Numerical Simulation Of Thermal Environment And Ventilation Characteristics Of Solar Greenhouse

As one of the most important parts of facility agriculture,solar greenhouse is the main agricultural production facilities in north China in winter.It has high thermal insulation performance,ensuring the realization of inter-seasonal crop production in north China is of great significance.Suitable temperature and humidity environment can effectively promote the healthy growth of crops and reduce crop disease and deterioration.In order to further clarify the distribution of temperature and humidity in solar greenhouse in winter,the temperature and humidity of solar greenhouse in winter were tested,and the temperature field was simulated by CFD modeling.Through the establishment of temperature and humidity measurement system,the CFD model is verified and improved,and the distribution of greenhouse temperature field is further analyzed through the simulation data,which provides the basis for further research and improvement of greenhouse temperature and humidity distribution.In summer,it is particularly necessary to improve greenhouse ventilation efficiency and ensure the supply of carbon dioxide to crops under the condition of no wind or low wind speed.Taking the climate environment of Zhengzhou as the background,the CFD three-dimensional thermal pressure ventilation model of greenhouse was established to simulate,and the changes of temperature distribution,pressure distribution,flow field and skylight outlet flow were studied by increasing the skylight height and changing the area of the skylight,so as to provide a theoretical basis for further research on the thermal pressure ventilation of greenhouse.The main conclusions of this paper are as follows:(1)The temperature distribution of 1/2 and 1/4 of the north-south section of solar greenhouse in winter was obtained.The temperature at the front of the two sections of the greenhouse is 27.5℃ and 26.8℃,the average temperature at two points near the back wall is 29.7℃ and 29.5℃,and the average temperature at the middle two points is 32.2℃ and 30.4℃,respectively.The temperature at the front of the greenhouse is the lowest,followed by the outlet temperature near the back wall,and the temperature at the middle two points is the highest.Through CFD simulation,we can know the simulated temperature distribution.Front triangle area of minimum temperature,greenhouse greenhouse triangle area in front of the low temperature air movement back to the greenhouse,greenhouse central being cold air mass,movement to the back wall of low temperature air with solar radiation was heated up by convection and radiation,and greenhouse central air at low temperature due to the location in the middle is continued to form the low temperature area.(2)The relationship between humidity and temperature in winter solar greenhouse and the relationship between daytime and nighttime humidity.There is a negative correlation between temperature and humidity in the greenhouse.During the day,the highest temperature and the lowest humidity are 50%-65% around noon,and the night temperature is low and the humidity is 85%-95% at the highest point,and it continues to be saturated.(3)The effect of skylight area and height on the efficiency of hot pressure ventilation in greenhouse in summer.The interior of the skylight in the raised part is in the negative pressure area.The raised skylight increases the outlet velocity of the skylight and effectively increases the air flow.Increasing the skylight area effectively improves the flow rate of the skylight outlet.When the ratio of the skylight area to the greenhouse floor area is 2%-4%,the increase rate of the flow rate is higher,and the increase rate of the flow rate is significantly lower at 4%-6%.When it is increased to 4%,the increase rate of the skylight outlet flow rate is significantly lower.Because the thermal pressure ventilation relies on heat source from the sun,the internal wind speed generated is relatively stable.After raising the skylight,not only the air flow at the outlet of the skylight is improved,but also the wind speed in the greenhouse is improved,which is obviously beneficial for plants to supplement carbon dioxide and regulate indoor micro-climate.In conclusion,the temperature distribution in the north and south sections of the solar greenhouse in winter is not uniform,and the temperature and humidity change in a day is negatively correlated.It is necessary to pay attention to the influence of local low temperature environment and humidity change on crops.Increasing the height of the skylight can effectively improve the greenhouse air flow.