COMBINED EFFECT OF WHITENING AND VENTILATION METHODS ON MICROCLIMATE AND TRANSPIRATION IN ROSE GREENHOUSE

In this c ommunication the e ffect 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 hu midity and transpiration rate in a single span rose greenhouse size 22 m x 10m x 4.90m located a t t he depa rtment of Environmental H orticulture, University of California, Davis, CA (38 0 N, 122 0 .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 e quations were solved b y adopting the finite difference technique. The results revealed that whitewash he lped to reduce the p lant temperature and transpiration rate significantly. The e ffect of opening angle for clear glazing was more prominent as compared to whitened glazing. For small vent opening angle (β=15 o ), the cooling was more e ffective in case o f roof & side ventilation a s c ompared to on ly roof ventilation whereas for large vent opening angle (β=45 o ), t he e ffect 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 0 C and 5.0 o C respectively for the clear and 8.98 0 C and 4.5 o C for whitened glass cover respectively.