Microclimate and cucumber crop transpiration in a greenhouse cooled by pad and fan system

摘要

The microclimate and cucumber soilless crop response in an evaporatively cooled greenhouse were studied in Cyprus during spring. Measurements were carried out in two greenhouse compartments: (1) a compartment in which a wet pad and fan system for evaporative cooling of the greenhouse environment was operated, and (2) a compartment in which greenhouse cooling was performed by means of forced ventilation with outside air. Compared to forced ventilation, evaporative cooling was able to reduce mean air temperature by about 7.5°C and maintained greenhouse air temperature below 28°C, while mean air temperature without cooling reached values higher than 34°C, closed to the external air temperature values. Furthermore, evaporative cooling reduced air vapor pressure deficit by about 60% and maintained mean greenhouse air vapor pressure deficit below 1.6 kPa. In addition, evaporative cooling resulted in an about 4°C lower leaf temperature values compared to the case of forced ventilation. The cucumber crop transpiration rate was about 20% higher in the compartment cooled by forced ventilation than in the one with evaporative cooling. Finally, it was estimated that the crop stomatal conductance was about 25% higher for the crop cooled by the evaporativecooling system than the crop cooled by forced ventilation.