Combined Effect of Whitening and Ventilation Methods on Microclimate and Transpiration in Rose Greenhouse

In this communication the effect of roof ventilation, roof & side ventilation (opening angle 15^o and 45^o) and fan-pad cooling methods on transient response of inside air temperature, plant canopy temperature, growing media temperature, relative humidity and transpiration rate in a single span rose greenhouse size 22m x 10m x 4.90m located at the department of Environmental Horticulture, University of California, Davis, CA (38⁰N, 122⁰.06’ W) have been studied theoretically. The results were compared for clear and whitewash coating on glass cover greenhouse. The theoretical investigation was carried out by writing energy and mass balance equations for different components of the greenhouse. The equations were solved by adopting the finite difference technique. The results revealed that whitewash helped to reduce the plant temperature and transpiration rate significantly. The effect of opening angle for clear glazing was more prominent as compared to whitened glazing. For small vent opening angle (b=15^o), the cooling was more effective in case of roof & side ventilation as compared to only roof ventilation whereas for large vent opening angle (b=45^o), the effect of whitening was found insignificant. During sunshine hours, the difference in average inside air and plant temperatures at pad and fan locations in fan-pad cooling system were 10.26°C and 5.0°C respectively for the clear and 898°C and 4.5°C for whitened glass cover respectively.