Evaluation of an intermittent mist spray cooling system for improving greenhouse eggplant cultivation

¹ Graduate School of Human Life and Ecology, Osaka Metropolitan University, Osaka, Japan
² Research Institute of Environment, Agriculture and Fisheries, Osaka Prefecture, Habikino City, Japan

^* Corresponding author: farnham@omu.ac.jp

Abstract

Cultivation of crops in greenhouses faces the issue of overheating, which can harm yields. A low-cost solution is evaporative cooling, which also reduces the vapor pressure deficit. Fine mist sprays can significantly reduce temperature and vapor deficit. However, the fast evaporation rate could cause air saturation and wetting of plants, causing damage. A simple method to control the effect is intermittent spraying. In this research, air temperature was continuously measured at 20 locations for a misted 98m² greenhouse during eggplant cultivation, as well as a control greenhouse without mist, while also evaluating the resulting crops. An array of 28 high pressure hydraulic nozzles, spraying 2.6kg/h each, intermittently sprayed 20 seconds on, then 10 seconds off throughout the day. The temperature in the misted greenhouse averaged 2.2K to 4.8K cooler than the control greenhouse. In the misted greenhouse, the total yield (+26%) and marketable fruits (+143%) were higher than the control. The cooling effect of the misted greenhouse compared to the control case tended to correlate with outdoor wind speed. The comparison of the misted greenhouse to its own initial condition did not. Evaluations of evaporation cooling may yield better understanding if compared to a control greenhouse at the same site.