Protected Cultivation
Ventilation, Air Exchange & Circulation
Ventilation replaces greenhouse air with outside air while circulation mixes air inside the structure; both matter, but they solve different problems.
Key concepts
- Air exchange can remove heat and water vapor when outside conditions allow
- Horizontal or vertical circulation reduces stagnant zones without necessarily exchanging outside air
- Canopy density changes resistance to air movement
- Openings, fans, screens, and structure geometry influence airflow patterns
What to measure or observe
- Compare temperature and RH at crop height in several locations
- Use lightweight indicators or smoke testing where safe to observe air paths
- Inspect dead zones behind dense canopy or structural barriers
- Record vent and fan state with sensor data
Common mistakes
- Calling circulation fans ventilation
- Pointing high-velocity airflow directly at one crop zone
- Ignoring blocked intake paths
- Assuming fan rating equals delivered airflow through the real structure
Visuals this lesson still needs
- Ventilation-versus-circulation diagram
- Airflow path map
- Canopy resistance cross section
- Fan and inlet placement comparison