Studies on the Heat Balance of Polyvinyl Chloride (PVC) Greenhouse with an Earth-Air heat Exchanger

The main objectives of this paper are to study and analyse the heat characteristics of an earth-air heat exchange system (EHES) and its effects both on the climatic environment of PVC-greenhouse and the crop yields. Based on the observed data, the heat balance of the two greenhouses has been calculated.In order to verify the feasibi lity and the practicality of the EHES, the economic benefit and the energy saving have also objectively been evaluated.The experimental results are as follow:1.The rate of the heat release from the EHES and the heat storage into the EHES were 8700kcal/ hr.and 18471kcal / hr.respectively.The ratio of the both rates was 0.47.2. The air temperature observed and calculated inside greenhouse A, which attached with the EHES, had risen 2.0-4.4℃ , and 2.6-9. 6℃ (u= 1.5m/sec) respectively at night, as compared with greenhouse B, which was without the EHES .On the contrary, the air temperature observed and calculated inside greenhouse A was 2.5-6.5℃ , and 6.2-15.1 ℃ lower than that of greenhouse B during the daytime (u = 2.0m / sec.) .3. The verage soil temperature observed and calculated at 0-50cm depth inside greenhouse A was 2.3℃ , and 1.8℃ higher than that of greenhouse B due to the influence of the EHES.4. The heat balance of greenhouse A was much different from that of greenhouse B not only at the daytime, but also at night.The energy shortage of greenhouse B was far greater than that of greenhouse A during the whole night.5.The yields of strawberry and cucumber planted in greenhouse A increased by 51% and 45% over that of greenhouse B respectively.6.It seemed very feasible and practical to apply this installation from the point of view of the economic benefit and the enery saving.