Field measurement of environmental parameters in solar greenhouses and analysis of the application of passive ventilation

Solar greenhouses are passive agricultural facilities that can realize off-season production. The growth of crops in greenhouses is affected by various environmental parameters. Therefore, it is necessary to understand the variations of environmental parameters in solar greenhouses through field testing to improve their internal environment. Through field tests, it was found that the temperature variation in solar greenhouses was positively correlated with the change in solar radiation. When the top vent was opened, the minimum temperature in the greenhouse remained higher than 30 °C. The temperature gradient in the tall-plant greenhouse was twice that in the short-plant greenhouse. The relative humidity at the bottom of the tall-plant greenhouse remained greater than 65%. Top-vent opening for greenhouse ventilation is not conducive to the cooling and dehumidification of these relatively large sized greenhouses tested in this study. Passive ventilation via an integrated solar chimney and earth-air heat exchanger was applied in an experimental solar greenhouse. The results showed that when the passive ventilation was turned on, the indoor air temperature in the horizontal and vertical direction could be maintained in the range of 25 ∼ 28 °C and 25 ∼ 30 °C, respectively. The air temperature in the vertical direction had been decreased by approximately 3.5 to 6.5 °C. The passive ventilation effectively prevented continuous increases in indoor temperature, improved indoor air distribution and was conducive to the normal growth of crops.