Long-term Measurement of Indoor Thermal Environment and Energy Performance in a Detached Wooden House with Passive Solar Systems

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Long-term Measurement of Indoor Thermal Environment and Energy Performance in a Detached Wooden House with Passive Solar Systems Yoshimi Ishikcnw, Tohoku Institute of Technology, Sendai, Japan

1 Long-term Measurement of Indoor Thermal Environment and Energy Performance in a Detached Wooden House with Passive Solar Systems Yoshimi Ishikcnw, Tohoku Institute of Technology, Sendai, Japan Hiroshi Yoshino, Tohoku University, Sendai, Japan Chikashi Sasaki, Tohoku institute of Technology, Sendai, Japan ABSTRACT The indoor thermal environment, energy performance and energy consumption for a detached wooden house equipped with two passive solar systems, were investigated over a period of three years. The house with a floor area of 188 m2 was constructed in the autumn of 1993 in Sendai, Japan; and was well insulated and very airtight compared with other houses in Japan. There are six occupants. Heating equipment is comprised of a thermal storage space heater using night-time electricity and a vented firewood fi.n-nace on the first floor. Each room is ventilated all day by a central ventilation system. Two passive solar systems were incorporated : a concrete floor in the southern perimeter of the living room as a direct gain system, and an earth tube embedded around the circumference of the house to supply fresh air. The principal results obtained are as follows : (1) The indoor environment during the heating season was more thermally comfortable, compared with that of ordinary houses in Japan. (2) The concrete floor played a role of thermal storage, which absorbed and released heat for decreasing the fluctuation of room temperature. (3) The earth tube supplied air with lower temperature in the summer and higher temperature in the winter to the room, than the outdoor air temperature. This thermal performance did not decrease in spite of the long-term use. (4) The annual amount of energy consumption of this house was less than that of ordinary houses in the northern part of Japan. Introduction Recently, the detached wooden houses in Japan have increasingly become well insulated and airtight, There is also greater interest in the application of passive solar systems. However, there have been few investigations on the indoor thermal environment and thermal performance of such Iiouses. In this study, the indoor thermal environment, energy performance and energy consumption for a detached wooden house equipped with two passive solar systems, were investigated over a period of three years. The house was constructed in the autumn of 1993 in Sendai, Japan ; and was well insulated and very airtight compared with other houses in Japan. Two passive solar systems were incorporated : a concrete floor in the southern perimeter of the living room as a direct gain system, and an earth tube embedded around the circumference of the house to supply fresh air. This paper describes the results of a long-term investigation. Description of Investigated House Figure 1 shows the plan of the house studied in this paper. This conventional wood-fkame house was built in October of 1993 in a residential area of Sendai at a northern latitude of 38. The floor area is 188 mz. The roof is composed of 4-cm hard polyurethane foam and 12-cm fiberglass insulation. The walls have 8-cm hard polyurethane foam insulation. The foundation insulation is composed by 4-cm Long-Term Measurement of Indoor Thermal Environment md Energy Peormtance

$5rn bel ow ground surface \ electric heater 11830 3640 910 1820 5460 II Study Master Trrlll Lroo - Dm L bedroom co 6 g II Children s bedro I 6370 5640 I $ g 11,- -J G m 11830 2nd floor plan 012345(m)$

2 earth tube embedded > 1.5rn bel ow ground surface \ electric heater II Study Master Trrlll Lroo - Dm L bedroom co 6 g II Children s bedro I I $ g 11,- -J G m nd floor plan (m) Fig. 1 Plan of the investigated house polystyrene foam of 0.9 meter width horizontally surrounding inside of the continuous footing. The windows have triple panes in the southern wall and double panes in the other orientation. Heating equipment is comprised of a thermal storage space heater using nighttime electricity and a vented firewood firnace on the first floor. There was no cooling apparatus for two years after construction. In the summer of 1996, a heat pump cooling system was firnished in the rooms on the second floor. Each room is ventilated all day by a central duct system with a mechanical exhaust fan. Heat loss coefficient per floor area is 1.2 W/m2K, calculated on the basis of design specifications. Equivalent leakage area per floor area was measured by the fan pressurization method. That value for the indoorout door pressure difference of 9.8 Pa was 0.72 cm2/m2 under the condition of ventilation inlets sealed. Two passive solar systems were incorporated into this house : a concrete floor in the southern perimeter of the living room as a heat storage of solar gain, and an earth tube embedded at 1.5 meter under the ground surface around the house to supply fresh air. Outdoor air is forcibly pulled into the earth tube by a fan and supplied into the southern corridor. The solar photovoltaic cells installed on the roof are used as a energy source of electricity for the earth tube fan and the ventilating fan. Family members are an elderly woman, a couple and three children. Three-year Measurement Results Figure 2 shows the fluctuations of the daily mean indoor and outdoor air temperatures and humidity for three years. During three winter of monitoring, indoor temperature of both the living room with space heating and the study room wit bout space heating was maintained between 18 c and 2ZOC, even though the outdoor temperature was less than O C. The area between indoor and outdoor temperature in this figure corresponds to heating degree days. The heating degree were 34OO in 1995, and 3900 in The HDD in 1996 was 15 /0greater than that in 1995 because of the low outdoor temperature from Mar. to Apr. in 1996 compared With that of The annual thermal load was estimated as 65 GJ/year on the basis of the HDD and the heat loss coefficient of this house. The thermal load is met by not only the space heating but also the solar radiation and internal heat gain. During the summer, indoor air temperatures was very high because there was no air conditioning sys Abikawa, et. al.

tern. Air conditioning system was installed in 1996 to cool the second floor rooms. It was not effective for decreasing room temperatures of the first floor.

3 tern. Air conditioning system was installed in 1996 to cool the second floor rooms. It was not effective for decreasing room temperatures of the first floor. Relative humidity of the living room was XOduring the winter and %0during the summer. That of the space under floor was more stable throughout the year. Absolute humidity of rooms was 6 7 g/kg(da) during the winter and around 20 #kg(da) during the summer. Figure 3 shows the relationships of daily mean temperature between the outdoor air and the living room for three years. There was no remarkable difference in 1994, 1995 and During the winter, the inclination of regression lines was very small, that is, the room temperatures were maintained around 20 C. During the summer, it is clear that the indoor air temperature depended on the outdoor temperature, because there was no air conditioning for the first and second summer and the occupants used the air conditioning for a short time during the third summer. Daily Profiles of Temperature and Humidity Figure 4 shows temperature and humidity profiles for three days in the winter and in the summer of In the winter, indoor air temperatures were C all day, with only the firewood fir-. (1994) (1995) (1996) I.3 20 I Living room - 20 :.d fd,.y:>plti.i ?%%.: 4 /+++ - : %.! =: 0 : Outdoor ale % ? 0 t,, t 02 ; (Month) < Fig. 2 Three-year fluctuations of daily mean temperature and humidity The area between indoor and outdoor temperature in this figure corresponds to heating degree days (HDD). The HDD in 1996 was greater than that in 1995 because of the low outdoor temperature from Mar. to Apr. in 1996 comparedwith that of The annualthermal loadwas estimatedon the basis of the HDD andthe heat loss coefficient. Long-Term Measurement of Indoor Thermal Environment and Energy Pormance

4 (1995) (1996) Y =0.47X :, o,, ummer> ,.: m..-. ; Y= 0.14X +19, [ r ==0,30 (Winter) Lti Daily mean outdgorzir tem () -lo m ; 10 -:-.::-.,. Y =-0.06X r =-0.12 (Winter) t E. % A Apr. -Jun., Oct. -Nov. o 0 Winter(Jan. -Mar., Dec.) 2 I. Summer(Jul,-Sep.) inl k * 0??. a:.--$.,..... : : -7.;--..- : Y : I i 1 -IOL ; ; ; : lo Daily mean outdoorzir tem ( C) Daily mean outdoor air tem ) 40 Fig. 3 Relationship of daily mean temperature between outdoor air and indoor air There was no remarkable difference in 1994, 1995 and During the winter, the inclination of regression lines was very small, that is, the room temperatures were maintained around 20 C. During the summer, the indoor air temperature depended on the outdoor temperature g room -T * bedroom 40 Children s bedroom Master bedroom 1 ; 20 -., : u a 1: g Aug.18,1885 Aug.19 Aug.20 I 0$ 0 80 x c g. 20 Living room Under floor 2 5 Living room -GO : Outdoor air log u : :..., / m Y Deci!6,1995 Dec.27 Dec E 40 - al. > % 20 u o, Aug.18,1995 Aug.19 Aug.20 Fig. 4 Temperature and humidity profiles for three days in the winter and in the summer In the winter, after the fi-u-nacewas turned off, the room temperatures fell slowly. Regarding the humidity, occupants reported that the air was thy. In the summer, the room temperatures did not decrease at night, when the outdoor temperature dropped. In orderto keepindoor temperatureborn rising dm-ingthesummer in awellinsulatedand airtight house, it is important to exhaust the indoor hot air during the night effectively Isbikawa, et. al.

5 nace used in the living room fi-om evening to midnight. After the furnace was turned off, the room temperatures fell slow]y. The indoor thermal environment of this house during the heating season was more comfortable than that of ordinary houses in Japan. The relative humidity of the living room was around 30 /0 all day. Occupants reported that the air was dry in the winter. In the summer, windows were open during the day and closed during the night except for August 18th. The room temperatures were lower than that of the outdoor air during the day, and did not decrease at night, when the outdoor temperature dropped. On August 18th, the room temperatures of second floor decreased at night in accordance with the outdoor air temperature because the windows were lefl open. In order to keep indoor temperature from rising during the summer in a well insulated and airtight house, it is important to exhaust the indoor hot air during the night effectively or to use air conditioning system. Air conditioning system was installed in 1996 for rooms of the second floor. But it did not decrease room temperatures of the first floor. Thermal Performance of Heat Storage Floor A concrete floor which was 20 cm in depth with a surface area of 6.6 m2 and a heat capacity of about 2,4 MJ/K, was installed in the southern perimeter of the living room. Figure 5 shows the temperature profiles at various points in the concrete floor and profiles of the amount of heat absorbed and released by the floor for three days in the winter. The amount of heat was calculated hourly on the basis of the measured temperatures in the concrete floor (Hasegawa 1986). The deeper the measurement point is, the narrower the temperature swing. The peak time of the temperature at the deepest point was delayed for 6 hours, compared with that of the surface temperature. These results reflect the heat transfer through an up-and-down direction in the concrete, that is, the concrete floor absorbed heat during the day and released it during the night. It can be said that the concrete floor played a role of thermal storage, which absorbed and released heat for decreasing the fluctuation of room temperature. R eleased heat o (hour) Feb.5, 1994 Feb.6 Feb, K OE -400 a Fig. 5 Temperature and heat profiles of concrete floor in the winter The deeper the measurement point is, the narrower the temperature swing. These results reflect the heat transfer through an up-and-down direction in the concrete, that is, the concrete floor absorbed heat during the day and released it during the night. It can be said that the concrete floor played a role of thermal storage,which absorbed and released heat for decreasing the fluctuation of room temperature. Long-Term Measurement of Indoor Thermal Environment and Energy Pe@ormance

6 Figure 6 shows the fluctuations of the daily mean temperature of the concrete floor, living room and outdoor air, and the amount of heat absorbed and released for three years. The winter temperature of the concrete floor was 15=17 C, similar to that of the space under the floor. After July, however, the temperature of the concrete floor rose to the level of the outdoor air temperature. The amount of heat flow fluctuates in a range of kwhlday, and shows a tendency to increase between winter and spring, and to decrease during the summer. The daily mean value of the heat flow estimated as about 0,8 kwh/day is less than 2 /0 of the daily mean thermal load in this house. 1 1 [,!! t 1 I % 1 I I I I, I, I 1 1 I 1 # I I, 1 1,, I # 1, 1, I -20 g e (Month) -f. Fig. 6 Three-year fluctuations of temperature and the amount of heat of concrete floor The amount of heat flow fluctuates in a range of kwhlday, and shows a tendency to increase between wkter and spring, and to decrease during the summer. Thermal Performance of Earth Tube The earth tube made of hard vinyl chloride, with a diameter of 20 cm and a length of 32 meters was embedded in the earth 1.5 m below the ground surface. The airflow volume of the earth tube fan was 140 m3/h. The airflow speed was 1.2 rds. Figure 7 indicates the temperatures at the different points in the soil and the earth tube on 7:20 a.m., Jan, 15, The outdoor air entered the inlet at a temperature of 6.O C and lefl the outlet with a temperature of 7. 5 C. The rate of temperature increase of the air in the tube, however, gradually lessened as the air temperature in the tube became close to the soil temperature around the tube. Figure 8 shows the three years fluctuations of the daily mean temperatures related to the earth tube and the amount of sensible heat exchange, which is calculated using the airflow volume and the temperature difference between inlet and outlet air. It is clear that the temperature of supply air into the room was lower in the summer and higher in the winter than the outdoor air. In both winter and summer, the largest difference in daily mean temperature between inlet and outlet air was 8 C. The earth tube acts as a heat source during the winter and a heat sink during the summer. As for the annual amount of heat transfer between the air in the tube and the earth around the tube, in 1995, the heat gain and the heat extraction was 3.1 GJ/year and 2.5 GJ/year, respectively. The tendency for heat gain to be 20% larger than heat extraction corresponds to the numerical simulation results estimated by authors (Ishikawa 1992). The annual amount of sensible heat gain was about 5 /0of the annual heating Isbikawa, et. al.

7 Inner Surface b,. 124 \ c x %t!( 50cm Inner Air -0.4 C - 1 / Earth (150cm) 8.9 T 1 Earth 6.9( 50c m) 8.5 t(looc m) 9.4 Y(150C m) ner Air 2T 7,5 c (m) 720 AMJin 15,1995 Fig, 7 Temperatures at the different points in the soil and the earth tube in the winter The outdoor air entered the inlet at a temperature of -6.0 C and left the outlet with a temperature of 7.5 C. The rate of temperature increase of the air in the tube, however, gradually lessened as the air temperature in the tube became close to the soil temperature around the tube. (1994) (1995) (1996) 30 - Outlet air(earth tube fan) Earth 1.5m under g m 20 P :. :... a f % I I 1 1 I, t I, 1 # I t 1 I I I 1 Heat extractiori eelolllzl (Month) Fig. 8 Three-year fluctuations of temperature and the exchanged heat in earth tube The temperature of supply air into the room was lower in the summer and higher in the winter than the outdoor air The earth tube acts as a heat source during the winter and a heat sink during the summer. Long-Term Measurement of Indoor Thermal Environment and Energy Pq$ormance

8 load in this house. The vapor condensation in the earth tube was also estimated, when the inner surface temperature of the tube was lower than the dew point of air passing through the tube. Then, it is necessary for calculating thermal efficiency of the earth tube to take into account the latent heat due to vapor condensation. Figure 9 shows the relationship of dail y mean air temperature between inlet and outlet of the tube for three years. The correlation coefficient is more than 0.9. There was no difference in regression line between 1994, 1995 and That means that the thermal performance of the earth..y tube did not decrease in spite of continuous operation throughout the year. The intersection of the regression line and the line y=x is about 15 C for each year. This is close to the yearly mean temperature of inner surface of the earth tube. (1 994) (1996) / I.4 :,/-.Y,.=.x..k.i Y.. =.X..>4L.. / :,/:,/ ; / o :..- - :/4 :.,...% r $ : P: i<(.. / :,:,,; //:.- /,< e,;... 1 /.?--...>......,..,,,.,.-O :..{.. -n ;gl?,...{....i....- o > / n - : 0 *:.? ; % : $ &,.L..;--7<j 4 4. :?%%:.: 10 *@ :...,. :..-.- ;10 i- [ / ; *;=055X ;. ;..- ; j Y =0.55 x +6.2 : /..-,/ :Ẇ*mpP-:;- ; Y O.56X j --- :, / ; R=,95 ;, ;R=oi / j R =o,93.../< _...#!......i i,/ ;,/ : ;;<: : ; :, i I I I / i j, i, I,/- I 1 I J o o o Inlet air temperature (t) Inlet air temperature ( C)..i. Inlet air temperature ) I?ig. 9 Relationship of daily mean air temperature between inlet and outlet of earth tube Therewas no differencein regression line between 1994, 1995 and Thatmeansthat the thermalperformanceofthe earthtube did not decreasein spite of continuous operationthroughout the year. Energy Consumption In this house, except for the firewood firnace and passive solar systems, the energy source is only electric power. Occupants use electric power from 11 p.m. to 7 a.m. for space heating, water heating, etc. Figure 10 shows the yearly changes in monthly electric power consumption for three years. The amount of electric power consumption was slightly large during the winter and small during the summer. There was no remarkable difference between 1995 and 1996, except In the winter, the electric power consumption in the second and third years was significantly smaller than that in the first year, because the firewood fi-umaceinstead of the electric space heater was used. The annual energy consumption was 56.4 GJ/year in 1994, 45.9 GJ/year in 1995 and 47.9 GJ/year in 1996, where the conversion value is 3.6 MJ/kWh. It s one of the reasons for large energy consumption that the first year was used to adjusting equipment. The energy consumption in 1995 and 1996 was less than that of ordinary houses in the northern part of Japan (Yoshino 1995) Isbikawa, et. al

9 3000 E - -a L Z5UI-\y... -, c.g \ g 'v...gg6... z \ \... b g 1000 Q.- o = UI 1 I I 1 I 1 I I 1 i Jn Feb Mar Apr May Jun Jul Aug Sep Ott Nov Dec Fig. 10 Monthly amount of electric power consumption for three years The amount of electricpower consumption was slightly large duringthe winter and small duringthe summer. In the winter, the electric power consumption in the second and third years was significantly smaller than that in the first year, because the firewood furnace instead of the electric space heater was used. Conclusions (1) The indoor thermal environment of the investigated house during the heating season was more comfortable than that of ordinary houses in Japan. But, during the summer, the indoor temperature was very high and did not decrease at night, when the outdoor air temperature dropped. (2) The concrete floor in a part of living room played a role of thermal storage, which absorbed and released heat for decreasing the fluctuation of room temperature. (3) The earth tube embedded around the house supplied fresh air with lower temperature in the summer and higher temperature in the winter than the outdoor air temperature. This thermal performance did not decrease in spite of continuous operation throughout the year. (4) The amount of energy consumption, after second year, was GJ/year, not including firewood. This energy consumption is less than that of ordinary houses in the northern part of Japan. Acknowledgement This study was conducted in collaboration with the National Institute for Environmental Studies, the Environment Agency, Tsukuba, Japan. References Solar Energy Research Institute, Solar Technical Information Program Passive Solar Performance, Summary of Class B Results. U.S. Government Printing Ofilce, Washington, D.C. hmg-term Measurement of Indoor Thermal Environment and Energy Ptvformance

10 Hasegawa, F. et al Experimental study on thermal storage floor system of passive solar systems using an actual test house. Transactions of Architectural Institute of Japan, 366: (In Japanese) Ishikawa, Y. et al Computational analysis of thermal performance of earth tube. The Proceedings of fhe International Solar Energ Conference - Solar Engineering 92, 1: The American Society of Mechanical Engineers. Yoshino, H. et al One-year measurement of indoor climate and energy consumption of superinsulated houses in a mild climate region of Japan. Indoor Air, 5(l): International Energy Agency, Solar Heating & Cooling Programme SOLAR LOWENERGY HOUSES OF IEA TASK 13. James & James (Science Publishers) Ltd. London. International Energy Agency SOLAR ENERGY HOUSES: S7RA 72ZGIES, TECHNOLOGIES, EXAMPLES. James & James (Science Publishers) Ltd. London Isbikawa, et. al.

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