Comprehensive energy analysis of a near zero energy home

Buildings consume nearly 40% of the entire energy used in the United States. To reduce the residential energy consumption, the Department of Energy (DOE) in partnership with Building America is evaluating various energy efficient technologies that might be integrated to produce a Zero Energy Home (ZEH). The research presented in this thesis focuses on evaluating the energy use of individual energy saving components and a near ZEH system in Salt Lake City, Utah. A state-of-the-art software tool, DesignBuilder, which employs an EnergyPlus simulation engine, was used to evaluate the performance of the prototype models. The major energy saving features in the house included photovoltaic thermal (PVT) panels; the hybrid solar panels that combine PV and solar thermal panel technology in a single entity; OASys, a new evaporative cooling unit that has a SEER 40+; structural insulated panels (SIPs); and a hydronic furnace. With real time data acquisition, the performance of the individual components and the near ZEH system was studied. PVT performs with nearly 20% greater efficiency than a conventional photovoltaic (PV) system. OASys reduces the cooling energy use by 60% in comparison with a regular vapor compression air conditioning system. Simulation results indicate 30% reduced energy use with SIPs. The hydronic furnace provides comfortable heating with 2% of the total heating energy as preheat to the water heater.

COMPREHENSIVE ENERGY ANALYSIS OF A NEAR ZERO ENERGY HOME by Madhuri Jannumahanthi A thesis submitted to the faculty of The University of Utah in partial fulfillment of the requirements for the degree of Master of Science Department of Mechanical Engineering The University of Utah December 2010 Copyright © Madhuri Jannumahanthi 2010 All Rights Reserved The Uni ve r si ty of Utah Gr adua t e School STATEMENT OF THESIS APPROVAL The thesis of Madhuri Jannumahanthi has been approved by the following supervisory committee members: Kent S. Udell , Chair 05/03/2010 Date Approved Kuan Chen , Member 05/03/2010 Date Approved Joerg Ruegemer , Member 05/06/2010 Date Approved and by Tim Ameel , Chair of the Department of Mechanical Engineering and by Charles A. Wight, Dean of The Graduate School. ABSTRACT Buildings consume nearly 40% of the entire energy used in the United States. To reduce the residential energy consumption, the Department of Energy (DOE) in partnership with Building America is evaluating various energy efficient technologies that might be integrated to produce a Zero Energy Home (ZEH). The research presented in this thesis focuses on evaluating the energy use of individual energy saving components and a near ZEH system in Salt Lake City, Utah. A state-of-the-art software tool, DesignBuilder, which employs an EnergyPlus simulation engine, was used to evaluate the performance of the prototype models. The major energy saving features in the house included photovoltaic thermal (PVT) panels; the hybrid solar panels that combine PV and solar thermal panel technology in a single entity; OASys, a new evaporative cooling unit that has a SEER 40+; structural insulated panels (SIPs); and a hydronic furnace. With real time data acquisition, the performance of the individual components and the near ZEH system was studied. PVT performs with nearly 20% greater efficiency than a conventional photovoltaic (PV) system. OASys reduces the cooling energy use by 60% in comparison with a regular vapor compression air conditioning system. Simulation results indicate 30% reduced energy use with SIPs. The hydronic furnace provides comfortable heating with 2% of the total heating energy as preheat to the water heater. The iv high efficiency water heater has a peak monthly efficiency of 83%. The actual data usage indicates that the energy efficient house has nearly 50% reduced energy use over a simulated model without the energy saving features and 60% fewer carbon dioxide emissions than a regular house. To eternal optimists, who always believe. TABLE OF CONTENTS ABSTRACT………… ........................................................................................... iii LIST OF FIGURES ............................................................................................. viii ACKNOWLEDGEMENTS ..................................................................................... x Chapter 1 INTRODUCTION ........................................................................................ 1 1.1 Objective ………………………………………………………………1 1.2 Energy saving features ………………………………………………3 1.2.1 Photovoltaic thermal panels (PVT) ……………………………..3 1.2.2 OASys ……………………………………………………………..3 1.2.3 Structurally insulated panels…………………………………….4 1.2.4 Hydronic furnace………………………………………………….5 1.2.5 Water heater………………………………………………………6 1.3 Overview 7 2 LITERATURE REVIEW ............................................................................... 9 3 PHOTOVOLTAIC THERMAL PANELS ..................................................... 12 3.1 Introduction ..................................................................................... 12 3.2 Description of the system ................................................................ 13 3.3 PVT performance ............................................................................ 14 3.3.1 Electrical (PV) performance of PVT ......................................... 16 3.3.1.1 Efficiency of PV .................................................................. 17 3.3.2 Thermal performance of PVT .................................................. 20 3.3.2.1 Thermal efficiency of the PVT ............................................ 22 3.4 Effectiveness of PVT ....................................................................... 23 4 OASYS………..... ...................................................................................... 25 4.1 Introduction and background ........................................................... 25 4.2 OASys system performance ............................................................ 27 5 WATER HEATER ..................................................................................... 32 vii 5.1 Introduction ..................................................................................... 32 5.2 Hot water heater performance ......................................................... 33 6 SIMULATION RESULTS ........................................................................ 36 6.1 Introduction ..................................................................................... 36 6.2 Parametric study ............................................................................. 37 6.3 Cooling loads summary ................................................................... 40 6.4 Heating loads summary ................................................................... 42 6.5 Net energy loads summary ............................................................. 43 6.6 Carbon dioxide emissions summary................................................ 43 7 RESULTS AND DISCUSSION .................................................................. 46 APPENDIX…………. .......................................................................................... 50 REFERENCES…………. .................................................................................... 54 LIST OF FIGURES Figure Page 1.1: Near ZEH located in Salt Lake City ................................................................ 2 1.2: Cross-sectional view of SIPs panel ................................................................ 5 1.3: Schematic for flow lines of the hydronic furnace ............................................ 6 1.4: Schematic of the sensors and the equipment in the house ............................ 8 3.1: PVT installed at the near ZEH ...................................................................... 13 3.2: PVT system configuration ............................................................................ 15 3.3: Comparison of electrical energy from PVT for a typical summer and winter day ..................................................................................................... 16 3.4: Comparison of electrical energy consumption and production for winter and summer ................................................................................................. 18 3.5: Annual electrical energy chart for PVT ......................................................... 19 3.6: Comparison of PV efficiency for a typical summer and winter day ............... 19 3.7: Thermal energy delivered by PVT to the attic heat exchanger .................... 20 3.8: Comparison of thermal energy from PVT to AHX and PVT to preheat tank ............................................................................................................. 21 3.9: Thermal energy gain form hydronic furnace ................................................ 22 4.1: Schematic of OASys .................................................................................... 26 4.2: Rate of energy consumption of OASys for a single day ............................... 27 4.3: Temperature history in the house for a single day ....................................... 28 ix 4.4: Humidity increase in the house due to OASys ............................................. 28 4.5: Water consumption of OASys for a single day ............................................. 29 4.6: Electrical energy consumption for OASys .................................................... 30 4.7: Water consumption of OASys for summer months ...................................... 30 5.1: High efficient water heater ........................................................................... 33 5.2: Hot water heater efficiency........................................................................... 34 6.1: Comparison of annual energy use for simulated models ............................. 40 6.2: Comparison of electrical energy use for cooling loads ................................. 41 6.3: Comparison of thermal energy use for simulated and prototype models ..... 42 6.4: Comparison of net energy use for the house ............................................... 44 6.5: Comparison of CO2 emissions ..................................................................... 44 ACKNOWLEDGEMENTS I would like to thank Dr. Kent S. Udell for his support, encouragement and eminent guidance throughout the course of my master‟s. He was a role model who inspired and enriched me to become a better student. I am indebted to him beyond what words can express. I would like to thank Consol for financial support. I am sincerely thankful to Mr. Abe Cubano and Mr. Greg Barker for filling me on the gaps during the exploration of my work. I am very grateful to Mr. Troy Harvey for providing me with the initial model for my simulation study. I would like to thank the support groups of EnergyPlus and DesignBuilder for helping me resolve the issues that arose during the course of my work. I would like to extend my special thanks to my labmate Bidzina Kekalia for being patient with me every time I asked him about trivial things that seemed like a new world to me. I convey my deepest regards to everyone else in the lab- Christopher Workman, Denis Balic, Philip Jankovich, Kevin Smith and Seth Craig and for being there to talk to and relieve my stress. I would also like to thank my roommate Himabindu Nunna exclusively for sharing my „eureka‟ moments and my gloomy days with the same composure and not complaining even once. Most of all I gratefully acknowledge my parents, my sister Neelima and my brother-in-law Venu for their unconditional support in all my endeavors. If not for xi my father telling me that „It is once in your lifetime that you do a master‟s I would have taken a master of engineering degree and would have regretted it later. I owe to my sister for everything and beyond but most importantly for just being there for me. Expression fails me to tell you how much you all mean to me. If I could thank a materialistic thing, I would love to thank my laptop for surviving until I completed though it despised doing all the simulations. Lastly, I would like to thank everybody who was important for the successful completion of this thesis. CHAPTER 1 INTRODUCTION 1.1 Objective The objective of this study was to evaluate the energy use of a near zero energy home (ZEH) through field testing and energy simulation. This near ZEH is located in the cold, dry climate zone of Salt Lake Valley, Utah, in the Daybreak sustainable development community. A photograph of the home is shown in Figure 1.1. The U. S Department of Energy (DOE) describes a „Zero Energy Home‟ (ZEH) as a home that can produce as much energy as it consumes in a year. When a building is provided with renewable energy sources and energy efficient appliances, it performs as a near ZEH. Residential housing requires a major portion of the United States energy [2]. In the cold/hot and dry climate of Utah, major portions of the energy bills in every household are due to the cooling/heating requirements. As the rates for electricity and natural gas are always on an ascent, it is necessary to implement energy saving techniques. Greenhouse gases endanger human life with climate change. Nearly 70% of the electricity produced in the nation comes from coal, natural gas and other oil burning power plants. As such there is an increasing demand for carbon 2 Figure 1.1: Near ZEH located in Salt Lake City neutral designs worldwide. To achieve this, ZEH designs need to be embraced. The concept of a „Zero Energy Home‟ facilitates global prosperity, reducing the dependence on fossil fuels. The concept of this ZEH was developed in Building America‟s efforts to work for a cleaner environment. The previous work on ZEH‟s and some of the innovative technologies included in the ZEH are discussed in Chapter 2. In this work, energy analyses were conducted to evaluate the total performance of the near ZEH and the various innovative equipment included. DesignBuilder, a state-of-the-art software tool employing EnergyPlus simulation engine was used to evaluate the performance of the building designs. The house is equipped with a comprehensive network of sensors monitoring nearly every aspect of energy usage that occurs. Thermocouples are embedded in the walls, floors, ducts and plumbing. Pulse meters track energy usage, water and gas flows. Real time data acquisition was facilitated by a 3 Campbell Scientific data logger, CR1000 and a CS-COM210 telephone modem connected via serial I/O port. The data were accessed remotely by a computer and downloaded for analysis. Simulation models are validated with the data on energy usage and the discrepancies are noted. Detailed analyses were performed using the collected data. 1.2 Energy saving features The major energy saving features in the house include photovoltaic thermal (PVT) panels; the new hybrid solar panels that combine PV and solar thermal panel technology in a single entity; OASys, a new evaporative cooling unit that has a Seasonal Energy Efficiency Ratio (SEER) 40+; structurally insulated panels (SIPs); and a hydronic furnace. The description and the type of energy savings by these features is discussed in the following sections. 1.2.1 Photovoltaic thermal panels (PVT) PVT panels are hybrid solar panels that combine photovoltaic and solar thermal panel technology in a single unit. Photovoltaic panels generally have an efficiency in the range of 15%, with the remaining 85% of incident energy wasted as heat [13]. The PVT panels utilize the waste heat, improving the efficiency of the PV panels and the overall energy production of the installation. The complete analysis of the PVT is detailed in Chapter 3. 1.2.2 OASys For several years, many energy saving technologies were employed for space conditioning. Evaporative cooling is used extensively in dry climates in the 4 form of swamp coolers. Two-stage evaporative coolers that used direct cooling and indirect cooling were a revolution in the field of evaporative cooling. An emerging technology in this area is a variation to the existing two-stage evaporative coolers. This technology varies slightly from the former coolers in the principle of operation. It has indirect and direct cooling, which reduces the cooling energy use and improves comfort. OASys has an advertised seasonal energy efficiency ratio of 40+ [17]. OASys is said to result in great energy savings over a conventional unit. Its energy use over a conventional unit is verified and its performance is validated. The exhaustive review is detailed in Chapter 4. 1.2.3 Structurally insulated panels Building insulation plays a crucial role in reducing the energy loads. From the fundamentals of heat transfer, heat flows from higher temperature zone to a cooler temperature zone at a rate proportional to material conductivity. In order to restrict heat from escaping to the cold ambient air in winter and to restrict hot air from entering the house in summer, it is necessary to provide an effective resistance to the heat flow. SIPs have an effective resistance of R-23 for a 6" panel [19]. Apart from having a high R-value, SIPs provide tight insulation that reduces the air infiltration, thereby reducing the energy loss. Structurally insulated panel (SIP) is essentially a layer of foam (polystyrene) sandwiched between two ply wood sheets [19]. SIPs provide a uniform insulation and better efficiency than traditional construction methods. SIPs are also easy to construct. Figure 1.2 depicts the pattern of SIPs 5 arrangement. Energy savings provided from SIPs is evaluated using simulation models. The total savings and the effective performance are discussed in Chapter 7. 1.2.4 Hydronic furnace The near ZEH employs a hydronic furnace for space heating. A hydronic furnace has a water heating coil that transfers heat for space heating air. This unit improves the comfort of the home vastly. It provides better circulation of hot air, avoiding cold spots. Figure 1.3 is a simple flow schematic of the system. Figure 1.2: Cross-sectional view of SIPs panel 6 Figure 1.3: Schematic for flow lines of the hydronic furnace The hydronic furnace is also solar hot water assisted. Apart from providing comfortable heating, it also utilizes the waste heat in the house and supplements the water preheat tank. The waste heat is in the form of hot water running from the showers, dishwasher, etc. In general, this is a better unit than conventional forced-air units. 1.2.5 Water heater The near ZEH has a high efficiency water heater burning natural gas. Natural gas is less carbon intensive than any other fuel generally used for water heating, such as electricity from coal fired power plants. Hence, this high efficiency water heater is chosen for the near ZEH. This has a spiral heat exchanger that increases the time flue gases are entrained in the water heater, thereby increasing its efficiency. The performance analysis is detailed in Chapter 5. Figure 1.4 details the location of the predominant sensors and the layout 7 of the equipment in the house. 1.3 Overview In order to meet the objectives, the following research was undertaken and documented. The real time data were obtained to facilitate detailed energy analysis for the near ZEH and various energy saving components. Analysis of the PVT system is presented in Chapter 3. Chapter 4 provides a technical assessment of the OASys system‟s performance. Chapter 5 describes the study on the water heater‟s efficiency and its annual performance. Simulation models were developed to assess the net energy saving from the near ZEH. Chapter 6 presents the energy use for the various simulation models and the results of the prototype models. Chapter 7 provides the summary of the work accomplished. A website was developed to plot the essential data patterns for any user-specified day on the near ZEH house. The URL for the website is: www.zeroenergyhome.utah.edu. 8 Figure 1.4: Schematic of the sensors and the equipment in the house CHAPTER 2 LITERATURE REVIEW The building sector consumes nearly 40% of the U.S. primary energy. Space heating and cooling make up an overwhelming 42% of this energy use [2]. This is the prime motivation for the U.S. Department of Energy (DOE) to develop programs to reach net zero energy buildings. Also, there is an increasing interest in carbon neutral designs for new building construction in the United States. There has been extensive research in the area of low energy consumption buildings and even ZEHs worldwide. A building‟s energy use can be reduced by myriad ways. The main objective approach towards achieving this is by using renewable energy sources, construction technology that reduces the total energy use of the home and energy efficient appliances that consume less energy. A study on energy efficiency housing indicates that residential energy consumption will drop from 193 in 1990 to 187 GJ in 2030 [5]. A ZEH built in the suburban of Las Vegas has been in operation since 2006 and has net-zero electricity usage [9]. In Tuscon, a ZEH has been operating efficiently since 2003 [6]. The U.S. Department of Energy's Buildings Technologies (BT) Program set a goal to reach net zero energy buildings by 2025 [4]. 10 The building envelope is a crucial component for reducing energy loads. The existing building thermal insulation codes have reduced the building energy consumption by 25 % in Bahrain [7]. The concept of Structural Insulated Panels (SIPs) has been in existence since 1935. However, only when CAD/CAM streamlined the SIPs manufacturing process in 1999 did it become economically more feasible [20]. Electricity generation in residential buildings that have renewable energy source has been primarily through photovoltaic (PV) panels. Photovolotaic Thermal (PVT) panels were a revolution to the PV panels developed in the 1970s [14]. PVT combi-panels can use air (PVT/a), water (PVT/w) or any liquid (PVT/l) as the heat transfer medium. Theoretical and experimental studies on PVT were documented by Wolf [14]. Experimental studies on a PVT/w system installed in Riyadh, Saudi Arabia showed that PV efficiency dropped in summer and thermal efficiency remained well and vice versa in winter [14]. Studies on PVT/air systems illustrated a peak efficiency of 55% [13]. Extensive studies have been conducted on PVT water systems in Greece. The commercial production potential of these systems has been limited so far. A Japanese company developed a PV/T collector for domestic hot water in 1999 [8]. A solar air collector integrated with PV cells and a fan was developed by the Danish company Aidt MiljΦ A/A. The main purpose of the product is for dehumidification of air in cabins, garages, etc., but it can be used for preheating ventilation air [8]. The Canadian company Conserval Engineering Inc., developed 11 a PVT air system called „PV SolarWall‟. Cool ambient air passing beneath these panels captures the heat from PV cells and is used for heating ventilation air [8]. A hybrid PVT collector in Japan used for residential domestic hot water converted 10% of solar energy into electricity and 30% into hot water on an annual average [8]. A roof integrated system that utilizes the waste heat from PV array for water heating is used in North Carolina [8]. A specific PVT system in Spain at Library of Mataro uses the waste thermal energy from PVT for pre heating water in a conventional gas-fired heating system [8]. The PVT air concept is being used for space heating application in Denmark [10]. Evaporative cooling is a phenomenon known since time immemorial. However, indirect-direct evaporative cooling has seen acceptance only in the last few years [12]. To reach the long-term objective of reaching carbon neutral homes, several technologies can be applied for existing or new construction homes. This near ZEH has many energy saving features. Detailed energy analysis for the prototype and the individual equipment will be discussed in the following chapters. CHAPTER 3 PHOTOVOLTAIC THERMAL PANELS 3.1 Introduction Photovoltaic thermal panels (PVT) are a new technical innovation. In many ZEHs, the primary source for electricity generation has been PV modules. Building integration of PV modules has increased in recent years. PV modules usually convert 10-15% of incident energy into electricity. The remaining 85-90% of incident energy is wasted as „heat‟ [13]. In an effort to effectively utilize the waste heat, the concept of PVT has evolved. PVT or the hybrid solar panel technology involves production of electricity and heat from an integrated system. During the last 35 years, several theoretical and experimental studies have documented PVT performance [13]. However, commercialization of PVT is very limited compared to conventional PV and solar thermal systems. PV modules generate heat while in operation. The increased temperature of the solar cells reduces its electrical performance. PVT, in addition to providing thermal energy, extracts heat from the PV modules, thereby enhancing the PV modules electrical performance. The efficiency of a PV module drops by 0.2- 0.5% per rise. The use of PVT increases the energy yield per unit area [13]. This optimizes the use of roof space for residential constructions. Hence, PVT is an aesthetic alternative to a conventional system for confined roof spaces. 13 The PVT collector design can use air, water or other liquids as the heat transfer medium. In this near ZEH, a PVT system using air (PVT/a) supplied by PVT Solar Inc. is used. Figure 3.1 is an image of the PVT installed in the near ZEH. 3.2 Description of the system In this PVT, fresh air passes beneath the PV panels extracting the excess heat from them. The hot air is then filtered and drawn to a heat exchanger. The hot air is used for space heating, water heating or exhausted to the outside depending on the need. The specifications of the system are listed in Table 3.1. Figure 3.1: PVT installed at the near ZEH 14 Table 3.1: PVT specifications Description Value in English units Value in SI units Total PV area 126 ft2 11.7 m2 Total thermal collector area 52.5 ft2 4.87 m2 PV panel dimensions 9 modules SW 165 - 63" X 32" 9 modules SW 165 - 1.6 m X 0.81 m Thermal collector dimensions 3 modules SW 165 - 63"X32" 3 modules SW 165 - 1.6 m X 0.81 m Roof mounting clearance 4.5" 0.11 m Wiring and power point tacking losses 8% 8% Inverter efficiency 92% 92% The rated power output for the system is 2.145 kWp (Kilo Watt peak), of which 1.485 kWp is part of the PVT system. This prototype consists of nine modules in the PVT array. Only four of the nine modules are freely vented. 3.3 PVT performance The annual performance of PVT is assessed. PV and thermal energy delivered as per rating of the current system of the same size is 2740 kWh electrical, 4080 kWh of water heating, 859 kWh of space heating (predicted performance for the current version of the system) [17]. The system‟s 15 performance, with respect to the actual rated performance, is compared. To monitor the performance of PVT, a network of sensors is connected at various locations on the PVT and the associated equipment. Figure 3.2 details the system configuration. The heated air delivers its heat to the glycol in the attic heat exchanger and glycol preheats water entering the domestic hot water heater (DHW). In summer the water that enters the DHW is preheated to temperatures ranging from 70 ° F to 90 ° F on a very hot day and is preheated to at least 80 ° F Figure 3.2: PVT system configuration 16 on other days. In winter, the PVT preheats the water from 60 ° F to 70 ° F before entering the DHW. The temperature of water delivered from the DHW is 120 ° F. PVT reduces the need of DHW to heat inlet water from a low temperature. The DHW provides heat necessary for heating warm water, which reduces the natural gas consumption. Electrical and thermal energy generation takes place simultaneously. 3.3.1 Electrical (PV) performance of PVT The performance of electrical energy production for a typical summer day (June 27 2009) and winter day (Dec 28 2009) is compared in Figure 3.3. On a typical winter day, the total electrical energy production is 30% of the electrical energy produced on a typical summer day. The annual performance of PV is illustrated in Figure 3.4. Figure 3.3: Comparison of electrical energy from PVT for a typical summer and winter day 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 2 4 6 8 10 12 14 16 18 20 22 24 Rate of energy in Kw Time (Hour of the day) PV power production comparison for a typical day in summer and winter Summer day Winter day 17 The winter season is considered from October through May, a total of eight months. The summer season is considered from June through September, a total of four months. PVT produces 1234 kWh of electrical energy in summer and 1223 kWh of electrical energy in winter. It supplements nearly 42% of the total electrical energy use in summer season, while in winter it provides nearly 30% of the total electrical energy use. On an average, it provides 34.3% of the total electrical energy use of the home for the year 2009. The monthly production of electrical energy for the PV system for 2009 is illustrated in Figure 3.5. The low productivity in June and October is due to stormy weather in those months. 3.3.1.1 Efficiency of PV The effective efficiency of PV varies with time, incident angle, cloud cover, etc. The efficiency of PV is defined as follows: ηe = * 100 where, I = Incident solar radiation in W/m2, A = Area of PV panel in m2 and Actual PV energy in Watts. The value of incident solar radiation is obtained from the collector plane pyrometer installed with the PVT panel. The data used to measure the value of PV efficiency for a typical summer day and winter day are 18 Figure 3.4: Comparison of electrical energy consumption and production for winter and summer given in the Appendix. It was observed to be varying over the seasons annually. Figure 3.6 shows the efficiency of the PV system for a typical summer day (June 27 2009) and winter day (Dec 28 2009). The efficiency of the PV module drops during the peak hours of the day in summer as the temperature of the solar cells rise. This, however, does not happen in winter as the temperature in the solar cell does not increase as much as it does in summer. On average, the efficiency of PV during mid day, when the incident solar radiation is maximum, is 13.5% in summer and nearly 14.5% in winter. 0 1000 2000 3000 4000 5000 Winter Summer Energy in Kwh Season Comparison of Electrical Energy from PVT for Winter (Oct through May) and Summer (June through September) Energy Supplemented by PV Total Electrical Energy Use 19 Figure 3.5: Annual electrical energy chart for PVT Figure 3.6: Comparison of PV efficiency for a typical summer and winter day 0 50 100 150 200 250 300 350 400 Energy in kWh Months Electrical Energy from PV PV 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 18 20 22 24 Efficiency in % Time (Hour of the day) Comparison of Efficiency of PV Summer day Winter day 20 3.3.2 Thermal performance of PVT From previous studies there were instances when nearly 60% thermal efficiency was achieved from a PVT collector [1]. In this PVT system, thermal efficiency comes from the thermal modules and the waste heat from PV. The thermal energy delivered by the PVT for solar water preheat on a typical summer day (June 27 2009) and winter day (Dec 28 2009) is shown in Figure 3.7. It is observed that the thermal energy produced by the PVT panels in winter is low. The thermal energy from PVT contributes to only 10.5% of the total building thermal energy use for winter. The thermal energy is transferred from the PVT to glycol in the heat exchanger. The hot air delivers its heat to glycol in the attic heat exchanger, which transfers its thermal energy to the preheat tank. The data logger is programmed to give the values of thermal energy delivered by PVT to glycol in the attic heat exchanger and thermal energy from PVT to the solar preheat tank. During the peak summer months, there is a difference of 32% in the thermal energy delivered from PVT to the heat exchanger in the attic heat Figure 3.7: Thermal energy delivered by PVT to the attic heat exchanger 0 0.5 1 1.5 0 2 4 6 8 10 12 14 16 18 20 22 24 Energy in Kwh Time (Hour of the day) Thermal Energy delivered by PVT to the attic heat exchanger Summer Winter 21 and in the thermal energy from attic heat exchanger (AHX) to the preheat tank. This discrepancy could be attributed to a higher flow rate of air (entering the AHX) used for the computation of the thermal energy delivered to the AHX than is actually realized in the system operation or a lower glycol flow rate than actual. The comparison of thermal energy from PVT to glycol in the AHX and the thermal energy from the PVT to the preheat tank is shown in Figure 3.8. There is nearly 31% difference in the values of thermal energy shown Figure 3.8 in summer and nearly 24% difference in winter. The preheat tank has some additional heat gain from the hydronic furnace. The heat gain from the hydronic furnace is shown in Figure 3.9. It is observed that in the summer months the percentage of heat gain is not significant. On an annual basis there is 2% additional heat gain from the hydronic furnace which uses waste heat to supplement this energy. Figure 3.8: Comparison of thermal energy from PVT to AHX and PVT to preheat tank 0 50 100 150 200 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Energy in Kwh Months Comparison of thermal energy from PVT to AHX and PVT to pre-heat tank Thermal energy from PVT to AHX Thermal energy from PVT to pre-heat tank 22 Figure 3.9: Thermal energy gain form hydronic furnace 3.3.2.1 Thermal efficiency of the PVT The thermal efficiency of the PVT system is defined by the following formula: ηe = * 100 where, I = Incident solar radiation in W/m2, A = Area of thermal modules in PVT panel in m2 and actual thermal energy from PVT in Watts. The value of incident solar radiation is obtained from the collector plane pyrometer installed with the PVT panel. The data for the thermal energy received and generated by the PVT system for typical summer and winter day are given in the Appendix. The efficiency of the system for hot water generation for a typical summer day is nearly 21% and 2% for a typical winter day. On average, PVT produced nearly 32% of the total thermal energy for water heating in summer (June through 0 20 40 60 80 100 120 140 160 180 200 Energy in Kwh Months Thermal energy gain from hydronic furnace Thermal energy from attic to pre-heat tank Thermal energy from solar pre-heat tank to hot water heater 23 September) and 10.5% of the total thermal energy for water heating in winter (January through May and October through December) for the year 2009. In addition to providing preheat for the domestic hot water heater (DHW), PVT provides thermal energy for space heating in the winter. Since the flow rate of hot air exiting the AHX that enters the living space was not measured, the thermal efficiency cannot be specified. 3.4 Effectiveness of PVT The overall efficiency of the system is the sum of PV and thermal efficiencies. This amounts to nearly 35% efficiency in summer and 16% + efficiency in winter (the "+" indicates the additional thermal energy gain attributed for space heating) for the year 2009. This is the efficiency for the field system in which all the modules were not freely vented. However, the operational efficiency is still lower than the rated values. In comparison with a conventional PV unit with 10-15% efficiency, the efficiency of the system is nearly 20% higher in summer and 4-5% higher in winter [13]. Hence, PVT operates better than a regular PV system of the same dimensions by at least 10%. A conventional solar thermal panel operates with an efficiency of 50-60% [1]. This PVT unit operated with an average of 10.5% efficiency, which is lower than a conventional solar thermal unit. The annual electrical energy savings from PVT for the year 2009 was 1565 kWh, which translates to 2112 pounds of carbon dioxide savings (1kWh of electrical energy generation in U.S yields 1.35 lbs of CO2) [15]. Thermal energy savings from PVT yielded 969 kWh of energy in the form of preheat to water. 24 This translates to 3307 cubic feet of natural gas and 387 lbs of CO2 savings for the year 2009. On an annual basis, PVT reduces the CO2 emissions by 2499 pounds. CHAPTER 4 OASYS 4.1 Introduction and background Evaporative cooling has been used by man for thousands of years. Our ancestors used earthen pots to store water in the summers to keep it cool. Evaporative cooling extensively reduces the energy consumption compared to more common vapor compression air conditioners. The combination of direct and indirect cooling usually has a dramatic effect on a building‟s cooling load, provided the ambient air has the capacity for additional humidity. For a climate like Utah‟s, i.e., hot and dry in the summers, evaporative cooling can be used effectively. Two-stage evaporative coolers are a breakthrough in evaporative cooling technology. In a regular two-stage evaporative cooler, there is direct and indirect cooling of the air. In direct cooling, air is blown over a medium, pads, which are kept wet by water that is sprayed or dripped on them. The vaporization of water produces cool humidified air, which can get to 70-95% of outside air‟s wet bulb temperature. In indirect cooling, the hot air does not come in contact with the cooling medium. The air is cooled without increasing its moisture content. In an indirect-direct two-stage evaporative cooler, the total humidity of the air is 26 reduced, improving the thermal comfort. Essentially there is indirect cooling and then direct cooling, which cools the air. Incoming air first experiences indirect cooling as it flows through a heat exchanger. The precooled air is then passed through water soaked pads (ridges) where it picks up moisture and cools down further. This method reduces the total humidity of the exiting air compared to a regular evaporative cooler. Figure 4.1 depicts the process of indirect-direct cooling in OASys. The indirect cooling module (ICM) of OASys is a heat exchanger with two paths. The wet path exits warm humid air to the back and the dry path provides cooled air to the front to the direct cooling module (DCM). DCM is wet cooling media that directs cooled air to the front. Two-thirds of the air from DCM is forced to exit through the front. Figure 4.1: Schematic of OASys 27 The remaining one third of the air from the DCM enters the wet path of ICM and undergoes evaporation to accelerate cooling and exits warm and humid [18]. OASys, as advertised, is SEER 40+ two-stage evaporative cooler as used in this home. It claims to achieve more than 60-80% energy savings [18]. The use of this innovative cooler provides fresh outdoor air improving the indoor air quality. 4.2 OASys system performance The systems performance for a typical summer day (July 20th) is discussed below. The electrical power consumption for OASys for a typical summer day is shown in Figure 4.2. The temperature history for the prototype for a typical summer day is shown in Figure 4.3. The humidity increase in the air due to OASys is shown in Figure 4.4. The water consumption for OASys operation for a typical summer day is shown in Figure 4.5. The behavior of the evaporative cooler on a typical summer day is seen in Figures 4.2-4.5. : Figure 4.2: Rate of energy consumption of OASys for a single day 0 0.1 0.2 0.3 0.4 0.5 0 2 4 6 8 10 12 14 16 18 20 22 24 Power in Kw Time (Hour of the Day) Rate of energy consumption of OASys Rate of Electrical Energy into OASys 28 Figure 4.3: Temperature history in the house for a single day Figure 4.4: Humidity increase in the house due to OASys 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 16 18 20 22 24 Temperature in degree Farenheit Time (Hours of the day) Temperature history for a day (July 20 2009) T_Outdoor_Avg T_Bsmt_Avg T_Main_Avg T_Upstairs_Avg 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 16 18 20 22 24 Relative humidity in % Time (Hour of the Day) Humidity increase due to OASys Intake air humidity Conditioned air humidity 29 Figure 4.5: Water consumption of OASys for a single day The temperature in the house is maintained at an average of 73.5 F and the humidity was increased by nearly 17% from the outdoor humidity, thereby maintaining comfort conditions in the house. The electrical consumption is also relatively lower than a regular refrigeration unit [see Chapter 6]. The entire electrical energy consumption for the operation period of OASys is shown in Figure 4.6. Another important aspect is the water consumption for OASys. It has been considerably high. Figure 4.7 gives the monthly water consumption for OASys. Considering the higher water consumption of the OASys unit, it may restrict its operation to geographic regions with natural water abundance. Another alternative would be to use the water drained from the OASys for potential irrigation purposes. 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 16 18 20 22 24 Gallons Time (Hour of the Day) Water consumption of OASys Water Consumption in Gallons 30 Figure 4.6: Electrical energy consumption for OASys Figure 4.7: Water consumption of OASys for summer months 0 100 200 300 400 500 600 700 800 May June July Aug Sep Energy in Kwh Months Electrical Energy Consumtion for OASys Electrical Energy 0 500 1000 1500 2000 2500 June July Aug Sept Gallons Months Water consumption for OASys Water Consumption for OASys 31 Low energy consumption of OASys, the geographic location of the energy efficient house (hot and dry climate) and the air tight construction that needs fresh air ventilation make OASys an effective choice for the energy efficient house. CHAPTER 5 WATER HEATER 5.1 Introduction A high efficiency water heater looks and operates almost like a regular gas-fired water heater but has an improved design that increases its efficiency. The high efficiency water heater has a rated efficiency of 96% unlike the regular water heater, which comes in a distant second with a rated efficiency of 80%. The high efficiency water heater used in this ZEH is Vertex™ 100 Power Direct- Vent Gas Water Heater, provided by A.O. Smith Water Heaters. A photograph of the DHW heater is shown in Figure 5.1. Regular water heaters burn the natural gas and flue gases escape into the air while they are still hot. In this high efficiency water heater, the flue gases are further cooled, allowing condensation of its water vapor, exhausting flue gases at ambient temperatures. The inside of the tank is glass lined to prevent corrosion. This also reduces the heat loss into the ambient air by reducing the overall heat transfer coefficient. The capacity of this system is 50 gallons. It can deliver 4 gallons hot water per minute. With its high efficiency it can deliver continuous hot water for longer than a regular water heater. It also has an aesthetic design that occupies a similar space as that of a regular hot water heater tank. 33 Figure 5.1: High efficient water heater The water heater is also solar hot water assisted. The photovoltaic thermal panels harness the useful thermal energy from the sun and give it as preheat to the hot water heater. During the times solar energy can be used, the water heater uses the free energy to provide hot water. Due to a high efficiency water heater, the gas consumption is 20% less than a regular water heater [17]. This high efficiency water heater has a spiral heat exchanger, which reduces scaling by mineral deposit and thus maintains efficiency over time. The eco friendly design also reduces the NOx emissions. 5.2 Hot water heater performance The overall performance of the hot water heater has been monitored for over a year. The total natural gas that is supplied to the house is distributed into the hot water heater and the hydronic furnace. The chemical energy from natural gas is compared with the thermal energy used in the ZEH for hot water and space heating. 34 Conversion factors for natural gas are: 1 cubic feet of Natural gas = 1000 Btu = 0.293kWh. Volume multiplier = 0.9 (value averaged for the months) *(Conversion factors are taken from Questar, the natural gas supplier). The efficiency, η is defined as the thermal energy of the hot water supplied by the heater divided by the chemical energy supplied by the natural gas to the heater. η = Input (Chemical energy from natural gas) Output (Thermal energy of the hot water) Figure 5.2 illustrates the performance efficiency. It is observed that the water heater performs at an average of 83% efficiency in the months when hot water is used for domestic hot water heating and space heating application. Figure 5.2: Hot water heater efficiency 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 Dec-08 Apr-09 Jul-09 Oct-09 Feb-10 Efficiency in % Months Hot Water Heater Efficiency Efficiency 35 However, in the summer when energy is used exclusively for water heating, the system‟s efficiency drops to 39%, which is considerably low. The difference is due to the heat lost to the inside ambient air when no hot water is used. The measured results indicate that the overall efficiency varies with the climate conditions. The actual performance is lower than the rated performance. CHAPTER 6 SIMULATION RESULTS 6.1 Introduction This prototype house combines several energy saving features. The purpose of this investigation is to identify the energy savings produced by these technologies. To accomplish this task, simulation models are used to quantify the energy use of the prototype house in comparison with a similar house that not incorporates the energy saving features. To perform the simulations for the prototype house, DesignBuilder (DB), a software tool for analyzing building energy performance is used. DB uses EnergyPlus (E+) simulation engine. E+ is the state-of-the-art simulation engine to calculate building energy loads [21]. EnergyPlus is used for performing energy analysis and thermal load simulations [23]. It is capable of calculating the heating and cooling loads of a building with its associated mechanical systems. It inputs ASCII text based weather files and intends to provide accurate simulation conditions. It can handle many simulation situations. It can deal with many building and HVAC design options. However, it does not contain a user interface. To assist in fine-tuning and to correct input mistakes, a graphical user interface is used [23]. 37 DesignBuilder facilitates whole building modeling and concentration of particular zones for more precise load calculations. Inbuilt data templates allow the user to pick the common building constructions, activities, HVAC systems, etc. It also allows data inheritance to create a user specific template detailing the actual conditions. It has the ability to generate data automatically after the simulations and/or calculations. It can give the energy consumption by fuel and end-use, heating and cooling loads, CO2 generation, etc. [21]. The initial prototype model for the near ZEH was developed in DesignBuilder (DB). DB has inbuilt weather data for several weather stations. However, the weather data are averaged over 40 years and the best weather data are approximated and used [21]. To provide the actual weather conditions, weather data for the simulations were taken from the local Salt Lake City weather station. The model was analyzed to specify the energy savings achieved from the near ZEH. A parametric study was conducted to verify the energy savings achieved by the ZEH. The parametric study is done by performing simulations for various construction conditions. The major components, i.e., the external walls, flat roof, pitched roof and semiexposed wall, are changed and the remaining and are set to be the same. 6.2 Parametric study The various cases that were studied are listed in the Table 6.1. The simulations were carried out using 2009 weather data. The simulated monthly energy uses for each case on an annual basis are illustrated in the Figure 6.1. 38 Table 6.1: Parametric case study Simulation Type Construction Conditions Case 1 Actual Conditions  External Wall: 6" SIP  Flat Roof: Roof - 8" SIP  Pitched Roof: Roof - 8" SIP  Semiexposed wall: Wall - 8" SIP Case 2 R-13 insulation  External Wall: 2 X 6" R - 13 batt  Flat Roof: Roof - R-38  Pitched Roof: Roof - R- 38  Semiexposed wall: 2 X 6" R - 13 batt - 16" OC Case 3 R-19 wall insulation  External Wall: R - 19 2 X 6" 16 " OC  Flat Roof: Best practice roof  Pitched Roof: Best practice roof  Semiexposed wall: Wall - R-19 2 X 6" 16 " OC Case 4 International Energy Conservation Code (IECC) Template  External Wall: 2 X 6" R - 19 - 16 " OCR Flat Roof: Roof - R-38  Pitched Roof: Roof - R-38  Semiexposed wall: Wall 2 X 6"- 39 Table 6.1: Parametric case study continued R-19 -16 " OC  Semiexposed wall: Wall - R-19 2 X 6" 16 " OC Case 5 R-23 insulation  External Wall: 2 X 6" R - 23 blown + 1"PUR-24" OC  Flat Roof: Roof - R-38  Pitched Roof: Roof - R- 38  Semiexposed wall: 2 X 6" R - 23 blown + 1"PUR-24" OC 40 Figure 6.1: Comparison of annual energy use for simulated models The simulation results indicate that the prototype having SIPs has significant energy savings in the heating season. However, the simulation results show that the building envelope does not reduce the cooling loads vastly. SIPs construction has nearly 30% reduced energy use over a benchmark home that uses R-13. It also has over 15% reduced energy use over buildings with standard construction codes like IECC. These results are in agreement with previous studies by Krarti and Hildereth., which indicated that effect of wall thermal insulation (R-value) does not reduce the annual cooling energy use [16]. 6.3 Cooling loads summary The simulations were also carried out for different cooling conditions. The cooling system‟s coefficient of performance (c.o.p) was varied to verify the energy savings from the OASys. For comparison, a vapor compression cooling system with a c.o.p of 3.43 was evaluated. The c.o.p chosen is a standard c.o.p 0 1000 2000 3000 4000 5000 6000 Jan-09 Apr-09 Jul-09 Oct-09 Energy use in kWh Months Comparison of annual energy use SIPs R 13 R 19 IECC R 23 41 that most Utah homes have [23]. Figure 6.2 shows the comparison in cooling energy use for the prototype with OASys and the simulation result for a vapor compression cooling system. The results indicated that OASys had an average of 60% reduced savings in comparison with a regular vapor compression air conditioning unit. Certain variations in the monthly distribution are interpreted as discrepancies in the weather data for simulation. Energy saving directly from the use of this evaporative cooler for the climatic conditions of Salt Lake City is 60%, which translates to 785 kWh of energy saving for the summer season. However, the water consumption of OASys was high. It was nearly 2,000 gallons per month. The OASys system, with the reduced energy savings and fresh air ventilation, is recommended for replacing conventional air conditioning units in hot and dry climates. Figure 6.2: Comparison of electrical energy use for cooling loads 0 100 200 300 400 500 600 Jun '09 Jul '09 Aug '09 Sept '09 Energy in kWh Months Comparison of electrical energy use for cooling loads OASys Regular vapor compression system 42 6.4 Heating loads summary The use of SIPs wall resulted in almost 30% energy savings from a home using standard construction practice over the year. The comparison of the actual heating load to the simulated load is shown in Figure 6.3. As shown in Figure 6.3, energy use for heating months varies slightly from the measured energy usage. The discrepancies result from energy use patterns of the people residing in the home, conditions of the building construction and real time factors such as different air infiltration, etc. This prototype had certain thermal leaks in the roof due to inefficient construction practices and a few leaks in the duct work. This and the other factors mentioned above may account for the increased thermal energy use from the simulated results. Figure 6.3: Comparison of thermal energy use for simulated and prototype models 0 500 1000 1500 2000 2500 3000 3500 Jan '09 Feb '09 Mar '09 Apr '09 Oct '09 Nov '09 Dec '09 Energy in kWh Months Comparison of thermal energy use for simulated and prototype models Simulated model Prototype 43 6.5 Net energy loads summary The annual net energy use of the prototype considering the electrical and thermal energy gain from the PVT has been lower than the simulation results. The monthly behavior of the prototype with the simulation result is illustrated in Figure 6.4. In the heating season the measured net energy use was lower than the simulation result. However, in June, July and August 2009, the peak summer months, the net usage was significantly lower than the simulation result indicating reduced energy use from OASys. The variation in December could be attributed to the discrepancies in weather data or the lack of the inclusion of the thermal energy gain from PVT. On an average the measured energy usage is 17.1% lower than the simulation result of the prototype with SIPs as the exclusive energy savings element. This concludes that the prototype has about 47% reduced energy use from a regular home. 6.6 Carbon dioxide emissions summary The carbon dioxide emissions were primarily from electricity and natural gas consumption. The carbon dioxide emissions from electricity and natural gas vary differently. Every kWh of energy from electricity and cubic feet of natural gas used generated 0.64 and 0.0546 Kgs of carbon dioxide, respectively [24]. Figure 6.5 illustrates the comparison of carbon dioxide emissions for the near ZEH and the simulation model of a regular home. 44 Figure 6.4: Comparison of net energy use for the house Figure 6.5: Comparison of CO2 emissions 0 500 1000 1500 2000 2500 3000 3500 4000 Energy in kWh Months Comparsion of net energy use for the house Simulated model Prototype 0 200 400 600 800 1000 1200 1400 1600 CO2 (Kg) Months Comparison of CO2 emissions Simulated model (regular home) Prototype 45 On an annual basis the near ZEH has 60% reduced carbon dioxide emissions from a prototype model that did not include any of the energy saving feature. The annual carbon dioxide savings recorded for the near ZEH was 5.6 tons. CHAPTER 7 RESULTS AND DISCUSSION Globally, sustainability and energy efficiency in buildings are a critical issue that has to be addressed. To achieve the goal of reaching „net zero energy buildings‟, Building America has been conducting research on „zero energy building designs‟ during the last few years. This ZEH project is a part of the Building America research program. This near ZEH built in Salt Lake City incorporated several innovative technologies. The actual performance of the equipment and prototype was analyzed in comparison with the simulation model of a home without any of the energy saving features. The performance of the key elements was analyzed. It is found that SIPs provides an excellent insulation for the house. The effective thermal load on the building for heating season is greatly reduced by the use of SIPs. However, SIPs have negligible impact on the cooling energy load in the summer. The simulation results indicate that SIPs provide nearly 30% reduced energy use for the building in heating season. The new two-stage evaporative cooler, OASys, provides a 60% reduced energy consumption compared to a vapor compression air conditioning system. However, the water usage is very high. There is fresh air circulation for a healthy living environment. As SIPs provide a very tight sealing with very low air 47 infiltration rate, OASys is an effective choice for ZEH constructions in Salt Lake City that which reduces the cooling energy use vastly. The water heater is relatively energy efficient and has a time averaged efficiency of 83% average efficiency. This is lower than the rated 96% efficiency, but includes heat loss to the air when heating is not occurring, thereby increasing the cooling energy loads in the summer. The solar power generation unit, PVT, provides nearly 42% of the electrical energy use in the ZEH in summer and an average of 30% in winter. There is also thermal energy gain from PVT. It supplements nearly 50% of the total thermal energy use in summer and nearly 10% of the total thermal energy use in winter. The effectiveness of PVT is analyzed seasonally. It has a total efficiency of 35% in summer and 16%+ efficiency in winter (considering it provides a certain amount of space heating that cannot be assessed accurately). The PVT unit proves to be a better choice than a conventional PV unit. However, the efficiencies of the system are much lower than the rated efficiency of 50-60%. From the real time data, the actual performance of this near ZEH was compared with the simulated model of a regular home without any of the energy saving features. It was observed that the prototype had nearly 47% reduced energy use over a regular house for the year 2009. The electrical energy consumption was 50% lower than a regular house and the thermal energy was lower by 16%. Reduction in fossil fuel use leads to greater carbon dioxide savings. The total annual carbon dioxide emissions were 60% lesser than a regular home. 48 Based on findings of this work, the following recommendations can be made for future energy efficient home construction: 1. Since the benefit of SIPs for reducing the building energy use is evident, it is recommended for future construction. Greater benefits may be obtained by using thicker or lower conductivity foam insulation in SIPs. 2. OASys clearly provided energy savings over a regular vapor compression system. However, the benefits of OASys over a regular evaporative cooler need to be studied. If the excess water consumption is directed towards irrigational use, the unit is an excellent choice for construction with the need for fresh air circulation and low energy consumption. 3. Although the high efficiency water heater showed a considerable performance improvement over conventional water heaters, further reduction in heat loss to the indoor air in summer months can achieved by the use of a tankless water heater. 4. PVT panels that were designed to potentially utilize 80% of the incident solar radiation had less significant thermal energy capture. The thermal energy obtained in summer is not utilized fully. The design needs to be improved with the aim of beneficially capturing thermal energy in summer for seasonal storage or another application that utilizes the available energy. 5. Most of the work presented in this thesis related to the evaluation of energy saving features associated with the house. Further research 49 needs to be conducted to investigate the interaction of building geometry, window placement and other construction practices to achieve a net zero energy home design. APPENDIX The data set for a typical summer day (June 27th 2009) used to compute the electrical efficiency of the PVT are listed in Table A.1. Table A.1: PV data history for June 27, 2009 Time (Hour of the day) June 27th PV power in KW June 27th Incident solar radiation in W/m2 June 27th PV power from the total incident solar energy in KW 1 0 0 0 2 0.001 0 0 3 0.001 0 0 4 0.001 0 0 5 0.001 0 0 6 0.001 0.59 0.006903 7 0.008 16.58 0.193986 8 0.042 35.69 0.417573 9 0.067 68.32 0.799344 10 0.302 257.1 3.00807 11 0.756 456.8 5.34456 12 1.116 654.1 7.65297 13 1.37 824 9.6408 14 1.539 951 11.1267 15 1.631 1015 11.8755 16 1.68 1025 11.9925 17 1.63 986 11.5362 18 1.475 886 10.3662 19 1.223 723.7 8.46729 20 0.763 465.1 5.44167 21 0.182 135.3 1.58301 22 0.001 1.734 0.0202878 23 0.001 0.001 0 24 0.001 0 0 51 The data history for a typical winter day December 28th 2009 that is used to compute the efficiency of the PVT are listed in Table A.2. Table A.2: PV data history for December 28, 2009 Time (Hour of the day) Dec 28th PV power in KW Dec 28th Incident solar radiation in W/m2 Dec 28th PV power from the total incident solar energy in KW 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 7 0 0 0 8 0 0 0 9 0 1.406 0.0164502 10 0.028 35.49 0.415233 11 0.141 116.3 1.36071 12 0.269 234.4 2.74248 13 0.559 387.6 4.53492 14 0.927 558.4 6.53328 15 0.96 576.2 6.74154 16 0.852 513.1 6.00327 17 0.467 290.6 3.40002 18 0.092 74.09 0.866853 19 0.001 1.403 0.0164151 20 0 0 0 21 0 0 0 22 0 0 0 23 0 0 0 24 0 0 0 52 The data used to compute the thermal efficiency of the PVT for a typical summer day (June 27th 2009) are shown in Table A.3. Table A.3: PVT data history for June 27, 2009 Time (Hour of the day) June 27th Incident solar radiation in W/m2 June 27th Rate of total thermal energy incident on the solar panel in KW June 27th Rate of total thermal energy captured by PVT in KW 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0.59 0.0028733 0 7 16.58 0.0807446 0 8 35.69 0.1738103 0 9 68.32 0.3327184 0 10 257.1 1.252077 0 11 456.8 2.224616 0 12 654.1 3.185467 0.428 13 824 4.01288 1 14 951 4.63137 1.212 15 1015 4.94305 1.265 16 1025 4.99175 1.139 17 986 4.80182 0.955 18 886 4.31482 0.753 19 723.7 3.524419 0.476 20 465.1 2.265037 0.078 21 135.3 0.658911 0 22 1.734 0.00844458 0 23 0.001 0.00000487 0 24 0 0 0 53 The data used to compute the thermal efficiency of the PVT for a typical winter day (December 28th 2009) are shown in Table A.4. 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