Abstract
Dry bulb (or air) temperature, leaf temperature of tomato plant (Tleaf), and relative humidity were measured under various fogging times (tf) around midday in summer inside a naturally ventilated single-span experimental greenhouse with a fogging system for cooling and with side-wall and roof ventilators which remained open. Then, the evaporative cooling efficiency (η) of the greenhouse, expressed as the ratio of the difference in dry bulb temperature between the outside (Todb) and the inside (Tidb) to the difference between Todb and the outside wet bulb temperature (Towb), was calculated. The fogging system was comprised of a water filter, a water reservoir, a fogging pump, a pressure regulator, and fog-generating nozzles. Fog was applied for periods between 20 and 75 s, separated by intervals of 160 s.For all tf, a drop in Tidb increased with increasing vapor pressure deficit of the inside air (VPDi) at the start of fogging. Tidb reached 6.0°C lower than Todb by fogging. During fogging, Tidb was more or less the same as Tleaf. During the interval, however, Tidb increased and Tleaf tended to remain unchanged. The increase in VPDi resulted in decreased (Tleaf-Tidb) . The η was in the range between -30% and 21% when using the average Tidb, and 57% and 80% when using the minimum Tidb. The η compares favorably with a conventional misting system.
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