Influence Of Different Ventilation Conditions On Air Flow And Temperature And Humidity In Plastic Greenhouse

Greenhouse ventilation is the main means of controlling indoor microclimate in plastic greenhouse,directly change indoor temperature,relative humidity,wind speed and other environmental factors,provide suitable growing environment for crops,improve crop yield and quality.Natural ventilation system is simple in structure,energy saving and wide in scope.It is the most common way of ventilation and ventilation.In order to determine the best ventilation method and vent height for greenhouses under different environmental requirements such as cooling and dehumidification,the plastic greenhouse in Yangling,Shaanxi Province was taken as the object.Experiments and computational fluid dynamics simulation methods were used to treat greenhouses under three ventilation methods(only the top ventilation is turned on,only the side ventilation is turned on,and open half of the side and top vents),four side vent heights(40,60,80 and 100 cm)indoor flow field,temperature,relative humidity changes and distribution uniformity.Analyze the indoor microclimate environment change rule under different ventilation conditions.The most suitable ventilation scheme were determined according to different ventilation requirements of plastic greenhouse,provide more effective theoretical basis for ventilation control in greenhouse production.The main conclusions of the study are as follows:1.The RNG k-ε turbulence model was used to construct a three-dimensional CFD model of plastic greenhouse.The simulated values variation trend of indoor air temperature and relative humidity were basically consistent with the measured values.In study on ventilation mode,the average relative errors of temperature and relative humidity at each measurement point were 2.4% and 2.5%.In study on the height of side vents,the average relative errors of temperature and relative humidity at each measurement point were 1.2%and 2.0%.The boundary condition is effective and can accurately simulate the distribution of temperature field and airflow field in plastic greenhouse.2.Under the same external environment conditions,the greenhouse with half of top and side vents open has the fastest cooling and dehumidification rate and the best ventilation effect.Within 2 minutes after the vents were opened,the instantaneous change rate of temperature and humidity in the greenhouse with half of the top and side vents open was significantly higher than that of the other two kinds of greenhouse.The maximum difference between temperature instantaneous change rate and humidity instantaneous change rate and other greenhouse in the same period is 2.09 ℃/min and 3.22%/min,respectively.3.The homogeneity of temperature and humidity in the greenhouse with half of top and side vents open was the worst.After the vents were opened for 10 min,the variation coefficients of temperature and humidity at the 27 measured points were 4.2% and 5.1%higher than those in the greenhouse with only the top vents open at the same time,and 5.4%and 6.9% higher than those in the greenhouse with only the side vents open at the same time.The greenhouse with only side vents open has the best overall cooling and dehumidification uniformity,which is suitable for the ventilation and ventilation needs of temperature and humidity sensitive crops.The cooling rate of the greenhouse with only top vents open can be slowed down while ensuring the effect of dehumidification,and it is suitable for the demand of heat preservation and dehumidification in winter and ventilation and ventilation in extreme weather.4.The height of the side vents will affect the indoor microclimate distribution.The average temperature in the greenhouse with the side vents 60 cm from the ground is always the lowest.When the vents are opened for 10-20 minutes,the temperature in some indoor areas is about 0.8 ℃ lower than that in the greenhouse with side vents 40 cm from the ground.Because the distance of greenhouse with side vents 100 cm from the ground between the side vents and the ground is too high,the airflow stagnation area below the greenhouse is too large,and the ventilation and cooling speed is slow.After the vents were opened for 20 minutes,the temperature in most areas of the room was higher than 36 ℃.If the distance between the side vents and the ground is too high or too low,the cooling and dehumidification effect in the ventilation process will be reduced.5.When the side vents are 100 cm away from the ground,the indoor temperature and humidity uniformity is optimal,followed by the greenhouse with the side vents are 60 cm away from the ground.The variation coefficients of temperature and humidity at the 27 measured points were 1.1% and 3.0% higher than those in the greenhouse with the side vents are 100 cm away from the ground at the same time.The greenhouse with the side vents are 60 cm away from the ground has active indoor air flow in the ventilation process,high uniformity of cooling and dehumidification,which is suitable for cooling and dehumidification and ventilation and air supply in summer for most crops.Raise the height of the side vents based on a distance of 60 cm from the ground,the cooling rate can be slowed down while ensuring the effect of dehumidification.Reducing the height of the side vents from the ground can slow down the indoor environment change rate,and it is suitable for the ventilation and ventilation in extreme weather.