Harmony Between Man And Nature : SS CHAUHAN* An energy-independent residential house (`HARBEMAN house'; Harmony Between Man And Nature), incorporating sky radiation cooling, solar thermal, and photovoltaic energies was built in Sendai, Japan during July, 1996. The HARBEMAN house, which meets almost all the energy demands, including space heating and cooling, domestic hot water, electricity generated by photovoltaic cell and rainwater for standard Japanese homes. Sky radiation cooling, solar thermal/photovoltaic (PV), and underground coolness as well as rainwater and waste heat were utilized in combination. Annual variations of water temperature in the underground main tank, heating/cooling/domestic hot water demands, collected and emitted heats by the solar collector and sky radiator have been monitored. ----------------------------------------------------------------------------------------------------------- Introduction The third conference of the Parties to the U.N. Framework Convention on Climate Change (COP3) held in December 1997 in Kyoto urged the industrialized nations to reduce CO2 emissions by 5.2% (on average) below 1990 levels until the period between 2008 and 2012 (Kyoto protocol). Presently Current energy consumption in the residential sector of Japan is about 14% of the entire primary energy consumption. The projected energy consumption upto 2010 is estimated to be as 24%. Except for lighting and electric appliances, most of the residential energy can be classified into the so-called low temperature level energy ranging from 5 to 60°C. For example, space heating, cooling, and domestic hot water supply are categorized into this range. For this reason, it is possible to provide these energies with natural energy including solar thermal, photovoltaic, sky radiation cooling, wind, rainwater, and underground coolness. About 20 years ago, was proposed an energy-efficient house in Japan incorporating solar thermal and sky radiation and the fundamental experiments were conducted by using facilities at the Tohoku university. Experimental data on long-term heat and cool storage modes were presented in Saitoh (1984), Saitoh et al. (1985) and Saitoh and Kuwabara (1987). Along with these experiments, theoretical analysis and simulation were done to obtain an optimal design for the proposed house (Saitoh and Ono, 1984a,b). The HARBEMAN house is having two major features; one is a large heat/cool storage tank (30-60 m3) which makes it possible to store energy seasonally. From a standpoint of storing solar energy, the storage capacity can be minimized if one allows a relative large temperature fluctuation and an increase of auxiliary heating need. However, in case of this long-term storage over 3 months, the storage capacity should be large enough. Another feature is to utilize seasonal sky radiation cooling. As is well known, sky radiation cooling appears most significantly under a clear weather condition in low relative humidity and low wind speeds. However, unfortunately, the weather in summer in Japan is not appropriate for sky radiation to be effectively used because of high ambient temperature and high humidity (80-90% in most areas). This difficulty was overcome by changing the period of sky radiator operation: the water of the underground tank is chilled in advance in spring when the ambient temperature and humidity are relatively low. The temperature of the tank is cooled down to 4°C with the aid of a small-capacity heat pump (600 W) that utilizes night-time electricity. The first example which utilizes a large underground tank for a residence was the MIT Solar house (Hottel et al., 1942) designed by Professor Hoyt C. Hottel in 1939. Later, George O.G. Löf, who was a student of Professor Hottel, built the Löf house (Löf et al., 1963) in Englewood, Denver. The performance of the low energy houses of the International Energy Agency (IEA) task 13; Solar Heating and Cooling Program was reported (IEA, 1995). The system has two operational modes: (i) a long-term thermal energy storage mode extending from September to March and (ii) a long-term cool storage mode extending from April to August. The system is intended to utilize as little energy as possible to collect and emit the heat. This reveals primary energy consumption, external costs (externalities) and the effect for reduction of carbon dioxide emissions for the house. The primary energy consumption and CO2 emissions of the house are only about one-tenth of those of a conventional, standard house. Moreover, the thermal performance of this house will be compared with the results of the IEA solar low energy house TASK 13. Finally, this validates the external costs of this house, which have been intensively discussed in recent years in European countries. The present energy-efficient house will give a promising concept for reducing CO2 emissions, and will contribute to mitigate global warming. THE HARBEMAN HOUSE Fig. 1 shows a schematic drawing of a residential house which is located in Sendai, Japan. An overall view is shown in Plate 1. The number of degree-days in Sendai is ~1580, the total cooling load is 2100 MJ on average, and the average solar energy received on a horizontal surface in January is 7.9 MJ/m2/day. Fig. 1. A schematic of the HARBEMAN house. Plate 1. Overall view of the HARBEMAN house. The solar collector, which is of a liquid-type (having an area of 30.4 m2), is installed on the top of this house with tilt angle of 45° from the horizontal. The azimuth angle of the collector is 20° to the east. To prevent freezing in winter, the water in the collectors and pipes is automatically drained back to the main tank by magnetic valves. The sky radiators used consist of uncovered copper tubes with aluminum fins (the same structure as in the solar collector, except for the glazing and insulation), which are painted black (partially selective surface, area: 15.2 m2), and placed with a tilt angle of 10° (azimuth angle: 20° to west). The entire housing was insulated with glass wool (density: 10 kg/m3) of 100-350 mm thickness. The total floor area is ~260 m2. In addition to the above mentioned features, this house has a 1.6-m3 auxiliary tank situated in the basement and a 600-W heat-pump, which utilizes night-time electricity. The auxiliary tank is utilized during the cool storage mode to provide space heating and domestic hot-water supply demands. The rainwater is collected in a rainwater tank (2 m3) buried underground and utilized for toilet flushing, watering of the garden, and car washing. The operation and control of this house is fully done by 128 microprocessors and a personal computer. The total maximum available energy for space heating, cooling, hot water supplying, and rainwater is ~117 GJ per year. This results in saving about 6300 US$ per year. If the HARBEMAN house was incorporated in all future residences, about 20% of the total primary energy consumed annually in Japan would be saved. PRINCIPAL SPECIFICATION Principal specifications of the present HARBEMAN house are shown in Table 1. Table 1. Specifications Location Sendai Latitude 38°17Ž00ŽŽ N Longitude 140°50Ž14ŽŽ E 124 m above sea level Solar collector Area 30.4 m2 Glazing Single Tilt angle 45° (due south) Azimuth angle 20° E Type Liquid U-value 5.0 kW/m2 K Intercept Fr 0.8 Flow rate 16.2 l/min Sky radiator Area 15.2 m2 Tilt angle 10° (due north) Flow rate 12.4 l/min Underground water tank Capacity 31.0 m3 (7.0 m×2.1 m×2.1 m) Insulation thickness 0.15 m/0.10 m (Polyurethane, FRP coated) Concrete thickness 0.20 m Auxiliary tank Capacity 1.6 m3 (2.0 m×0.6 m×1.4 m) Insulation thickness 0.07 m Photovoltaic cell Type Single crystalline Area 11.5 m2 Output 1.5 kW Heated floor area 185 m2 Total floor area 260 m2 Housing insulation Roof 25-35 cm (glass wool) The others 10 cm Windows Glazing Pair-pane glass Overall heat transfer coefficient (U-value) Living room 0.78 W/m2 K Japanese room 0.69 W/m2 K Low emission film Transmissivity 0.5 Reflectivity 0.78 Overall heat transfer coefficient (U-value) 4.53 W/m2 K Rainwater tank Capacity 2.0 m3 Heat pump Type Liquid-liquid, motor-driven Power 600 W COP 2.0-3.0 The airtightness of this house is the same as one of the conventional airtight houses. Copper-constantan thermocouples are set up at more than 35 points in the wall, water and soil in order to measure the temperature and the heat fluxes around the tank. Fan coil units (FCUs) are used for space heating and cooling, and thermopanels (TPs) are used for space heating for the entrance hall, toilet, and stairway space. Photovoltaic cells with a capacity of 1.5 kW are installed both on the top part of the roof facing due south and in the parking lot. Electricity (about 1000 kWh per year) produced by the PV system is utilized to operate the solar pump, the computer system and so on. The operational control of this house is quite complicated because there are more than 100 controlling solenoid valves, motored valves, and other valves as well as thermocouples and sensors with length of more than 2000 m. Furthermore, there are two operational modes; thermal storage and cool storage modes. For this reason, it was decided to operate this house by a personal computer and 128 microprocessors. Relatively simple operations like controlling the fan coil units and the pumps are done by the microprocessors. The solar collector and sky radiator loops are controlled by a personal computer. A special computer code for this system was made in the BASIC language. Owing to many difficulties in construction and controlling processes, it took almost 8 months. TWO OPERATIONAL MODES FOR THE HARBEMAN HOUSE There are two operational modes for this house; (i) long-term heat storage mode, and (ii) long-term cool storage mode. 4.1. Long-term heat storage mode In Fig. 2, the piping network for the heat storage mode is schematically shown. Fig. 2. Schematic flow network for the long-term heat storage mode. This mode covers from end of summer (usually end of August or the beginning of September) to end of winter (usually end of March). The water is fed to the solar collector by the circulating pump, and the heated water is returned to the storage tank underground. The inclination angle (45°) was selected so that good collector efficiency is achieved especially in winter. The hot water is pumped to fan coil units, thermopanels, and floor heating coil in the bathroom, bath, and shower (room on the second floor). Domestic hot water is supplied through copper-coil heat exchangers immersed in the main and sub tanks. If auxiliary heating is necessary in mid-winter, an auxiliary boiler (fuel: city gas) is fired. However, use of this auxiliary boiler is limited to emergency situations. 4.2. Long-term cool storage mode In Fig. 3, the piping network for the cool storage mode is schematically shown. This mode begins in early April and lasts until the end of summer (end of August or early September). Fig. 3. Schematic flow network for the long-term cool storage mode. Firstly, the water in the main tank is pumped up to the sky radiators placed on the roof facing due north. The photograph of the sky radiators is shown in Plate 2. Aluminum reflectors are patched on to the vertical wall of the house to present back radiation to the sky radiators. Plate 2. Sky radiator. The tank water temperature can be decreased to about 10°C by the sky radiators alone. Beyond this point, a small-capacity heat pump is used in combination to decrease the water temperature further to 4°C. Space cooling is done by introducing the cold water to the FCUs. Since the atmosphere of the earth is relatively transparent in the infrared wavelength region between 8 and 13 µm, what we call the atmospheric window, a part of the thermal radiation at the surface of the earth is lost into space. Hence cooling takes place. This effect is especially evident on a clear night with low humidity. The sky radiation cooling power in Japanese southern cities like Osaka and Fukuoka is not sufficient to provide cooling energy in summer. In this case, the water in the subtank is chilled by operating the sky radiator loop in mid-night and early morning hours. The heat pump works very well with high COP (coefficient of performance) between the subtank and main tank. Recent simulation results performed by Saitoh and Marushima (1998) indicate that this system will work even in Fukuoka and Osaka, where the average ambient temperatures in summer are very high (27-28°C). The heat pump operated by night-time electricity also contributes for leveling, i.e. peak cut of the electricity demand. HIGH-PERFORMANCE INSULATIONS, WINDOWS, LIGHTINGS, AND APPLIANCES The final goal for the house was to reduce total purchase energy to a very low level without compromising human comfort. To this end, the active solar thermal system, sky radiation cooling design, and the photovoltaic system were of primary importance. Besides these, high-performance insulation and windows, an airtight construction, ventilation heat recovery, energy-efficient lightings and appliances, and the use of rainwater were also among the requirements. The building envelope is insulated with glass wool (density: 10 kg/m3 and thickness ranging from 0.1 m for vertical walls to 0.35 m for ceiling), with U-values of 0.44 W/m2 K for the walls and 0.14 W/m2 K for the ceiling, respectively. The windows are double-pane glass with an air layer thickness of 6 mm. The low-emission film (transmissivity: 0.5 and U-value: 4.53 W/m2 K) is placed on the inner side of the glass. Moreover, the polyethylene film (thickness: 20 µm) was pitched on to the inner frame of the window. The air layer thickness between the glass and the film was 10 mm. For the room, additional glass and shoji (Japanese lattice paper) were placed for traffic noise reduction. Also the room has similar insulations including two curtains to prevent heat loss and for noise reduction. As a consequence, the U-value of the windows is 0.78 W/m2 K except for the window in the room, which has a U-value of 0.69 W/m2 K. The main tank is insulated on the inside with 0.15 m polyurethane. The insulation was water-proofed with three-ply fiber reinforced plastic (FRP). Two cross-flow and counterflow plate heat exchangers are equipped in the living room and the basement. This type of heat exchanger has been very common as a ventilation heat-recovery system in the Japanese market in the past decade. The house has a grid-connected 1.5-kW PV system. The expected annual generated electrical power is about 1000 kWh, which is utilized for the circulating pump and data acquisition system including the personal computer and microprocessors. Surplus electricity was sold to the local electric power company at a good rate of 23 yen (19 cents) per kWh in the year 1996. Further, rainwater collected is stored in a stainless steel tank buried in the garden. More than 150 m3 of rainwater are utilized annually for toilet and garden water feeding etc. Since the costs of making city water and sewage treatment are very expensive in Japan, conservation of water is very important. The average electricity required to make 1 m3 of city water in Japan is currently 1.5-3 kWh. Therefore, utilization of rainwater saves much electricity. CONCLUSION The following conclusions may be derived from this study. The fundamental operational performance was clarified by the monitored data from August 1996 to March 1999. This house consumes only one-sixth of fossil energy compared with the conventional house. It also emits very low amounts of carbon dioxide and other pollutant gases. The external costs of this house are considered to be at least 28,000 US$ per year. This house uses sky radiation energy for space cooling and this would be particularly effective to prevent urban warming (i.e. heat island) in metropolitan areas where it is estimated that the ambient temperature in the summer evening around 2030 will exceed 40°C. About Author : S.S.CHAUHAN*, 48 Years, working as Chief Manager (Engg.) in Power Grid Corporation of India Ltd. Nagpur Presently assigned the job of technical vetting of EHV S/S & transmission lines construction proposals. List of articles published: 1. Number of technical articles in Powergrid/NTPC House journals. 2. Atomic energy and the problems of radiation control. TOI 3. Ecology and environment. Indian Institute of Environment journal, Vaigyanik (BARC) 4. Many a articles in Hindi magazines on environment issues 5. Literary creative writing in all standard Hindi magazines/Newspapers.