakkar / Layyah Panjgur Faisalabad Lasbella Gawadar Chaghi Dera bugti / Barkhan Khuzdar Kharan Lahore Sargodha DG Khan Jacobabad Jhelum Karachi Keemari Sibi / Bolan / Bannu Chakwal/ Attock Hangu / Karak / Kohat Mastung / Kalat/Nushki Sialkot / Narowal / Gujrat/Mandi Bahuddin Gujranwala/Hafizabad/Shekhupura Chaman / Qilla Abdullah Qilla Saifullah / Loralai Quetta / Pishin Islamabad / Rawalpindi Zhob Peshawar/charsadda/noshera Mardan / Swabi Muzaffarabad / Balakot

245 25 Year Monthly & Annual Average Relative Humidity (%) for Districtcities of Pakistan Sr.No City Latitude Longitude Elevation Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec Annual 1 Karachi Keemari Muzaffarabad / Balakot Karachi city / Thatta Gawadar Lasbella Mardan / Swabi Islamabad / Rawalpindi Sialkot / Narowal / Gujrat Gujranwala/Hafizabad/Shekhupura Lahore Badin Attock / Chakwal Okara /Sahiwal /Vehari /Pakpatan Jhelum Faisalabad Peshawar/charsadda/noshera Sargodha Hyderabad / Jamshoro Jhang /Rajanpur /Toba Tek Singh Hangu / Karak / Kohat Mirpur khas Tharparker Bhakkar / Layyah Bahawalpur Multan / Muzaffargarh Umar kot Bannu Awaran Panjgur Nawabshah /Sanghar/Shahdadkot/Nosheroferoz Rahim yar khan Kech (Turbat) DG Khan Dadu Dera bugti / Barkhan Zhob Ghotki Quetta / Pishin Qilla Saifullah / Loralai Sukkur / Larkana/ Shikarpur/khairpur Chaman / Qilla Abdullah Mastung / Kalat/Nushki Sibi / Bolan / Khuzdar Jafarabad /Nasirabad /Jhal Magsi Jacobabad Kharan Chaghi

246 Appendix B: World and Pakistan Solar Energy Maps with Solar Insolation for District Cities of Pakistan 246

247 247

248 248

249 249

250 250

251 251

252 22 year Monthly & Annual Average Solar Insolation (Kwh/m2/day) on a horizontal surface in District cities of Pakistan Sr.No City Latitude Longitude Elevation Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec Annual 1 Karachi Keemari Jacobabad Kech Chaman / Qilla Abdullah Panjgur Awaran Mastung / Kalat/Nushki Khuzdar Chaghi Karachi city / Thatta Kharan Quetta / Pishin Lasbella Sukkur / Larkana/ Shikarpur/khairpur Sialkot / Narowal / Gujrat Gujranwala/Hafizabad/Shekhupura Mirpur khas Lahore / Qasur Zhob Mardan / Swabi Qilla Saifullah / Loralai Dadu Hyderabad / Jamshoro Ghotki Nawabshah /Sanghar/Shahdadkot/Nosheroferoz Islamabad / Rawalpindi Sibi / Bolan / Peshawar/charsadda/noshera Badin Jhelum Dera bugti / Barkhan Attock / Chakwal Rahim yar khan Gawadar Jafarabad /Nasirabad /Jhal Magsi Tharparker Bahawalpur Umar kot Sargodha Muzaffarabad / Balakot Faisalabad Jhang /Rajanpur /Toba Tek Singh Hangu / Karak / Kohat Okara /Sahiwal /Vehari /Pakpatan Bannu Bhakkar / Layyah DG Khan Multan / Muzaffargarh

253 Appendix C: Equipment Operation Parameters Typical Construction Materials and Dimensions Used in Pakistan 253

254 Evacuated Tube Collector Type71 Parameters Parameter Value Unit Number in series 1 - Collector area 12 m 2 ( optimised value) Fluid specific heat 4.19 kj/kg.k Efficiency mode 2 (optimised Value) Flow rate at test conditions 3 kg/hr.m 2 Intercept efficiency 0.7 (default) Negative of first order efficiency coefficient 9 kj/hr.m 2.K (Reference Model) Negative of second order efficiency coefficient 0.03 kj/hr.m 2.K 2 (Reference Model) Logical unit of file containing biaxial IAM data 60 (default) Number of longitudinal angles for which IAMs are provided 5 (default) Number of transverse angles for which IAMs are provided 5 (default) Inlet temperature Inlet flow rate C (Storage tank cold side temperature) 165kg/hr Ambient temperature Incident radiation Incident diffuse radiation Solar incidence angle Input from weather data Solar zenith angle Solar azimuth angle Collector slope 0 Degrees (optimised) Collector azimuth 90 Degrees (optimised) Auxiliary cooler Type 1246 Parameter Value Unit Rated capacity kj/hr (optimised) Specific heat of fluid 4.19 kj/kg.k Inlet fluid temperature C (Chiller outlet cooling water) Inlet flow rate 800 kg/hr (optimised) Control function 1 - Set point temperature 25 C (optimised) Overall loss coefficient 0 kj/hr.k (default) Temperature of surroundings C (Input from weather data) 254

255 Hot water storage tank Type4a Parameter value Unit Fixed inlet positions 1 default Tank volume 2.0 m 3 (optimised ) Fluid specific heat 4.19 kj/kg.k Fluid density 1000 kg/m 3 Tank loss coefficient 0.6 kj/hr.m 2.K (Referenced) Height of node m Height of node m Height of node m Height of node m Height of node m Height of node m Height of node m Height of node m Height of node m Height of node m Auxiliary heater mode 1 (off) Node containing heating element 1 1 (top most element) Node containing thermostat 1 1 (top most element) Set point temperature for element 1 0 (off) Dead band for heating element 1 5 delta C (default) Maximum heating rate of element 1 0 kj/hr (off) Node containing heating element 2 1 (top most element) Node containing thermostat 2 1 (top most element) Set point temperature for element 2 0 (off) Dead band for heating element 2 5 delta C (default) Maximum heating rate of element 2 0 kj/hr (off) Not used (Flue UA) 0 W/K (not in use for storage tank) Not used (T flue) 20 (not in use for storage tank) Boiling point 100 C Hot-side temperature C (Collector Outlet water Temperature) Hot-side flow rate 165 Kg/hr Cold-side temperature C (Chiller Outlet water Temperature) Cold-side flow rate 150 Kg/hr Environment temperature C(Input from weather data) 255

256 Chiller Type 107 Parameter Value Unit Rated capacity kj/hr (design) Rated COP (Referenced) Logical unit for S1 data file 40 (default) Number of HW temperatures in S1 data file 5 (default) Number of CW steps in S1 data file 3 (default) Number of CHW set points in S1 data file 7 (default) Number of load fractions in S1 data file 11 (default) HW fluid specific heat 4.19 kj/kg.k CHW fluid specific heat 4.19 kj/kg.k CW fluid specific heat 4.19 kj/kg.k Auxiliary electrical power 220 kj/hr (Referenced) Chilled water inlet temperature C (chilled water outlet from Cooling coil) Chilled water flow rate 250 kg/hr (optimised) Cooling water inlet temperature C (Cooled water outlet from cooling tower) Cooling water flow rate 800 kg/hr (optimised) Hot water inlet temperature C (Hot water outlet from storage tank) Hot water flow rate 150 kg/hr (optimised) CHW set point C (default) Chiller control signal 1 (default) Fan Type 112b Parameter Value Unit Humidity mode 2 default -% relative humidity Rated flow rate 300 kg/hr (optimised) Rated power 80 kj/hr (Referenced) Motor efficiency 0.9 -(default) Motor heat loss fraction 0 -(default) Inlet air temperature C (Room air temperature) Not used (w) (default) Inlet air %RH 0 % (base 100) (dry air) Inlet air pressure 1 atm (default) Control signal 1 (default) Air-side pressure increase 0 Atm (default) 256

257 Cooling Coil Type 697 Parameter Value Unit Humidity mode 2 default -% relative humidity Logical unit - water corrections 52 (default) Number of water flow rates 3 -(default) Number of water temperatures 3 -(default) Logical unit - air flow corrections 53 -(default) Number of air flows 7 -(default) Logical unit - air temperature corrections 54 -(default) Number of dry-bulb temperatures 7 -(default) Number of wet-bulb temperatures 6 -(default) Fluid density 1000 kg/m 3 Fluid specific heat 4.19 kj/kg.k Rated volumetric air flow rate 200 l/s (optimised) Rated volumetric liquid flow rate 0.3 l/s (default) Total cooling capacity 9000 kj/hr (optimised) Sensible cooling capacity 7150 kj/hr (optimised) Fluid inlet temperature 7 C (Chilled water from chiller outlet) Fluid flow rate 250 kg/hr Inlet air temperature Fan outlet air Inlet air flow rate 300 kg/hr (Fan outlet flow rate) Inlet air pressure 1 atm (default) Air-side pressure drop 0 atm (default) Thermostat Type 108 Parameter Value Unit No of oscillations permitted 5 (default) 1st stage heating in 2nd stage? 0 No heating 2nd stage heating in 3rd stage? 0 No heating 1st stage heating in 3rd stage? 0 No heating 1st stage cooling in 2nd stage? 1 cooling Temperature dead band 0.5 Delta C (optimised) Monitoring temperature Room air temperature 1st stage heating set point 10 C 2nd stage heating set point 10 C 3rd stage heating set point 10 C 1st stage cooling set point C (optimised) 2nd stage cooling set point 28 C (optimised) 257

258 YAZAKI (HWF-SC5) CHARACTERISTICS ABSORPTION CHILLER PERFORMANCE 258

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