Experimental Reaearch On Heat Transfer Performance Of The Sunlight Greenhouse Earth-to-Air Heat Exchanger And The Earth Temperature Field In Winter

In recent years,the greenhouse industry has become the subject of the facility agriculture industry in China.In the current background of the worsening climate environment,the increasing natural disasters,the exhausting fossil energy and the increasingly serious environmental pollution,seeking the economic,energy-saving and environmental friendly treatment technology about heat and moisture in the greenhouse will be the focus of our attention.Researchs on earth-to-air heat exchanger,especially in the north of China,which is applied in sunlight greenhouse is hardly to find.The research on earth-to-air heat exchanger,which is applied in sunlight greenhouse in the north of China in winter,is elaborated in this article.The development process and the present situation of the greenhouse and the earth-to-air heat exchanger were firstly presented in this article.The establishment of experimental platform,the introduction of experimental instrument,the selection of stationary position and the wiring process of sensors were also briefly introduced.The effect of outdoor weather 'changes on the temperature and humidity of indoor air was researched in the continuous test on different weather conditions in winter,such as sunny day,cloudy day,snowy day and rainy day.Then,in different weather conditions,the inlet and outlet air temperature of one PVC pipe which is horizontally buried on the location for buring under 1m,and 17.2 meters long,and the soil temperature field around the buried pipes were tested continuously.The wind speed in the pipes were 4.5m/s?3.5m/s?1.5m/s and 0.5m/s,respectively.The variation regular of inlet and outlet temperature between the horizontal buried pipes and the system were contrasted and analysed.The attenuation,latency and fluctuation of soil temperature were researched in the radial direction,the vertical direction and the slant direction.The hourly calculation of every 1 hour and the comparison and analysis of the heat exchange capcity per unit length pipe and the moisture content of inlet and outlet air were studied.The results show that in the condition of 4.5m/s,the maximum drop of temperature is 9?,the average value is 4.6?,and the maximum rise of temperature is 4.1?,the average value is 2.5?.The maximum heat exchange is 41.48W/m,and the average heat exchange is 16.74 W/m in the daytime.The maximum and the average heat exchange are 11.79W/m and 8.21 W/m,respectively at night.The smaller the speed of air in the horizontal pipe is,the more stable the temperature of outlet air is;nevertheless,the amount of heat exchange is smaller.During the snowy day,under the speed of 1.5m/s,the outelet air temperature is 14.2?14.8?,the maximum rise of temperature is 5.3?,the average value is 4.3?,the average heat exchange is 4.2 W/m.The sunlight greenhouse earth-to-air heat echanger has a good prospect of energy saving.The scope of delivery,the range of attenuation,and the distinction of latency of the air temperature field are concerned with the temperature difference between the air in the pipes and soil and the flow.In the air speed of 4.5m/s,the maximum thermal radius is 0.5m in the radial direction,which are 0.45m in the vertical direction and the slant direction.At 0.07 m from the center of buried pipe,the soil temperature is 1.6?.In the wind speed of 3.5m/s,the above datum are 0.5m,0.45m,0.45m and 1.1?,in the wind speed of 1.5m/s,the above datum are 0.35m,0.25m,0.25m and 1?,However,in the wind speed of 0.5m/s,the above datum are 0.25m,0.25m,0.25m,0.4 ?,respectively.In the condition of 4 days of cloud and snow and in the wind speed of 1.5m/s,the above datum are 0.35m,0.45m,0.45m and 1.0?,respectively.