Experimental Investigation of High-pressure Fogging System Applied with Natural Ventilation in Large Span Greenhouse

In order to increase land use efficiency and operation space of solar greenhouse，a new type of long-span greenhouse with north-south trend was designed.When planting crops in summer，the indoor temperature of the greenhouse is higher，especially in sunny days.Even if ventilation vents are fully opened for natural ventilation，temperature in the greenhouse at noon can be as high as 40 ℃.In order to reduce temperature in a large span greenhouse，a high-pressure spray cooling method was proposed.The high-pressure spray device consisted of a filter，a storage tank，a pipeline，a high-pressure pump，a controller decompression valve and a sprinkler.According to previous research theory，spray volume of greenhouse was calculated to be 0.27 g/（m2·s），the nozzle was cone shaped，nozzle diameter was 0.3 mm，droplet diameter was 0.02~0.03 m，nozzle flow rate was 1.3~2.4 g/s，and nozzle mounting density was 0.3 /m2.During the test period，3 spray operation modes，60 s opening 300 s off，90 s 300 s off and 120 s opening 300 s off，were set up，and spray cooling experiments were conducted on typical sunny days in summer.Test results showed that temperature of experimental greenhouse was 3.0，5.1 and 6.0 ℃ lower than that of control greenhouse respectively under three operation modes of spray device，and relative humidity of air increased by 10.2%，20.1% and 23.8% respectively.Spray evaporative cooling efficiency of three spray operation modes was 26.3%，39.4% and 47.2% respectively under outdoor environment approaching condition.Combined with cooling effect of greenhouse，relative humidity of air and efficiency of spray evaporative cooling，cooling effect of 120 s intermittent 300 s spray system was ideal.It was concluded that this study provided a reference for regulation of summer cooling in large-span greenhouses in North China.