Articles
THERMAL PERFORMANCE OF A SOLAR GREENHOUSE WITH AN UNDERGROUND HEAT STORAGE SYSTEM
However, at present, most of them have not been used commercially, because of the relatively high initial investment cost and the relatively low thermal performance.
As one of the exceptions, a solar greenhouse with an underground heat storage system developed by Yamamoto (1967) has been widely used commercially in the regions along the Pacific coasts of Central and Western Japan (Kozai, 1986).
The solar greenhouse is of the active type, but, because the greenhouse acts as its own solar collector, no extra land area is required for an external collector.
With this system, excess transmitted solar heat is stored during the day by circulating the warm air in the greenhouse through pipes buried in the greenhouse soil, and the stored heat is released from the soil to air flowing through the pipes during the night when heating is required.
Some experimental (Sasaki et al., 1981) and theoretical (Takakura and Yamakawa, 1981) studies have been conducted on solar greenhouses with an underground heat storage system, but only a few experimental studies based upon heat balance analyses have been conducted on the relatively large-scale commercial solar greenhouses.
The purpose of the present study is to analyse the heat balance and to evaluate the thermal performance of the commercial solar greenhouse during the winter.
Nomenclature
| Aw | = exposed greenhouse roof/wall area |
| Af | = floor area |
| CFf | = solar energy collection factor of the floor |
| CFh | = solar energy collection factor of the heat exchange system |
| CFt | = solar energy collection factor of the greenhouse ( = CFf + |
| CFh) | |
| d | = day |
| DHd | = degree-hour during the day (from sunrise to sunset), |
| integral of the difference in air temperature between | |
| inside and outside |