After the Great East Japan Earthquake in 2011, the energy-saving and utilizing renewable energy has been a growing issue in Japan. In houses, the energy consumption mainly goes for hot water supply, space heating and other equipment. Therefore, in housing sector, solar energy seems to be the most useful renewable energy because it can be used for both; to generate electricity and provide heating.
In this paper, we planned five model houses with air-based solar system for each climate zone defined by Japanese energy-saving standard and later evaluate their annual performances by measurement. To improve the thermal comfort and reduce energy use, the insulation level was raised beyond the Japanese energy-standard levels. In addition, we adopted some energy-saving techniques e.g. using bottled water as heat storage medium. The annual measurements showed excellent improvements in the energy-saving performance of each house compared with the energy-saving standard model in Japan.
We adopted some techniques to improve air-based solar system. For winter, we adopted; an internal protection enclosure of a Vacuum Insulation Panel (VIP) to reduce the heat loss through window during night, a heat storage medium is achieved by having water bottles and phase change material sheets under the suspended floor. Solar shading strategies were adopted in summer e.g. eaves, movable outer blinds and louvers to reduce the cooling load.
Through the annual measurements, we evaluated these techniques together with the air-based solar system, the results are as below;
1) Firstly, it is to confirm the excellent energy-saving performance of all the houses when compared with the energy-saving standard models in Japan.
2) In all houses, the efficiency of the air-based collectors are about 14 to 20% for the pre-heating photovoltaic panels, and from 23 to 34% for the glass panels.
3) The energy-saving from the solar system hot water supply differs from one location to another and also vary during seasons. In general, about 27 to 56% of the annual energy used for water heating could be saved.
4) In Hamamatsu and Sendai, the indoor thermal comfort was achieved during all the winter days with minor operation of air-conditioning.
5) The effect of heat storage media of water bottles and the phase change material sheets were evaluated. In the daytime, the hot air from the solar system is usually stored in these media (located under the suspended floor). In the cases when there is no solar energy or if it is not enough collected, the previously stored thermal energy is then released to the internal space.
6) The thermal insulation performance of VIP inner window enclosure was evaluated. In Hokkaido, heat loss through the triple-glass window is reduced to the half when VIP is closed.
7) The performance of solar shading strategies and the air-based solar cooling system were evaluated in summer. For houses in Hamamatsu and Kagoshima, the shading strategies and the solar cooling system decreased the cooling load by about 50% compared to the houses without these systems.
