| This study bases on the full use of solar radiant energy in winter and the reduction of indoor heat accumulation in summer in greenhouses,in order to reduce the vacancy rate of plastic greenhouses and improve the land utilization rate of horticultural facilities in the Yangtze River basin.Based on the geographical location and climate characteristics of this region,we designed and built a new type of north wall structure in a multi-span solar energy greenhouse(SEG),by learning from the experience of solar greenhouse construction in the Northern China.Using an ordinary multi-span plastic greenhouse(PG)as a control greenhouse,the microclimate characteristics in summer and winter,efficacy of crop cultivation,natural ventilation effect in summer and wall insulation effect in winter were studied.The main findings of the paper are as follows:(1)In the test of the thermal properties of jute fiberboard and peat,it was found that the density of jute fiberboard was 60kg·m-3 compared with wall materials such as straw boards and clay bricks,which facilitates the construction of the wall.The thermal conductivity of the fiberboard was only 0.147 W·m-1·℃-1,which indicated that the jute fiberboard had a good thermal insulation performance and was suitable for wall insulation layer.The thermal conductivity,heat storage coefficient and specific heat capacity of peat were 0.27-0.45 W·m-1·℃-1,5.46-6.04 W·m-2·℃-1,3709 J·kg-1·℃-1.Therefore,peat can be used as a new type of friable insulation material in the middle of the sandwich wall.(2)Aiming at the problem of poor thermal insulation of plastic greenhouses in winter and difficulty in cooling in summer in the Yangtze Basin in Jiangsu Province,according to the geographical location and climate characteristics of the region,a new type of north wall inside the SEG was designed and constructed.A thermal insulation wall was built on the north side of the rear span of SEG,with a wall height of 4 m and a thickness of 60 cm.The north wall was divided into upper and lower halves,each with a height of 2 m.The lower half of the wall was a three-layer composite heterogeneous fixed wall,the inner side was a 24 cm hollow clay brick thermal storage layer,and the outer layer was a 10 cm polystyrene board,between them was a 26 cm peat insulation layer;the upper half of the wall was a removable hollow wall,both inner and outer layers were 10 cm jute fiberboard,and the middle was 40 cm air layer.In summer,the ventilation area of SEG can be increased by disassembling the jute fiberboard;it can be reinstalled in winter to increase the thermal insulation performance.(3)During the summer test,the indoor temperature of the SEG was 2.3℃ lower than the PG,and the highest temperature was 7.3℃ lower than the PG.On the sunny day in summer,because SEG opened the external sunshade at noon,and the vent area was larger than PG,the average daily temperature of SEG was 3.0℃ lower than PG,the average daytime temperature was 5.7℃ lower than PG,and the maximum temperature of SEG was not more than 38.℃;The maximum temperature of the SEG at the heights of 1m,2m and 3m were 12.3℃,8.9℃ and 11.8℃ lower than PG,respectively,while the daily average temperature were 4.3℃,3.5℃ and 4.0℃ lower than PG,respectively.The average relative humidity of SEG was 8.4%higher than PG;The uniformity of air temperature was higher than PG,while the uniformity of relative humidity was lower than PG.On the typical cloudy day in summer,both greenhouses adopted the natural ventilation to cooling greenhouse.The average daily temperature,average daytime temperature and average nighttime temperature of the SEG were 1.1℃,1.8℃ and 0.2℃ lower than PG,respectively.The ventilation cooling effect of the SEG was better.The highest temperatures of the SEG at the heights of 1 m,2 m and 3 m were 1.4℃,1.9℃ and 0.3℃ lower than PG,respectively,while the average daily temperature was 0.8℃,0.9℃ and 0.4℃ lower than PG,respectively.The average relative humidity of the SEG was 6.1%higher than PG;The uniformity of air temperature was lower than PG,and the humidity uniformity was higher than PG.(4)During the winter experimental periods,the average daily temperature of the SEG was 2.6℃ higher than PG,and the lowest temperature of the SEG was 5.6 ℃ higher than PG.On a typical sunny day,the average daily temperature of the SEG was 2.1℃ higher than PG;the effective accumulated temperature of the SEG was 2.8 h℃-3.0 h℃ higher than PG.The average relative humidity of the SEG was 4.0%higher than PG;the average transmittance of the SEG was 13.6%lower than PG.The average daily soil temperature at each depth inside the SEG were 0.4 ℃,0.7 ℃,0.5℃,1.1℃,and 1.2℃ higher than PG,respectively.On a typical cloudy day,the average daily temperature of the SEG was 2.3℃higher than PG;the effective accumulated temperature of the SEG was 17.3 h℃-37.6 h℃higher than PG;the average transmittance of SEG was 26.3%lower than PG.The average daily soil temperature at each depth of the SEG were 0.1℃,0.6℃,0.8℃,1.4℃,and 1.2℃ higher than PG,respectively.(5)In the summer cultivation experiment,compared with PG,the plant height and stem diameter of the lettuce inside the SEG were increased by 41.8%and 13.2%,respectively.The fresh weight and dry weight of the lettuce inside the SEG were increased by 220%and 222.2%,respectively.In the winter cultivation experiment,the plant height of the lettuce inside the SEG increased by 47.2%compared with PG,and there was no significant difference in the stem diameter;the fresh weight of the lettuce inside the SEG increased by 27.4%compared with PG,and there was no significant difference in the dry weight. |
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