Study On Natural Ventilation And Enhancement In Single-Slope Solar Greenhouse

Protected agriculture,which is less affected by climatic conditions,has obvious advantages over traditional planting.As a unique greenhouse type in China,the development of single-slope solar greenhouse is important in increasing crop yield and farmers’ income.A reasonable air distribution design is essential for creating a satisfactory indoor environment,such as indoor air temperature,humidity,solar radiation and other important factors in greenhouses.In this paper,a field test and numerical simulation were carried out to investigate the single-slope solar greenhouse in Yangling,Shaanxi :1)The indoor and outdoor environmental parameters of the single-slope solar greenhouse were measured.It was found that during the test period(May 9-10,2019),the solar radiation in the greenhouse was attenuated by the greenhouse film;Crop photosynthesis,respiration,and opening and closing of vents affect indoor carbon dioxide concentration;The highest temperature in the greenhouse during the day reaches 47.69°C;the temperature in the greenhouse at night is close to 15°C,and the relative humidity is above 90%;The temperature difference between the indoor length and the span is small,and there is temperature stratification in the height direction;The average wind speed at the side vent is 0.50 m/s;The temperature variation of the envelope structure is similar to that of the indoor air temperature,and the maximum temperature of different envelope structures is different,which shows the influence of solar radiation on the temperature of the envelope structure.2)A three-dimensional full-size physical model was built up to perform numerical simulations.The adopted numerical method was proved to be accurate by comparing with the measured results.The flow field of a single-slope solar greenhouse was studied under three working conditions: wind pressure,thermal pressure,and combined wind pressure and thermal pressure.The air distribution characteristics were analyzed and the ventilation volume expression were drawn under different conditions,such as the ratio of vent area,inlet and outlet area ratio,outdoor wind speed,outdoor temperature.The air volume increases with an increase in the vent area ratio,outdoor wind speed and indoor and outdoor temperature difference.The optimum air inlet and outlet area ratio is 1.0.Compared with the wind pressure or thermal pressure,the ventilation volume is larger and the air distribution is more uniform under the coupling wind pressure and thermal pressure.3)The effect of solar chimney enhanced ventilation was analyzed under different conditions(such as air outlet form,solar chimney form,solar chimney height,chimney channel width and north wall vent height).The result shows that the partitioned solar chimney combined with the upper air outlet achieves good ventilation effect when the chimney height is 1.5 m,the channel width is 0.5 m,and the north wall vent is 1.0 m.The ventilation effect was compared before and after the addition of solar chimneys.