Temperature and Humidity Environments inside a Naturally Ventilated Greenhouse with the Evaporative Fog Cooling System.

Abstract

Temperature and humidity environments inside an evaporative-fog air cooling greenhouse with natural ventilation were measured on a clear day in summer. The fog was sprayed intermittently (spraying time: 1 min at 3 or 4-min intervals) from nozzles installed 2 m above the floor inside the greenhouse. The side, end, and roof ventilators of the greenhouse remained open to increase air circulation and fog evaporation during cooling. The results of the experiment are summarized below. (1) The inside air temperature reduced to approximately the inside wet bulb temperature within 1 min after the start of fog spraying. (2) The vertical air temperature differences below the nozzles (plant growing zone) were within 1 °C, and the horizontal air temperature differences at 1.5 m above the floor in the greenhouse cooled with fog spray system were within 2.5°C. (3) The reduction of leaf temperature of the tomato plant by fog spray was smaller than that of air temperature. The difference between the leaf temperature and the air temperature inside the greenhouse decreased as the saturation deficit of the air increased. (4) From these measurements, when fog fills the greenhouse atmosphere, the air is rapidly cooled at a rate of 10°C per min, a small sensor, such as a small diameter thermocouple in which heat capacity is small, is recommended to prevent errors in measuring air temperature.

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