| The traditional plastic arch greenhouse has the advantages of simple structure,low construction cost and good light transmission performance,and is widely used in various regions of China,but there are also problems such as poor heat preservation,small span and operating space which is not conducive to mechanization work and performance.Therefore,our team designed a large-span asymmetric plastic greenhouse according to the principle of lighting and thermal insulation.In order to study the characteristics of the warm and light environment of this type of plastic greenhouse,and to screen out the large-span plastic greenhouse type suitable for the annual production of facility crops,this study selected five large span asymmetric plastic greenhouses,namely 17 m span single layer(FG-17-1)and double-layer plastic greenhouse(FG-17-2),18 m span single(FG-18-1)and double-layer plastic greenhouse(FG-18-2)and 20 m span single layer plastic greenhouse(FG-20-1),to measure and analyze the temperature and light environment of typical weather and compared with traditional arch plastic greenhouse(G-8-1)and Chinese solar greenhouse(CSG)as the control.The results are as follows:1.In terms of temperature,the lowest temperature in each greenhouse in autumn and winter was CSG>FG-18-2>FG-18-1>FG-17-2>FG-20-1>FG-17-1>G-8-1.In spring,CSG and FG-18-2 had higher air temperatures and there was no difference between the night average temperature and minimum temperature;FG-17-1,FG-17-2,FG-18-1 and FG-20-1 had lower temperatures and were less different from each other and higher than G-8-1.It could be seen that the large-span asymmetric plastic greenhouse can significantly increase the nighttime average temperature and the minimum temperature,but the span was not as large as possible.The warming effect of FG-17-2 was higher than that of FG-20-1,which was higher than that of FG-17-1,indicating that the effect of multi-layer coverage on the thermal insulation performance of greenhouses was greater than the influence of span on its thermal insulation performance.Among the five large-span asymmetric plastic greenhouses,the lowest temperature in the FG-18-2 was the highest.In the sunny and cloudy weather in autumn,winter and spring,the minimum temperatures were above 9.0,5.4,and 14.0 °C,respectively,which was 4.7,11.7,and 3.3 °C higher than G-8-1,respectively.The average daily temperature in snowy day in winter was 6.0 °C,which was 6.2 °C higher than that of G-8-1.The temperature distribution in the north-south span was 0.6 °C in typical winter weather.The distribution was relatively uniform.Therefore,the FG-18-2 greenhouse has better insulation performance and relatively stable temperature changes,which can provide a relatively good temperature environment for facility crops.2.In terms of soil temperature,the average daily soil temperature in five large-span asymmetric plastic greenhouses in autumn and winter was FG-18-2>FG-18-1>FG-17-2>FG-17-1>FG-20-1>G-8-1.In spring,FG-18-2 and FG-17-2 were higher than G-8-1,FG-17-1,FG-18-1 and FG-20-1 were lower than G-8-1.The average daily temperature of FG-18-2 in autumn,winter and spring was 14.9~19.1,10.9~12.7,18.5~22.8 °C,respectively,which was 4.8~8.3,5.5~6.3,0.1~1.2 °C higher than G-8-1.It can be seen that FG-18-2 can accumulate more heat during the day,increase soil temperature,and provide relatively good rhizosphere temperature for facility crops.3.In terms of illumination,FG-18-1 had the highest light intensity in the shed,more uniform distribution of light in the north and south,and better lighting performance.The maximum light intensity values in the south,middle and north of FG-18-1 of the autumn,winter and spring were 34 400,32 520,29 100 lx,34 400,32 520,29 100 lx and 43 848,42 984,39 655 lx,respectively.FG-18-2 was slightly lower,and the maximum light intensity values in the south,middle and north of the autumn,winter and spring were 32 150,31 203,27 442 lx,33 620,31 190,26 970 lx and 41 184,39 120,35 352 lx,respectively.FG-20-1 and FG-17-1 have lower light intensity and FG-17-2 is the lowest.This showed that increasing the span and adopting an asymmetric structure can significantly improve the light intensity in the greenhouse,greatly improve the northern illumination,and make the light distribution in the north-south direction more uniform,but the span increase is kept within a reasonable range,not the bigger the better.4.In terms of annual temperature changes,the FG-18-2 had a high minimum temperature throughout the year in five large-span asymmetric plastic greenhouses,with no extreme low temperatures and good thermal insulation properties.The minimum temperature of FG-18-2 in spring and autumn was about 0.5 °C lower than CSG,which was about 4.0 °C higher than G-8-1.The minimum temperature of FG-18-2 in winter was 4.2 °C,which was 16.3 °C higher than G-8-1 and 2.1 °C lower than CSG.At the same time,the maximum temperature in the FG-18-2 was relatively low,there was no extreme high temperature,and the daily variation of temperature was relatively small.The results of the above ambient temperature and light environment show that the 18 m span double-layer asymmetric plastic greenhouse can significantly improve the temperature and soil temperature,and the thermal insulation performance is better.And the light intensity is high,the distribution is relatively uniform in the north and south,and the lighting performance is good.It can provide suitable temperature and light environment for facility crops,and is more suitable for promotion and application in the annual production of facilities. |
