The main purpose of Greenhouse ventilation is to remove excess heat and moisture from the greenhouse, adjust the air composition, remove harmful gases, and ensure that the temperature, humidity, and air quality conditions are suitable for plant growth.
1. Natural Ventilation
Glass Greenhouse rely heavily on natural ventilation to regulate the indoor environment. Large-scale production Glass Greenhouse are typically double-sloped, multi-span greenhouses, with ventilation achieved through ventilation windows on the side walls and roof ridge. The total ventilation area should be no less than 15% of the greenhouse floor area, and ideally greater than 30%.
When the roof ridge windows are open, the window sashes should ideally tilt upwards above the horizontal plane, forming a 100-degree angle with the horizontal when fully open, to achieve good ventilation. The ventilation volume is related to wind speed, wind direction, ventilation window location, ventilation window area, and the temperature difference between the inside and outside of 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 with an outdoor wind speed of 10 km/h, the ideal air exchange rate of 0.75 times per minute will not be achieved. However, when both the roof ridge ventilation windows and side wall ventilation windows are fully open, the air exchange rate can reach 0.68 times per minute even in near-zero wind conditions, approaching the recommended 0.75 times per minute.
2. Forced Ventilation
While Glass Greenhouse rely primarily on natural ventilation to regulate the environment, in hot summer weather, especially when outdoor temperatures exceed 33°C, natural ventilation alone is insufficient to meet the greenhouse cooling requirements. Therefore, forced ventilation combined with other cooling measures is a common practice in production.
Forced ventilation uses fans to convert electrical or other mechanical energy into wind energy, forcing airflow to exchange air in the greenhouse and achieve a cooling effect. The theoretical cooling limit of forced ventilation is when the indoor air temperature equals the outdoor air temperature.
Because at this point the temperature difference between the inside and outside of the greenhouse is zero, and the ventilation volume is infinite, which is impossible in practical applications. Due to mechanical equipment and plant physiology, the ventilation intensity of a typical greenhouse is 0.75 to 1.5 times per minute, which can control the temperature difference between the inside and outside of the greenhouse to within 5℃.