ENERGY BALANCE OF LOW ENERGY HOUSE WITH GHPS IN HOKKAIDO

Transcription

1 ENERGY BALANCE OF LOW ENERGY HOUSE WITH GHPS IN HOKKAIDO Yasuhiro Hamada, Kiyoshi Ochifuji, Makoto Nakamura and Katsunori Nagano Division of Urban and Environmental Engineering Graduate School of Engineering, Hokkaido University N13-W8, Kita-ku, Sapporo 060 Japan Phone: Fax: ABSTRACT A low energy house with GHPS (Geothermal Heat Pump System) was built in Hokkaido University, Japan in March, This project has been supported by the Japan Science and Technology Corporation and conducted by a research group of eleven members from Hokkaido University and Hokkai Gakuen University. A total floor area of the house is approx. 192 m 2 (2067 ft 2 ). A calculated value of a coefficient of heat loss is 0.97 W/(m 2 C)(0.17 Btu/(h ft 2 F)). This house is super insulated and air-tightened. Also, it has various passive strategies including direct solar heat gain and a ventilation system with an exhaust stack. It is estimated that energy consumption for heating would be less than a quarter of typical house's one in Hokkaido. PV (PhotoVoltaic) modules, wind power and solar collectors are used in order to achieve selfsufficiency in electric power and DHW (Domestic Hot Water) supply. GHPS is adopted for heating and cooling. Two vertical steel wells are used as VHE (Vertical Earth Heat Exchanger(s)). In summer, floor cooling, directly brings underground cold into the house, is operated. This report describes an outline of the low energy house and estimated and experimental energy balance in INTRODUCTION A low energy house with GHPS was constructed in Hokkaido University, Japan in March, This study is one link in the national project Development of Urban Metabolic Systems for Sustainable Cities (the Project representative: Prof. T. Kashiwagi), which is as part of the domain of research Realization of Environment Friendly Society (the Leader: Prof. Y. Kaya).

2 Fig. 1 Elevation of low energy house Fig. 2(a) The 1st floor plan Fig. 2(b) The 2nd floor plan It has been supported by the Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Corporation. It started in 1996, and has been carried out by the research group of eleven members (Prof. K. Ochifuji et al.) from Hokkaido University and Hokkai Gakuen University. It will end in In order to minimize energy consumption, an ideal house should be in harmony with the environment and also be assisted by natural energy resources and unused energy. The construction and evaluation of a low energy house is a step toward an autonomous house which is individually decentralized and utilizes renewable energy. This study is focused on unification and integration of various passive and active strategies including GHPS which take account of an annual energy balance. 2. AN OUTLINE OF A LOW ENERGY HOUSE Fig. 1 and Fig. 2 shows an elevation and plans of the low energy house. Its building area is 64 m 2 (689 ft 2 ), which is close to the average of a house in Japan. The house has a semi-basement in order to utilize UTES (Underground Thermal Energy Storage). A total floor area including the basement is 192 m 2 (2067 ft 2 ).

3 This house is super insulated and air-tightened. A thermal insulation panel construction was adopted for this house. This method may be effective for saving materials and energy. These panels have expanded polystyrene boards of 236 mm(9.3 in.) thickness for the insulation of all walls and the roof. The glazing in the south wall is 21 m 2 (226 ft 2 ). Double-glazed, argon-filled windows with low-emissive coating, which have 1.38 W/(m 2 C) (0.24 Btu/(h ft 2 F)) heat transfer coefficient, are used. In addition, awnings are used for solar shading. A calculated value of a coefficient of heat loss was 0.97 W/(m 2 C) (0.17 Btu/(h ft 2 F)). And a measured value of an equivalent leakage area per floor area was 0.85 cm 2 /m 2 (0.012 in. 2 /ft 2 ) with ventilation inlets sealed. The house has two kinds of main passive strategies; direct solar heat gain and natural ventilation with an exhaust stack. Daily variation of room temperature is reduced in range by the large heat capacity of concrete slabs and PCM (Phase Change Material) in the 2nd floor. The PCM has a 20 C(68 F) melting point. 3. EQUIPMENT DESIGN Fig. 3 shows an equipment design for the low energy house. An electric power is supplied by grid-connected PV. This is composed of single-crystalline silicon PV modules(24 m 2 (258 ft 2 ): 3.1 kwp) and triple amorphous silicon PV modules(24 m 2 (258 ft 2 ):1.3 kwp) integrated with roofing materials. Also, a 0.6 kwp-wind power generator was adopted. GHPS was adopted for floor heating and cooling. Two vertical steel wells(i.d. 81 mm(3.2 in.)) are used as VHE. The two VHE were installed 5 m(16 ft) apart. Each of them was buried into the borehole which was 30 m(98 ft) in depth and 110 mm(4.3 in.) in diameter. Gaps between the VHE and soil were filled up with mortar. Brine is injected from the bottom part in the VHE and Fig. 3 Equipment design for low energy house

4 return from the upper part. In this process, heat is exchanged between brine and soil. Propylene glycol solution(35 wt%) is used as brine. In summer, a floor cooling, which directly brings underground cold into the house, is operated. Solar heating and an exhaust heat recovery systems supply DHW. Flat plate type solar collectors, which have 8 m 2 (86 ft 2 ) gross area, are used. A 1.0 m 2 (11 ft 2 )-flat plate type evaporator of a heat pump(rated output 0.4 kw) for heat recovery was installed outside of an opening at the top of the exhaust stack. The volume of a hot water tank is 0.3 m 3 (10.6 ft 3 ). Underground is charged in summer and fall by means of solar collectors. HHE(Horizontal Earth Heat Exchanger(s)) at the depth of 2.15 m(7 ft) are used for UTES in order to reduce a heating load in winter. They consists of 300 m(984 ft) cross-linked polyethylene pipes. Each pipes has a distance of 0.2 m(0.66 ft), then all the pipes are subdivided into three parallel segments. A ventilation system using the exhaust stack is one of the passive strategies. It is driven by the temperature difference between indoor and outdoor air. Utilizing earth tubes and thermal capacity of the semi-basement and underground makes the fluctuation of air supplying temperature stable. The earth tubes are used for pre-heating/cooling of supply air for ventilation. They are made of polyvinyl chloride pipes(i.d. 200 mm(7.9 in.)). Two different types of earth tubes were symmetrically installed at the depth of 1.3 m(4.3 ft). One is 2.2 m(7.2 ft) long, and the other is 20.7 m(67.9 ft). Either of the two is utilized for air supply in the semi-basement. 4. ESTIMATED ANNUAL ENERGY CONSUMPTION In Table 1 and Table 2, estimated annual energy consumption of a typical house and the low energy house is shown. The amount of annual energy consumption of the typical house in Hokkaido is GJ( Btu). 81 % of the amount is from kerosine. From the viewpoint of energy use, energy consumption for heating is 68 %. Therefore, it is necessary to improve the thermal insulation of a house and utilize passive techniques in order to save unrenewable energy resources. An estimated amount of electric power consumption in the low energy house is 20.9 GJ( Btu). 78 % of the amount(i.e GJ( Btu)) is from the PV. Meantime, estimated energy consumption for heating is 15.6 GJ( Btu) and 1.1 GJ( Btu) Table 1 Estimated annual energy consumption (Typical house) Lights and Appliance Cooking Domestic hot water supply Space heating Space cooling Total[GJ/a] Kerosine Utility power City gas LPG Others Total[GJ/a]

5 Table 2 Estimated annual energy consumption (Low energy house) Lights and Appliance Cooking Domestic hot water supply Space heating Space cooling Total[GJ/a] Utility power Photovoltaic Solar collector Underground Exhaust heat Total[GJ/a] Table 3 Conditions of cooling experiments Cooling period Mode of operation Jul. 13, 97 - Jul. 15, 97 ( 3 days) Thermostatically controlled operation(2nd floor, 26 C) Jul. 22, 97 - Jul. 24, 97 ( 3 days) 4 hour-intermittent operation(2nd floor, 9:00-13:00) Jul. 25, 97 - Aug. 12, 97 (19 days) Continuous operation(2nd floor) for cooling. The amount for heating is less than a quarter of typical house s one in Hokkaido. The total amount of annual energy consumption in the low energy house is 47.3 GJ( Btu) which is almost a half of the typical house s one. Approx. 90 % of the total energy is provided from PV modules, solar collectors, underground and exhaust heat, and the rest from utility power. A calculated value of total purchased energy per floor area is 23.8 MJ/(m 2 a) (2095 Btu/(ft 2 a)). It is considered that the total performance of this house would be comparable to that of the advanced houses in Germany or UK. 5. EXPERIMENTAL RESULTS IN Cooling Experiment A floor cooling experiment with VHE was operated in summer, Table 3 shows conditions of cooling experiments. Indoor thermal environment, a cooling load, COP (Coefficient Of Performance) and so forth were measured. Three kinds of tests were carried out. A thermostatically controlled operation and a 4 hour-intermittent operation were running for 3 days. A 19 day-continuous operation from July 25, 1997 to August 12, 1997 was experimented in order to verify the performance and stability of the VHE for underground cold utilization. The total volume flow rate in the VHE was m 3 /s(0.01 ft 3 /s). During the period of cooling operations, awnings were used for solar shading of the south glazing. 2.2 m(7.2 ft)-earth tubes were utilized for air supply. The ventilation rate by the tubes ranged between 23(812) and 230 m 3 /h(8124 ft 3 /h).

6 Table 4 Experimental results of each cooling operation Mode of operation Thermostatically controlled 4 hour-intermittent Continuous Date July 15, 1997 July 24, 1997 July 28, 1997 Outdoor air temperature [ C] Room temperature (1st floor) [ C] Room temperature(2nd floor) [ C] Brine s temperature *) [ C] Amount of heat rejection [MJ/d] Heat rejection rate [W/m] Operation time [h/d] COP [ND] SCOP [ND] *) Average temperature of brine s flow and return Table 4 shows experimental results in each cooling operation. A particular day was chosen for each operation; July 15 for the thermostatically controlled operation, July 24 for the 4 hourintermittent one and July 28 for the continuous one. These results are daily average values. Each average value of the outdoor air temperature was 22.4 C(72.3 F) on July 15, 23.9 C(75.0 F) on July 24 and 24.9 C(76.8 F) on July 28. And each maximum value was 28.6 C(83.5 F) on July 15, 30.8 C(87.4 F) on July 24 and 29.2 C(84.6 F) on July 28. Regarding the room temperatures (1st floor and 2nd floor), the 2nd floor s room temperature was higher throughout all the operations. Each average daily temperature difference between the 2nd floor s room and the outdoor air was 3.1 C(5.6 F) in the thermostatically controlled operation and 3.2 C(5.8 F) in the 4 hour-intermittent one. Each average daily temperature of the 1st floor s room was 23.4 C(74.1 F) in the thermostatically controlled operation and 24.9 C(76.8 F) in the 4 hourintermittent one. In both operations, each average daily temperature difference between the 1st floor s room and the outdoor air was approx. 1 C(1.8 F). The operation time of the thermostatically controlled operation was 8.3 hours. The heat rejection rate of the VHE into the underground per unit well length was 20.9 W/m(21.7 Btu/(h ft)). At this time, COP [ = (Amount of heat rejection) / (Power of circulating pump for the VHE) ] was 7.0, and SCOP(System COP)[ = (Amount of heat rejection) Fig. 4 Brine s temperature and heat rejection rate

7 / (Power of circulating pumps for the VHE and floor cooling) ] was 4.6. The SCOP was about 34 % lower than the COP. It is considered that subdivision of the floor piping and improvement in the efficiency of circulating water pump should be effective for this problem. In the 4 hourintermittent operation, the heat rejection rate of the VHE was 30.3 W/m(31.5 Btu/(h ft)) and COP 9.1, SCOP 6.0. Therefore, it was experimentally found that GHPS utilizing about 10 C(50 F)-constant earth temperature layer was efficient for cooling. On the other hand, the heat rejection rate of the continuous operation was 18.1 W/m(18.3 Btu/(h ft)) and COP 5.4, SCOP 3.6. COP s value was about 41 % lower than that of 4 hour-intermittent operation. Fig. 4 shows brine s temperature and heat rejection rate of the VHE in the first week of the continuous operation period. Both of the brine s temperature and the heat rejection rate were quite stable. The average brine s temperature of the first week was 15.9 C(60.6 F), and the average temperature during the whole operation period(19 days) 15.7 C(60.3 F). And the heat rejection rate were around 17 W/m(17.7 Btu/(h ft)). 5.2 Heating Experiment The heating started from November 5, Fig. 5 shows an outline of GHPS with the two VHE. Rated output of an installed heat pump is approx. 1 kw. A heat storage tank(0.93 m 3 (32.8 ft 3 )) were set up for peak demand. A floor heating is controlled thermostatically. It starts when the room temperature goes down less than 18 C(64.4 F). Fig. 5 Outline of GHPS

8 Table 5 shows the experimental results in November, The average operation time per day in November was 8.3 hours. As a result, the daily amount of thermal output was 97.8 MJ/d( Btu/d), heat extraction 78.1 MJ/d( Btu/d) and electric energy for the heat pump 22.0 MJ/d( Btu/d). Each average value was 4.4 for COP [ = (Thermal output) / (Electric energy for compressor of heat pump) ], 3.5 for SCOP 1 [ = (Thermal output ) / ( (Electric energy for heat pump) + (Power of circulating pumps for the VHE and the storage tank) )] and 2.9 for SCOP 2 [ = (Thermal output) / ( (Electric energy for heat pump) + (Power of circulating pumps for the VHE, the storage tank and floor heating) ) ]. The value of COP was quite high due to the adoption of low temperature floor heating. However, the SCOP 2 was about 34 % lower than the COP. The same result was shown in the cooling experiments before. Fig. 6 shows heat extraction rate from the underground(per unit well length) of the VHE. Owing to the intermittent operating controlled by temperature, the average rate was quite high; 36.8 W/m(38.3 Btu/(h ft)). Fig. 7 shows each temperature of brine and water for floor heating. Brine s temperature was stable at around 5 C(41 F); therefore it was considered that the GHPS was operated well. Table 5 Experimental results of the heating operation (Average daily values in Nov. 5-30, 1997) Operation time [h/d] 8.3 Thermal output [MJ/d] 97.8 Amount of heat extraction [MJ/d] 78.1 Heat extraction rate [W/m] 36.8 Electric energy for heat pump [MJ/d] 22.0 COP [ND] 4.4 SCOP 1 [ND] 3.5 SCOP 2 [ND] 2.9 Fig. 6 Average heat extraction rate from the underground (November, 1997) Fig. 7 Average temperature of brine and water for heating (November, 1997)

9 6. ENERGY BALANCE IN 1997 In Fig. 8, Fig. 9 and Fig. 10, energy balance of the low energy house on June 16, 1997(spring), July 24, 1997(summer) and November 7, 1997(winter) are shown. On June 16, 41 % of the collected solar heat amount was utilized for DHW, and the rest for UTES by HHE. 54 % of the PV power was supplied through the grid as the reverse power. On July 24, the ratio of DHW to UTES in the solar heat amount was almost the same as one on June 16. The amount of heat rejection of the VHE into the underground was 26.3 MJ/d( Btu/d) during the 4 hourintermittent cooling operation. It was found that all energy for the low energy house was produced by the solar collectors, the PV system and the VHE in both days. On the other hand, 24 % of the used energy on November 7(52.2 MJ/d( Btu/d)) was provided from utility power. And 34 % of DHW was supplied through the exhaust heat recovery. Fig. 8 Energy balance on June 16, 1997 Fig. 9 Energy balance on July 24, 1997 Fig. 10 Energy balance on November 7, 1997

10 7. CONCLUSIONS This paper described an outline of a low energy house with GHPS and its equipment design which was built in Hokkaido University, Japan in March, The following results were obtained through experiments and analyses on energy balance of this house. 1) It was estimated that approx. 90 % of the energy consumption was provided from PV modules, solar collectors, underground and exhaust heat, and the rest from utility power. A calculated value of total purchased energy per floor area was 23.8 MJ/(m 2 a)(2095 Btu/(ft 2 a)). 2) It was experimentally found that GHPS utilizing about 10 C(50 F)-constant earth temperature layer was efficient for cooling. The heat rejection rate of VHE in the 4 hour-intermittent cooling on July 24, 1997 was 30.3 W/m(31.5 Btu/(h ft)). COP was 9.1 and SCOP ) The heating operation of GHPS started from November 5, Experimental results showed that the average heat extraction rate of the VHE from the underground was high; 36.8 W/m(38.3 Btu/(h ft)). COP was 4.4 and SCOP Brine s temperature was around 5 C(41 F). 4) All energy for the low energy house was produced by the solar collectors, the PV system and the VHE on June 16 and July 24, On the other hand, 24 % of the energy consumption on November 7 was provided from utility power. ACKNOWLEDGEMENTS We are grateful to Mr. Y. Fujiwara (Fujiwara Environmental Science Institute Co., Ltd.) and Mr. T. Nakamura (Shimizu Corporation) for helping this study. Also, we would like to thank a lot of corporations including Shinryo Corporation, Mitsui Home Co., Ltd. and Takenaka Corp. for the construction of the house. We appreciate Prof. T. Kashiwagi and Prof. Y. Kaya supporting our research. REFERENCES 1. Hamada, Y., Nagano, K., Nakamura, M., Ochifuji, K. et al.(aug., 1997). Equipment design for a low energy house. SHASE annual technical meeting, Hamada, Y., Ochifuji, K., Nagano, K. and Nakamura, M.(Jun., 1997). Study on the heating and cooling by long-term heat storage with underground vertical U-tubes. Proceedings of 7th international conference on thermal energy storage(megastock 97), IEA/OECD(May, 1995). Learning from experiences with advanced houses of the world. CADDET analyses series, 14, Nagano, K., Nakamura, M., Hamada, Y., Ochifuji, K. et al. (Nov., 1997). Low energy house in Hokkaido. 4th Japan/Canada Housing R&D workshop proceedings, V168-V Nagano, K., Nakamura, M., Hamada, Y., Ochifuji, K. et al.(aug., 1997). Total plan of studies about low energy house and outline of house. SHASE annual technical meeting, Nagano, K., Ochifuji, K., Nakamura, M., Hamada, Y. (Jun., 1997). Study on the ground heat extraction utilizing horizontal earth coils. Proceedings of 7th international conference on thermal energy storage(megastock 97), Nishida, K. and Akao, K.(Mar., 1994). A survey of residential energy consumption in Sapporo. Summaries of technical papers of annual meeting, Architectural Institute of Japan, Hokkaido branch, 67,