Aachen University of Applied Sciences Jülich Division

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1 Aachen University of Applied Sciences Jülich Division Master of Science in Energy System s Modelling and Assessment of Solar Process Heat Systems in India By, Miss. Deepika Baskar Matriculation number: Jülich, July 2015 A thesis subm itted in partial fulfillm ent of the requirem ents for the degree of Master of Science in Energy System s

2 This thesis is produced and written independently. Only the cited sources and references have been used. Ms. Deepika Baskar Jülich, July 2015 This m aster thesis was supervised by: Prof. Dr. Ulf Herrm ann Fachhochschule Aachen Jülich Dipl. Phy. Gerhard Stryi-Hipp Fraunhofer I SE Freiburg Annabell Helm ke M.Sc Fraunhofer I SE Freiburg II

3 Acknowledgements I express my sincere respect and thanks to my mother Vimala and my father Baskar for their unconditional love, support, motivation and blessings. My deepest gratitude and respect to my supervisor at Fraunhofer ISE, Mr. Gerhard Styri-Hipp for his immense guidance, encouragement and a pristine way-forward approach which helped to a maximum extent in the completion of this thesis. I thank the Almighty for blessing me with such a great personal and professional environment. My special thanks to Ms. Annabell Helmke for her guidance and encouragement. She has been extraordinarily tolerant and supportive in providing me valuable feedbacks in every stage of this thesis. I would also like to thank the persons who helped in materializing this thesis. In particular I thank- -Prof. Dr. Ulf Herrmann from Fachhochschule Aachen for his support, feedback and recommendations. -Ms. Annette Anthrakidis for all the fundamental guidance and the opportunities provided. -Mr. Florian Gross for helping me in understanding the functioning of the monitoring system and his valuable feedbacks and suggestions. -Dr. Anton Neuhaüser and Dr. Pedro Horta for their feedback and recommendations during the Process heat - team meetings. -Mr. Abhinav Goyal, GIZ India for his fullest cooperation in establishing contacts with the installers/owners and gathering all the required technical data. -Mr. Stefan Mehnert and Mr. Konstantin Geimer from Collector testing department at ISE for their guidance in finding the collector parameters. -My student colleagues Shahab, Pankaj, Davide, Clare and Theda for all the fruitful technical discussions and constant motivation. -My dear ones, Dharshana and Bharathy for motivating and supporting me during all the hardest times of my life. III

4 ABSTRACT India, a country with immense solar potential has set a clear roadmap to meet its energy demands by harnessing the available solar energy. The main focus of this work is to utilize this energy using solar thermal technologies to meet the heat demands in the industrial sector. Although Solar Heat for Industrial Processes (SHIP) systems with total installed capacity of 11 MWth exist across India, the proliferation of these systems faces challenges in gaining market importance, reliability and trust due to non-availability of performance data. This performance figures can be extracted only by means of monitoring the SHIP systems. An analysis of the monitoring results paves the way to identify the operating manner of the plant. It will then help to estimate the system s energy yield and further optimize the SHIP systems design by proposing suitable options for improvement. To set an example for the Indian solar thermal Industry, as a part of SoPro India project, two SHIP systems namely at Synthokem Labs and at HP Dairy are being monitored from 15 th October The scope of this thesis is to analyze the monitoring results in order to extract the design and operational characteristics of the two monitored SHIP plants and further to compare the measured data with the simulation result of a model with the extracted characteristics implemented into it. To do that, one of the SHIP plant (at Synthokem Labs) is chosen for simulation with TRNSYS 17 software. The results from the simulation and the monitoring system are compared on the basis of energy yield and efficiencies using a mean deviation index. Further in this thesis, the drawbacks of this existing system configuration are analyzed to provide possible improvements on the system design. The analysis of the monitoring results shows that the SHIP plant at Synthokem Labs yielded a net system energy gain of 8171 kwh for a total three months from Dec 6 th 2014 to February 21 st 2015 and the SHIP Plant at HP Dairy yielded 6639 kwh for a total five months from Nov 2014 to Mar For the SHIP plant at Synthokem Labs, comparison between simulated and monitored values of net system yield shows a mean deviation of 4.3% while the net solar collector yield deviates on an average by 3.6% for a total of three months. The possible improvement options of having tanks in series and having collector fields connected to single tank configuration are simulated to indicate the possible increase in system performance and energy yield from the existing system. The results show an increase respectively of 6% and 11% from the monitoring results for IV

5 the whole period of three months. While an investigation on the options of changing the flowing direction in collector field and bypassing the shaded collector array yielded a net collector output deviating 1% and -3% respectively from the simulated outputs for the total three months period. The fuel cost saved by the existing SHIP system at Synthokem Labs during the three months considered is Rs (608 1 ) saving 775 L of fuel oil. Among all the possible options for improvement suggested, collector fields connected to single tank configuration saved Rs (675 1 ) for the same operational timing of the SHIP plant. Key words: SHIP systems, monitoring, simulation, system design 1 (1 = Rs.70 considered) V

6 Table of Contents 1 Introduction Motivation Problem statement Objective of the thesis Methodology Theoretical background Solar thermal technology for low temperature applications Solar thermal energy Solar radiation and solar angles Solar thermal collectors Collector technologies for process heat applications System components Solar process heat system configurations System performance evaluation methodology SoPro India Monitored Case Studies Case Study 1: Synthokem Labs Case Study 2: HP Dairy Assessment of monitored data Online scientific integrated monitoring system Monitored Data Processing Data processing Data availability Case study 1: Synthokem Labs System description with monitoring scheme Results Case study 2: HP Dairy System description with monitoring scheme VI

7 4.4.2 Results Modelling of Systems TRNSYS 17 program description Mathematical description of the system modelled using TRNSYS Energy balance equations for the system modelled Parameters of the model Considerations in the model Physical considerations Operational strategy considerations Validation of simulated model and possible improvement options Validation of simulated model with measured data Validation results Possible improvement options Conclusion and future work Conclusion Future recommendations References Annexe VII

8 Glossary of Terms and Abbreviation Abbreviation & Acronym SHIP SWHS PV FPC ETC PC HC Solar Heat for Industrial Processes Solar Water Heating Systems Photo Voltaic Flat Plate Collector Evacuated Tube Collector Personal Computer Heat Counter TRNSYS Transient System Simulation tool Md CO 2 Lpd L Sq.m a d RO IAM Mean Deviation Carbon di-oxide Liters per Day Liters Square meters annum Day Reverse Osmosis Incidence Angle Modifier Latin Symbols A c A C p m D Absorber area Total surface area Specific heat capacity of water Mass flow rate Diameter H Q T Height Thermal energy Temperature VIII

9 G U Global irradiation Overall heat loss coefficient Greek Symbols h E Angle of incidence Zenith angle Solar altitude angle Solar azimuth angle Slope Absorptivity Transmissivity Efficiency Temperature Emissivity Difference Density Subscripts Coll Pro D N abs in out Sol_irr E_sol s,p amb Collector loop Process loop Day Night absorber Inlet Outlet Global Solar irradiation Total Global solar irradiation during pump operation Storage to Process Ambient IX

10 Table of Figures Figure 1-1: Total installed capacity for power generation in India as of 30th Sep 2014 (Left); Total renewable installed capacity for power generation in India as of 30 th Sep 2014 (Right) [1]... 1 Figure 1-2: Estimated solar potential in India [3]... 3 Figure 1-3: Estimated breakup of functional SWHS installations till 2009 [5]... 4 Figure 1-4: Heating load requirements in different industrial sectors [6]... 5 Figure 1-5: Methodology of work... 8 Figure 2-1: Representation of solar angles [13] Figure 2-2: Collector efficiency curve [15] Figure 2-3 : Sun's height during the year Figure 2-4: Collectors for process heat applications over the working temperature range [17] Figure 2-5: Components of a standard Flat Plate Collector [18] Figure 2-6: Simplified illustration of the loss mechanisms of a standard Flat Plate Collector [19] Figure 2-7: Evacuated Tube Collector types Direct Flow type (Left) and Heat Pipe type (Right) [22] Figure 2-8: Comparison of characteristic collector efficiency curves [13] Figure 2-9: Storage strategy- mixed (Left) and stratified (Right) [15] Figure 2-10 :Example of supply level and process level integration of solar thermal systems [26] Figure 2-11: An indirect solar hot water/hot air system [25] Figure 2-12: Mixed tank, recirculation system [25] Figure 2-13: Variable volume storage configuration [25] X

11 Figure 3-1: Solar hot water system installed at Synthokem Labs [28] Figure 3-2: Hydraulic scheme of solar hot water system installed in Synthokem Labs [7], adapted to show energy balance regions Figure 3-3: Collector field Layout of the solar hot water system installed at Synthokem Labs [28] Figure 3-4: Picture of the solar hot water system installed in HP Dairy [28] Figure 3-5: Hydraulic scheme of solar hot water system installed at HP Dairy [7] Figure 3-6: Collector field Layout of the solar hot water system installed at HP Dairy (self drawn) [30] Figure 4-1: Heat Meter components [self-drawn] Figure 4-2: Steps involved in data processing [34] Figure 4-3: Raw data file to a corrected raw data file processing steps Figure 4-4: Data processing steps for validation Figure 4-5: Monitoring scheme of solar hot water plant in Synthokem Labs Figure 4-6: Operational behavior (Start and Stop time) of the solar hot water system in Synthokem Labs Figure 4-7: Volume of water in Tank 'Night' Synthokem Labs Figure 4-8: Volume of water in Tank 'Day' Synthokem Labs Figure 4-9: Fresh water refill time identified from the inlet collector temperature Collector Loop Day of measurement data for the month of January 2015 Synthokem Labs Figure 4-10: Shading effect on Collector Loop 'Day' due to obstruction (building) Figure 4-11: System behavior analysis of Process Loop Synthokem Labs Figure 4-12: Specific energy yield of the system - Synthokem Labs Figure 4-13: Monitoring scheme of solar hot water plant in HP Dairy XI

12 Figure 4-14: Functioning of differential temperature controller in collector loop - HP Dairy Figure 4-15: Functioning of differential temperature controller in Storage to Process loop & Process loop - HP Dairy Figure 4-16: Electric heaters inside the storage tank operated on cloudy days to suffice the demand HP Dairy Figure 4-17: Fluctuations in Mass flow rate - HP Dairy Figure 4-18: Shading on the collector field HP Dairy Figure 4-19: Mixed storage tank - HP Dairy Figure 4-20 : Specific energy yield of the system HP Dairy Figure 5-1: Hydraulic scheme of Synthokem Labs presented in TRNSYS 17 as information flow diagram Figure 5-2: TRNSYS 17 deck file showing the Synthokem Labs SHIP system modelled Figure 5-3: Row shading effect on Collector field 'Night' representative Figure 5-4: Shading effect due to obstructions on Collector field 'Day' Figure 6-1: Temperature analysis of Collector Loop 'Day' - Synthokem Labs Figure 6-2 : Mean absorber temperature - Collector Loop 'Day' Figure 6-3 : Temperature analysis of Collector Loop 'Night' - Synthokem Labs Figure 6-4 : Temperature analysis of Process loop - Synthokem Labs Figure 6-5 : Specific heat gain diagram - January Synthokem Labs Figure 6-6 : Possible improvement option 1 - Tanks in series configuration Figure 6-7: Process outlet temperature - comparison between the tanks in series configuration and existing configuration Figure 6-8 : Possible improvement option 2 - Collector fields connected to single tank XII

13 Figure 6-9 : Process outlet temperature - Comparison between the collector fields connected to single tank configuration and existing configuration Figure 6-10 : Proposed fluid flow direction in Collector field Day to increase the net collector gain Figure 6-11 : Collector outlet temperature simulated outputs of the existing and proposed flow direction in Collector field 'Day' Figure 6-12 : Bypassing the shaded collector array in Collector field Day Investigation on net collector gain Figure 6-13: Instantaneous energy gain in Collector Loop 'Day' comparison between the simulated outputs of existing configuration and bypassing the shaded collector array configuration XIII

14 List of Tables Table 4-1: Components of a scientific monitoring system indicating the Manufacturer & Model Number Table 4-2: Data availability - Synthokem Labs and HP Dairy Table 4-3: Monitoring scheme Synthokem Labs - Sensor and its Position Table 4-4: Parameter identifier table - Synthokem Labs Table 4-5: Number of days in a month the collector loop 'Day' and 'Night' are operated - Synthokem Labs Table 4-6: Total volume of fresh water filled in the tanks (Predicted vs. Actual) Table 4-7 : Daily performance of the collector system Table 4-8 : Performance analysis of the monitored hot water system at Synthokem labs Table 4-9 Monitoring scheme - HP Dairy - Sensor type and position Table 4-10: Parameter identifier table - HP dairy Table 4-11: Daily performance of Collector Loop HP Dairy Table 4-12: Reasons for mass flow rate fluctuation - HP Dairy Table 4-13 : Variation in operational hours of the plant due to shading effect HP Dairy Table 4-14: Maximum Process outlet temperature for each month HP Dairy Table 4-15 : Performance analysis of the monitored hot water system at HP Dairy. 72 Table 5-1: Parameters of the simulated model - Synthokem Labs Table 5-2: Parameters considered for row shading effect -Synthokem Labs Table 5-3: Operational strategy followed in simulation model - Synthokem Labs Table 6-1 : Heat gained in Collector Loop 'Day' - comparison between simulated and measured results XIV

15 Table 6-2 : Heat gained in Collector Loop 'Night' - comparison between simulated and measured results Table 6-3: Comparison of month-wise efficiency parameters of the solar hot water system at Synthokem Labs Table 6-4 : Drawbacks of the hot water system installed in Synthokem Labs - at design and operational level Table 6-5 : Performance analysis Comparison between existing and recommended configurations Table 6-6 : Specific energy yield - Comparison between existing and recommended configurations for January Table 6-7: Comparison on the fuel savings between the existing system and the proposed improvement options XV

16 1 Introduction 1.1 Motivation Energy is essential for a country s economic growth, for improving the quality of life of the people and for increasing its opportunities for development. India, a country with rapidly growing economy, faces major challenges of (a) providing energy access to all its citizens (b) mitigating fuel import dependency thereby enhancing energy security, and (c) complying with the international protocols on climate change mitigation plans. The increasing growth rate of population, industrialization and the awareness on the depletion rate of fossil energy resources has stimulated the country to take efforts in adopting heat and power generation methods through renewable energy resources. With all the Governmental policies and a steady encouragement to adopt renewable power generation, India now occupies fifth position in the world for renewable power generation. As of 2014, the share of renewable power generation stands at 31.7 GW (12.5%) of 250 GW total power generation [1]. Figure 1-1 (Left) below shows the sector wise installed capacity for power generation in India. It can be seen that renewable energy is becoming an important part of India s energy mix. Figure 1-1: Total installed capacity for power generation in India as of 30th Sep 2014 (Left); Total renewable installed capacity for power generation in India as of 30 th Sep 2014 (Right) [1] Figure 1-1 (Right) shows the distribution of renewable sources in the total installed capacity of renewable power (including on-grid and off-grid). It can be seen from Figure 1-1(Right) that the largest share is 25 GW (65%) from wind power, followed by small hydro power and then solar power. Even though India being a tropical country blessed with 300 sunny days in a year which accounts to a solar power potential of 1

17 Introduction 748 GWp, only 2.97 GW has been utilized so far. Owing to the increase in energy demand, the Indian Government has consciously taken steps to act upon the available energy resources and has proposed to reach a target of 100 GW of solar and 175 GW of total renewables by the year Thus, it is very clear that India has chosen Renewable energy, in particular solar, as its flagship energy initiative to meet its energy demand. Experts say that solar energy which is available in plenty in India has the potential to possibly make India energy independent nation in long run [2]. Figure 1-2 shows the state wise estimated solar potential in India. The two concentric circles depicted in the Figure 1-2 indicate the intensity of solar irradiation available in the site. The inner circle indicates the state average Direct Normal Irradiance in GWh and the outer circle indicates the state average Global Horizontal Irradiance in GWh. Indicated inside each state in bold black letters are the solar potential in GW available at that particular state. To get the exact numerical data on the state wise solar irradiance, refer to Ministry of New & Renewable Energy, India website [3]. 2

18 Introduction Figure 1-2: Estimated solar potential in India [3] This energy resource which is available in plenty can be utilized in a better manner to cater for the energy demand through the right choice of technology. With technologies already available in the market, the energy demand in the form of electrical power requirement can be met through solar photovoltaic technology and in the form of heat power requirement through solar thermal collector technology. Solar thermal collector technology can help to convert the available solar irradiation into heat energy carried by a fluid. This technology finds its end-users ranging from conventional power generation (converting heat to electrical energy), in the industrial 3

19 Introduction sector (process heating, drying, distillation/desalination, space heating & refrigeration) to the residential sector for water heating. Nearly 25 million households use electric geysers for water heating, consuming 7500 GWh of electricity (assuming minimum annual consumption of ~ 600 kwh/ year/ geyser) and 15 million tons/year of petroleum fuels are used in industries in thermal form at temperatures below 300 C. 30% of energy consumed in industry is used for heating water, which shows that there is a huge potential [4]. The main motive of this thesis is to focus on implementation of solar thermal technology to meet the heat demands in the industrial sector, which hasn t been tapped to the maximum extent. India has taken sufficient steps through the Jawaharlal Nehru National Solar Mission to provide hot water to the residential and industrial sector through solar thermal collector technology. Installed capacity of solar thermal collectors for India stands at million sq. m equivalent to 5082 MWth till 30 th October 2013 [4]. The target for solar thermal collector area by the end of 2017 is set to be 15 million sq.m. Hence, 8 million sq.m of additional collector area is to be added in the 5 year period from [4]. However, this growth has so far been restricted to the domestic hot water segment [5]. There is tremendous potential in India for solar thermal systems for process heat requirements. However, in spite of all promotional schemes and efforts, the deployment of solar thermal systems in industries has remained low. The following Figure 1-3 clearly reveals the residential segment as the dominant market for solar thermal systems. Figure 1-3: Estimated breakup of functional SWHS installations till 2009 [5] 4

20 Introduction The Figure 1-4 below illustrates the heat requirement in different industrial sectors in India. Figure 1-4: Heating load requirements in different industrial sectors [6] These heating requirements vary from around 30 C in sectors such as paper and pulp to 250 C in other sectors. These loads can be met with solar thermal systems utilizing different collector technologies [6]. With the sumptuous amount of solar energy resource available in India and all the efforts taken by the Governmental directives, it is evident that there is tremendous potential for integration of solar thermal systems in different applications and sectors. 1.2 Problem statement From Figure 1-3, it is quite evident that the penetration of solar thermal technology in the sector for industrial process heating is as low as 6% of the total solar hot water systems installed in India. Even though the utilization of solar thermal in process heat application can be seen as a promising option from Figure 1-4, the challenges upon setting up these systems lie both in technical and financial means which need to be addressed [7]. In order to increase the market share of solar thermal technology for industrial process heating, to create awareness and build trust in the minds of the industrial owners and to enhance the quality of these systems, measures have been taken jointly by Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) India, together with the Ministry of New and Renewable Energy Sources, Government of India (MNRE) and Fraunhofer ISE, Germany through the Project SoPro-India, as a part of the Comsolar Project of GIZ India. 5

21 Introduction According to the project objectives, required amount of work have been already carried out on the topics namely, Improved market deployment of Solar process heat systems in India [8] addressing the need for creating a database to build awareness and indicate in particular the economic and technical feasibility of solar heat use in industrial processes and Development of a monitoring mechanism for Industrial solar process heat applications in India [9] addressing the need for the introduction of low cost, robust monitoring system in order to build confidence in this technology by providing reliable performance data. The project has been successful in compiling a database of 20 Solar Heat for Industrial Processes (SHIP) plants in various industrial sectors in India and for two case studies, monitoring systems have been established to produce reliable performance data [7]. One of the key challenges faced by the SHIP systems is to indicate the reliable and stable heat supply for the production processes which is of high priority for most of the industry owners. The performance of the SHIP plants which can be obtained with the help of monitored data is the key factor which can significantly increase the trust in this technology and also help the industrial owners in knowing the operating condition of the system. Apart from improving the reliability and trust, the challenge in facilitating the diffusion of SHIP technology in India lies in providing a good know-how on the system design and its standardization. This can further lead to the development of best practice approach to design and implement SHIP systems after learning from a series of trial & error method. To proceed in this direction, it is important to implement the design of the SHIP plant proposed in a modelling tool and simulate the annual performance of the system. The validation of the designed system with the monitored data can be further beneficial for the industrial owners by supporting them in identifying problems in their systems and making improvements and on the other hand, the system installers can derive a best practice approach by calculating the differences in the solar energy yield data and return on investment between the predicted design tool and the results from the site. The main motive of this thesis is to address the key challenges of building reliability and trust through performance analysis and to give a starting point for the best practice approach for designing a SHIP plant using a modelling tool. 1.3 Objective of the thesis As a part of the So-Pro India project, two SHIP plants are being monitored from October 2014 for a period of 15 months. The key challenges stated in the previous 6

22 Introduction sub chapter form the fundamental objectives of this thesis. The objectives presented below are addressed based on the details and the monitored data available from two SHIP plants monitored in India. i. Elaboration of a description on the typical design characteristics and operational strategies of the monitored Indian SHIP systems. ii. Development of a simulation model which can simulate the typical design characteristics and operational strategies of the monitored Indian SHIP systems and further, the simulated model is validated with the monitored data (is done for one of the case studies). iii. Identification of the optimization potential on the monitored Indian SHIP system which is modelled and validated. 1.4 Methodology The objectives of the thesis are achieved by following the methodology depicted in Figure

23 Introduction Figure 1-5: Methodology of work 8

24 Introduction This methodology helps in scaling down the work and defining the structure of the thesis. The details regarding the monitored SHIP systems are described in Chapter 3. For these monitored systems, performance analysis needs to be carried out. One part of the methodical work deals with analyzing the actual performance of the system through the data obtained from the monitoring system established at site. Chapter 4 provides details on the monitoring system, data collection, data processing methodology and determining the results (actual performance of the system). The other part is to model the system using a simulation tool. In chapter 5, details on the modelling of one of the systems (at Synthokem Labs) using TRNSYS software and the assumptions made are explained in detail. Further, the system modelled is validated with the measured data and the gap analysis is performed in Chapter 6. Optimization potential pertaining to the system established in Synthokem Labs is explained as possible options for improvement in the same chapter. A conclusion on the results and the future recommendations are stated in Chapter 7. 9

25 2 Theoretical background This section of the thesis will briefly explain about solar thermal technology implemented for low temperature industrial applications in India. In this regard, the first part of the chapter will give a brief overview on solar thermal energy, collector technologies, system components and configurations used for low temperature solar process heat applications. Along with it, in the second part of the chapter the basic methodology for evaluating the performance of the solar process heat system is described. Planning and execution of this methodology shall help to achieve best practices in system design and operation. In this thesis work, the solar process heat system has been related to solar hot water system, since this thesis focusses on solar hot water systems for industrial applications. 2.1 Solar thermal technology for low temperature applications Solar thermal energy Solar energy is the radiant energy from the sun that can be converted into thermal or electrical energy. The radiation intensity on the surface of the sun is approximately 6.33 x 10 7 W/m 2. Since radiation spreads out as the distance squared, by the time it travels to the earth, the radiant energy falling on 1 m 2 of surface area is reduced to 1367 W [10]. 174 Peta Watt ( PW ) of energy comes in the form of solar irradiation and hits our atmosphere (almost one third of it is reflected back into space) [11]. This cleanest and the most abundant renewable energy resource can be harnessed through the available technologies namely, photovoltaic (PV) technology and solar thermal technology. Photovoltaic cells convert solar irradiation into electrical energy using photoelectric effect. Solar thermal systems use a solar collector which absorbs solar irradiation and convert it to thermal energy which is transferred into heat transfer fluid. The thermal energy carried by the fluid can be used directly or alternatively can charge a thermal storage, which can supply heat also when there is no availability of solar energy. The solar thermal systems use collectors of concentrating type to generate higher temperatures, while the non-concentrating type are used to generate lower temperatures up to 100 C Solar radiation and solar angles Definitions on solar radiations and solar angles are given in this chapter. These are essential for comprehending the parameters used in the next chapter. [12] has been used as a reference for writing this chapter. 10

26 Theoretical background The input energy source for a solar collector is the incident solar radiation. The solar radiation arriving on earth first passes through the atmosphere. A part of it gets scattered, changes its direction, while the rest continues the same trajectory until it reaches some surface. Beam Radiation The solar radiation received from the sun without being scattered by the atmosphere. Diffuse Radiation The solar radiation received from the sun after its direction has been changed by scattering in the atmosphere. The rest is reflected by the ground or surrounding. Global Radiation Sum of beam and diffuse radiation incident on a surface. Irradiance G (W/m 2 ) The rate at which the radiant energy is incident on a surface per unit area of the surface G depends on the relative position of the surface to the direct radiation, described by the angle of incidence ( ) shown in Figure 2-1. Figure 2-1: Representation of solar angles [13] 11

27 Theoretical background Angle of Incidence or Incidence angle ( ) - the angle between the beam radiation on the surface and the normal to that surface. Sun Position angles: Zenith angle ( ) the angle between the vertical and the line of the sun, i.e. the angle of incidence of beam radiation on a horizontal surface. Solar altitude angle (h) complement of the zenith angle. Collector surface orientation angles: Solar azimuth angle ( ) - the angle between the south and the projection of the normal to the surface on the horizontal surface (west positive and east negative; ). Slope ( ) - angle between the plane of the surface and the horizontal surface. An understanding of the solar radiation and solar angles will be helpful in comprehending the application of these terminologies to solar thermal collectors Solar thermal collectors A solar thermal collector is a heat exchanger which absorbs solar irradiation on a dark surface area called absorber, and then transfers it to a fluid. The solar thermal collector is mounted with a slope ( ) to the horizontal surface and is oriented at an azimuth angle ( ) towards south in Earth s northern hemisphere and towards in North in Earth s southern hemisphere. The performance of the solar collector is determined by the incident solar radiation to the output delivered for an assigned collector absorber area. The output delivered is affected by the optical and thermal losses from the collector. Given below are definitions for the terminologies associated with collector area. The definitions for gross area, aperture area and absorber area are given according to ISO 9488:1999. It is important to know these definitions in order to realize the area which has to be used while calculating the effective heat gained by the collector module. The gross area is defined as the maximum projected area of a collector. Pipe connections and parts for mounting the collector are not included in gross area [14]. 12

28 Theoretical background The aperture area is defined as the maximum projected area where un-concentrated solar radiation enters the collector [14]. Collector frame is excluded. The absorber area is defined in two different categories, for collectors without and with reflector. For solar collectors without reflector it is the maximum projected area of the absorber, for collectors with reflector it is the area which is designed to absorb solar radiation [14]. The useful net heat gained by a solar thermal collector is dependent upon the net optical and thermal losses. The optical losses are the amount of incidence solar irradiation that is not transferred to the fluid. In general, solar radiation hitting a surface of a body will be reflected, absorbed or transmitted through. These are defined as reflexivity ( ), absorptivity ( ) and transmissivity ( ). A solar thermal collector is always designed to have the maximum absorptivity and transmissivity ( ) of incident solar irradiation through the collector surface to the absorber surface. In short, this factor determines the percentage of incident solar irradiation absorbed by the solar collector [15]. Hence, the total solar irradiation absorbed by the absorber (collector gain) is given by = ( ) = Where Total incident solar irradiation on the collector surface in W/m 2 Effective collector absorber area [m 2 ] η0 Optical efficiency [-] 0 is called the optical efficiency and depends on the incidence angle θ. Each collector is characterized by the parameter η 0,θ=0, which is the optical efficiency for null incidence angle and for other incidence angle is given by the function K (θ). τα, which characterizes the optical efficiency is a function of the incidence angle (θ) between the direct solar radiation and the normal to the collector surface, which means the optical losses changes with (θ). Hence, this must be corrected by a coefficient K (θ) called incidence angle modifier, described in Equation 2-2. The optical losses change with (θ) and when the (θ) becomes more shallow, the solar irradiation striking the collector plane gets reduced. The losses incurred whenever the collector is not oriented perpendicular to the rays of direct solar radiation are 13

29 Theoretical background called as cosine losses. To reduce these losses, collectors are tilted from the horizontal or are constantly moved by trackers in an attempt to keep the incident angle as close to ninety degrees as possible at all times. ( ) = ( ( )) ( ( = 0 )) 2-2 The thermal losses associated with the collector are due to conduction, convection and radiation. = The in the equation 2-3 is the useful heat transported by the heat transfer fluid and is given as, = (,, ) 2-4 Where, Mass flow rate of the heat transfer fluid [kg/h] Specific heat capacity of the heat transfer fluid [kj/kg. K], Collector fluid outlet temperature [K], Collector fluid inlet temperature [K] The in the equation 2-3 mainly depends upon the convection and radiation losses. The conduction losses are considerably small and depend on the thickness of the insulating material. Hence, the equation 2-3 is rewritten in an elaborated manner as = ( ) + E ( 4 4 ) 2-5 Where, Convection Radiation Convective heat loss coefficient [W/K] E Emissivity of the surface [-] Stefan Boltzmann constant [W/m 2.K 4 ] 14

30 Theoretical background Mean absorber temperature [K] Ambient temperature [K] Using the Equations 2-3, 2-4 & 2-5, the steady state collector efficiency can be derived as = = = = (,, ) 2-6 In simplified form, 0 = = = ( 0 ) 2-7 An expression for steady state efficiency equation as a function of difference in temperature between the absorber and the environment and the global irradiance on collector surface is [13]: =

31 Theoretical background Where 1 and 2 are heat loss coefficients. Figure 2-2 shows the collector efficiency curve, the graphical form of equation 2-8. The theoretical minimal losses in the collector is reached when = 0, when only the optical losses are considered. The higher the higher the thermal losses, while the lower the higher the thermal losses in comparison with the absorbed energy: therefore higher and lower causes a reduction in collector efficiency [16]. Figure 2-2: Collector efficiency curve [15] Apart from the optical and thermal losses from the collector, the other physical factors which can affect the net heat delivered by the collector are strong presence of wind, humidity and shading effects. Shading effect: The shadow cast on the collector may be due to trees, collector array in front, obstructions such as high raised buildings, mountains, window overhangs and wing walls. The sun s height, collector slope & azimuth determine the percentage of collector area which is shaded. The sun s height varies continuously throughout the year. During winter, the sun s height is lower and in case of high raised obstructions, the collector field can be partially/completely shaded, while in summer due to higher sun s height, the collector array may /may not be shaded. The following Figure 2-3 illustrates the continuously varying sun s height during the year. 16

32 Theoretical background Figure 2-3 : Sun's height during the year Collector technologies for process heat applications Given below in Figure 2-4 are the available collector technologies used in process heat applications for different working temperature levels. Figure 2-4: Collectors for process heat applications over the working temperature range [17] For lower temperature range applications, stationary non-concentrating collectors such as Flat plate and Evacuated Tube collectors are widely preferred. On the other hand, to gain higher temperatures concentrating collector technologies such as Parabolic trough, Fresnel collectors and Compound Parabolic Concentrators (CPC) 17

33 Theoretical background are used. Since, this thesis is more oriented towards low temperature process heat applications; the collector types which are most often used for this application are described below in detail. Flat Plate Collectors (FPC): Flat Plate Collectors are stationary collectors composed of pipes in which the heat transfer liquid flows, covered by an absorber usually coated with blackened surface in order to increase the energy gain. They are relatively cheap and simple for operation. They are simple for construction and need low maintenance. The components of a standard flat plate collector are indicated in Figure 2-5. Figure 2-5: Components of a standard Flat Plate Collector [18] 1. Selective coating 2. Absorber 3. Absorber pipe 4. Insulation 5. Rear panel 6. Header pipe 7. Frame 8. Transparent cover Good thermal conduction is needed for effectively transferring the heat generated on the absorber to the absorber pipes and finally to the heat carrier fluid of the solar 18

34 Theoretical background loop. Figure 2-6 shows the main loss mechanisms of a standard flat plate at nonperpendicular irradiance under operation conditions. The values are indicative and vary highly for different constructions, temperatures and locations. Figure 2-6: Simplified illustration of the loss mechanisms of a standard Flat Plate Collector [19] Evacuated Tube Collectors (ETC): Evacuated Tube Collectors normally have high thermal performance and can reach temperatures as high as 120 C 150 C. ETCs consist of glass vacuum -sealed tubes with the absorber surface located in the inner glass tube having different shapes. ETCs may be subdivided in two types: direct flow through (or water-inglass ) and heat pipe. The types are shown in Figure 2-7. Direct flow through ETCs consists of a set of glass tubes connected to a tank or shell. A larger diameter glass tube is used to surround each tube with the annular space between the tubes evacuated to reduce heat losses. The heat transfer liquid is heated as it circulates in the tubes [20]. On the other hand, a heat pipe evacuated tube collector consists of a heat pipe inside a vacuum-sealed tube and a small amount of working fluid inside it. The heat is transferred as latent heat energy by evaporating the working fluid in a heating zone and condensing the vapor in a cooling zone. The circulation is completed by the return flow of the condensate to the heating zone through the capillary structure which lines the inner wall of the container [21]. The tubes are mounted with the metal tips projecting into a manifold containing flowing water or 19

35 Theoretical background water glycol mix. Heat is transferred into the manifold and through circulation pipework it is used in heating and/ or hot water applications. The vacuum envelope reduces convection and conduction losses, so the collectors can operate at higher temperatures than Flat Plate Collectors (FPCs). Figure 2-7: Evacuated Tube Collector types Direct Flow type (Left) and Heat Pipe type (Right) [22] The Figure 2-8 below shows the efficiency curves for flat plate collectors and evacuated tube collectors, also indicating the process heat application working range. Figure 2-8: Comparison of characteristic collector efficiency curves [13] 20

36 Theoretical background System components In general, collectors for hot water supply are connected to storage tanks with/without auxiliary heaters, connected to the collector circuit with/without recirculation pumps, to heat exchangers, to pipes and controllers. It is important to know about these components as they are further discussed in the case studies in the next chapter. The collectors described in are used in solar hot water systems. A solar hot water system is said to be an active system when a pump is used for circulating the heat transfer fluid through the solar collectors and on the other hand, in a passive system (thermo-siphon systems) natural circulation of working fluid is used. The active solar water heating systems are broadly classified as direct circulation systems and indirect circulation systems. In direct circulation systems, the pump circulates the water through the collector and the water from the thermal storage tank is directly drained to the process and refilled. In an indirect circulation system, a pump recirculates the heat transfer fluid through the collector and a heat exchanger. Direct circulation systems can serve the purpose directly and can effectively transfer heat due to the absence of heat exchanger, while indirect circulation systems are used for freeze protection and protect the collector & piping from aggressive water [23]. The components used in solar hot water systems are described below in a short manner. Thermal Storage tanks: Solar energy is a time dependent energy resource and thermal storage is required for solar thermal systems because time and rate of energy generation do not always coincide with energy needs. Energy storage may be in the form of sensible heat of a fluid or solid medium. A thermal energy storage system is characterized based on its capacity per unit volume, the temperature over which it operates (i.e. the temperature at which heat is added or removed from the system), its associated components connected in the system, presence of controllers in the system and the cost. Based on the temperature difference between storage top and storage bottom, storage tanks are classified as mixed storage tank and stratified storage tank. In a completely mixed storage tank shown in Figure 2-9 (Left), the entire volume of the fluid attains a mean temperature. Hence, the liquid temperature entering the 21

37 Theoretical background collector is same as that of the storage tank. If the mixed storage tank is with a fixed volume, it can exhibit a certain degree of stratification in reality [12]. Stratified storages shown in Figure 2-9 (Right) have a temperature differential between the top and bottom of the storage. The temperatures are hot at the top and cold at the bottom because of the natural process. Stratification allows an optimal use of the storage with limited heat losses and in addition ensures that the collector inlet temperature is as low as possible. Hence, stratification is the key to maximize the collector efficiency, increase the system performance and reduce the auxiliary input [24]. Various stratifying devices are used such as addition of stratifying tube to internal heat exchangers which transfers heat as result of natural convection or a stratifying unit with different outlets where the water exits the unit at the height with approximately the same temperature in the storage tank, thus maximizing stratification [24]. Figure 2-9: Storage strategy- mixed (Left) and stratified (Right) [15] Pumps: Pumps are used in active solar systems for recirculation of the heat transfer fluid inside the system. Pumps are selected for their specific task in the circulation system, according to required flow rate, system pressure head, and power consumption. Typically, centrifugal pumps with motor are used and the capacity of the pump depends on the head it has to work against. Heat exchangers: Heat exchangers transfer heat from one medium to another while separating the media physically. Effective heat transfer depends on the temperature between the two media, the area of heat exchanger, the heat transfer medium and flow speed on both sides of the heat exchanger. In a solar thermal system, both internal and external heat exchangers are used. Internal heat exchangers are placed inside the thermal storage tanks and don t require lot of space. Straight tube and ribbed tube heat exchangers are used in this case and for effective heat transfer require large temperature differences between the medium. In case of external heat exchangers, they are placed externally and have high heat transfer with lower temperature differences between the hot and the cold medium. The typical heat 22

38 Theoretical background exchangers used are counter current type plate heat exchanger and shell and tube heat exchangers. External heat exchangers have high thermal losses to the surroundings, require more space and have an additional pump within the secondary circuit (circuit connected to storage tank) [24]. Controllers: Two types of control schemes are used to control the volumetric flow rate of the pumps, namely on-off control and proportional control. In an on-off controller, a decision is made to turn the circulating pumps on or off based on the differential temperature set between the hot fluid and the cold fluid. With a proportional controller, the pump speed is varied to maintain a specified temperature at the outlet [12]. The collector technology and the system components described above finds its applications in supplying process heat to the industry. Very large amounts of energy are required for low temperature process heat in the industry for diverse applications such as food drying, crop drying, in chemical processing, in cooking, washing utensils on large scale and many others. Temperatures required for these applications can range from above ambient temperature to those corresponding to low-pressure steam temperature [12]. The solar process heat systems are designed based on 1. the scale on which they are used 2. system configurations and controls needed to meet industrial requirements 3. integration of the solar energy supply system with the auxiliary source 4. the industrial process load The scale on which the systems are built depend upon the available space for system installation and the amount of energy to be delivered to the process by the solar thermal system. The system configurations are chosen based on the load schedule and load interface. The total load, load temperature, flow rate & pressure in the system, available space, and solar radiation data helps in selecting the collector technology [25]. The integration of solar energy supply system with the auxiliary source is done in two different ways namely, supply level integration & process level integration. Supply level integration can be described as supplementing the heat demand by providing it into the heat distribution network. The process level integration can be described as providing the heat at the point of need in the industrial process. Determining if a solar thermal system can be integrated at the supply level or process level depends on lots of factors. The temperature of heat and the amount of energy that needs to be delivered plays a role in this decision [26], [8]. 23

39 Theoretical background Figure 2-10 :Example of supply level and process level integration of solar thermal systems [26] The process level integration can be used for processes such as washing, cleaning, heating of industrial baths, hot air drying. The process level integration can support one part of the process in the industry and is useful the most when the heat requirement is restricted to one or two processes. The supply level integration of solar thermal systems is used in steam networks and hot water networks where the solar thermal system delivers pre-heated feed water to the boiler to reduce the energy consumption of the boiler [26]. Under suitable radiation and space conditions, steam can be generated by the solar collectors and fed into an existing steam network Solar process heat system configurations The solar process heat system configurations for low temperature applications described below have been referred from the literature [25] and are more suitable for hot climatic zones. Energy to be delivered to the process depends upon the type of collector, collector area & orientation, its fluid specific heat capacity, heat exchanger effectiveness, storage tank size, process load supply temperature, process load energy requirement, and the hours the process operates. Based on these parameters and to suit the low temperature process requirement, three types of configurations suitable for low temperature applications are explained below. 24

40 Theoretical background i. No - storage tank system Figure 2-11: An indirect solar hot water/hot air system [25] In the configuration shown in Figure 2-11, the pumps are turned on and the solar energy is collected from the collectors. The process side heat transfer fluid gains heat as it passes through the heat exchanger. While designing the system, the collector field has to be sized optimally to meet the process requirements. A back up boiler has to be connected in series with the solar collectors and should be operated in case of difficulties faced in meeting the process requirements. Due to the absence of the storage tank, this configuration is best suitable for 7 day-per-week, day time loads. The industrial plants adapting to this type of configuration should have process load during the complete daylight hours, otherwise the collectable energy is lost. ii. Mixed tank, recirculation System Figure 2-12: Mixed tank, recirculation system [25] In the configuration shown in Figure 2-12, the energy collected by the collectors is stored in a storage tank. The storage tank consists of two inlets and two outlets, one pair for each flow loop. The storage tank here is assumed to be completely mixed at one average temperature. From performance point of view, on a conservative note a 25

41 Theoretical background small amount of stratification can occur. Most often, the process side demands a constant temperature output. Hence, the presence of the mix valve helps in maintaining a fixed temperature on the process side. In order to have 24-hour per day load profiles, the collectors and the storage tanks have to be dimensioned accordingly. The storage tank temperature is not at constant temperature as it heats up and cools down during the day due to refilling with cold water; this depends upon the return line temperature which is a function of the load profile. Hence, the system based on this configuration needs to have optimal collector configuration & sizing, storage tank sizing in order to meet the process requirements. iii. Variable volume tank system Figure 2-13: Variable volume storage configuration [25] In the configuration shown in Figure 2-13, the heating the fluid is done through a single pass in the collector field and the water is not recirculated between the storage tank and the collector field. When the process load exists, the hot water is pumped from the hot water tank. The advantage of this configuration is that the collector is always supplied with a cold fluid and this can considerably increase the collector performance. It is one of the most efficient configurations which can cater to all load profiles day and night time shifts due to the presence of a storage tank. For efficient operations, during the design of the system it has to be taken into account that the volume of water heated during the day by the collectors and delivered to the storage tank should not exceed the volume of water the process needs for one day of operation. 2.2 System performance evaluation methodology It is important to evaluate the performance of the system in technical and financial aspects. This can be realized by modelling the system using a simulation tool during the planning phase and by setting up a monitoring system to measure the physical parameters at site during the execution phase. A comparison between the designed 26

42 Theoretical background value and the results from the physical measurements at site gives the installer details on the system performance, its operation and thereby helps in calculating the amount of fuel and fuel cost saved in reality vs. proposed savings. i. Simulation Methods: Simulations are numerical experiments and can give the same kinds of thermal performance information as physical experiments [12]. A simulation tool gives the opportunity to design the system for parametric studies and configuration studies. Understanding of the system dynamics and performance through simulations can further lead to improvement in parameters and configurations. The advantage of using a simulation tool is that they are quick, inexpensive and can provide information on each design variable of the system. ii. Physical Measurement using Monitoring system: The objective of establishing a monitoring system is to validate the output predictions, optimize the system operation, for fault detection and analysis, to communicate the results and build confidence in the technology. A monitoring system essentially comprises of a sensor unit, control and data storage unit, communication unit and power supply. For the monitoring of a solar thermal system the following components have to be installed and connected to the system. A sensor unit comprising of temperature sensors, flow sensors, radiation sensor and heat meters, a control and data storage unit containing a data logger system with an in-built communication device and a power supply unit with rechargeable batteries. It is important to design the monitoring system with an optimal instrumentation so that the basic and essential data can be collected at required measurement time intervals (time steps can range from 1 minute / 5 minutes or half an hour) along with lower investment costs and maintenance period. The following parameters are required to analyze the system performance of a solar thermal system. Fuel savings: The amount of conventional energy resource and the fuel costs saved per year due to the implementation of a solar system. Collector efficiency: The efficiency of the collector is calculated based on the collector heat output to the total solar energy input. System efficiency: The system efficiency is defined based on the heat output to the process to the total solar energy input. 27

43 Theoretical background Solar Fraction: It is the ratio of solar heat yield to the total energy requirement to heat the fluid. These parameters help to determine the technical performance as well as the amount of auxiliary heating fuel cost saved using a solar thermal system. The basic theoretical background provided in this chapter shall be useful in understanding the system and implementing the methodology to the case studies further described in Chapter 3. 28

44 3 SoPro India Monitored Case Studies As a part of the So-Pro India project, two Solar Heat for Industrial Processes (SHIP) plants have been selected and are being monitored by an online scientific real time monitoring system to evaluate their performance and system behavior. The SHIP plants identified for monitoring are located at 1. Synthokem Labs Limited. - Chemical plant in Hyderabad. 2. HP state Cooperative Milk Production Federation Limited (HP Dairy) Dairy plant in Rampur in the State Himachal Pradesh. In this chapter, a description on the components of the SHIP system and its working are discussed in detail. This basic understanding on the functioning of the system is necessary to realize the performance of the system described in the next chapter. 3.1 Case Study 1: Synthokem Labs Synthokem Labs Limited is a pharmaceutical company located at Sanathnagar, Hyderabad, India (Latitude N, Longitude E). The site receives an average global irradiation of 5.3 kwh/m 2. day (1953 kwh/m 2.a) [27]. The plant produces pharmaceutical ingredients and drug intermediates for the pharmaceutical industry. For the production process, steam of about 1.5 tonnes per hour at 110 C at 6-7 bar is required to heat the solvents and liquids, to remove the moisture content from the materials and to create vacuum in the steam jackets. To cater to this demand of steam, a non-pressurized solar hot water system has been commissioned in March 2009, which aims at preheating the feed water sent to the steam boiler [7]. The solar hot water system installed at Synthokem Labs is designed to deliver preheated boiler feed water during day and night. The system is setup with two collector fields, one to cater to the day demand and the other for the night demand. The fields are connected to storage tank and the hot water is withdrawn based on the demand. According to the literature presented in Chapter 2, the system configuration is a variable volume tank with a supply level integration method. Presented below are some of the photographs showing the collector fields and the storage tanks installed at Synthokem Labs. 29

45 SoPro India Monitored Case Studies Collector Field Storage tank Night demand Day demand Figure 3-1: Solar hot water system installed at Synthokem Labs [28] The hydraulic scheme of the solar hot water system at Synthokem Labs is shown in Figure 3-2. Figure 3-2: Hydraulic scheme of solar hot water system installed in Synthokem Labs [7], adapted to show energy balance regions 30

46 SoPro India Monitored Case Studies In order to calculate the energy gained and to have a quick understanding of the system, the system is assumed to be split into three energy balance regions which are described below. The notations used in Figure 3-2 have been used in the system description below. The operation of the plant described below is based on the conversation with the personnel at Synthokem Labs. A reference to this conversation is attached as a questionnaire in Annexe 1. The system is a non-pressurized system. The water to be heated is RO (Reverse Osmosis) water prepared by a RO facility of the company. The RO water is pumped from the non-pressurized RO water tank in two hot water storage tanks, circulated through the collectors and then used as preheated feeding water for the steam boiler. There are two collector circuits installed. Collector Loop Night : This solar loop consists of ten Evacuated Tube Collector (ETC) modules of m 2 total aperture area, oriented towards south, at a slope of 30, laid as 5 x 2 collectors in parallel (5 collector subfields in series, subfields of 2 collectors in parallel, layout of the field is indicated in Figure 3-3) and is connected to a storage tank (hot water tank 1 Tank Night ) of 5000 L capacity. The hot water tank 1 is filled with 4500 L of fresh water from the Reverse Osmosis (RO) fresh water tank during the morning hours from 8:30 am to 9:30 am by manually opening a valve. During the day, this water is recirculated inside the solar collector loop by operating the pump P2 manually between 9 am (start) and 5 pm (stop) time. In the evening from 8:30 pm onwards, this hot water is discharged into the storage tank Day (Hot water tank 2). The complete setup is located on the roof terrace as shown in Figure 3-1. Collector Loop Day : This solar loop consists of ten Evacuated Tube Collector modules (ETC) of m 2 total aperture area as well, oriented towards south, at a slope of 30, laid a s 2 x 4 collectors in parallel and 1 x 2 collectors in parallel connected in series (layout of the field is indicated in Figure 3-3) and is connected to a storage tank (hot water tank 2) of 5000 L capacity. The hot water tank 2 is filled with 3500L of fresh water from the RO fresh water tank during the morning hours from 7:30 am to 8:30 am by manually opening a valve. The hot water tank 2 has two outlets: one outlet connecting the solar collector loop and the other outlet is directly connected to the steam boiler. The water level in the hot water tank 2 drops continuously, since the water is directly drained to the load while the remaining water in this tank is continuously recirculated in the solar loop. In order to meet the demand, which is varying daily in dependence on the production of the company hot water tank 2 is refilled with 2500 L of fresh water during the day from 1 pm to 2 pm. 31

47 SoPro India Monitored Case Studies Water refill is done manually by checking the level of water in the tank with a water level indicator and opening the valve connected to the RO water tank. The solar collector loop is located on the roof, while the hot water tank 2 is located on the ground inside the building as shown in Figure 3-1. Process feeding: The preheated feed water from hot water tank 2 is intermittently pumped using the pump P4 or P5 into the steam boiler based on the demand. The pumps P4/P5 are automatically controlled by a controller based on the steam boiler demand. Pump P5 is kept as a spare pump and is used at times when maintenance work is carried out on Pump P4. These pumps can be subjected to wear and tear since they are operated throughout the day (24 hours) owing to the demand. According to installer specification, the hot water tank 2 is designed to meet the preheated boiler feed water demand during day time and hot water tank 1 to suffice the same during night time. (Hot water is discharged from tank 2 to tank 1 from 8:30 pm onwards to meet the preheated boiler feed water demand as indicated before). The common terms are frequently used in this thesis for description purpose. From Figure 3-2, Collector Field 1 Collector Loop Night Collector Field 2 Collector Loop Day Hot water tank 1 Tank Night Hot water tank 2 Tank Day 32

48 Figure 3-3: Collector field Layout of the solar hot water system installed at Synthokem Labs [28] 33

49 3.2 Case Study 2: HP Dairy Himachal Pradesh Diary plant is located at Duttnagar, Rampur, Himachal Pradesh [Latitude N Longitude E]. The site receives an average global irradiation of 4.8 kwh/m 2.day (1776 kwh/m 2.a) [27]. The plant processes between 34,000-40,000 L of milk per day. In the production process, steam of about 2.5 tonnes per hour at 110 C, 6 7 bar is required for processes such as Pasteurization, cream separation etc. [29]. To cater to this demand, a non-pressurized solar water heating plant for preheating the feed water to the steam boiler has been established in the year The system is designed to deliver about 6000 Liters per day of hot water at 60 C [7]. Figure 3-4 shows the solar hot water system installed at HP Dairy. According to the literature presented in Chapter 2, the system configuration is a mixed tank with a supply level integration method. The flat plate collector field (on the flat roof) and the storage tank (on the ground, right) of the solar hot water system can be viewed from photograph shown in Figure 3-4. Solar hot water system HP Dairy Collector Array Horizontal Storage tank with Plate heat exchanger Figure 3-4: Picture of the solar hot water system installed in HP Dairy [28] 34

50 SoPro India Monitored Case Studies The solar system is a non-pressurized system with 2 hydraulic loops separated by a heat exchanger. The solar collector loop, storage tank and the storage-to-process loop are connected and refilled by a make-up water tank on the flat roof, which is installed at the same height as the collectors. Therefore the storage tank is only under pressure from the static difference between the flat roof and the ground. The process loop is circulating water from the open feeding water tank on the flat roof and is therefore also only under static pressure. In order to calculate the energy gained and to have a quick understanding of the system operation, the system is assumed to be split into three energy balance regions which are described below. The notations used in Figure 3-5 have been used in the system description. Figure 3-5: Hydraulic scheme of solar hot water system installed at HP Dairy [7] Solar Collector Loop: This loop consists of 60 Flat Plate Collector (FPC) modules with a total gross area of 120 m 2, total aperture area of 111 m 2 oriented towards south east 30, at a slope of 45, laid as 5 collector fields in parallel. The layout of the field is attached in Figure 3-6. The collector field is connected to a horizontal storage tank (solar hot water tank) with a capacity of 5000 L and the water is recirculated inside this loop using the recirculation pumps P3 or P4. The solar collector loop differential temperature controller controls the on/off operation of the pump P3 or P4 based on the temperature difference (dt) between the collector outlet measured by temperature sensor T3 and the bottom of the storage tank measured by temperature sensor T2 at temperatures between 0 C and 10 C. The pump P3 / P4 is switched on by the controller when 0 C < dt<10 C. 35

51 SoPro India Monitored Case Studies Storage to Process Loop: The hot water from the solar hot water tank is forced into a plate heat exchanger using the pump P5 or P6. Inside the heat exchanger the hot water exchanges heat with the cold water pumped from the process loop and returns to the solar hot water tank. The make-up water is used to refill the tank if there are some water losses in the system due to pipe leakages or during maintenance period and provides the static pressure to the system. Process Loop: The boiler feed water tank has two inlets and two outlets. On one side, the boiler feed water tank is connected to the plate heat exchanger and on the other side, fresh water is pumped in using pump P7 and the outlet is connected to the steam boiler. The water from this tank is pumped using the pump P1 or P2 into the cold side of the plate heat exchanger, where it is pre-heated by the solar hot water and returns to the boiler feed water tank. The process loop differential controller controls the On/Off operation of the pumps P5/P6 and P2/P1 based on the temperature difference (dt) between the top of the storage tank measured by temperature sensor T4 and the fresh water inlet measured by temperature sensor T1 at temperatures between 0 C and 10 C. The pumps P5/P6 and P2/P1 are switched on by the controller when 0 C< dt< 10 C. From the boiler feed water tank, preheated hot water is sent to the steam boiler based on the demand. 36

52 Figure 3-6: Collector field Layout of the solar hot water system installed at HP Dairy (self drawn) [30] 37

53 4 Assessment of monitored data In this chapter, the purpose of monitoring a solar thermal system and the components essential for setting up monitoring system are explained. The explanation is specific to the monitoring system setup at both the case studies described in Chapter 3. Further, in this chapter the methodology followed for data processing and assessment of the data obtained from the monitoring system is explained. The performance of the solar thermal system based on the monitored data is indicated as results. The following points explain the need for installing a scientific monitoring system in a SHIP plant. 1. Identification of detailed system behavior from measured data 2. Evaluating the efficiency of the SHIP plant in operation 3. As a fault diagnostic tool and to put the system back into operation 4. Enabling to calculate the fuel savings The above mentioned points 1 to 3 help in analyzing and optimizing the system design and operation which is one of the main objectives of this thesis. This effort can help in realizing a better performance of the system, thereby saving the additional fuel cost. It is one of the aim of this SoPro India project, to propose a low cost monitoring system which can collect the basic and essential data from the solar thermal system to help the system owner in monitoring the effective functioning of the solar hot water system. To develop a deeper understanding on the challenges of monitoring, in a first step an online scientific monitoring system has been established at both the SHIP plants discussed in Chapter 3. An online scientific monitoring system consists of heat meters coupled with temperature sensors and flow rate sensors, pryanometer, and a data logger system connected to the modem (Online communication device). The output data are logged into the data logger system and transmitted via modem online to the internet server. 4.1 Online scientific integrated monitoring system The details regarding an online scientific monitoring system have been explained in the introduction of Chapter 4. The term integrated monitoring system is additionally coined here to indicate that the sensors are integrated to the SHIP system and not as a clamp on type system. A brief description on the components involved and the 38

54 Assessment of monitored data working principle of the online monitoring system integrated to the SHIP plants is described below in Figure 4-1. Figure 4-1: Heat Meter components [self-drawn] TEMPERATURE SENSOR: The measurement of temperature is done using Pt-500 sensor,4-wire Class B type. It is a resistive temperature detector and sends an analog signal to the heat meter every 4 seconds. FLOW RATE SENSOR: The measurement is done using an ultrasonic flow rate sensor, which sends ultrasonic signals downstream and upstream. The difference in time taken by these waves is measured and is directly proportional to the flow through the meter. The ultrasonic flow sensor sends an impulse signal to the heat meter every second. HEAT METER: It is essentially a microprocessor where the data from the sensors are retrieved and stored at different address points. The filters present inside the heat meter convert the analog signal from the temperature sensor into a digital signal. The fluid volume which is counted as an impulse signal is converted into a digital signal. The heat meter calculates the heat gain every 4 seconds with the temperature and the average (of 4 seconds) mass flow rate available. The average value of every 15 seconds of heat gain is stored in the Heat Meter. M-Bus (Meter Bus) system is a common transmission line (two wire connecting cable) which connects the MASTER and the SLAVE. Master is essentially an embedded system/personal Computer (PC) with a data logger system and the SLAVE is an end equipment meter, in this case it s a Heat Meter. The transfer of data occurs through the bus line by means of voltage shifts. These M-Bus signals are converted to signals required for RS232 interface by a local repeater connected to the embedded system. RS232 serial port in the PC is further connected to modem 39

55 Assessment of monitored data and other data storage devices [31]. The data is retrieved from the Slave unit at the end of 1 minute and transmitted to the Master. Pyranometer with an amplifier is directly connected to the data logger system and the measurement data interval is every second. One minute average value is logged into the data logger system. The following provides details on the manufacturer, model number & accuracy of the components described above. Table 4-1: Components of a scientific monitoring system indicating the Manufacturer & Model Number Component Manufacturer & Model Accuracy Temperature Temperature sensor - Pt500, 4 - ±0.15% * temperature ±0.02 C sensor wire, Class B [32] Flowrate sensor Ultrasonic flow sensor ±1% [33] Heat meter ELSTER vital connections (Heat - meter with sensors as a complete package) custom made M-Bus system Bär Industrie Elektrotechnik GmbH - Pyranometer Kipp & Zonen SMP3-A Non-linearity <1% 4.2 Monitored Data Processing After establishing the monitoring system, the next step is to acquire the data and process it. Processing of the acquired data from online scientific monitoring system is important for evaluating the performance of the monitored solar hot water systems in both the case studies. Evaluating this data further helps in optimizing the system configuration and performance. The flow chart in Figure 4-2 indicates the general steps involved in data processing [34]. 40

56 Assessment of monitored data Data Acquistion Data validation and filtering of raw data measurements Data reconciliation of filtered measurements Result verfication Result storage Figure 4-2: Steps involved in data processing [34] As the first step, data needs to be acquired. The monitored data is made available on the server by online synchronization with the data logger system located at the site. From the server, the data is downloaded at the end of the day and is stored in a database. The data thus obtained constitutes the raw data file. This raw data file acquired has a file extension of.dat and contains information on temperature, volume flow rate and the heat gain values from each Heat Meter on a minute basis. The sub chapter below describes the methodology for processing the raw data file into a final processed file. This final processed information can be used later on to analyze monitored system performance Data processing The data processing steps involve 1. Some general steps/actions to be followed when the raw data file is obtained for the first time after system installation or during regular maintenance check 2. A specified routine / program which have to be run every day in order to receive the final data file. The general steps which have to be followed while processing the raw data file obtained for the first time after installation / as maintenance check are as follows: 1. Hardware: Check for possible faults in the system installation such as placement and functioning of sensors, transmission of data from the sensor to the specified address in the microprocessor of the Heat Meter and to the data logger 41

57 Assessment of monitored data system. The possible faults that can occur in the monitoring system and their reasons are listed out in Annexe Software: Check the configuration file, whether the data from the sensors match the address points in the microprocessor of the Heat Meter with the units required. The Heat Meter manufacturer issues a table for each parameter with SI units with different decimal points (for example, for volumetric flow rate as 0.1 m 3 /h, 0.01 m 3 /h, and m 3/h so on). For each decimal point, a different address point in the microprocessor of the heat meter is specified by the manufacturer in the specification sheet. In case of any discrepancy, find the appropriate correction factor for units and apply to the existing raw files. Notify the changes to be done in the software with correct address points to avoid such errors in raw data file in future. For further information, specification sheet given by the installer with the heat meter address points and a table containing the heat meter and the sensors installed with their identifiers and units, correction factor (if required) for both the case studies are indicated in Annexe 3 and Annexe 4. The major step of data processing is a specified routine / program which has to be run every day in order to receive the final processed file. The following flow chart in Figure 4-3 shows the general check - step by step algorithm on how the raw data file is processed into a corrected raw data file. 42

58 Assessment of monitored data Figure 4-3: Raw data file to a corrected raw data file processing steps 43

59 Assessment of monitored data The reasons for the unavailability of data indicated as missing values in Figure 4-3 are explained in detail in Annexe 2. The following flow chart in Figure 4-4 illustrates how the corrected raw data file is further processed to obtain the final data file. The final data file stored in a database is used for analyzing the system behavior and performance. Figure 4-4: Data processing steps for validation Data availability Unexpected problems can cause stop the functioning of the monitoring system and lead to days with missing data. The possible faults that can occur are listed under the column Fault in Annexe 2. The Table 4-2 gives a glimpse of the number of days of data available for both the case studies. 44

60 Assessment of monitored data Table 4-2: Data availability - Synthokem Labs and HP Dairy Month Synthokem Labs HP Dairy Oct Nov Dec Jan Feb Mar Case study 1: Synthokem Labs The data processing steps have been followed and the final data is evaluated to analyze the system performance. In order to do that, the system with the monitoring scheme and the sensors installed are described below for the ease of understanding of the system System description with monitoring scheme The integrated online monitoring system which has been installed is described below with the monitoring scheme showing the sensor type and position. For the ease of evaluating the system performance, the system has been segregated into different energy balance regions. Each energy balance region consists of Heat Meters connected to the temperature sensors and flowrate sensors are indicated below in the following Figure 4-5. The basic understanding of Figure 4-5 helps in figuring the position of the sensors mentioned in Table

61 Assessment of monitored data Figure 4-5: Monitoring scheme of solar hot water plant in Synthokem Labs From Figure 4-5, T Temperature sensor gives the temperature in C F Flow rate sensor gives the volumetric flow rate in m 3 /h G Pyranometer gives the Global solar irradiation on the tilted plane (30 ) in W/m 2 HC Heat Counter gives the energy gain in kwh The output from these sensors is measured and logged into the data logger system with a time interval of 1 minute. Table 4-3: Monitoring scheme Synthokem Labs - Sensor and its Position Energy Balance Region Heat Counter [HC] Position T1 Collector Inlet Pipe (cold) Collector Loop Day HC1 T2 Collector Outlet Pipe (hot) F1 Collector Inlet Pipe 46

62 Assessment of monitored data T3 Collector Inlet Pipe (cold) Collector Loop Night HC2 T4 Collector Outlet Pipe (hot) F2 Collector Inlet Pipe T5 Pipe to boiler from hot water tank 2 Process Loop HC3 T6 Pipe fresh water inlet line from RO tank F3 Pipe to boiler from hot water tank Results The performance of the monitored SHIP system is evaluated in this part of the chapter. The physical parameters which are monitored are denoted by identifiers and are listed below in Table 4-4. Table 4-4: Parameter identifier table - Synthokem Labs Parameter Sensor Identifier Unit Collector loop Day Mass flow rate F1 m_d_coll kg/h Collector loop Day - Outlet Temperature T2 T_D_out C Collector loop Day - Inlet Temperature T1 T_D_in C Collector loop Day Heat Gain HC1 Q_coll,D,loop kwh Collector loop Night Mass flow rate F2 m_n_coll kg/h Collector loop Night - Outlet Temperature T4 T_N_out C Collector loop Night - Inlet Temperature T3 T_N_in C Collector loop Night Heat Gain HC2 Q_ coll,n,loop kwh Process loop - Mass flow rate F3 m_pro kg/h Process loop Outlet temperature T6 T_pro_out C Process loop Fresh water inlet T5 T_fresh water_in temperature C Process loop Heat Gain HC3 Q_pro,loop kwh Total Global Irradiation (30 degrees) Sol_Irr W/m 2 Total Global Irradiation (30 degrees) during Pump operation E_Sol kwh 47

63 Assessment of monitored data Operational behaviour identification As the first step towards finding the system behaviour and its performance, it is important to understand how the plant is being operated. The method of operation of the solar hot water system has been already discussed in Chapter 3. With the help of the measurement data and by communicating with the personnel in Synthokem Labs given in Annexe 1, the operational strategy followed is jotted down. The described system has been monitored from 17 th October 2014 till 21 st February 2015 with a measurement interval of 1 minute. The operational behaviour is evaluated from the data which is available continuously from 6 th December 2014 to 21 st February Daily operation schedule: The solar hot water system running in Synthokem Labs is completely manually controlled, the different start and stop time of the collector loop for two days is indicated in Figure 4-6. The schedule is extracted from the mass flow rate measurement data of Collector loop Day. Figure 4-6: Operational behavior (Start and Stop time) of the solar hot water system in Synthokem Labs Fresh water fill in Tank Day & Night : Before the start of the solar collector loop pumps, the hot water tanks Day & Night are filled with RO fresh water in the morning hours between 7:30 am 8:30 am & 8:30 am - 9:30 am with 3500 L & 4500 L respectively as communicated by the 48

64 Assessment of monitored data personnel. The temperature of this fresh water inlet is monitored as a reference temperature for the process loop heat counter. The maximum volume of water level in the tanks can be assumed to be with 5000 L, but the actual water level cannot be concluded due to the absence of water level sensors in each tank. Figure 4-7 indicates the volume of water in Tank Night with the hourly values. Figure 4-8 indicates the volume of water filled in Tank Day with the hourly values. In Figure 4-7 and Figure 4-8, the solid bars in blue indicate the volume of water contained in the tank and the solid bars in green indicate the fresh water fill and refill volume into the tank. The bars in red with void space indicate the volume of water discharged from the tank. Figure 4-7: Volume of water in Tank 'Night' Synthokem Labs Figure 4-8: Volume of water in Tank 'Day' Synthokem Labs 49

65 Assessment of monitored data Fresh water refill in Tank Day : From the Tank Day, hot water is continuously discharged to the process side according to the feed water demand and the remaining water is continuously recirculated into the solar collector loop Day. Figure 4-8 indicates the volume of hot water discharged to process every hour. Owing to the direct discharge, the water level in tank Day decreases rapidly and to meet the demand is supposed to be replenished with fresh water during the day between 1 pm - 2 pm with a volume of 2500 L according to the personnel. But it can be found in the Figure 4-6 that the time of replenishment varies every day. The refilling volume is not monitored and hence it is not exactly known. From Figure 4-8, it is also clear that the refill volume in tank Day cannot suffice the process demand and an extra volume of fresh water needs to be filled in during the night. Figure 4-9 shows the different refilling time of fresh water into the tank day during each day of the month - January This refill can considerably affect the collector inlet temperature in Collector loop Day. Lowering the temperature of the collector inlet at the mid noon can considerably decrease the heat losses from the collector and increase the collector efficiency. Figure 4-9: Fresh water refill time identified from the inlet collector temperature Collector Loop Day of measurement data for the month of January 2015 Synthokem Labs Tank Night to Day discharge: The Collector Loop Night constituting the collector and hot water tank 1, functions as a closed loop recirculation during day time. In the evening between 4 pm - 5 pm, the solar hot water Collector Loop pumps are turned 50

66 Assessment of monitored data off. The hot water of 4500 L is discharged from tank Night to tank Day from 8:30 pm onwards. Since, this operation is carried out by the same pump which recirculates the water in Collector loop Night, the same fixed mass flow rate is considered. The temperature and the flow rate during this operation are not monitored, hence the actual time and volume transferred is unknown. Figure 4-7 indicates the discharge volume & time as communicated by the personnel. Plant shutdowns: From the measurement data, it could be concluded that the solar hot water plant is completely shut down during public holidays and there exists a trend that on every Sunday the collector loop Night is not operated. Every alternate week, both Saturday and Sunday the plant is not operated. There are days in which only one of the collector loops is being operated. But this operational strategy is not fixed, as it could be seen from the measured data that even during weekdays the plant is shutdown/not operated. There can several reasons which could abstain the plant operator from following a fixed operational strategy, such as maintenance of the plant, decrease in demand from the production, absence of man power etc. The number of days in a month when the hot water plant is operated is depicted in Table 4-5. Table 4-5: Number of days in a month the collector loop 'Day' and 'Night' are operated - Synthokem Labs Month Number of days in the month Number of days Collector loop Day operated Number of days Collector loop Night operated Dec * Jan Feb ** *(26 days - data available) **(21 days - data available) Process demand: According to the personnel, the tanks are filled with 5000 L each on the starting day of operation (first time after installation) and from then on, tank Night is filled with 4500 L and tank Day is filled with 3500 L and refilled with 2500 L every day. This accounts to a total of L per day. The volume of fresh water input into the tanks for a particular month with the operational days taken into account is indicated in Table 4-6. On the other hand, the demand to the process varies each day. Volume discharged to the process monthly values are indicated in Table 4-6. Hence, it is clear from the column % deviation of volume in Table 4-6 that an additional volume of water has to be pumped into the system, in order to meet the demand. 51

67 Table 4-6: Total volume of fresh water filled in the tanks (Predicted vs. Actual) Assessment of monitored data Month Volume of fresh water input (predicted) Volume discharged to Process in actual (from measurement data) Difference - volume required Predicted vs. Actual % deviation of volume L L L % *Dec ,3% Jan ,0% ** Feb ,8% *(26 days - data available) **(21 days - data available) System behaviour analysis After identifying the operational profile of the SHIP plant, it is important to analyse how the system behaves and this can be done with the help of the measured collector inlet and outlet temperature data at a specified mass flow rate. This is an indication of the daily performance of the system. In order to analyse the temperature, the days have been characterised into three different days (assumed): the days with a solar irradiation greater than 750 W/m 2 during the peak operating hours are considered as sunny days and the days which have solar irradiation between W/m 2 during the peak operational hours are considered as intermittently cloudy days and those less than 400 W/m 2 as cloudy days. The peak operational hours are considered between 11 pm 3:30 pm, since the collectors are facing south (azimuth 0 ) and the solar noon time is between 13:00 and for the three months of monitored data considered. Collector Loop Day and Night : For the above categorised three characteristic days, the collector outlet and mean absorber temperatures have been extracted from the measurement data for both Collector Loop Day and Night. The Table 4-7 below indicates the values where the days have been sorted from the whole period of measurement data for three characteristic days and for each parameter, the average during the peak operational hours considered is calculated. Out of this calculated average for each parameter, the average maximum (minimum value) and the average maximum (maximum value) are indicated as a variation range in the Table 4-7. The ambient temperature is not indicted in Table 4-7 below since it is not measured at site. 52

68 Assessment of monitored data Table 4-7 : Daily performance of the collector system Parameter Identifier Unit Variation Range Overcast Sunny Intermittently day day Cloudy day Solar irradiation Sol_Irr W/m 2 <400 > Collector Loop Day Maximum collector outlet temperature T_D_out C Mean absorber temperature T_D_abs C Average Heat gain Q_coll,D,loop kwh/d Collector Loop Night Maximum collector outlet Not T_N_out C temperature available Mean absorber Not T_N_abs C temperature available Average Heat gain Q_coll,N,loop kwh/d For the Collector Loop Day the mass flow rate is approximately 1260 kg/h and that of Collector Loop Night is 1560 kg/h. The area of both the collector fields is m 2. Hence, the collector gain from both the collector fields is expected to be nearly the same. But, it can be seen from the Table 4-7, the average heat gained in the Collector Loop Night is greater than the Collector Loop Day. This is due to the reason that the last row of collector array in the Collector Loop Day is shaded due to an obstruction (building) in the front as shown in Figure Shading on the collector array due to obstruction Figure 4-10: Shading effect on Collector Loop 'Day' due to obstruction (building) 53

69 Assessment of monitored data As it has been discussed in Chapter 2, that the sun s height varies during the course of the year and this has considerable effects on shading the collector field by an obstruction. Since, the measurement data available is for three winter months when the sun s height is considerably lower; this shading effect on the last array of collector (2 collector modules) predominantly affects the collector gain. Apart from this, from the operational point of view, on an analysis conducted on the measurement data, it was quite clear that the collector loop Night is not being operated on cloudy days. Process side: The process outlet temperature is the same as the collector inlet temperature of the collector loop Day, since both the outlets are at the bottom of the tank Day. The tank Day is a completely mixed tank (not ideally mixed at it depends on the volume of water contained in the tank owing to the different discharge rates to the process). The process outlet temperature cannot be indicated as a variation range (during the operational hours assumed) due to the different fresh water refilling time and the volume refilled. Hence, three days from the measurement data have been identified which fall under the characteristic day categories specified above in this sub chapter. Figure 4-11: System behavior analysis of Process Loop Synthokem Labs Figure 4-11 indicates that on a sunny day, the process outlet temperature can go as high as 45 C during the day and during the night as high as 40 C. This is a clear 54

70 Assessment of monitored data disadvantage of this type of system configuration as amount of the energy gained in the collector loop Night cannot be completely utilized during night time due to the transfer losses from tank Night to tank Day and the storage losses from the tanks Performance analysis With an understanding of the operational profile and the system behaviour of the plant, the performance of the system is evaluated for the data which is available continuously from 6 th Dec 2014 to 21 st February The performance analysis of the system is done based on the following equations stated below and is specific for this case study in alignment with the general definitions stated in Chapter 2. Net Collector Loop gain in kwh [Q_coll,loop ]: Q_coll,loop = Q_coll,D,loop + Q_coll,N,loop,, = _ ( _ _ ) In HC1,,, is calculated as,, = 1 ( 2 1),, = _ ( _ _ ) In HC2,,, is calculated as,, = 2 ( 4 3) 4-5 Net System gain in kwh [Q_pro,loop ]: Q_pro,loop = Q_coll,loop Q_loss, = ( _ ( _ ) In HC3,, is calculated as, = 3 ( 6 ( )) 4-8 Collector Loop efficiency in % [η CL ]: η CL = Heat delivered by the collector loop 'Day' and 'Night' (Q_coll,loop) Solar Irradiation on tilted aperture area during pump operation (E_sol)

71 Assessment of monitored data System efficiency in % [η system ]: η system = (Q_pro,loop) (E_sol) Useful heat delivered to Process = Solar Irradiation on tilted aperture area during pump operation 4-10 Net thermal losses in the system in % [q loss ]: Utilization Ratio in %: Utilization Ratio = qloss = Q_loss Q_coll,loop Total useful heat delivered to Process Total solar Irradiation on tilted aperture area Considerations in heat gain calculation: The fresh water inlet into the tanks is not controlled based on the water withdrawn to the process. The plant is operated with specific fill and refill time of fresh water into the tanks during the day. Hence, the instantaneous temperature at every time step from the fresh water inlet temperature sensor (T5) cannot be taken into account for the heat gain calculation in the process loop. From Chapter 3.1, it is known that the storage tanks Day and Night are filled with fresh water once in the morning between 7:30 am and 9:30 am, and tank Day is refilled during the day between 1 pm and 2 pm. Hence for the heat gain calculation,**t_fresh water_in (measurement data from Temperature sensor T5) is taken and an average temperature from the measurement data between the time interval 7:30 am to 9:30 am (water filling time in storage tank Day and Night ) is considered for the heat gain calculation for the time period from 7:30 am till 1:00 pm & also from 8:30 pm to next day 7:30 am. The latter time interval has the same consideration because the tank Night is discharged into tank Day, but the heat gained is from the fresh water filled in the morning. For the time period between 1 pm and 8:30 pm, the average temperature from the measurement data between the time interval 1 pm to 2 pm is considered (water refilling time in storage tank Day ). The water from the tank Night is not completely discharged in to tank Day during night. Only 4500 Liters of hot water is being transferred. Hence, 500 Liters of hot water (10% of the volume of tank Night ) remains unused in the storage tank Night. This has been taken into account while calculating the system gain during night time. 56

72 Assessment of monitored data Performance of the system: The performance of the system is evaluated from the available measurement data and is presented in Table 4-8 and in the Figure The system analyzed has a collector efficiency of 28% and a system efficiency of 23% for the whole time period of 3 months. The collector and system efficiencies month-wise are stated below in Table 4-8. The specific monthly yield for the collector and the system are shown in Figure Table 4-8 : Performance analysis of the monitored hot water system at Synthokem labs Parameter Unit Measured Value *Dec 14 Jan 15 **Feb 15 Total 3 months Total Global irradiation (30 ) kwh Total Global irradiation (30 ) during pump operation kwh Net Collector Loop gain kwh Net System gain kwh Total Collector efficiency % 28% 27% 30% 28% Collector efficiency Day % 24.5% 24.8% 25.9% 24.9% Collector efficiency Night % 33.9% 29.8% 32.4% 31.7% System efficiency % 27% 21% 23% 23% Net thermal losses % 4% 21% 24% 16% Utilization Ratio % 17% 14% 14% 15% *December 26 days **February 21 days 57

73 Assessment of monitored data Figure 4-12: Specific energy yield of the system - Synthokem Labs The collector efficiencies of Collector Loop Night is greater than Day by 21% due to the shading effect on the Collector Loop Day (2 out of 10 collector module in Collector Loop Day is shaded) as discussed in System behavior chapter. The net thermal losses in the system account for 16% when the whole time period is considered. The net losses are calculated as losses between the heat gained in Collector Loop and the heat delivered to Process Loop, while the proper way is to calculate the losses between the heat gained by the collector itself and the heat delivered at the end to the process. Since, the sensors are placed on the inlet and outlet pipes of collector, this consideration had to be made. From Table 4-8, it can be noticed that the Net thermal losses of the system for the month of December 2014 is considerably less when compared to January 2015 & February One of the reasons known is due to huge volume of water being pumped into the system during the month of December as discussed in the operational behavior. From Table 4-8, it can be found that the utilization ratio of the system is 34 % (for Total 3 months) lower than the system efficiency. Manual operation with reduced operational hours of the solar hot water system has led to a lower utilization ratio. 58

74 Assessment of monitored data This indicates the necessity for the installation of an ON/OFF controller in the solar loop through which the pump starts as soon as the critical solar irradiation (the minimum solar irradiation required to have an energy gain through the collector) is attained. 4.4 Case study 2: HP Dairy In the similar manner as the case study above, the data processing steps have been followed on the raw data obtained from HP Dairy data logger system to obtain the final processed file. The final data is evaluated to analyze the system performance. In order to do that, the system with the monitoring scheme and the sensors installed are described below for the ease of understanding of the system System description with monitoring scheme As stated for the case study before, this system has also been segregated into different identified energy balance regions. Each energy balance region consists of Heat Meters connected to the temperature sensors and flowrate sensors are indicated below in the Figure The basic understanding of Figure 4-13 helps in figuring the position of the sensors mentioned in Table 4-9. Figure 4-13: Monitoring scheme of solar hot water plant in HP Dairy From Figure 4-13, T Temperature sensor gives the temperature in C F Flow rate sensor gives the volumetric flow rate in m 3 /h 59

75 Assessment of monitored data G Pyranometer gives Global Irradiation on tilted plane (45 ) in W/m 2 HC Heat Counter gives the energy gain in kwh The output from these sensors are measured and logged into a data logger system with a time interval of 1 minute. Table 4-9 Monitoring scheme - HP Dairy - Sensor type and position Energy Balance Region Heat Counter [HC] Position T1 Collector Inlet Pipe (cold) Collector Loop HC1 T2 Collector Outlet Pipe (hot) F1 Collector Inlet Pipe T3 Return line pipe - heat exchanger to storage tank (cold) Storage to Process loop HC2 T4 Feed line pipe - Storage tank to heat exchanger (hot) F2 Return line pipe - heat exchanger to storage tank T5 Feed line pipe Boiler feed water tank to heat exchanger (cold) Process Loop HC3 T6 Return line pipe - heat exchanger to boiler feed water tank (hot) F3 Feed line pipe - heat exchanger to boiler feed water tank Results From the monitored data the performance of this system is evaluated. The physical parameters which are monitored are denoted by identifiers and they are listed below in Table

76 Assessment of monitored data Table 4-10: Parameter identifier table - HP dairy Parameter Sensor Identifier Unit Collector Loop - Mass flow rate F1 m_coll kg/h Collector Loop - Outlet temperature T2 T_coll_out C Collector Loop - Inlet temperature T1 T_coll_in C Collector Loop - Heat gain HC1 Q_coll kwh Storage to Process Loop - Mass flow rate F2 m_s,p kg/h Storage to Process Loop - Outlet T_s,p_out T4 temperature C Storage to Process Loop - Inlet T_s,p_in T3 temperature C Storage to Process Loop - Heat gain HC2 Q_s,p kwh Process Loop - Mass flow rate F3 m_pro kg/h Process Loop - Outlet temperature T6 T_pro_out C Process Loop - Inlet temperature T5 T_pro_in C Process Loop - Heat gain HC3 Q_pro kwh Solar Irradiation on tilted aperture area (45 ) Sol_Irr W/m 2 Solar Irradiation on tilted aperture area (45 ) during pump operation E_Sol kwh Operational behaviour identification The simple operational manner of the plant has been already discussed in Chapter 4.4. With the help of the continuously available measurement data from 15 th October 2014 till 31 st December 2014 & few weeks of measurement data which is available from the months of January 2015, February 2015 & March 2015, the operational strategy of the plant has been derived and described below in detail. The measurement data time interval is 1 minute. Daily operation schedule: The solar hot water system in HP dairy is operated automatically by a controller. The presence of differential temperature controllers in Collector Loop and the Process Loop ensures the continuous operation of the plant by switching ON and OFF the pump under the condition that the required temperature difference exists between the hot and cold fluid at required position. The operation of Collector Loop and Process Loop differential loop temperature controller is described below. 61

77 Assessment of monitored data Collector loop differential temperature controller: As it can be seen from Figure 4-14, the differential temperature controller starts the pump when the temperature difference between the collector outlet and the bottom of the storage tank lies between 0 C and 10 C. For all the three days selected from three different months out of the measurement data, this characteristic control strategy for the collector loop pump is observed. In Figure 4-14, the global solar irradiation for the selected three days is presented. It can be noticed that, the controller starts the pump when a critical irradiation is reached. This critical solar irradiation is the minimum amount of solar irradiation required to raise the temperature of the heat transfer fluid and thus brings in a temperature difference between the collector outlet and the bottom of the storage tank. The critical irradiation value couldn t be calculated since the collector parameters are not available with the installer. Figure 4-14: Functioning of differential temperature controller in collector loop - HP Dairy Process Loop differential temperature controller: According to the installer, the differential temperature controller switches on the pumps in the Storage to Process Loop and in the Process Loop when the temperature difference between the top of the storage tank and the fresh water inlet lies between 0 C and 10 C. From the Figure 4-15, it is seen that the pumps in both the loops are switched ON continuously with a temperature difference between 0 C and 20 C and above it. This contradicts to the installer specifications on the lower and upper limit temperature of the controller. Despite this contradiction, it is a clear advantage that 62

78 Assessment of monitored data the operation of pumps continuously in this scenario leads to the extraction of each unit of energy gained in the Process Loop. Figure 4-15: Functioning of differential temperature controller in Storage to Process loop & Process loop - HP Dairy Working of electric heaters inside storage tank: From the available measurement data, a characteristic cloudy day (25 th February 2015) is chosen. The maximum global solar irradiation during this day is 220 W/m 2. The Figure 4-16 shows the inlet and outlet temperatures, mass flow rate of all the loops (energy balance regions) for the above specified day. It has been also taken into account that the energy stored in the storage tanks in not carried over from the day before. On viewing the measurement data of the day before (24 th February 2015), it is a moderately cloudy day with a maximum solar irradiation of 640 W/m 2 and the energy gain during the day from the Collector Loop was being completely delivered to the process on the same day. For the characteristic cloudy day, Figure 4-16 shows the outlet temperature of all the loops. For the day considered, it can be seen that even though there is no collector gain, there is heat delivered from the Storage to Process Loop to the Process Loop. It can be seen from Figure 4-16 the outlet temperature of the storage tank to the process starts at 40 C and gradually decreases to 30 C at the end of the day, under the following physical conditions 1. The pumps on the Storage to Process & Process Loop are continuous operating based on the demand 2. The ambient temperature 63

79 Assessment of monitored data outside is 15 C 17 C (taken from the collector inlet temperature on pipes). This strongly indicates the presence of electric heaters inside the storage tank and the operating it during the cloudy days to supply the required temperature level for the process. The installers have specified in the operation manual, the presence of 3 electric heaters of 4 kw capacities with a thermostat. Figure 4-16: Electric heaters inside the storage tank operated on cloudy days to suffice the demand HP Dairy Plant shutdowns: The solar hot water plant is continuously operating as it is automatically controlled. Shutting down of the entire plant on the verge of public holidays or weekends couldn t be observed from the measurement data but on the other hand, lower demand/ load profile could be seen System behaviour analysis As indicated in the previous case study, the system behaviour analysis indicates the daily performance of the system. The same measurement period mentioned above in the identifying the operational behaviour of the plant is used here for system behaviour analysis. In order to analyse the temperature, the days have been characterised into three different days (assumed): the days with a solar irradiation greater than 750 W/m 2 64

80 Assessment of monitored data during the plant operating hours are considered as sunny days and the days which have solar irradiation between W/m 2 are considered as intermittently cloudy days and those less than 400 W/m 2 as cloudy days. Collector Loop: For the above categorised three characteristic days, the collector outlet and mean absorber temperatures have been extracted from the measurement data. The Table 4-11 below indicates the values where the days have been sorted from the whole period of measurement data for three characteristic days and for each parameter, the average during the plant operational hours is calculated. Out of this calculated average for each parameter, the average maximum (minimum value) and the average maximum (maximum value) are indicated as a variation range in the Table From the measurement data, it could be seen the sunny days indicated below constitute the days in the month of October and that of November & December fall into the category of intermittently cloudy day. Few days can be exceptional in this case. Table 4-11: Daily performance of Collector Loop HP Dairy Parameter Unit Overcast Sunny Intermittently day day Cloudy day Time Period 15 th October th January 2015 Variation Range (Average values) Solar irradiation W/m 2 <400 > Collector Loop Maximum collector outlet temperature C Mean absorber temperature C Heat gain kwh/d The ambient temperature is not measured at site and hence not indicated in Table The mass flow rate through the collector loop is indicated for three chosen days from three different months of the measurement data in Figure According to the system details provided by the installer, all the pumps installed in the plant are fixed flow, single stage pumps. Also, the static pressure of the tank is balanced with the help of a make-up water tank and the valves are completely opened. Hence, the exact reason for the fluctuation in the mass flow rate of water flowing through the 65

81 Assessment of monitored data Collector Loop is unknown. The fluctuation pattern of the mass flow rate and its moving average (m_coll_mavg) is shown as in Figure The possible reasons for the fluctuation in mass flow rate are indicated in Table Figure 4-17: Fluctuations in Mass flow rate - HP Dairy Table 4-12: Reasons for mass flow rate fluctuation - HP Dairy Nr. Fault Reason 1 Pressure drop occurs in the system - Insertion of the measurement rod tip of the Pt -500 temperature sensors completely through the pipe obstructing 66

82 Assessment of monitored data the flow - The diameter of the flow meter measuring pipe is less which is suitable for accurate measurements, on the other hand decreases the mass flow rate into the system. - Pumping of water to process side may create disturbance inside the storage tank, which affects the suction effect. 2 Total blockage in the - Particles blocking the flow rate sensor system in the running circuit and thus, the flow rate will decrease gradually. 3 Voltage supply fluctuations - The motor running the pump may receive fluctuating voltage from the grid (without a voltage stabilizer) which fluctuates the mass flow The reasons stated above in Table 4-12 do not appear to be the possible reasons for this cause and hence this parameter has to be investigated as future work. Shading effect: The effect of shading on the collector arrays can be realized by looking at the global solar irradiation incident on the site as shown for three chosen days from the measurement data in Figure Figure 4-18: Shading on the collector field HP Dairy 67

83 Assessment of monitored data The solar collector field is oriented towards south east 30. This orientation helps to have higher collector gain during morning hours. From Figure 4-18, it can be seen that the peak of global solar irradiation measured at site (at a slope of 45 and azimuth of south east 30 ) is earlier during the day, when compared to the maximum sun s height during the day at azimuth south 0. Even though the plant has been designed to have higher collector gain during the morning hours, the operational hours of the plant is considerably reduced due to the shading effect on the collector field during winter months. As discussed in the operational behaviour of the plant, the differential temperature controller in the solar loop starts the pump only when the critical solar irradiation is achieved. Hence, during the months of winter season when the sun height is low, and the incident solar irradiation is considerably blocked by the hill which casts a shadow on the collector field. The effective functioning of the solar collector loop starts nearly around 10:15 am in the months of December and January. With the increasing the sun s height, the blockage is less and the number of operational hours is increasing steadily. The operational hours logged by the monitoring system for the months where the measurement data is available are indicated in Table Table 4-13 : Variation in operational hours of the plant due to shading effect HP Dairy Month Operational hours in a day Operational Time (approx.) [Hour] (approx.) November :00 16:00 December :30 15:30 January :30 15:30 February :30 16:00 March :30 16:30 The increased operational hours leads to increased collector gain and percentage of increase in collector gain during these months is given the chapter performance analysis. Storage to Process Loop: From the horizontal storage tank, the hot water is pumped to the heat exchanger according to the load demand controlled by the process loop controller. On analyzing the measurement data, it could be realized that the horizontal storage tank is a completely mixed tank. In Figure 4-19, this characteristic of the tank is explained through three different days chosen from three different months from the available 68

84 Assessment of monitored data measurement data. As it can be seen in Figure 4-19, that the temperature of water at the collector inlet point (at bottom of the tank T_coll_in) is nearly the same as that of the hot water temperature at the outlet of storage tank to the Process (at the top of the tank T_s,p_out). This explains the nature of a completely mixed storage tank where the temperature of the tank is the average of the hot and the cold fluid entering the tank (In this case, the average temperature of Collector outlet temperature (T_coll_out - hot) and Return fluid temperature from the heat exchanger to storage tank (T_s,p_in cold) is to be taken). Also from Figure 4-19 can be seen the average temperature of the tank which increases from an average of 40 C during the winter months to an average of 50 C during the start of the spring. This clearly indicates the increase in intensity of solar irradiation, operational hours and higher ambient temperatures from January 15 to March 15. Figure 4-19: Mixed storage tank - HP Dairy Process Loop: The fresh water is pumped into the boiler feeding water tank and from this tank the water is forced into the plate heat exchanger where the cold water gains heat and returns to the boiler feeding water tank. The process outlet temperature varies ~15 C fro m winter months to summer months due to the differences in the collector heat gain and the variation in ambient temperature. The Table 4-14 below shows the 69

85 Assessment of monitored data maximum process outlet temperature achieved during each month when the measurement data is available. The days with an incident solar irradiation greater than 600 W/m² during the operational hours were considered. The heat exchanger effectiveness couldn t be calculated since the design values of mass flow rate are not available from the installer. Also, the heat losses from the heat exchanger to the ambient couldn t be calculated as the ambient temperature is not measured at site. Table 4-14: Maximum Process outlet temperature for each month HP Dairy Month Maximum Process Outlet temperature (Average maximum per day, days with solar irradiation <600W/m2 during operational hours) Unit C October 2014 (15 days) November December January 2015 (11 days) February 2015 (19 days) March 2015 (13 days) The figures in Table 4-14 are indicative of the outlet temperature that is achieved at the end of the solar process heat system. Since, the mass flow rate through the process loop is fluctuating and the design values are unknown, the typical values of temperature and heat gain which can be achieved from the solar thermal system cannot be calculated Performance analysis With an understanding of the operational profile and the system behaviour of the plant, the performance of the system is evaluated for the data which is available continuously from 1 st Nov 2014 to 22 st March The performance analysis of the system is done based on the following equations stated below and is specific for this case study in alignment with the general definitions stated in Chapter 2. Net Collector Loop gain in kwh [Q_coll ]:, = ( _ _ )

86 Assessment of monitored data In HC1,, is calculated as 4-14, = 1 ( 2 1) Heat transferred from the storage tank to process in kwh [Q_s,p,loop]:,, =, (, _, _ ) 4-15 In HC2,,, is calculated as,, = 2 ( 4 3) 4-16 Net System gain in kwh [Q_pro,loop ]: Q_pro,loop = Q_coll,loop Q_loss 4-17, = ( _ _ ) 4-18 In HC3,, is calculated as, = 3 ( 6 5) 4-19 Collector loop efficiency in % [η CL ]: Heat delivered by the collector loop(q_coll,loop) η CL = Solar Irradiation on tilted aperture area during pump operation(e_sol) 4-20 Percentage of collector heat gained transferred from storage to process: η transfer, s,p = Heat delivered from storage to Process (Q_s,p,loop) Total collector loop gain (Q_coll,loop) 4-21 System efficiency in % [η system ]: η system = (Q_pro,loop) (E_sol) Useful heat delivered to Process = Solar Irradiation on tilted aperture area during pump operation 4-22 Net thermal losses in the system in % [q loss ]: qloss = Q_loss Q_coll,loop

87 Assessment of monitored data Performance of the system: The system analysed for its performance has a collector efficiency of 27 % for the total 4 months except for the deviation during the month of December and the exact reason for the deviation is unknown. The system efficiency of the plant is 15 % for the total 4 months leaving out of December. Only 60 % of the net heat gained in the collector loop is transferred from the storage tank to the process loop. The monthwise details of the heat gained in each loop obtained from the monitoring system are listed in Table The specific energy yield of the system [Reference effective collector field area 111 m 2 ] is indicated in Figure Table 4-15 : Performance analysis of the monitored hot water system at HP Dairy Parameter Unit Measured Value Nov 14 Dec 14 Jan 15 Feb 15 Mar 15 Total Global irradiation (30 ) during pump operation kwh Net Collector loop gain kwh Net heat transferred from the storage tank to Process kwh Net System gain kwh Total Collector efficiency % 26% 19% 27% 27% 28% % of collector heat gain transferred from storage to % 76% 51% 53% 64% 61% process System efficiency % 17% 8% 12% 17% 16% 72

88 Assessment of monitored data Figure 4-20 : Specific energy yield of the system HP Dairy The net thermal losses in the system, as defined above in Equation 4-23 account to about 40 % for the total 5 months. The major share of this net thermal loss in the system is the heat which is not transferred from the storage tank to the process. The reasons which attribute to the higher thermal losses are the physical effect such as the heat losses from the storage tank to the surroundings (the storage tank is located in outdoor area), absence of non-return valve in the collector outlet pipe due to which the hot fluid from the storage tank flows back through the collector during night and the fluctuating load demand from the process side. To conclude, the operational strategies identified and the performance results indicated in this chapter will serve as the base information for modelling the system using a simulation tool. 73

89 5 Modelling of Systems One of the case studies described in chapter 3, Case study 1: Synthokem Labs is chosen to be modelled using a dynamic system simulation tool TRNSYS 17 in order to study the system performance and behavior. Further, the simulated model is validated with the monitored data and the actual yield is compared with the simulated yield of the system. 5.1 TRNSYS 17 program description TRNSYS is an acronym for a transient simulation program and is a quasi-steady simulation model [35]. The software consists of components in the form of sub systems and the mathematical model for each component is given in terms of ordinary differential or algebraic equations. In TRNSYS, interconnecting of system components is done in desired manner and after solving the differential equations, it facilitates to give the output information. As the first step of modelling it is required to identify the components in the system and to study the mathematical model associated with each of the component. After the identification of the components of the system, it is necessary to construct an information-flow diagram for the system. The purpose of the information flow diagram is to facilitate identification of the components and the flow of information between them. Each component is represented as a box, which requires a number of constant PARAMETERS and time dependent INPUTS and produces time dependent OUTPUTS. An information flow diagram shows the manner in which all system components are interconnected. A given OUTPUT may be used as an INPUT to any number of other components. An information flow diagram constructed for the Case study 1: Synthokem Labs is shown in Figure

90 Modelling of Systems Figure 5-1: Hydraulic scheme of Synthokem Labs presented in TRNSYS 17 as information flow diagram A deck file constructed in TRNSYS 17 containing information on all the components of the system, weather data file, and the output format is illustrated in Figure

91 Modelling of Systems Figure 5-2: TRNSYS 17 deck file showing the Synthokem Labs SHIP system modelled 5.2 Mathematical description of the system modelled using TRNSYS 17 All the components stated in the information flow diagram are described mathematically in this chapter for better understanding of the simulated system and finally the heat balance for each energy region is done to calculate the final output from the solar hot water system. TRNSYS 17 employing Type 1e for the solar collector considers the second order performance equation for the modelling of the collector [35].The Incidence Angle Modifier (IAM) values are given as input to the model in the form of a text file. The mathematical equation for this model for calculating the heat gained (Q coll ) in the collector is described in equation 5-1. = (( 0 ) = ( ) 5-2 The constants are listed in the list of constants and already stated in Chapter 2. Mass flow rate [kg/h] C p Specific heat capacity of fluid [kj/kg.k] 76

92 Modelling of Systems T out Outlet temperature from the collector [K] T in Inlet temperature into the collector [K] T amb Ambient temperature [K] In order to calculate the final heat delivered to the process from the collector, it important to take into account the piping and the storage tank losses. From the information flow diagram, it can be seen that the collector is connector to pipe of Type 31. The heat loss associated with the pipe(, ) is given in Equation 5-3., = ( ) 5-3 Where, U Overall heat loss coefficient of the pipe [W/K] A Total surface area of the pipe [m 2 ] T out, T amb described as above. The heat contained in the storage tank is finally delivered to the process. This depends upon the net heat gained from the collector including the piping losses and storage losses. In TRNSYS, a variable volume tank of Type 31 is used for modelling purpose and the mathematical equation is given in equation 5-4 below. = ( ) = ( ) ( ) ( ) 5-4, = ( ) ( ) 5-5 Where, M Instantaneous mass of fluid in the tank [kg] T Instantaneous temperature of the tank [K] (UA) t Time dependant Heat loss coefficient of tank depending on the level of fluid contained [W/m 2.K] The net heat delivered to the process loop is given in Equation 5-6., =,,

93 Modelling of Systems 5.3 Energy balance equations for the system modelled The hot water system installed at Synthokem Labs is modelled with TRNSYS 17 and analyzed based on the heat balance equations stated below. As described in Chapter 3, the system is divided into three energy balance regions namely, Collector Loop Day ( Coll,D,Loop ), Collector Loop Night (Coll,N,Loop) and the Process Loop (Pro,Loop). The shortened forms indicated in brackets are used in equations below. The heat gained in each energy balance region is indicated in the following equations. Collector Loop Day, = (( 0 ) 1, +, 2 2, +, , =, 5-8,, = (,, ) 5-9,, =,, 5-10 Collector Loop Night, = (( 0 ) 1, +, 2 2, +, , =, 5-12, =, 5-13,, = (,, ) 5-14,, =,,, 5-15 Since, the hot water is continuously recirculated in Collector Loop Night, the tank losses are considered in the calculation of the net heat gained in Collector Loop Night. Whereas, in Collector Loop Day which is directly connected to the Process Loop, the tank losses are considered in the net useful heat gained in Process Loop. Process Loop, = ( )

94 Modelling of Systems, = ( ) (, ) 5-17, =, 5-18, h =, 5-19, = (,, h ) 5-20, =,,, 5-21, h 5.4 Parameters of the model The Table 5-1 below indicates the parameters considered for simulation. In case of unavailability of data from the installer, realistic values are assumed and indicated as assumed in the remark column. Table 5-1: Parameters of the simulated model - Synthokem Labs Parameter Value Unit Remark General Global Solar Irradiation Measurement data (on collector plane) W/m 2 Given Incidence Angle Radiation processor (TRNSYS) Given Ambient Temperature Location Medak (135 km away from site) C Assumed Collector Loop Day Collector Total Collector area m 2 Identified Number of collectors 10 Given Layout 2*4 in parallel & 1*2 connected in series Given Collector type Evacuated Tube Collector Given Optical efficiency η Given Heat loss coefficient a W/m 2.K Given Heat loss coefficient a W/m 2.K 2 Assumed Azimuth 0 Given Slope 30 Given IAM Refer to Annexe 5 Assumed 79

95 Modelling of Systems Piping Details Diameter m Given Length from hot water tank to collector inlet 38 m Given Length from collector outlet to hot water tank 30 m Given Heat loss coefficient W/m 2.K Assumed Storage Tank Height 2.5 m Given Diameter 1.6 m Given Volume 5000 L Given Wet loss coefficient 1.3 W/m 2.K Assumed Dry loss coefficient 2 W/m 2.K Assumed Pump Type Fixed flow Given Mass flow rate From measurement data kg/h Assumed Rated Power 0.75 kw Given Collector Loop Night Collector Total Collector area m 2 Identified Number of collectors 10 Given Layout 2 * 5 connected in series Given Collector type Evacuated Tube Collector Given Optical efficiency η Given Heat loss coefficient a W/m 2.K Given Heat loss coefficient a W/m 2.K 2 Assumed Azimuth 0 Given Slope 30 Given IAM Refer to Annexe 5 Assumed Piping Details Diameter m Given Length from hot water tank to collector inlet 23 m Given Length from collector outlet to hot water tank 12.5 m Given Heat loss coefficient W/m 2.K Assumed Storage Tank Height 2.5 m Given Diameter 1.6 m Given Volume 5000 L Given 80

96 Modelling of Systems Wet loss coefficient 1.3 W/m 2.K Assumed Dry loss coefficient 2 W/m 2.K Assumed Pump Type Fixed flow Mass flow rate From measurement data kg/h Rated Power 0.75 kw Given Process Loop Piping Details Diameter m Given Length from storage tank to inlet of steam boiler 13.5 m Given Heat loss coefficient W/m 2.K Assumed Pump Type Fixed flow Given Mass flow rate From measurement data kg/h Given Rated power 0.75 kw Given 5.5 Considerations in the model Physical considerations Collector array shading effects: The collector array shading effect is quite visible in collector field Night and Day. In Figure 5-3 below indicates the layout of the collector field Night explaining the need for including the collector array shading effect into the simulation model. Type 30a from TRNSYS17 is used for the inclusion of this effect into the simulation model. The mathematical description is given in TRNSYS17 Manual [35]. Similarly, this effect on collector field Day is indicated in Figure 5-4. The highlighted area in the Figure 5-3 and Figure 5-4 are representative, as they vary depending on the sun s height during the year. 81

97 Modelling of Systems The first array (front) collectors shall cast shadow on the second array of collectors and further on. * Only the first and second array are indicated in this Figure, this effect have to be considered also for the collectors in the back. Figure 5-3: Row shading effect on Collector field 'Night' representative The row shading parameters given as input into the simulation model (in TRNSYS 17) are given in Table 5-2 below. Table 5-2: Parameters considered for row shading effect -Synthokem Labs Parameter Value Unit Remark General Tilted surface Radiation From measurement data W/m 2 Given Incident beam Radiation 85% of Tilted surface radiation [36] W/m 2 Assumed Solar Zenith Angle Radiation processor (TRNSYS 17) Given Solar Azimuth Angle Radiation processor (TRNSYS 17) Given Collector field Day Collector height 1.74 m Given Collector row length 14.4 m Given Number of identical rows of collector 1 - Given Collector Slope 30 Given Collector row separation 2 m Assumed 82

98 Modelling of Systems Collector field Night Collector height 1.74 m Given Collector row length 7.2 m Given Number of identical rows of collector 4 - Given Collector Slope 30 Given Collector row separation 2 m Assumed Shading effect due to obstructions: Due to improper planning on the layout of the collector field Day, the last row of collector array (with two collectors) as shown in Figure 5-4 is subjected to shadowing effect due to obstruction (in this case it is an office building). This effect is modelled through the TRNSYS block Type 64. The mathematical description can be found in TRNSYS 17 manual [35]. The surface angles and opening angles are given as a user input file in to the block. The other parameters required are solar zenith angle, azimuth angle, Tilted surface radiation and Incident beam radiation, for which the same values as stated in Table 5-2 are given as input. Collector Array shading effect Shading effect due to Obstruction Figure 5-4: Shading effect due to obstructions on Collector field 'Day' 83

99 Modelling of Systems Operational strategy considerations The operational strategy is followed by giving the control signal to the pumps with the help of the block -Type 9a in which the User input file prepared manually by the user is fed in. This file contains the same operational strategy of the plant identified from the measurement data and of those stated in Chapter 3 as communicated with the personnel in the plant. These operational parameters are listed down in Table 5-3. Table 5-3: Operational strategy followed in simulation model - Synthokem Labs Operation Fresh water fill Tank Day Fresh water fill Tank Night Fresh water refill Tank Day Tank Night to Tank Day discharge Additional water refill in Tank Day Timing Volume filled in Temperature considered 7:30 am - 8:30 am 3500 L Measured fresh water inlet temperature 8:30 am -9:30 am 4500 L Measured fresh water inlet temperature 1 pm - 2 pm 2500 L Measured fresh water inlet temperature 8:30 pm -11:30 pm 4500 L Temperature of Tank Night Fresh water temperature in Based on the water - the morning between level in tank 7:30 am and 8:30 am In reality, an additional volume of water which is filled in the Tank Day and the refill volume and time varies each day, whereas in simulation for this refill a specific time indicated by the personnel in Synthokem Labs is incorporated. Hence, discrepancies relating to the volume of the tank going to zero can occur. In order to overcome this emptying effect, the control signal is given to the pumps in TRNSYS block when the volume of water goes in the tank below 100 L and this pumping operation is stopped when the volume of the tank is higher than 100 L. The mass flow rate for this pump operation is 1500 kg/h. The parameters stated in this chapter along with the physical and operational conditions are incorporated in the TRNSYS simulation model and the model is validated with the measurement data. The validation results are described in Chapter 6. 84

100 6 Validation of simulated model and possible improvement options 6.1 Validation of simulated model with measured data The simulation model of hot water system installed at Synthokem Labs is to be validated with measured data. In order to validate the model, the system behavior and performance analysis result of the simulation model are compared with that of the measured data. Mean deviation index as shown in Equation 6-1 is used for comparing the simulation result and measured data. The mean deviation index is given as [ ] % = ( ) Where is the measured value at the time step i and is the simulated result at the same time step. As a part of system behavior analysis, a graphical comparison of the temperatures which includes the collector inlet & outlet temperatures and process inlet & outlet temperatures along with the mass flow rate are carried out. From the point of performance analysis, a graphical comparison on the heat gained in each energy balance region is done. A tabular comparison which indicates the mean deviation index is also made to compare the collector efficiency, system efficiency and the net thermal loss percentage. It is to be mentioned that the simulation is carried out from 6 th December 2014 till 21 st February 2015 owing to the continuous availability of measured data. The measured data interval is 1 minute. Hence values of temperatures, mass flow rate and heat gain in energy balance regions are printed for the same time interval in the simulation. All the considerations and inputs stated in Chapter 5 have been given in the model for a time interval of 1 minute. The identifiers of all the parameters indicated in Chapter 3 are used here. It is to be noted that, for further reading of the parameters mentioned in the graphical and tabular comparison, the simulated data parameter has a suffix (sim) and the measured data parameter has the suffix (meas). 85

101 Validation of simulated model and possible improvement options Validation results The comparison of system behavior and performance between the simulation result and measured data has been carried out in the following sub chapters System behavior Collector Loop Day : Three days with peak solar irradiation of nearly 980 W/m 2 have been considered for the temperature analysis of the model and measured data. Figure 6-1 shows the inlet and outlet temperatures of Collector loop Day for the simulated and measured values. As it can be seen from Figure 6-1, the deviation between the simulated and measured values occur during the hours when the fresh water is refilled in the tank Day. In reality, they follow different refilling times each day, while in the simulation the fresh water is refilled in the noon from 1 pm to 2 pm. In order to minimize this deviation in the model, a flow meter on the fresh water inlet pipe needs to be installed. Also, other minor deviations occur due to the inaccuracy in the shading effect implemented in the simulation model. Additionally Figure 6-1 shows the solar irradiation blocked by the obstruction [blocked_sol_irr] on the last array of collector field Day (2 Collector modules). The fraction of solar irradiation which is not incident on this last collector array due to shading effect is not measured at site and this parameter remains invalidated. Figure 6-1: Temperature analysis of Collector Loop 'Day' - Synthokem Labs 86

102 Validation of simulated model and possible improvement options Explained below in Figure 6-2 is the mean absorber temperature denoted as T_mean_abs for the collector loop Day. Mean absorber temperature is the average temperature of heat transfer fluid flowing through the absorber pipes. It can be seen from Figure 6-2 that the mean absorber temperature of the collector poses a good correlation between the simulated model and measurement data except for the deviation during fresh water refill times. Figure 6-2 : Mean absorber temperature - Collector Loop 'Day' The heat gained in the collector loop Day is analyzed for three days (same as above) and is given as below. Table 6-1 : Heat gained in Collector Loop 'Day' - comparison between simulated and measured results Heat Gained in Collector Loop Day Day Measured (kwh) Simulated (kwh) Mean Deviation (%) 12 th January % 13 th January % 14 th January % The reasons for the deviation between simulated and measured heat gain values are mainly as following: 1. Different refill times Lowering the mean absorber temperature by mixing cold water can considerably increase the collector efficiency (by decreasing the heat losses through the collector). 87

103 Validation of simulated model and possible improvement options 2. Differences in Ambient temperature used in the simulation model. 3. Differences in the Heat loss coefficients of pipes and tank used in the model, since the design values are not available. 4. Errors of measurement of different sensors. Collector Loop Night : Two days with peak solar irradiation of nearly 980 W/m 2 have been considered for the temperature analysis of the simulation model and measured data. Figure 6-3 shows the inlet and outlet temperatures of Collector Loop Night of simulated and measured values. The fresh water is filled in the morning between 8:30 am to 9:30 am is continuously recirculated and stored in Tank Night. The outlet and inlet temperatures find a good correlation between the measurement data and the simulation result. Minor differences in the collector outlet and inlet temperature between the simulated model and the measurement data is due to the fact that the ambient temperature used in the simulation model differs from that of the site. In order to have minimized deviations, ambient temperature needs to be measured at site and used in the simulation model. Figure 6-3 : Temperature analysis of Collector Loop 'Night' - Synthokem Labs The heat gained in the collector loop Night is analyzed for the two days (same as above) and is given below. 88

104 Validation of simulated model and possible improvement options Table 6-2 : Heat gained in Collector Loop 'Night' - comparison between simulated and measured results Heat Gained in Collector Loop Night Mean Deviation Day Measured (kwh) Simulated (kwh) (%) 12 th January % 13 th January % The reasons for the deviation between the simulation and measured heat gain values are mainly because of 1. Differences in ambient temperature used in the simulation model. 2. Differences in the heat loss coefficients of pipes and tank used in the model, since the design values are not available. 3. Can be due to other physical effects such as presence of dirt on the collector and defective absorber pipes in the collector module. 4. Errors of measurement of different sensors. Process Loop: The same three days which have been considered for analysis in collector loop Day are considered here for analyzing the process outlet temperature of the model and measurement. The measured fresh water inlet temperature is given as input to the simulation. Therefore only the process outlet temperatures are compared. From Figure 6-4, it can be seen that the deviations between the simulation model and measured data are due to different fresh water refill time into Tank Day during the day. During night time, the simulation model suffers huge deviation due to the reason that the hot water is discharged from Tank Night to Day every day evening between 8:30 pm and 11:30 pm as indicated by the personnel at Synthokem Labs. But it can be seen from the measurement data that this discharge time varies each day. Due to the absence of a flow meter and temperature sensor on the discharge line, the exact operational manner couldn t be included into the simulation model. The other point to be noted from Figure 6-4 is ideal mixing of hot and cold water in Tank Day in the model. The process outlet temperature is the same as that of the fresh water inlet temperature in the morning filling hours since the TRNSYS 17 model uses an ideally mixed tank. In reality, the tank doesn t exhibit active mixing; it takes more time for complete mixing to happen. This is the reason why the operating process outlet temperature is higher compared to simulation result even during fresh water filling time. 89

105 Validation of simulated model and possible improvement options Figure 6-4 : Temperature analysis of Process loop - Synthokem Labs Performance Analysis The performance of the system is analyzed for the same time period between 6 th December 2014 to 21 st February Given below in Figure 6-5 is the specific heat gain diagram of the hot water system at Synthokem Labs for the month of January The specific heat gain in each energy balance region - the simulated and the measured values are indicated inside each loop as a table. The net specific solar irradiation incident on each collector field during pump operation is indicated as E_sol in Figure 6-5. The specific heat gained in each energy balance region for the month of January 2015 is analyzed below. Collector Loop Night : The simulation model has a specific heat gain of 33.9 kwh/m 2 while the specific heat gain measured at site is 30 kwh/m 2 for the month of January The mean deviation of the simulated value from the measurement result is +13%. This deviation is comparatively really high only for January 15, while the other months deviate less than 5%. One of the main reasons could be due to the ineffective functioning of absorber pipes which are replaced later in the month. The other reasons for this deviation have been indicated in the system behavior analysis in the previous chapter. 90

106 Validation of simulated model and possible improvement options Collector Loop Day : The simulation model has a specific heat gain of 32 kwh/m 2 while the specific heat gain measured at site is 31.2 kwh/m 2. The mean deviation of the simulated value from the measurement result is +2%. The deviation between the simulated and the measured value is comparatively less only when complete month is taken into consideration for performance analysis. A mean deviation of +5% occurs when the daily performance data is considered. Figure 6-5 : Specific heat gain diagram - January Synthokem Labs Process Loop: This loop is analyzed for the day demand which is met by the collector loop Day between 8:30 and 20:30 and the night demand met by the collector loop Night between 20:30 and 08:30 of next day morning. Night demand: The differences between the heat gained in the collector loop Night and the heat delivered to the process are due to transfer losses from Tank Night to Day, tank losses to the surroundings and the heat losses from the pipes. From Figure 6-5, it can be seen that in both simulation and measurement ~25% of collector loop gain is not delivered to the process and is lost as thermal losses. Day demand: The differences between the heat gained in the collector loop Night and the heat delivered to the process are due to tank losses to the surroundings and 91

107 Validation of simulated model and possible improvement options the heat losses from the pipes. From Figure 6-5, it can be seen that the simulated model has lower thermal losses of about ~14%, while in reality (from measurement) ~25% of collector loop gain is not delivered to the process and is lost as thermal losses. The deviation between the simulation model and measured data can be due to differences in the assumed heat loss coefficients, in particular the wet heat loss coefficient of the tank in the simulation model, since the water level in the tank can be different between the model and in reality. Performance of the system: The output of the simulation model is compared with the measured data. Outputs are the performance parameters such as collector efficiency, system efficiency, and net thermal losses of the system which have been already defined in Chapter 4. Table 6-3 shows the month-wise comparison of collector and system efficiency parameters and the mean deviation of the simulation result from the measurement results. Table 6-3: Comparison of month-wise efficiency parameters of the solar hot water system at Synthokem Labs Gap Analysis on the performance of the model and measurement is stated below. 92

108 Validation of simulated model and possible improvement options Collector efficiency Day : The mean deviation between the simulation result and the measured data is as low as 0.9% for the whole considered three months. This implies the proper functioning of the shading effect introduced in this model. The mean deviation is higher in the month of February due to the differences in the percentage of beam irradiation which is considered to include shading effect in the model. Collector efficiency Night : The simulation results are 6% higher than the measurement results. The highest deviation occurs in the month of January with the value of 12.8%. The exact reason for this deviation is unknown. Some of the possible reasons could be the improper assumptions made in the simulation model, physical effects such as dirt on the collector or non functioning absorber pipes which are later replaced in the month of February. System efficiency: The simulation result exhibits 4.3% higher system efficiency than the measured data. This deviation is mainly due to the differences in volume of fresh water filled and refilled in the simulation model and in reality. This error can be mitigated only when a water level sensor is installed to the monitoring system The Gap analysis stated above focusses more on the deviation of the simulation model from the measured data but on the other hand, the uncertainties in the measurement concerning the accuracy of the sensors needs to be also taken into account. In order to minimize the deviation between the simulation and the measurement, some additional basic data are required. Hence, additional sensors need to be installed in the system. They are: 1. Ambient temperature sensor 2. Tank water level Indicator 3. Fresh water inlet flow rate sensor 4. Tank Night to Tank Day Discharge Flow meter & temperature sensor 93

109 Drawbacks of this system: Validation of simulated model and possible improvement options The drawbacks of this system at design and operational level are indicated below. Table 6-4 : Drawbacks of the hot water system installed in Synthokem Labs - at design and operational level Parameter Design - Layout Design Component level Design System configuration Operational level Drawback Shading effect on the collector unnoticed by the system installer. Two of the ten collector modules in Collector Loop Day are shaded due to obstruction from office building. Non-optimal usage of the storage tank. As communicated by the personnel, only 4500 L of hot water is withdrawn every day from the tank Night, therefore assumably 500 L of hot water is left unused at the bottom of the storage tank Night. In this case, different design concepts for maximum water withdrawal from the bottom of the storage tank would increase the energy yield. Non-optimized system configuration leading to lower system efficiency. The general design idea is to cover a part of the day and the night demand of process water with solar heated water by two separate collectors and storage tank systems. However, to split the solar system in two parts increases the energy losses by storing the solar heated water stored in the Night tank during the day and pumping it in the second tank in the evening. These losses could be avoided, if the solar hot water would be used instantaneous. To store a part of the solar yield from day to night would only be necessary, if the yield of the entire solar system during a day is higher than the process heat demand during the day, however this is not the case at Synthokem Labs. Emptying of Tanks Discharge from tank Night to tank Day. 94

110 Validation of simulated model and possible improvement options The hot water from Tank Night has to be discharged in the night time only when the volume of hot water in Tank Day is nearly empty. This has to be manually operated accordingly. Discharging of the tank Night, while the tank Day still contains adequate volume of water leads to storage of hot water in Tank Night which will be unused. Manual control of the collector loop pumps Due to manual control of the collector loops, the solar yield could be lowered if the operational times are lower than the optimal times, or the electricity demand for pumping is higher than necessary, if the operational times are higher. However, it can be assumed that the difference is relatively low as long as the manual operation has a high reliability and the solar heat supplied has a low share on the process heat demand as it is the case in the Synthokem Lab system. 6.2 Possible improvement options The operating solar hot water system has some drawbacks which were explained in the sub section above. This provides the scope for system optimization. As a starting point, some possible improvements which can be done to the system are discussed and evaluated below. (1) Improvement of operational manner without changing the existing system configuration (2) Changing the existing system configuration Changes are restricted to piping interconnections and installation of additional valves and controllers The existing system with proposed changes in configuration is simulated with TRNSYS 17 to evaluate the possible performance improvements. The simulated values of these systems are finally compared with the measured values to put forth the additional possible heat gain from the system. 95

111 Validation of simulated model and possible improvement options Possible operational changes in the existing system a) Utilize the system to the maximum - Follow specific and extended operational time for the plant and also increase the number of plant operating days in a month to have higher collector gain. b) Fill and refill the storage tanks to the maximum possible volume during operation so that the inlet collector inlet temperature is always a low as possible and the resulting collector yield maximized. c) Empty the storage tank Night to the technically possible minimum level of the tank. As communicated by the personnel the maximum volume withdrawn from the tank is 4500 L, when the technically possible minimum level is reached. It has to be taken care that if at 8:30 pm the storage tank Day can additionally hold only a portion of this 4500 L, then the remaining portion from tank Night has to be discharged into tank Day during the night time. The above mentioned points haven t been implemented in the simulation model and the possible solar yield improvements are unknown. This can be a part of the future work. Options for improving the system performance by changing the existing system configuration: Since the solar system is a preheating system, this means that not a specific temperature level must be achieved but only the solar energy yield counts, it is beneficiary to use the entire storage volume and have the storage tanks always completely filled. The tank could be filled with cold fresh water immediately by an automatic refilling device after hot water is withdrawn to the process. This fresh water lowers the temperature of the water contained in the storage tank. Recirculation of water at lower temperatures leads to higher collector efficiency, thereby reduced heat losses to the surroundings from the collector and storage tanks. The proposed changes in configuration are: a) Tanks in series configuration b) Collector fields connected to single tank. The simulated outputs of the proposed system configurations are compared with measured values and not with the simulated results of the existing system, since the validated simulation model suffers some deviation due to the differences in 96

112 Validation of simulated model and possible improvement options operational strategy of the system which is not followed in the proposed system configuration. The operational timing of the plant implemented in the simulation model for proposed changes is the same as the existing system. The hydraulic scheme and the operational strategy of the proposed system configurations are explained below. Possible improvement option 1:- Tanks in series configuration Depicted below in Figure 6-6 is the hydraulic scheme of the tanks in series configuration. This configuration uses the Collector Loop Night for pre-heating the fresh water and this preheated water further is heated up by recirculating in Collector Loop Day. Figure 6-6 : Possible improvement option 1 - Tanks in series configuration As seen in Figure 6-6 the existing components and the piping systems remain unchanged. An additional pump is required for discharging the hot water tank 1 and filling tank 2. Also shown in Figure 6-6, there is a requirement for the installation of an additional controller which controls the operation of all the three pumps i.e. pumps on the fresh water inlet line, hot water tank 1 to 2 and to the process. In the existing system, a controller from the steam boiler which gives control signal to the pumps operating on the process side (Pumps P4 or P5) based on the demand exists. The same controller can be used to give control signals to the pumps on the fresh water inlet line and hot water tank 1 to 2 discharge if it has the required hardware and software provision. Otherwise, an additional controlled needs to be installed in this 97

113 Validation of simulated model and possible improvement options case. The functioning of this controller helps to maintain the volume of water contained in the tank to 5000 L. The system explained above is implemented in TRNSYS 17 and simulated. Both the physical and operational considerations which were considered in validating the simulated model are used here as well. The time period (months) and time interval (1 minute) are same as the validated model. The behavior of the simulated system is further analyzed below. Figure 6-7 shows the outlet temperature to the process of the proposed configuration and the existing configuration. These 5 days shown in Figure 6-7 have been chosen for analysis out of the whole simulation time period. Figure 6-7: Process outlet temperature - comparison between the tanks in series configuration and existing configuration It can be seen from Figure 6-7 that the modified layout helps to achieve higher temperatures at the process outlet during the day than the existing layout. The first and fifth day in Figure 6-7 show lower temperatures due to the fact that only one of the collector loops is in operation during these days. This configuration is more suitable when the demand during the day is higher and helps to achieve higher system efficiencies. Possible improvement option 2: Collector fields connected to single tank 98

114 Validation of simulated model and possible improvement options Depicted below in Figure 6-8 is the hydraulic scheme of the collector fields connected to single tank configuration. In this configuration, both collector fields heat up the water from the same storage tank. Hot water is then discharged to the process from this tank. The controller which controls the Pumps P4 or P5 based on the demand shall be used to control the Pump P1 on the fresh water inlet line. This ensures that the storage tank is always filled with a volume of 5000 L and is able to suffice the demand. Figure 6-8 : Possible improvement option 2 - Collector fields connected to single tank The same considerations and time period as the improvement option 1 have been followed for simulating this configuration in TRNSYS 17 software. The behavior of the simulated system is analyzed below. Figure 6-9 shows the process outlet temperature for the simulated configuration and existing configuration. Five days out of the whole simulated time period have been chosen for analysis. The simulated results and the measured data find a good correlation on the first day and fifth day as only one of the collector loop is set into operation. On the other days, the modified configuration achieves higher energy gain during the day time period. The same energy gain as of the existing configuration is exhibited by the simulated model during the night. This configuration suits for systems which have a balanced load demand requirement during both day and night time periods. 99

115 Validation of simulated model and possible improvement options Figure 6-9 : Process outlet temperature - Comparison between the collector fields connected to single tank configuration and existing configuration Comparison on the performance of the proposed configurations with the existing plant in operation: The collector gain and system gain parameters of the proposed system configurations simulated are compared with the measured data for the whole time period from 6 th December 2014 till 21 st February The results are indicated in Table 6-5. The definitions of the parameters are the same as defined in Chapter 4. In addition, the system gain is differentiated as System gain Day and System gain Night. The former relates to the heat delivered by the system to the process during the day between 8:30 am to 8:30 pm and the latter indicates the same during night between 8:30 pm to next day 8:30 am. It can be inferred from Table 6-5, that changing the existing configuration to the proposed configurations can lead to additional net system gains. The proposed improvement options of having tanks in series and having collector fields connected to single tank configuration show an increase respectively of 6% and 11% from the monitoring results for the whole period of three months. 100

116 Validation of simulated model and possible improvement options Table 6-5 : Performance analysis Comparison between existing and recommended configurations Configuration Existing Tanks in Series Collector field connected to single tank Total three months - 6th Dec st Feb 2015 Total Solar Irradiation during 'Pump' operation Net Collector gain Net System gain Net System gain 'Day' Net System gain 'Night' Additional system gain from existing system kwh kwh kwh kwh kwh kwh (+6%) (+11%) The specific energy yield of the system for different configurations is analyzed for the month of January 2015 and is shown in Table 6-6. The specific energy yield values are predicted using the simulation model. Since, the simulation model has lots of consideration taken into account, the predicted specific energy yield values can vary. This variation range is typically unknown since the system installer has not provided the predicted system yield values for the existing system configuration. It can be inferred from Table 6-6 that the series configuration of the tanks exhibits higher system gain during the day with an increase of 23% (predicted) from the existing system. This configuration does not show a remarkable increase during night, the increase at the maximum is 8% during the month of January, which is even lower during the other months where the measured data are available. Hence, this configuration shall be used only if the load requirements during the day are much higher than in the night. The configuration in which the collector fields is connected to single tank exhibits an increase in system gain during both day and night times. The percentage increase is almost the same ~15 % throughout the day (day time and night time). Hence, this configuration shall be adapted after investigating the load demand if they are nearly the same during both day and night. 101

117 Validation of simulated model and possible improvement options Table 6-6 : Specific energy yield - Comparison between existing and recommended configurations for January 2015 Specific energy yield - January 2015 System Configuration Parameter Unit Existing Tanks in Series Collector fields connected to single tank Net Collector Gain kwh/m 2 (% increase from existing) (+20%) 70.9 (+15%) Net System Gain 'Day' kwh/m 2 (% increase from existing) (+23%) 29.5 (+8%) Net System Gain 'Night' kwh/m 2 (% increase from existing) (+18%) 27.1 (+15%) Possible Improvement Options on Collector Loop Day 1. Changing the flow direction through the collector field: The scope of this improvement option is to investigate the net collector gain by changing the flow direction through the collector field Day. In the collector loop Day, the last array of collectors (2 collector modules 1x2 ETCs in parallel as indicated in Figure 6-10) are shaded due to an obstruction. In the existing collector field layout, the water flow direction through the field is as follows: The water initially enters the 2x4 ETCs in parallel. After recirculating through the 2x4 ETCs the hot water further finally flows through the shaded collector row (1x2 ETCs in parallel) and returns to the storage tank. Due to the effect of shading, the incident solar irradiation on the 1x2 ETCs is blocked. As a result, the absorber pipes in this collector array are not as hot as 2x4 ETCs. Hence, the hot water tends to lose more heat rather than gaining when it enters the 1x2 ETCs. In order to minimize this effect, the opposite flow direction has been proposed as indicated in Figure 6-10 where the fresh cold water first enters the 1x2 ETCs in parallel (collectors which are shaded) and later on into 2x4 ETCs in parallel. The proposed flow direction shall achieve higher collector efficiency than the existing layout by minimizing the heat losses. To implement this flow direction, the interconnection of the pipes should be done in the existing system. While, 102

118 Validation of simulated model and possible improvement options implementing this change, the concept of balancing the pressure in the circuit with equal length of the pipes in the inlet and outlet of the collectors should be followed (Tichelmann approach). Existing Flow direction Proposed Flow direction Figure 6-10 : Proposed fluid flow direction in Collector field Day to increase the net collector gain The proposed flow direction as shown in Figure 6-10 has been implemented in TRNSYS 17 software. Indicated in Figure 6-11 are the simulation outputs of the collector outlet temperature of the existing and proposed flow directions. The proposed flow direction improved the collector outlet temperature by 1%. While, the collector inlet temperatures are nearly the same with the proposed flow direction showing a very minimal increase of (0.02%). Figure 6-11 : Collector outlet temperature simulated outputs of the existing and proposed flow direction in Collector field 'Day' The proposed flow direction could not show a major improvement in this case as the shaded collector area is less than 1/5 th of the total collector field area. The other 103

119 Validation of simulated model and possible improvement options reason is that the heat loss reduction is considerably small because of the minor changes in temperature distribution owing to the small temperature differences between the collector field inlet and outlet. The results of the simulation are highly uncertain since the shading effect implemented in the simulation model is not validated with the measured data. Also, the heat loss coefficients for the collector provided by the installer seem to be extremely low. These factors mainly influence the output of the proposed flow direction of the collector field Day. 2. Bypassing the shaded collector array This work is carried out to investigate the net collector gain by bypassing the shaded collector array during the time period when the incident solar irradiation on the 1x2 ETCs is blocked. Shown in Figure 6-12 is the modified configuration where the shut off valves V1 and V2 on the outlet pipes are opened and closed based on the shading effect on the collector array. Existing configuration Bypassing the shaded collector array Figure 6-12 : Bypassing the shaded collector array in Collector field Day Investigation on net collector gain This modified configuration has been implemented in TRNSYS 17. An analysis on the simulated outputs of the existing and modified configuration show that the net collector gain in the modified system is 3% lower than the existing system. Three days from the whole period of measured data have been considered for the comparison between the simulated outputs of instantaneous collector gain between the existing and modified configuration. Figure 6-13 reveals that the existing configuration exhibits slightly higher gains which can be possibly due to the absorption of the diffuse irradiation. 104

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