| In this paper,a 6m multi-span greenhouse was taken as the research object,and an experimental study of indoor wind speed and temperature distribution under different ventilation modes in summer was conducted.The CFD method was used to establish a three-dimensional CFD numerical model of 6m greenhouse under natural ventilation and mechanical ventilation conditions,which provided theoretical support for production regulation and structural design of greenhouses in summer.The main research contents and results are as follows:(1)Carrying out the study of decreasing temperature of different ventilation methods during the summer of 6m greenhouse.The results showed that when the outdoor temperature was 30?,the canopy temperature of the crop in the closed greenhouse reached 44?.After using top window + side window combination ventilation,the canopy temperature dropped by 10?.After increasing the internal and external shading nets,the indoor temperature could be reduced to be similar to that of the outdoor,and the indoor radiation value was only 55W·m-2,which was about 9% of the outdoor.(2)Analysis of the 6m greenhouse cooling effect in mechanical ventilation conditions,the results showed that: the wet curtain fan cooling effect was obvious,when the outdoor 36.6 ?,the indoor crop height temperature could be reduced to 30.8 ?,lower than the outdoor 5.8 ?.After using the wet curtain fan cooling system,the indoor humidity reached more than 90%.Therefore,regular dehumidification was required.(3)A greenhouse CFD model was established for the piloted glass greenhouse.Comparing the simulated values with the measured values,the results showed that the maximum relative error of the measuring points was 3.42% and the average relative error was 2.13%.The maximum relative error of the measuring point during mechanical ventilation was 6.70%,and the average relative error was 2.87%,indicating that the established CFD model was effective.(4)The CFD model was used to further explore the effects of height and area changes on the indoor environment under natural ventilation conditions.The results showed that: With the height increasing from 3.8m to 6m,the indoor temperature was reduced at different heights.At an outdoor temperature of 33?,the canopy temperature of the 6m greenhouse crop was 37.2?,which was 0.6? lower than that of the 3.8m greenhouse.After increasing the greenhouse area,the indoor wind speed increased.When the outdoor environment was 33?,the average east-west temperature at 2m was 37?,which was 0.4? lower than that before the increase,and the temperature distribution in the east-west direction of the greenhouse was more uniform.The analysis also found that the side windows of the greenhouse had an effect on the internal temperature of the greenhouse with approximately two roofs.With the increase in the greenhouse area,the side windows played a smaller role,and the up window was used for ventilation and heat exchange with the outside.(5)The influence of the circulation fan arrangement on the cooling effect of the mechanical ventilation was analyzed.The results showed that when the outdoor temperature was 36.6?,the temperature difference between the north and south of the room was decreased by 0.5? and the area below 32? was increased by 20%compared with the case where only the wet curtain fan was turned on.At the same time,it showed that when the circulation fans were arranged in opposite directions on different transverse sections,the indoor hot and cold air mixed better and the temperature distribution was more uniform. |
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