Study On Thermal Characteristics Of Venlo Glass Greenhouse

At present,with the rapid development of modern agriculture,solar greenhouse has become the main type of facility agriculture.With the society's increasing demand for the quality of agricultural products,the regulation of greenhouse environment is particularly important,among which the regulation of temperature is particularly important for the growth of crops in greenhouse.In this paper,Venlo glass greenhouse is studied.The indoor heat transfer characteristics of the greenhouse in different seasons are discussed by combining experimental analysis with numerical simulation.The specific research contents and results are as follows:1.The indoor temperature variation and distribution of greenhouse in summer were experimentally studied under the condition of opening both internal and external shading systems separately and simultaneously.The results show that the indoor cooling effect is obvious when both internal and external shading are opened at the same time.The maximum temperature difference between indoor and outdoor reaches10.5?.When the internal shading is opened alone,the indoor temperature distribution is more uniform,and the average temperature deviation at each time is1.4?.2.The correlation of temperature changes inside and outside the greenhouse under different weather conditions in winter and the temperature distribution at different heights in the greenhouse were studied.The results show that the main sources of heat in Greenhouse in winter are solar radiation,surface heat storage and outdoor snow cover.The average temperature in Greenhouse in sunny weather is the highest and the highest temperature reaches 16.1?.The surface heat storage in three weather conditions makes the indoor greenhouse decrease first and then increase with the increase of height.The uniformity of indoor temperature distribution in cloudy day is the best,with a level of 1.5m.The maximum surface temperature is only1.1?higher than the surface temperature.The indoor temperature field under snowy weather is affected not only by solar radiation and surface heat storage,but also by snow cover.3.The calculation results show that the total heat transfer coefficients of the glass wall and windows around the greenhouse are 3.18 W/m~2.K and 2.87 W/m~2.K,respectively.The average heat flux of the inner wall surface of the greenhouse in sunny,cloudy and snowy weather is 18.28 W/m~2,-3.68 W/m~2 and 3.36 W/m~2 in one day,respectively.The heat transfer tribute of the greenhouse in three weather conditions is 3.68 W/m~2 and 3.36 W/m~2.The contribution rates were 35.94%,43.42%and 49.52%respectively.4.The indoor ventilation system is simulated.The results show that in different vertical planes,the cooling effect of mechanical ventilation in the central part of greenhouse is better than that in the East and west sides of greenhouse.The operation effect of the cooling system will be significantly improved with the increase of the inlet wind speed at the wet curtain,but too high wind speed will disturb the uniformity of temperature distribution in the greenhouse.