THEORETICAL ANALYSIS OF SOLAR WATER HEATING SYSTEM AHMAD ASYRAF BIN RAMLI

Transcription

1 THEORETICAL ANALYSIS OF SOLAR WATER HEATING SYSTEM AHMAD ASYRAF BIN RAMLI Thesis submitted in partial fulfilment of the requirements For the award of the degree of Bachelor of Mechanical Engineering Faculty of Mechanical Engineering UNIVERSITI MALAYSIA PAHANG 2010

2 UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING I certify that the project entitled THEORETICAL ANALYSIS OF SOLAR WATER HEATING SYSTEM is written by AHMAD ASYRAF BIN RAMLI. I have examined the final copy of this project and in our opinion; it is fully adequate in terms of scope and quality for the award of the degree of Bachelor of Engineering. I herewith recommend that it be accepted in partial fulfillment of the requirements for the degree of Bachelor of Mechanical Engineering. (Maisara Mohyeldin Gasim Mohamed) Examiner Signature

3 ii SUPERVISOR S DECLARATION I hereby declare that I have checked this project and in my opinion this project is adequate in terms of scope and quality for the award of the degree of Bachelor of Mechanical Engineering. Signature Name of Supervisor: AMIR BIN ABDUL RAZAK Position: Lecturer Date: 6 th DECEMBER 2010

4 iii STUDENT S DECLARATION I hereby declare that the work in this thesis is my own except for quotations and summaries which have been duly acknowledged. The project has not been accepted for any degree and is not concurrently submitted for award of other degree. Signature Name: AHMAD ASYRAF BIN RAMLI ID Number: MA07024 Date: 6 th DECEMBER 2010

5 vi ACKNOWLEDGEMENT Assalamualaikum Warahmatullah Wabarakatuh First of all, thanks to Allah The Almighty because giving me blessing, health and ideas to finish my project successfully. Hopefully, Allah always blesses me in the future. InsyaALLAH.. I am grateful and would like to express my sincere appreciation to my kind project supervisor, Mr. Amir bin Abdul Razak for his germinal ideas, valuable guidance, advice and continuous encouragement, constructive criticism and suggestion throughout this project. Without his continued support and interest, this thesis would not have been the same as presented here. My deeply thanks also extends to my dearest family especially to my father Ramli bin Shamsudin and mother Zaiton bt Ab Kadir which always support and pray throughout this project. Their blessing gave me high spirit and strength. Lastly, thanks to all my friends and all people who involve direct and indirect in provides assistance and co-operations at various occasions. Their view tips are useful indeed in helping me finish my thesis. Thanks

6 vii ABSTRACT Renewable energy is important for replace the using of electrical energy generated by petroleum. Energy consumption from petroleum must be reduced because of the limited petroleum resources and contribute of pollution to the earth. Solar power has become a source of renewable energy and solar energy applications should be enhanced. Solar water heating system was a practical application to replace the using of electrical water heater. More research is needed to increase capability and reduce production costs of solar water heating system and make the solar water heating system more efficient and practical. The objective of this project is to do investigation on solar water heating system in terms of mathematical theory to produce a mathematical model of solar water heating system. The analysis done by using a mathematical model developed to obtain data on temperature in the changes of flat plate collector area, storage tank insulation volume, piping size and mass flow rate of water. Efficiency of flat plate collector and storage tank insulation is calculated for any changes in size and volume. Solar fraction is calculated for any changes in the size of a flat plate collector and storage tank insulation in the consideration of changes in temperature and mass flow rate of water. Analysis showed the water temperature will increase with increasing area of flat plate collector, decreased with the increasing volume of insulated storage tank, and decreased with increasing size of the pipe. an These studies can provide data for the optimum design with high capacity and the mathematical models will facilitate the future study.

7 viii ABSTRAK Tenaga boleh diperbaharui amat penting bagi menggantikan penggunaan tenaga elektrik yang dijanakan oleh petroleum. penggunaan tenaga daripada petroleum perlu dikurangkan kerana sumber petroleum semakin terhad dan menyumbag kepada pencemaran yang merosakan bumi. Tenaga suria menjadi salah satu sumber tenaga yang boleh diperbaharui dan aplikasi tenaga suria perlu dipertingkatkan. Sistem pemanasan air suria menjadi satu aplikasi yang praktikal untuk digunakan bagi menggantikan pemanas air menggunakan elektrik. Lebih banyak kajian perlu dilakukan bagi meningkatkan keupayaan dan mengurangkan kos penghasilan system pemanasan air suria supaya lebih cekap dan praktikal. Objektif projek ini adalah untuk membuat kajian terhadap system pemanasan air suria dari segi teori dengan mendapatkan persamaan matematik dari segi keseluruhan untuk menghasilakan model matematik bagi system pemanas air suria. Analisis akan dibuat dengan menggunakan model matematik yang dihasilkan bagi mendapatkan data perubahan suhu terhadap perubahan luas plat pengumpul datar, perubahan isipadu tangki simpanan berpenebat, perubahan saiz saluran paip, dan perubahan kadar aliran jisim air. Kecekapan untuk plat pengumpul datar dan tangki simpanan berpenebat akan dikira untuk setiap perubahan saiz dan isipadu. Pecahan suria akan dikira untuk setiap perubahan saiz plat pengumpul datar dan tangki simpanan berpenebat dengan mengambil kira perubahan suhu dan kadar aliran jisim air. Analisis menunjukan suhu air akan bertambah dengan pertambahan luas plat pengumpul datar, menurun dengan pertambahan isipadu tangki simpanan berpenebat dan menurun dengan petambahan saiz paip. Kecekapan akan bertambah dengan pertambahan luas plat pengumpul datar dan berkurang dengan pertambahan isipadu tangki simpanan berpenebat. Kajian ini dapat memberi data untuk rekabentuk yang optimum dengan keupayaan yang tinggi dan model matematik akan memudahkan kajian pada masa akan datang.

8 xi TABLE OF CONTENTS TITLE PAGE SUPERVISOR S DECLARATION STUDENT S DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOL LIST OF ABBREVIATIONS Page i iii iv v vi vii viii xi xiv xv xvi xviii CHAPTER 1 INTRODUCTION Project Background Problem statement Project objective Project scope 3 CHAPTER 2 LITERATURE REVIEW Introduction Solar Water Heating System Types of Solar Water Heating System Natural Circulation Systems (thermosyphon 5 solar system) 2.32 Forced-Circulation System 7

9 xii 2.4 Low Flow Pumped System Auxiliary Flat Plat Collector Solar Collector Orientation Fluid Flow Rates Specification of Solar Water Heating System Solar Energy Terminology: Sun Earth Geometry: 22 CHAPTER 3 METHODOLOGY Introduction Flow Chart Component Of Solar Water Heating System Designing of the mathematical model Analysis of mathematical model Input data 28 CHAPTER 4 RESULTS AND DISCUSSION Introduction Mathematical Model Energy Balance for Flat Plate Collector Energy Balance of Insulated Storage Tank Complete Equation of System Estimation of Hourly Radiations Limits in Storage Temperature Profile Efficiency Solar Fraction Temperature Profile For Different Area of Collector Temperature Profile for Different Volume of Insulated Storage Tank 37

10 xiii 4.5 Temperature Profile for Different Configuration of 39 Water Flow Rates 4.6 Efficiency of Insulated Storage Tank and Flat Plate 40 Collector 4.7 Fraction of Insulated Storage Tank and Flat Plate 42 Collector 4.8 Design of SWH From Mathematical Model 44 CHAPTER 5 CONCLUSION Introduction Conclusion Recommendation 47 REFERENCES 48 APPENDICES 50 A1 Gantt chart FYP 1 50 A2 Gantt chart FYP 2 51

11 xiv LIST OF TABLES Table No. Page 2.1 Details of solar water heating system (Indian standard 12933) Details of Collector (Indian standard 12933) Supply Of Insulated Storage Tanks (Indian standard 12933) Details Of Stand for Insulated Hot Water Tank (Indian standard 12933) Input data Constants for predicting hourly solar radiation with ASHRAE model Table of temperature profile base on specification of Solar Water heating system 44

12 xv LIST OF FIGURES Figure No. Page 2.1 Natural circulation system (thermosyphon) Three configurations of forced circulation systems An example of solar fraction Schematic of alternative location for auxiliary energy supply Flat Plate Collector functions Zenith and solar altitude angles Slope β Surface azimuth angle γ and solar azimuth angle γ 19 s 2.8 Declination and hour angle The Flow Diagram of the Project schematic of solar water heating system schematic of solar water heating system Mass and energy balance of Solar Water Heating System Storage Temperature vs Area of collector Storage temperature vs Volume of insulated tank Storage temperature vs Overall piping diameter Temperature vs Mass flow rates Efficiency vs volume of storage tank Efficiency vs area of collector Fraction Vs Volume of storage tank Fraction vs Area of collector 43

13 xvi LIST OF SYMBOLS A c A st C p F R F h/d I g I d I T J K K m c m L m R m st m x q aux q L Q L q Ls q R q s q stl collector area, m 2 surface area of the storage tank, m 2 specific heat of working fluid, J/kg C collector heat removal factor solar fraction over a specified time horizon height to diameter ratio of storage tank global solar radiation intensity, W/m 2 diffuse radiation intensity, W/m 2 solar radiation intensity on tilted surface, W/m 2 fraction of net storage heat gain in a time step fraction of makeup water supplied in a time step thermal conductivity of storage tank insulation, W/mK collector mass flow rate, kg/s desired load mass flow rate, kg/s storage makeup water mass flow rate, kg/s mass flow rate from storage to load, kg/s mass flow rate for mixing, kg/s auxiliary energy required, W desired hot water load, W desired hot water load over a specified time horizon, J load met by solar energy or energy extracted from the storage, W energy added to storage through makeup water, W solar useful heat gain rate, W rate of storage loss, W

14 xvii R R b T a T L T R T sat T st T sti T stf t t ins t t U st U L V st V sti V stib V L V R Β Φ ρ ρ g ρ t (τα) maximum auxiliary heater power, W tilt factor ambient temperature, C desired load (hot water) temperature, C makeup water temperature, C saturation temperature, C storage temperature at any instant of time, C storage temperature at the beginning of a time step, storage temperature at the end of a time step, C time step in the analysis, s storage tank insulation thickness, m storage tank wall thickness, m storage heat loss coefficient, W/m 2 C collector overall heat loss coefficient, W/m 2 C storage volume at any instant of time, m 3 initial storage volume in a time step, m 3 initial Storage volume at the beginning of the day, m 3 volume of water withdrawn by load in a time step, m 3 volume of water replenished to the storage tank in time step, m 3 collector tilt, rad latitude of location, rad density of working fluid, kg/m 3 ground reflectance density of storage tank material, kg/m 3 average transmittance absorptance product

15 xviii LIST OF ABBREVIATIONS ISO LPD SWH international organization for standardization liters per day Solar water heating

16 CHAPTER 1 INTRODUCTION 1.1 PROJECT BACKGROUND The solar energy is the most capable of the alternative energy sources. Despite this hopeful evaluation of the potential of solar energy, considerable technical and economic problems must be solved before utilization of solar energy can occur. The solar power development will depend on how we deal with a number of serious constraint, including scientific and technological problem, marketing and financial limitations, and political. In addition, the education of engineers will have to changes its focus from non-renewable fossil-fuel technology to renewable power source. There has been a general agreement that the most significant of the renewable energy sources is solar radiation. Thermal conversion is a technological scheme that utilizes a solar radiation. When a dark surface is placed in sunshine, it absorbs solar energy and heats up. Solar energy collector working with sun facing surfaces will transfer energy to the water that flow through it. To reduce heat loses to atmosphere and to improve it efficiency, one or two sheet of glass are usually placed over the absorbed surface. This type of thermal collector suffers from heat losses due to radiation and convection. Such losses increase rapidly as the temperature of the working fluid increases. Improvement such as the use of selective surfaces, evacuation of the collector to reduce heat losses, and the special glass is use to increase the efficiency of the absorber. Solar water heating (SWH) is a proven and famous renewable energy technology and has been used in many countries of the world. The SWH system

17 2 investigated consists of mainly three parts, namely a flat plate solar collector, a heat exchanger (storage tank) and a circulating pump. Solar water heating system have been the famous application that using solar radiation as an energy sources that using thermal conversions. This project will analyze the Solar Water Heating System based on the theoretical analysis from the mathematical model. The mathematical model will be consider all the part of the solar water heating system to find the solar water heating system temperature when the size and the behavior of solar water heating is changing. 1.2 PROBLEM STATEMENT In today s modern world, where new technologies are introduced every day, electrical energy use is increasing quickly Fossil fuel particularly petroleum fuel is the major contributor to electrical production. Quickly depleting reserve of petroleum and decreasing air quality raise question about the future. Solar can be use as a clean alternative energy to reduce electrical production and is promising in the effect to establish environmentally friendly for electrical system. So far, many extensive studies investigated solar water heating system and become the famous application for home and building. The using of solar water heating system not familiar in Malaysia and the people in Malaysia still not realize about the practical of using solar water heating systems. It s important to study about the power produce to heat the water using solar water heating system and proving about energy saving of solar water heating system. 1.3 PROJECT OBJECTIVE The objectives of this analysis are to: i. Find the mathematical model of solar water heating system. ii. Find the change in water temperature from variable behavior of all part in solar water heating system. iii. Find the efficiency and fraction of design using mathematical model.

18 3 1.4 PROJECT SCOPE The project scope is to: i. study on solar water heating system ii. Design a mathematical model of solar water heating system iii. Simulate the behavior of the Solar Water Heating System using the mathematical model

19 CHAPTER 2 LITERATURE REVIEW 2.1. INTRODUCTION A solar water heating system (SWH) is the device that uses solar energy for hot water production. Solar water heating system (SWH) is renewable energy technology and has been used in many countries of the world. This natural energy is absolutely free and the supply is unlimited in the day whenever there is sunlight. The usage of this energy does not produce any pollutant and therefore is most Environment Friendly. In residential countries, energy consumption in the building sector need of high energy budget. Most energy is needed production of hot water and space heating. Hot water is important for bathing and for washing, utensils and other domestic purpose in urban as well as in country areas. Heating water is usually burning by firewood in the country areas and by fossil fuel energy such as kerosene oil, petroleum gas (LPG), coal and electricity in metropolitan areas. In this consider, consumption of solar energy through solar water heating (SWH) systems can be replace to reducing energy amount required. (Staff, D., and Campbell, S., 1978) SWH is approve and readily available technology use renewable energy for conventional water heating. A lot of types of SWH are available and can be used in much application. Domestic hot water usually uses small system applications while larger systems are used in industrial applications. There are two types of water heating systems based on the type of the circulation: natural circulation and forced circulation. Natural circulation solar water heaters are simple in design and low cost. Forced circulation water heaters are used in freezing climates and for commercial and industrial process heat. (Staff, D., and Campbell, S., 1978)

20 5 Suitable design of solar water heating system is will give maximum benefit to the user, mainly for a large system. Designing solar hot water system need suitable sizing of different components and must considering on solar insulations and hot water demand. In this review, the effect of sizing of part on the system is studied and a novel strategy for the system part is proposed to improve the design and performance of solar water heating systems. 2.2 SOLAR WATER HEATING SYSTEM Energy application from the sun to heat water is nothing new. Solar water heaters have been use since the 1800s. What's difference is configuration is most modern solar water heaters are placing in the roof with resembles to sky. Solar water heaters are an environmentally and to reduce energy bills. (Staff, D., and Campbell, S., 1978) Solar water heaters come in differences of configurations in the design, cost, performance, and level of system. Most systems have auxiliary such as electricity or gas. A solar water heating system has a part of a insulated water storage tank, a solar collector, a back-up energy source, and a pump and controls. (Staff, D., and Campbell, S., 1978) 2.3 TYPES OF SOLAR WATER HEATING SYSTEM There are basically two types of solar water heating system(d. Yogi Goswami, Jan F. Kreider, 1999): Natural Circulation Systems (thermosyphon solar system) The natural tendency of a less dense fluid to rise above a denser fluid can be used in a simple solar water heater to cause fluid motion through a collector. The density difference is created within the solar collector where heat is added to the liquid. In the system shown in Figure 2.1 as water gets heated in collector, it rises to the tank and the cooler water from the tank moves to the bottom of the collector, setting up a

21 6 natural circulation loop. It also called a thermosyphon loop. Since these water heaters not use a pump, it is a passive water heater. For the thermosyphon to work, the storage tank must be located higher than the collector. (D. Yogi Goswami, Jan F. Kreider, 1999) Figure 2.1: Natural circulation system (thermosyphon) Source : D. Yogi Goswami, Jan F. Kreider, 1999 Since the driving force in a thermosyphon system is only a small density difference and not a pump, larger-than-normal plumbing fixtures must be used to reduce pipe friction losses. In general, one pipe size larger than normal would be uses with a pump system are satisfactory. Since the hot-water system load vary little during a year, the angle of tilt is that equal to the latitude, that is,. The temperature difference between the collector inlet water and collector outlet water is usually 8-11 C during the middle of a sunny day. After sunset, a thermosyphon system can reverse its flow direction and lose heat to the environments during the night. To avoid reverse flow, the top header of the absorber should be at least 30cm below the cold leg fitting on the storage tank, as shown; otherwise a check valve would be needed.. (D. Yogi Goswami, Jan F. Kreider, 1999) Several features inherent in thermosyphon design unit utility. If it s to be operated in a freezing climate, a nonfreezing fluid must be used, which in turn requires a heat exchanges between collector and portable water storage. (If portable water is not required, the collector can be drained during cold period instead). Heat exchanger of either the shell-and-tube type or the immersion-coil type required higher flow rates for efficient operation than a thermosyphon can provide. Therefore, the thermosyphon is

22 7 usually limited to nonfreezing climates. For mild freeze climates, a heat exchanger coil welded to the outer surface of the tank and filled with antifreeze may work well.. (D. Yogi Goswami, Jan F. Kreider, 1999) Forced-Circulation System If a thermosyphon system cannot be used for climatic, structural, or architectural reason, a forced- circulation system is required. In order to accommodate the thermal expansion of water from heating, a small (about 2 gallon capacity) expansion tank and a pressure relief valve are provided in the solar loop. Because water always stays in the collector of this system, antifreeze (propylene glycol or ethylene glycol) is required for location where freezing condition can occur. During stagnation condition (in summer), the temperature in the collector can become very high, causing the pressure in the loop to increase. This can cause leak in the loop unless some fluid is allowed to escape through a pressure-release valve. Whether the result of leaks or of draining, air enters the loop causing the pumps to run dry. This disadvantage can be overcome in a closed loop drain back system which is not pressurized. In this system, when the pump shut off, the water in the collector drains back into a small holding tank while the air in the holding tank goes up to fill the collector. The holding tank can be located where freezing does not occur, but still at a high level to reduce pumping power. In all three configuration differential controller measures the temperature differential between the solar collector and the storage, and turns the circulation pump on when the differential goes below a set limit (usually 2 C). Alternatively, a photovoltaic (PV) panel and d DC pump may be used. The PV panel turns on the pump only when the solar radiation is above a minimum level. Therefore, the differential controller and the temperature sensors may be eliminated.. (D. Yogi Goswami, Jan F. Kreider, 1999)

23 8 (1) (2) (3) Figure 2.2: Three configurations of forced circulation systems: (1) open loop, (2) closed loop, and (3) closed loop with drain back. Source: D. Yogi Goswami, Jan F. Kreider, 1999 Figure 2.2 show in an open loop system the solar loop is at atmospheric pressure, therefore, the collectors are empty when they are not providing useful heat. A disadvantage of the system is the high pumping power required to pump the water to the collector every time the collectors become hot. This disadvantage is overcome in the pressurized closed loop system since the pump has to overcome only the resistance of the pipes. In this system, the solar loop remains filled with water under pressure. (D. Yogi Goswami, Jan F. Kreider, 1999)

24 9 2.4 LOW FLOW PUMPED SYSTEM The collector flow rates in the range of 0.01 to 0.02kg/m 2 s, lead to high values of collector heat removal factor, F R. However in direct system (without a collector heat exchanger) they also lead to relatively high fluid velocities in piping and subsequent mixing (or partial mixing) in tanks. Van koppen et al. (1979) suggested the advantages of low flow and stratified tanks, and recent work has confirmed that it can be advantageous to use reduced fluid flow rates in the collectors loops, accept a lower F R and gain the advantages of increase stratification with resulting reduced collector inlet temperature. The result can be a net improvement in system performance. Lower flow rates result in greater temperature rise across collectors, and if tanks are perfect stratified, the temperature difference from top to bottom will increase as the flow rates decreases. As pointed out by Hollands an Lightstone (1989) in very useful review, the use of lower flow rates can have the additional advantages of reduction in both the first cost and operating cost of the system through use of smaller pipes and pumps and reduction of operating cost for pumps operation. Flow rates used in Swedish flat-plates collector have typically been in range of to 0.007kg/m 2 s. (Dalenback, 1990). Figure 2.3 from simulation studies by wuestling et al. (1985), illustrates for a specific example the effect of collector flow rates per unit area of system performance (expressed as solar fraction, F) for a fully mixed tank and for a highly stratified tank. The potential advantages of the low-flow system are evident; the maximum performance for the stratified tank (F = 0.66) is a third grater than that for the fully mixed tank (F =0.48). This level of improvement is not realized in practice, as real tanks are in general neither fully mixed nor fully stratified. As Holland and Lightstone (1989) point out, the degree of improvement depend in part on load patterns, as loads that draw the tanks down completely by the beginning of collection in the morning will result in less improvement in performance that if the tanks is hot in the morning. However, the gains that have been reported in experiment are significant.