Ventilation is a critical issue in multi-span greenhouse film structures. Good ventilation is directly related to the growth of plants. Next, let's delve into the specific principles of ventilation design:

The design principles of the ventilation system should meet the requirements for controlling the temperature, humidity, and carbon dioxide concentration within the greenhouse.

The large-capacity design of the ventilation system should ensure that indoor temperature, humidity, and carbon dioxide concentration meet the appropriate environmental conditions required for crop growth under adverse external conditions throughout the planned service life.

3. The design of the ventilation system should consider the characteristics of the external environment across different seasons, and demonstrate the requirements for greenhouse temperature, humidity, and carbon dioxide concentration during each season. The design requirements for the ventilation system in different seasons should be based on one or more indicators. In winter, the indoor environment with high humidity, low carbon dioxide levels, and high concentrations of harmful gases caused by sealed greenhouses should be taken into account. In summer, the indoor high temperature caused by the greenhouse should be addressed, along with other cooling measures.

4. Natural ventilation should be the choice for interlinked film greenhouses. When the natural ventilation system fails to meet the greenhouse design requirements, a fan ventilation system should be installed.

5. When the summer fan ventilation is insufficient to meet the temperature requirements for crop growth, other cooling measures should be taken simultaneously. 6. When the ventilation rate exceeds 0.02 m/(5S+m2), other methods should not be used to supplement CO2.

To ensure even distribution of indoor temperature, humidity, and CO concentration, and to facilitate plant growth through proper air flow, a relative number of circulation fans should be installed in the room.

7. Ventilation system design should consider the location, climate type, structural type, and purpose of the connected film greenhouse to determine the type, size, and location of ventilation openings, as well as the type, quantity, and layout of fans.

Section 8: The design of the ventilation system should be determined by the purpose, scale, usage characteristics, outdoor meteorological conditions, and crop parameter requirements of the greenhouse, through a combination of technical and economic considerations.