Research On The Effect Of Solar Chimney Coupled With Buried Air Duct Ventilation Mode On The Environment Of Solar Greenhouse

The solar greenhouse uses solar radiation and the excellent thermal insulation performance of the envelope structure to maintain the indoor temperature in the range suitable for crop growth in winter.However,the indoor temperature of the solar greenhouse rises extremely rapidly at noon,making the greenhouse in a state of high temperature and humidity,resulting in reduced crop yields.At present,the common cooling measure is to open the vents at the top of the shed film for ventilation,but there are problems such as excessive hot air loss in the head space,slow temperature drop in the crop area and affecting the service life of the shed film.On the basis of previous researches,this thesis adopts the method of combining field measurement and numerical calculation,and introduces solar chimney and buried air duct into the ventilation system of solar greenhouse according to the principle of thermal pressure.The chimney effect of the solar chimney is used to realize the natural ventilation of the greenhouse and improve the cooling effect.The effects of the installation height of solar dampers,the number of solar chimneys and buried ducts on ventilation and cooling were discussed,and the ventilation scheme was optimized.The main research contents and conclusions are as follows:（1）Field measurements were carried out on Weifang Shouguang civilian solar greenhouse,and the changes of temperature and humidity,CO₂ concentration,and solar radiation in the greenhouse were recorded over time,so as to obtain the change law of environmental parameters in the solar greenhouse with time.Provide data support for choosing a reasonable ventilation method to improve the solar greenhouse environment.The test results show that the change trend of solar radiation intensity and the temperature of the envelope structure in the greenhouse in winter is consistent with the change trend of the outdoor solar radiation intensity.When the nighttime thermal insulation is turned off,the indoor temperature drops slowly and the humidity rises slowly due to the good thermal insulation performance of the envelope structure.When the daytime insulation is turned on,it is affected by solar radiation,and the indoor temperature rises rapidly.The temperature in the greenhouse is higher from 11:00 to3:00 pm,which is beyond the suitable range for plant growth,and needs to be ventilated to cool down and dehumidify.The top ventilation can relieve the indoor high temperature and high humidity environment,and can replenish the indoor carbon dioxide content in time to ensure the growth of crops.However,due to the upward movement of the air after being heated and expanded,the hot air at the top of the greenhouse loses more to the outside than the crop area.The method of top ventilation makes the temperature and humidity of the crop area decrease slowly,especially for low-plant crops,the temperature of the crop canopy area is high,which is difficult to meet the growth needs;in winter,the use of ventilation at the bottom of the greenhouse can easily cause frost damage to the plants.Therefore,this traditional ventilation method needs to be improved.（2）Affected by solar radiation,the temperature of the solar greenhouse is relatively high during the period from 11:00 to 3:00 pm.In order to improve the ventilation and cooling effect of the greenhouse,a natural ventilation method of solar chimney coupled with buried air ducts is proposed.A three-dimensional numerical ventilation model of solar greenhouse with solar chimney coupled with buried air duct is established,and the accuracy of numerical calculation is verified by measured data,and the ventilation effect of solar wind valve at different heights is studied.The study found that when the diameter of the buried air outlet is 0.4 m,the size of the solar air valve is 0.5 m×0.5 m,and the installation height is 3.5 m,the combination of the solar chimney and the buried air duct can effectively reduce the indoor temperature.When 10are taken,the ventilation volume can reach 4.85 m~3/s,the average indoor wind speed can reach0.276 m/s,and the average indoor temperature can be maintained at 21.3℃.（3）Due to the large number of solar chimneys and buried air ducts,the ventilation and ventilation volume of the solar greenhouse is large,resulting in an excessive cooling effect on the greenhouse,and the initial investment and maintenance costs are high.Therefore,this study reduces the number of solar chimneys and buried air ducts,and discusses the influence of different tuyere arrangements on the airflow organization in the greenhouse to obtain a more uniform indoor airflow distribution.The research shows that when the number of tuyere is 6～8,the distance between each tuyere is within 4.6 m～6 m,the air distribution is relatively uniform,the average wind speed is maintained at 0.219～0.247 m/s,and the indoor temperature is maintained between 24～26.2℃,in line with the growing needs of crops.（4）The study found that the wind speed at the air outlet of the buried air duct is too large,which is not conducive to the growth of plants at the outlet.Therefore,in this study,the air outlet of the buried air duct was improved.The results show that when the width of the rectangular air outlet is 0.5 m and the length is in the range of 3～4 m,it can not only improve the uniformity of indoor air distribution,but also effectively meet the wind speed requirements in the greenhouse.It can be maintained within a suitable wind speed range.