Greenhouse evaporative cooling: Measurement and data analysis

Abstract

Temperature and humidity gradients were investigated during summer in a rose production greenhouse equipped with a ventilated cooling-pad system and a half shaded plastic roof. In a steady regime, the cooling process reached a good efficiency (60%, in agreement with the theoretical value) and succeeded in maintaining the greenhouse temperatures up to 10°C lower than outside. The temperature of the fresh air rose from the pads to the middle of the greenhouse, while the humidity content did not increase. On the contrary, plant transpiration humidified the air on through the second half of the greenhouse, but the temperature rose only moderately. In early morning and late afternoon, the fresh air provided by the pads seemed to induce condensation on the soil, especially in the first half of the greenhouse. The physical data were compared with those predicted by an analytic model describing the greenhouse as a heat exchanger. The model helps to understand the particular temperature and humidity profiles of the air flow along the greenhouse. It also suggests that greenhouse roof shading could be avoided under dry climates, because the evaporative cooling process is sufficient to prevent overheating.