Air and leaf temperatures and relative humidity in a naturally ventilated single-span greenhouse with a fogging system for cooling.

摘要

Dry bulb (or air) and leaf temperatures of tomato plant (Tleaf) and relative humidity were measured around midday in summer inside a naturally ventilated single-span experimental greenhouse with a fogging system for cooling, and with sidewall and roof ventilators which remained open. Evaporative cooling efficiency ( eta ), 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 consisted of a water filter, water reservoir, fogging pump, pressure regulator, and fog-generating nozzles. Fog was applied for periods between 20 and 75 s, separated by intervals of 160 s. During fogging, Tidb and Tleaf sharply decreased, while RHi sharply increased. During the interval, however, Tidb gradually increased and Tleaf tended to remain unchanged, while RHi gradually dropped. Tleaf was 1 degrees C higher than Tidb when VPDi was 4 hPa, and the difference between Tleaf and Tidb decreased with increasing VPDi. The eta was in a range between 57% and 80%, and more than 20% higher than that of a typical conventional misting system..