Greenhouse evaporative cooling: Measurement and data analysis

Abstract

Temperature and humidity gradients were investigated during summer in a commercial greenhouse producing cut roses, equipped with a ventilated cooling-pad system and a half-shaded plastic roof In a steady regime, the cooling process reached 80% efficiency and succeeded in maintaining greenhouse temperatures that were cooler (up to 10 degreesC lower) than outside. In the unshaded half of the greenhouse, the inlet air temperature increased from. the pads to the middle of the greenhouse, while the humidity content remained constant. In the shaded half of the greenhouse, plant transpiration humidified the air, but the air temperature increased only moderately. In early morning and late afternoon, the moist and cool air coming from the pads seemed to induce condensation on the soil, especially in the first (unshaded) half of the greenhouse. The physical data were compared with those predicted by an analytical model describing the greenhouse as a heat exchanger The model helped to understand the particular temperature and humidity profiles of the airflow along the greenhouse. It also suggested that greenhouse roof shading could be avoided in dry climates because the evaporative cooling process was sufficient to prevent overheating.