Airflow covers two jobs. Circulation stirs air inside the grow space so there are no hot, humid or CO2-depleted pockets. Exchange replaces room air with fresh air to remove heat and moisture and bring in CO2. Both work by reducing the boundary layer, the thin film of still air around each leaf that slows gas and heat exchange.
In practice
Kitaya and colleagues (2003) showed that leaf gas exchange improves sharply as air speed rises from still air to around 0.5–1 m/s, with little extra benefit beyond that. A practical target is canopy leaves that flutter gently, not whip. Constant strong wind dries leaves, can cause windburn (clawed, papery leaves on the fan side) and wastes energy.
Good airflow means air moving above the canopy, through it and below it. Dense flower rooms need fans under the canopy too, because the inside of a cola is where botrytis starts. If leaves at the back of the tent are still while the front ones dance, add or reposition a fan.
Don't confuse with
- Exhaust (ventilation): removes air from the space; circulation fans only mix it.
- CFM: a fan rating, not a measure of air speed at the leaf.
