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Thermal performance evaluation of an energy and environmental research center building during winter
Applied Energy 65 (2000) 231±238
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Thermal performance evaluation of an energy and environmental research center building during winter A. Al-Karaghouli*, I. Abood Energy and Environment Research Center PO Box 13026 Baghdad, Iraq
Abstract The building is constructed on a ground area of 3300 m2 and consists of ®ve ¯oors of total area of 6361 m2 with an air conditioned area of 3351 m2. The heating system comprises 1577 evacuated-tube collectors, two accumulation tanks of 15 m3 each, two thermal storage tanks of 150 m3 each, two auxiliary boilers of 443,000 kcal/h each, pumps, heat exchangers and control equipment. The thermal performance evaluation shows that the inside temperature was kept at the desired value (22 C) which demonstrates the system's ability to meet the building load. The performance also shows that the collection eciency for the whole season was 50% and the collected and stored energy was higher than the required load which indicates that the solar fraction to the load was 100%. # 1999 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction In recent decades, there has been an increasing interest in the use of solar energy: projections suggests that it could provide a large saving in conventional energy consumption [1±10]. Solar space-heating has been applied widely around the world. One of the strongest arguments in favour of the solar space-heating is that the heat required, in the residential sector, is in the low-temperature range (i.e. less than 100 C). Electricity and fossil fuels can be used to perform many tasks, and it is wasteful to use such energy to produce low-temperature heat. Solar space-heating systems have been shown to function properly; eorts are being made to improve equipment reliability and the methods of installation. Several heating projects have been implemented in several locations in Iraq. One of these is for the Energy and Environmental Research Center Building. * Corresponding author. 0306-2619/00/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S0306-2619(99)00081-1
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A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
2. Building design and description The building is located at Jadriyah area in Baghdad (33 320 N latitude and 44 40 longitude). It is constructed on a ground area of 3300 m2 and consists of ®ve ¯oors in addition to two penthouse ¯oors, which accommodate the air-conditioning equipment. The total ¯oor-area is 6361 m2 with an air-conditioned area of 3351 m2. The building contains laboratories in all ®elds of solar-energy applications, a computer room, adminstration and researcher oces, a library, a lecture theatre, workshop and an air-raid shelter. The front surface of the building is inclined at 45 and oriented at 22 east of south. On this surface 1017 evacuated-tube solar collectors have been erected. Another 560 similar collectors have also been installed in the front of the building at an angle of 17 from the horizontal. The outer walls of the building were built using, gypsum board, air space, ®berglass and concrete. Its heat-loss coecient is 0.811 W/m2 K. The roof section consists of polystyrene, concrete, an air space and gypsum board. The heat loss coecient is 1.57 W/m2 K. 3. Heating load calculation There are two kinds of heat losses from the building; (1) the heat transmitted through the walls, ceiling, ¯oor, glass or other surfaces; (2) the heat required to warm the outdoor air entering the space. The heating load was calculated by dividing the building into four zones; the ®rst two comprise the administration and the researcher oces, while the other two are the building laboratories. The ASHRAE procedure was used in the calculation, assuming 3 C and 40% RH as outside conditions and 22 C as the inside building temperature. The heating load for the four zones was calculated and found to be 35,180, 47,430, 19,350 and 22,500 kcal/h, respectively. Therefore the total building heating load was 124,460 kcal/h. 4. Solar heating system This and the domestic hot water system consists of three loops; the solar-collectors' loop, the heating loop and a domestic hot-water loop (Fig. 1). 5. The system's operation 5.1. Collector loop The heat-collection controller automatically governs the operation of the circulation pumps. The pumps start to operate when sucient insolation is available and
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
233
Fig. 1. Schematic diagram of the building's air-conditioning system.
the temperature dierence between the absorber of the collector and the accumulation tank water reaches 7 C and stops after 5 min, when the temperature dierence reaches 4 C. The loop is equipped with boiling and freezing controls. When the collector temperature reaches 115 C, the circulation pumps will stop and the collector water will be drained. It re-operates the system again after 5 min from when the collector temperature becomes 100 C. If the collectors' temperature becomes lower than 2 C, then the circulation pumps operate and hot water from the accumulation tank recirculates in the collector's loop to protect the collector and the piping loop from damage. After 5 min from the collector temperature becoming 7 C, the pump circulation will stop. 5.2. Heating loop During daytime and when the temperature of the accumulation tank is higher than the temperature of the thermal storage tank by 5 C, the hot-water pump operates and circulates the water between the accumulation tank and the thermal storage tank through the heat exchanger. This will continue until the water temperature in the thermal storage tank reaches 45 C or when the water temperature of the accumulation tank drops to 50 C. If the building needs heat, then a pump will be activated to circulate the hot water between the thermal storage tank and the heating coil of the air-handling unit. When the thermal storage tank temperature drops to 30 C and the accumulation tank temperature is still less than 50 C, then the auxiliary heating system will operate as follows: the auxiliary boilers are activated to heat the thermal storage tank through the heat exchangers. If the auxiliary energy will not satisfy the load, then
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A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
the heat-pump chillers will operate to increase the temperature of the thermal storage tank. The auxiliary heating system was never used during the previous operation period of the building due to sucient solar energy being collected. To control the room temperature, the temperature dierence between the room and the air-handling unit, the outlet air was measured in order to control the quantity of hot water enter the air-handling unit coil. 5.3. Domestic hot-water loop The fresh water supplied from the domestic tank will be heated by exchanging heat with hot water from the accumulation tank inside the heat exchanger. Then it is pumped to the electric auxiliary boiler to increase its temperature to 45 C. This water circulates through the domestic loop and returns back to the electric boiler. Make-up water is supplied from the heat exchanger when needed. 6. Results and discussion The building temperature is maintained by various thermostats, which control the operation of the four air-handling units. Therefore, the inside temperature could be set dierently for each zone according to the desired temperature. Fig. 2 shows the variations of inside and outside temperatures for a selected day during the winter season. The inside for this day was set at 22 C for the whole building. The data show that the outside temperature is low in the early morning, then starts to increase until it reaches its maximum value in the afternoon before decreasing again. This is typical during winter due to the fact that more than 90% of the days are sunny in
Fig. 2. Inside and outside temperature variations for a selected winter day.
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
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this area. Fig. 2 also shows that the inside temperature was kept within the desired value, which demonstrates the system's ability to meet the building load. The accumulation tank is used to collect the energy gained by the solar collectors; then its heat is transmitted to the thermal storage tank to be used for heating purposes. Hourly measurements of both tanks' temperatures were taken for several locations inside both tanks. The mean temperatures of both tanks for clear and cloudy days are shown in Fig. 3. For a clear day, the ®gure shows that the accumulation tank temperature was low in the morning, increases until it reaches around 55 C in the afternoon and then decreases again. Correspondingly, the thermal storage tank temperature increased until it reached around 45 C which is its maximum set temperature. The thermal storage tank temperature increases during the day due to the extra heat collected from the dierence between the heat gained and the building heating load. Also, Fig. 3 shows that, for cloudy days, the heat gain could not cover the building's heating load and for this reason extra heat should be withdrawn from the thermal storage tank which, as can be seen, results in decreasing its temperature. The daily average temperature of the thermal storage tank for the whole season is shown in Fig. 4. As expected, the data show that the average daily temperature is greater in March. The thermal storage tank temperature was kept within the designed value, which is 45 C, for the whole season except for a few cloudy days. To analyze the collector's performance, the global radiation for 45 and 17 tilts, the inlet and outlet temperatures, ¯uid ¯ow rates and the pumps operation time were monitored hourly. The collector's temperature dierences for a winter typical day for the two tilt angles (45 and 17 ) are shown in Fig. 5. More heat is collected from the collectors
Fig. 3. The daily temperature variations inside the accumulation and thermal storage tanks for a clear and a cloudy day.
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Fig. 4. Daily mean storage temperature for the heating season.
Fig. 5. Collectors' temperature-dierence for a selected winter day.
tilted at 45 than that at 17 . This is attributed to the fact that 45 is nearer the optimum tilt angle for the winter season (Baghdad lies at 33 30 N latitude). The collector's eciency is the ratio of the collected energy to the incident energy. The collector's eciency for both tilt angles for a selected winter day is shown in Fig. 6. It can be seen from this ®gure that, as expected, the eciency for both cases starts to increase after dawn until it reaches its maximum value at noon, and then decreases again. It is also noticed that the collector's eciency at 45 was higher
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
237
than that at 17 , as discussed above. The average daily collector's eciency was 56 and 47% for 45 and 17 tilt angles, respectively, during the month of January (Fig. 7). The building's energy-balance consists of the incident energy, the collected energy, the stored energy and the load Ð see Table 1. This indicates that the solar collection eciency was 50% the system losses 35% and the solar fraction to the load was
Fig. 6. Collector's eciency for both tilt angles for a selected winter day.
Fig. 7. Daily collector's eciency for both tilt angles for January.
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Table 1 The building energy balance during winter season Incident energy (Mcal/day)
Collected energy (Mcal/day)
Stored energy (Mcal/day)
Load (Mcal/day)
Collection eciency
Solar fraction
7478
3739
2430
995
50%
100%
100%. This high solar-fraction is attributed to the fact that the load is much less than the stored energy in the winter season. 7. Summary For the building during the heating season: (i) the average daily incident energy was 7478 Mcal, the average daily collected energy was 3739 Mcal corresponding to a system-collection eciency of 50%; (ii) the daily average load is 995 Mcal. This is much less than the collected energy, which indicates that the solar fraction to the load is 100%. For this reason, the auxiliary energy supply system was never used. References [1] Due JA, Beckman W. Solar energy thermal processes. New York: Wiley and Sons Inc, 1974. [2] Kreith F, Kreider J. Principles of solar engineering. New York: Hemisphere Publishing Cooperation, 1978. [3] Jager F. Solar energy applications in houses. Luxembourg: Commission of the European Communities, 1981. [4] ASHRAE. Handbook of fundamentals. New York: American Society of Heating and Air Conditioning Engineers, 1977. [5] Yellott JI. Solar heating and cooling of houses. In: Sayigh AM, editor. Solar energy engineering. Academic Press, New York, 1971 (chapter 17). [6] Kiruma K. Utilization of solar energy, the Japanese experience in solar energy application in the tropics. New York: Reidel Publishing Company, 1983. [7] McVeigh J. Sun power, an introduction to the application of solar energy. Oxford (UK): Pergamon Press, 1983. [8] Lof G, Karaki. System performance for the supply of solar heat. Mechanical Engineering, Des 33± 47. 1983. [9] Tanni R. et al. Technical Report No. 2 for Jordan solar house. Amman (Jordan): Royal Scienti®c Society, 1983. [10] Plaze W, Steemers T. Solar houses in Europe. Oxford (UK): Pergamon Press, 1981.
www.elsevier.com/locate/apenergy
Thermal performance evaluation of an energy and environmental research center building during winter A. Al-Karaghouli*, I. Abood Energy and Environment Research Center PO Box 13026 Baghdad, Iraq
Abstract The building is constructed on a ground area of 3300 m2 and consists of ®ve ¯oors of total area of 6361 m2 with an air conditioned area of 3351 m2. The heating system comprises 1577 evacuated-tube collectors, two accumulation tanks of 15 m3 each, two thermal storage tanks of 150 m3 each, two auxiliary boilers of 443,000 kcal/h each, pumps, heat exchangers and control equipment. The thermal performance evaluation shows that the inside temperature was kept at the desired value (22 C) which demonstrates the system's ability to meet the building load. The performance also shows that the collection eciency for the whole season was 50% and the collected and stored energy was higher than the required load which indicates that the solar fraction to the load was 100%. # 1999 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction In recent decades, there has been an increasing interest in the use of solar energy: projections suggests that it could provide a large saving in conventional energy consumption [1±10]. Solar space-heating has been applied widely around the world. One of the strongest arguments in favour of the solar space-heating is that the heat required, in the residential sector, is in the low-temperature range (i.e. less than 100 C). Electricity and fossil fuels can be used to perform many tasks, and it is wasteful to use such energy to produce low-temperature heat. Solar space-heating systems have been shown to function properly; eorts are being made to improve equipment reliability and the methods of installation. Several heating projects have been implemented in several locations in Iraq. One of these is for the Energy and Environmental Research Center Building. * Corresponding author. 0306-2619/00/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S0306-2619(99)00081-1
232
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
2. Building design and description The building is located at Jadriyah area in Baghdad (33 320 N latitude and 44 40 longitude). It is constructed on a ground area of 3300 m2 and consists of ®ve ¯oors in addition to two penthouse ¯oors, which accommodate the air-conditioning equipment. The total ¯oor-area is 6361 m2 with an air-conditioned area of 3351 m2. The building contains laboratories in all ®elds of solar-energy applications, a computer room, adminstration and researcher oces, a library, a lecture theatre, workshop and an air-raid shelter. The front surface of the building is inclined at 45 and oriented at 22 east of south. On this surface 1017 evacuated-tube solar collectors have been erected. Another 560 similar collectors have also been installed in the front of the building at an angle of 17 from the horizontal. The outer walls of the building were built using, gypsum board, air space, ®berglass and concrete. Its heat-loss coecient is 0.811 W/m2 K. The roof section consists of polystyrene, concrete, an air space and gypsum board. The heat loss coecient is 1.57 W/m2 K. 3. Heating load calculation There are two kinds of heat losses from the building; (1) the heat transmitted through the walls, ceiling, ¯oor, glass or other surfaces; (2) the heat required to warm the outdoor air entering the space. The heating load was calculated by dividing the building into four zones; the ®rst two comprise the administration and the researcher oces, while the other two are the building laboratories. The ASHRAE procedure was used in the calculation, assuming 3 C and 40% RH as outside conditions and 22 C as the inside building temperature. The heating load for the four zones was calculated and found to be 35,180, 47,430, 19,350 and 22,500 kcal/h, respectively. Therefore the total building heating load was 124,460 kcal/h. 4. Solar heating system This and the domestic hot water system consists of three loops; the solar-collectors' loop, the heating loop and a domestic hot-water loop (Fig. 1). 5. The system's operation 5.1. Collector loop The heat-collection controller automatically governs the operation of the circulation pumps. The pumps start to operate when sucient insolation is available and
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
233
Fig. 1. Schematic diagram of the building's air-conditioning system.
the temperature dierence between the absorber of the collector and the accumulation tank water reaches 7 C and stops after 5 min, when the temperature dierence reaches 4 C. The loop is equipped with boiling and freezing controls. When the collector temperature reaches 115 C, the circulation pumps will stop and the collector water will be drained. It re-operates the system again after 5 min from when the collector temperature becomes 100 C. If the collectors' temperature becomes lower than 2 C, then the circulation pumps operate and hot water from the accumulation tank recirculates in the collector's loop to protect the collector and the piping loop from damage. After 5 min from the collector temperature becoming 7 C, the pump circulation will stop. 5.2. Heating loop During daytime and when the temperature of the accumulation tank is higher than the temperature of the thermal storage tank by 5 C, the hot-water pump operates and circulates the water between the accumulation tank and the thermal storage tank through the heat exchanger. This will continue until the water temperature in the thermal storage tank reaches 45 C or when the water temperature of the accumulation tank drops to 50 C. If the building needs heat, then a pump will be activated to circulate the hot water between the thermal storage tank and the heating coil of the air-handling unit. When the thermal storage tank temperature drops to 30 C and the accumulation tank temperature is still less than 50 C, then the auxiliary heating system will operate as follows: the auxiliary boilers are activated to heat the thermal storage tank through the heat exchangers. If the auxiliary energy will not satisfy the load, then
234
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
the heat-pump chillers will operate to increase the temperature of the thermal storage tank. The auxiliary heating system was never used during the previous operation period of the building due to sucient solar energy being collected. To control the room temperature, the temperature dierence between the room and the air-handling unit, the outlet air was measured in order to control the quantity of hot water enter the air-handling unit coil. 5.3. Domestic hot-water loop The fresh water supplied from the domestic tank will be heated by exchanging heat with hot water from the accumulation tank inside the heat exchanger. Then it is pumped to the electric auxiliary boiler to increase its temperature to 45 C. This water circulates through the domestic loop and returns back to the electric boiler. Make-up water is supplied from the heat exchanger when needed. 6. Results and discussion The building temperature is maintained by various thermostats, which control the operation of the four air-handling units. Therefore, the inside temperature could be set dierently for each zone according to the desired temperature. Fig. 2 shows the variations of inside and outside temperatures for a selected day during the winter season. The inside for this day was set at 22 C for the whole building. The data show that the outside temperature is low in the early morning, then starts to increase until it reaches its maximum value in the afternoon before decreasing again. This is typical during winter due to the fact that more than 90% of the days are sunny in
Fig. 2. Inside and outside temperature variations for a selected winter day.
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
235
this area. Fig. 2 also shows that the inside temperature was kept within the desired value, which demonstrates the system's ability to meet the building load. The accumulation tank is used to collect the energy gained by the solar collectors; then its heat is transmitted to the thermal storage tank to be used for heating purposes. Hourly measurements of both tanks' temperatures were taken for several locations inside both tanks. The mean temperatures of both tanks for clear and cloudy days are shown in Fig. 3. For a clear day, the ®gure shows that the accumulation tank temperature was low in the morning, increases until it reaches around 55 C in the afternoon and then decreases again. Correspondingly, the thermal storage tank temperature increased until it reached around 45 C which is its maximum set temperature. The thermal storage tank temperature increases during the day due to the extra heat collected from the dierence between the heat gained and the building heating load. Also, Fig. 3 shows that, for cloudy days, the heat gain could not cover the building's heating load and for this reason extra heat should be withdrawn from the thermal storage tank which, as can be seen, results in decreasing its temperature. The daily average temperature of the thermal storage tank for the whole season is shown in Fig. 4. As expected, the data show that the average daily temperature is greater in March. The thermal storage tank temperature was kept within the designed value, which is 45 C, for the whole season except for a few cloudy days. To analyze the collector's performance, the global radiation for 45 and 17 tilts, the inlet and outlet temperatures, ¯uid ¯ow rates and the pumps operation time were monitored hourly. The collector's temperature dierences for a winter typical day for the two tilt angles (45 and 17 ) are shown in Fig. 5. More heat is collected from the collectors
Fig. 3. The daily temperature variations inside the accumulation and thermal storage tanks for a clear and a cloudy day.
236
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
Fig. 4. Daily mean storage temperature for the heating season.
Fig. 5. Collectors' temperature-dierence for a selected winter day.
tilted at 45 than that at 17 . This is attributed to the fact that 45 is nearer the optimum tilt angle for the winter season (Baghdad lies at 33 30 N latitude). The collector's eciency is the ratio of the collected energy to the incident energy. The collector's eciency for both tilt angles for a selected winter day is shown in Fig. 6. It can be seen from this ®gure that, as expected, the eciency for both cases starts to increase after dawn until it reaches its maximum value at noon, and then decreases again. It is also noticed that the collector's eciency at 45 was higher
A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
237
than that at 17 , as discussed above. The average daily collector's eciency was 56 and 47% for 45 and 17 tilt angles, respectively, during the month of January (Fig. 7). The building's energy-balance consists of the incident energy, the collected energy, the stored energy and the load Ð see Table 1. This indicates that the solar collection eciency was 50% the system losses 35% and the solar fraction to the load was
Fig. 6. Collector's eciency for both tilt angles for a selected winter day.
Fig. 7. Daily collector's eciency for both tilt angles for January.
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A. Al-Karaghouli, I. Abood / Applied Energy 65 (2000) 231±238
Table 1 The building energy balance during winter season Incident energy (Mcal/day)
Collected energy (Mcal/day)
Stored energy (Mcal/day)
Load (Mcal/day)
Collection eciency
Solar fraction
7478
3739
2430
995
50%
100%
100%. This high solar-fraction is attributed to the fact that the load is much less than the stored energy in the winter season. 7. Summary For the building during the heating season: (i) the average daily incident energy was 7478 Mcal, the average daily collected energy was 3739 Mcal corresponding to a system-collection eciency of 50%; (ii) the daily average load is 995 Mcal. This is much less than the collected energy, which indicates that the solar fraction to the load is 100%. For this reason, the auxiliary energy supply system was never used. References [1] Due JA, Beckman W. Solar energy thermal processes. New York: Wiley and Sons Inc, 1974. [2] Kreith F, Kreider J. Principles of solar engineering. New York: Hemisphere Publishing Cooperation, 1978. [3] Jager F. Solar energy applications in houses. Luxembourg: Commission of the European Communities, 1981. [4] ASHRAE. Handbook of fundamentals. New York: American Society of Heating and Air Conditioning Engineers, 1977. [5] Yellott JI. Solar heating and cooling of houses. In: Sayigh AM, editor. Solar energy engineering. Academic Press, New York, 1971 (chapter 17). [6] Kiruma K. Utilization of solar energy, the Japanese experience in solar energy application in the tropics. New York: Reidel Publishing Company, 1983. [7] McVeigh J. Sun power, an introduction to the application of solar energy. Oxford (UK): Pergamon Press, 1983. [8] Lof G, Karaki. System performance for the supply of solar heat. Mechanical Engineering, Des 33± 47. 1983. [9] Tanni R. et al. Technical Report No. 2 for Jordan solar house. Amman (Jordan): Royal Scienti®c Society, 1983. [10] Plaze W, Steemers T. Solar houses in Europe. Oxford (UK): Pergamon Press, 1981.