Effect of Different Height of Side Vents on Microclimate in a Single-Span Greenhouse during Natural Ventilation

This study was carried out to investigate the effect of side vent heights on temperature and relative humidity inside and outside the single-span plastic greenhouse (W: 7 m, L: 40 m H: 3.9 m) during natural ventilation.Four different heights (120, 100, 80, 60 cm) of the side vent were used as an experimental condition.Variations of temperature and relative humidity inside and outside the greenhouse and the differences between heights were compared by using one-way ANOVA.In the daytime, the difference in temperature between inside and outside the greenhouse was dropped from 14.0°C to 7.1°C as the side vent height increased.The temperature difference in the nighttime was less than 0.2°C regardless of the height.One-way ANOVA on the temperature difference between heights presented that the statistical significance was founded between all of the combinations of height in the daytime.The difference in relative humidity between inside and outside the greenhouse was grown from -13.8% to -22.2% with a decrease in the side vent height.The humidity difference in the nighttime was less than 1% regardless of the height.One-way ANOVA on the humidity difference revealed that most of the side vent heights showed significance in the daytime but between 100 and 80 cm was not significant.It seemed because the external air became cooler during the experiment with a height of 80 cm.Conclusively, this study empirically demonstrated that the higher side vents resulted in the decrease of differences in temperature and relative humidity between inside and outside the greenhouse, and also the effect of side vent height was statistically significant.This study may be helpful for deciding the height of the side vent effective for controlling temperature and relative humidity in a single-span greenhouse during natural ventilation.