The cost of maintaining the desired temperature in winter is a principal element in the production of vegetables in greenhouse culture. Consequently, much lower costs of heat and more profitable operations will be possible if warm water from the condenser of a power plant can be used as the heat source for greenhouse heating.
In order to investigate the possibility of utilizing thermal effluent as the heat source of greenhouse heating, the experiments by a miniature greenhouse equipped with PVC-pipes as indirect heat exchangers were carried out (see Fig. 1).
The results obtained can be summarized as follows.
1. Under the conditions of warm water of 25.5°C and an outside air temperature of -6.8°C at calm clear night, air temperatures at inlet and outlet of the heat exchanger pipes in the greenhouse were 9.0°C and 16.5°C, respectively (see Fig. 2).
2. From an experimentally obtained relationship between the heat transfer coefficient and air speed in the pipes, the heat transfer coefficient at an air speed of 10m/sec was 2.5 times as much as that at 2m/sec (see Fig. 3).
3. From a theoretically obtained formula yielding required number of pipes for the model greenhouse utilizing thermal effluent, it was shown that 16 PVC-pipes, 23m long and diameter of 20cm, were required to maintain 12°C inside the greenhouse with thermal effluent of 25°C and an outside air temperature of -10°C (see Fig. 5, Fig. 6 and Fig. 7).