| The Yangtze River Basin is the main agricultural production area,which lies on the border between the north and the South in China.Plastic greenhouses are widely used for its simple structure and low cost,and it is the main facility type in this area.However,the area has a subtropical monsoon climate,with low temperatures and light in winter,high temperatures and humidity in summer,and frequent natural disasters.The ability of environmental control of plastic greenhouses is weak,and it is difficult to produce in winter and summer.Therefore,a large-span thin greenhouses are designed and constructed based on previous experience,greenhouse construction theory,and the advantages of existing large-span greenhouses,combined with the climate characteristics of the Yangtze River Basin in this research.In order to explore the adaptability of the large-span thin greenhouses in the Yangtze River Basin,the change characteristics of indoor environment of the greenhouses in typical months and typical weather were studied by comparing three-span plastic greenhouses of the same area.The main results of the paper are as follows:(1)According to the climate characteristics of the Yangtze River Basin,a large-span film greenhouses were designed and constructed.The main structural parameters of the greenhouse are 48 m in length,20 m in span,6 m in ridge height,1.8 m in shoulder height and 7 m in sunshade height.The greenhouse arch is divided into east and west parts,which are symmetrically installed into arches through longitudinal beams.The longitudinal beams connect two adjacent columns,and the spacing between two columns is 4m.The greenhouse framework is a hot-dip galvanized steel structure.Except for the door,the greenhouse is covered with plastic films.The north and south walls are double-layer plastic films with a spacing of 0.1 m.The greenhouses are equipped with an external heat preservation system that can be opened in both east and west directions to improve the heat preservation capacity at night in low temperature seasons..Both the east and west sides of the greenhouses are provided with bottom and top ventilation of 1 m in width,and the top ventilation is a mechanical extrapolated hanging window to ensure ventilation in rainy days.In addition,the greenhouse is equipped with an external sunshade system,which can reduce the light intensity,thus reducing the indoor temperature in high temperature seasons.(2)The results of winter test show that the daily average temperature,the lowest temperature,the average relative humidity and the lowest relative humidity of the large-span film greenhouse are 1.6℃,4.8℃,4.1%and 12.8%higher than those of the three-span plastic greenhouse respectively,and the average transmittance is 28.6%lower than that of the three-span plastic greenhouse.Under typical sunny conditions,the average temperature and relative humidity of the large-span film greenhouse are 2.6℃ and 6.7%higher than those of the three-span plastic greenhouse respectively,and the average light transmittance of the large-span film greenhouse is 28.9%lower than that of the three-span plastic greenhouse.Moreover,the uniformity of air temperature and relative humidity of the large-span film greenhouse are better,and the uniformity of light is worse.Under typical cloudy conditions,the average temperature and relative humidity of the large-span film greenhouse are 1.6℃ and 3-4%higher than that of the three-span plastic greenhouse,and the average light transmittance is 23.7%lower than that of the three-span plastic greenhouse.The air temperature uniformity of the Large-span film greenhouse is better,and the uniformity of illumination and relative humidity are worse than those of the three-span plastic greenhouse.(3)Summer test results show that the daily average temperature,the highest temperature and the average relative humidity of the large-span film greenhouse are 1.3℃,7.8℃ and 5.3%lower than those of the three-span plastic greenhouse respectively,and the minimum relative humidity is 6.9%higher than that of the three-span plastic greenhouse.Under typical sunny conditions,the average temperature and the average relative humidity of the large-span film greenhouses are 3.4℃ and 4.3%lower than those of the three-span plastic greenhouses.Moreover,the uniformity of the air temperature and relative humidity of the large-span film greenhouse are better.Under typical cloudy conditions,the average temperature and relative humidity of the large-span film greenhouse are 0.2℃ higher and 5.3%lower than those of the three-span plastic greenhouse.In addition,the uniformity of air temperature and relative humidity in large-span film greenhouse are better. |
