Effects of vent opening, wind speed, and crop height on microenvironment in three-span arched greenhouse under natural ventilation

Multi-span arched plastic greenhouse is an important horticultural facilities structure. The main problem to be faced is ventilation and cooling in summer. Therefore, 3-span arched plastic greenhouse with better adjustable performance were used as a research object. The effects of vent opening, wind speed and crop height on the microenvironment under natural ventilation were studied by means of in-situ observation and computational fluid dynamics (CFD) analysis. By analyzing the space-time evolution of microenvironment and ventilation efficiency in the greenhouse, this paper aims to explore the change process of microenvironment and the reasonable matching relationship between various factors. The results show that side vent opening and crop height significantly affect the microenvironment in the greenhouse, and they have the optimum matching relationship. When the crop height is 1.0 m and the wind speeds are 0 m/s, 1.0 m/s and 2.0 m/s respectively in the dynamic stability stage, the temperatures of point Q2 under the condition that the side vent opening is 0.8 m are 3.00 °C, 1.49 °C and 0.51 °C lower than temperatures under the condition that only the inter valley vent is opened. When the crop height is 1.8 m and the wind speed is 0 m/s, the difference of temperature of point Q3 is 3.50 °C, 0.97 °C and 2.15 °C respectively. The larger the opening of the side vent, the better the ventilation and cooling effect. Compared with the influence of the size of the side vent opening on the microclimate in the greenhouse, the influence of wind speed on it is weak. When side and inter valley vent are opened at the same time, the horizontal layer height of the lowest temperature at the crop height of 1.0 m is lower than that of 1.8 m. The influence of side vent opening on heat removal efficiencies (HREs) takes precedence over the influence of wind speed. When only the inter valley vent is opened, the HREs are the smallest and close at various crop heights and wind speeds. These results provided a control strategy with lower energy consumption and higher efficiency for 3-span arched greenhouses.