Glass Greenhouse Ventilation

The main purpose of ventilation in a glass greenhouse is to eliminate the waste heat and moisture in the greenhouse, adjust the air composition in the greenhouse, eliminate harmful gases, and make the environmental temperature, humidity, and air conditions in the greenhouse suitable for the requirements of plant growth.
1. Natural ventilation glass greenhouses rely mostly on natural ventilation to regulate the indoor environment. The structural form of large-scale production glass greenhouses is generally a double slope multi-span greenhouse, with ventilation windows installed on the side walls and roof ridges. The total ventilation area should not be less than 15% of the greenhouse area, preferably greater than 30%. When the ridge wind window is opened, it is best to tilt the window sash upwards beyond the horizontal plane. When fully opened, it forms a 100 angle with the horizontal plane to achieve good ventilation effect. The ventilation amount of natural ventilation is related to wind speed, direction, position and area of ventilation windows, as well as the temperature difference inside and outside the greenhouse. When the total area of ventilation windows is 27% of the indoor floor area, if only the roof ridge ventilation is used, even if the outdoor wind speed reaches 10 kilometers/hour, it cannot reach 0 75 ideal ventilation rates; When the roof ridge ventilation windows and side wall ventilation windows are fully open, the air change rate can reach 0.68 times/minute even in almost no wind, close to the normal recommended 0.75 times/minute air change rate.
2. Although forced ventilation glass greenhouses mostly rely on natural ventilation to regulate the environment, when the summer temperature is high, especially in hot weather where the outdoor temperature exceeds 33 ℃, and natural ventilation alone is difficult to meet the cooling requirements of the greenhouse, using forced ventilation combined with other measures for cooling is a commonly used method in production. Forced ventilation is the use of fans to convert electrical or other mechanical energy into wind energy, forcing air flow for greenhouse ventilation and achieving cooling effects. The theoretical cooling limit of forced ventilation is that the indoor air temperature is equal to the outdoor air temperature. Because the temperature difference between the inside and outside of the greenhouse at this time is zero, and the ventilation amount is infinite, it is impossible in practical applications. Due to mechanical equipment and plant physiology reasons, the ventilation intensity of a typical greenhouse is 0.75 to 1 5 times, able to control the temperature difference inside and outside the greenhouse within 5 ℃.