| The solar greenhouse production has been developing rapidly and the total area is large in Northern Jiangsu Province.Numerous types of solar greenhouse designs exist.Development of solar greenhouse led to the development of local agriculture,while improving the income of farmers.However,most of them do not take into consideration the local weather conditions.Crop grown in the greenhouses suffer from unfavorable conditions such as low temperature(in winter),high temperature(in summer),and high humidity.Therefore,optimization of existing greenhouse designs and coming up with new designs that adapt well to local weather conditions is the key to the development of greenhouse industry in Northern Jiangsu Province.This study first surveyed the basic types and application status of the solar greenhouses in Northern Jiangsu.The purpose was to find out the drawbacks and operational problems of solar greenhouses in practice.Based on the survey and analyses,two new designs of solar greenhouse was put forward after the common north wall was improved and optimized in Northern Jiangsu.One is the 'improved greenhouse' and the other is 'removable greenhouse' that has dismountable upper section in the north wall.The'removable greenhouse' was put forward based on consideration that solar greenhouses should be able to operate both in winter and summer.The thermal environment and crop performance in the two new types of solar greenhouses were measured in the field and compared with traditional solar greenhouse.The results are as follows:1.The solar greenhouses in Northern Jiangsu were divided into three categories including 20 kinds of configurations.The common ones were 8?12 m span,3.0?4.0 m ridge height,2.5-3.0 m the height of north wall,and 0.9-1.1 m the level projection of north roof.Most of the north wall materials were clay brick,hollow brick and compacted soil.Parts of the walls were layered wall while few walls were straw.The stubbles arrangements of the crop in solar greenhouses were mainly anniversary production,one crop a year,two crops a year and three crops a year.Among all of the stubbles arrangements,two crops a year got the highest proportion.The vacancy rate of solar greenhouses in July and August was higher affected by the high temperature.The land utilizations of most solar greenhouses were lower than 50%,especially the greenhouses with earthen wall.Though the configurations of solar greenhouse in Northern Jiangsu are diversiform,the structure need to be further optimized.The emphasis of optimization was as follows:structure parameters adjusted the local weather conditions should be selected to improve the lighting and insulation performance.The materials of wall and arching should both take account of heat preservation,safety and economy.In summer,temperature inside greenhouse should be cooled down by nature ventilation for crop production to reduce the vacancy rate.2.'Improved greenhouse' was composed through improving the north wall with hollow blocks.The structure parameters of the improved greenhouse are:span is 9.0 m;height of ridge is 3.8;height of north wall is 2.8 m;thickness of north wall is 0.6 m.The angles of north and south roofs are 45°and 25.4°,respectively.The perpendicular projection of north roof on the horizontal surface is 1.0 m long.Hollow blocks are filled by perlite to increase the thermal insulation of the north wall.Galvanized steel pipe truss is used in the arch of south roof.Two vents were set in the south roof.The size of upper and bottom chord was ?32.0×2.0 mm and?25.0×2.0 mm respectively and articulated by adapting piece.Vents sized in 40 cm×40 cm are installed in the north wall and spaced at 4 m intervals.The north roof is constructed of 5 cm asbestos board,10 cm polystyrene board,3 cm cement mortar layer and SBS waterproofing materials from inside to outside.3.According to the weather condition of Northern Jiangsu,this study composed the design concept of making the solar greenhouse can be used both in summer and winter.A novel solar greenhouse with removable north wall was designed(removable greenhouse).The north wall of 'removable greenhouse' has two sections:lower section and upper section.The lower section is stationary and composed of three layers:heat storage layer,thermal insulation layer and heat keeping layer from inside to outside.Heat storage layer was built with hollow blocks filled by soil;the thermal insulation layer is built with polystyrene boards;the heat keeping layer is built with the hollow blocks filled by perlite.The upper section can be disassembled and it is constructed by compact straw bales piled up on the lower section.The straw bales are dismounted in summer to create an continuous vent in the north wall and promote natural ventilation.Plastic film and insect screen cover the outside and inside surfaces of the upper section of the north wall,respectively.The structural parameters of the removable greenhouse are:span is 9.0 m;ridge of height is 3.8 m;height of north wall is 2.8 m;and thickness of north wall is 0.63 m.The angles of north and south roof are 45°and 25.4°,respectively.The perpendicular projection of north roof on the ground is 1.0 m long.For the lower stationary wall,the thicknesses of the heat storage layer,thermal insulation layer and heat keeping layer are 0.4 m,0.03 m and 0.2 m,respectively.4.In winter the average nighttime air temperatures in the 'improved greenhouse' and'removable greenhouse' were 1.5?and 0.6?higher than the traditional greenhouse,respectively.The average relative humidity was 1.6%and 6.0%lower.With improved natural ventilation,the average daytime temperatures in the 'improved greenhouse' and'removable greenhouse' was 2.2?and 5.4?lower than the traditional greenhouse,respectively.The average relative humidity of two new greenhouses was 2.8%and 4.7%lower than the traditional greenhouse.The crop yield from the 'removable greenhouse'increased significantly over the traditional greenhouse both in winter and summer.The crop yield increased significantly from the 'improved greenhouse' compared traditional greenhouse in winter,but not as much as the 'removable greenhouse' in summer.Considering its capability of year around production,better performance on insulation and humidity control in winter and cooling in summer,'removable greenhouse' is considered a suitable type of greenhouse for and recommended for Northern Jiangsu Province. |
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