Ventilation in glass greenhouses is a key measure for regulating the internal environment, directly affecting crop growth quality, pest and disease control, and energy consumption efficiency. Its core objectives are to control temperature and humidity, replenish carbon dioxide, and remove harmful gases. Depending on the ventilation power and structural design, it can be primarily categorized into the following three types: natural ventilation, mechanical ventilation, and hybrid ventilation.

I. Natural Ventilation System

Roof Ventilation: Operable roof vents are installed at the top of the greenhouse, utilizing the chimney effect created by the principle of hot air rising. When the indoor temperature increases, hot air is expelled through the roof vents, while outdoor cool air enters through side or bottom vents. This method requires no additional energy consumption but demands high structural airtightness. Proper design of vent area and opening angle is essential; typically, a vent area accounting for 15%-30% of the roof area achieves optimal air exchange efficiency.

Side Ventilation: Vertical or horizontal sliding windows are installed on the north and south sidewalls of the greenhouse, creating horizontal airflow through natural wind. Modern multi-span greenhouses often employ continuous electric side vents, paired with rack-and-pinion transmission systems for precise opening control, making them particularly suitable for large greenhouses with spans exceeding 8 meters.

II. Mechanical Ventilation System

Negative Pressure Fan Ventilation: Axial fans are installed at one end of the greenhouse, while evaporative cooling pads are placed at the opposite end, creating a negative pressure environment to force air movement. This system can achieve complete air exchange within 5-10 minutes during high summer temperatures. When combined with evaporative cooling pads, it can reduce indoor temperatures by 5-8°C.

Circulation Fan Assistance: Horizontal circulation fans are installed inside the greenhouse to promote air mixing at speeds of 0.5-1.5 m/s, eliminating temperature stratification. This is particularly suitable for elevated cultivation scenarios (e.g., tomatoes, cucumbers), allowing canopy temperature differences to be controlled within ±1°C.

III. Auxiliary Ventilation Techniques

Underground Pipe Ventilation: Underground pipes (20-40 cm in diameter) are buried at depths of 2-4 meters, utilizing soil heat storage properties to pre-cool/preheat air. In winter, outdoor air at -10°C can be warmed to 5°C before entering the greenhouse, while in summer, air at 35°C can be cooled to 28°C. This requires centrifugal fans for operation, resulting in higher initial investment but reducing operational energy consumption by over 40%.

Shade Net Synergy with Ventilation: External aluminum shade nets (30-70% shading rate) can reduce solar radiation heat by more than 50%, lowering the load on ventilation systems. Intelligent control systems can synchronize the opening and closing of shade nets with ventilation equipment to achieve comprehensive temperature control.

IV. Intelligent Ventilation Control

IoT-based environmental monitoring systems collect real-time data from multiple temperature, humidity, CO?, and light sensors, using PID algorithms to dynamically adjust ventilation equipment. For example, when indoor temperature exceeds the set threshold by 1°C, natural ventilation is prioritized; if it exceeds by 2°C, the fan-pad system is activated. Dutch Venlo-type smart greenhouses have achieved a 25% reduction in ventilation energy consumption and an 18% increase in yield.

V. Technical Selection Recommendations

The choice of ventilation method for glass greenhouses should be flexible based on actual needs: natural ventilation is economical and eco-friendly, suitable for basic cultivation; mechanical ventilation is precise and efficient, ideal for large-scale production; hybrid ventilation balances energy savings and performance through intelligent control. In the future, with the advancement of smart agriculture, ventilation systems will increasingly integrate with IoT and big data to achieve dynamic and precise environmental regulation, further enhancing crop yield and quality.