Optimum air circulation prevents mould and strengthens plants. Plan fan strategies and fresh air systems correctly.
Air circulation is fundamental for healthy cannabis plants and mould prevention:
Air circulation basics:
Why air movement is critical:
- Strengthens stems through wind simulation
- Prevents stagnant air zones
- Reduces mould and fungus risk
- Improves CO2 distribution
- Optimises temperature distribution
Air exchange principles:
- Fresh air supply (passive or active)
- Used air extraction
- Internal circulation
- Temperature management
- Humidity control
Ventilation systems:
Passive ventilation:
- Utilise natural buoyancy
- Inlet at the bottom, outlet at the top
- Cost effective and quiet
- Limited control
- Suitable for small setups
Active ventilation:
- Axial or centrifugal fans
- Precise airflow control
- Timer and thermostat control
- Higher cost but more control
- Standard for professional setups
Hybrid systems:
- Passive supply air, active extract air
- Cost saving
- Good basic ventilation
- Flexible adaptation
- Ideal for medium-sized setups
Fan size calculation:
Air exchange rate:
- Minimum: 1x room volume per minute
- Optimal: 2-3x room volume per minute
- With high heat: 4-5x per minute
- Consideration of resistances
- Allow for safety surcharge
Example calculation:
- Room: 2m x 1m x 2m = 4m³
- Optimal: 4m³ x 3 = 12m³/min = 720m³/h
- With resistors: +30% = 936m³/h
- Fan selection accordingly
Fan positioning:
Supply air fans:
- Position at the bottom or side
- Bring in cooler outside air
- Even distribution
- Avoid direct draught on plants
- Filter for outdoor air purification
Exhaust air fans:
- High at the top or side
- Remove warm, humid air
- Through activated carbon filter for odour
- Highest point in the room
- Short distances to the outside
Recirculation fans:
- Various heights and positions
- Oscillating movement ideal
- 30-45° angle to plants
- Not direct continuous bombardment
- Smooth canopy movement
Climate zone management:
Temperature stratification:
- Warmer at the top, cooler at the bottom
- Aim for even distribution
- Identify and eliminate hotspots
- Thermometers at different heights
- Air movement for homogenisation
Humidity zones:
- Substrate proximity often more humid
- Canopy area critical
- Air movement reduces local humidity
- Hygrometer in various places
- Observe mould-prone areas
Seasonal adjustments:
Summer ventilation:
- Higher air change rates
- Use night air for cooling
- Additional recirculation fans
- Possibly integrate air conditioning
- Maximise heat dissipation
Winter ventilation:
- Reduced air exchange
- Partially recirculate warm exhaust air
- Frost protection for supply pipes
- Heating integration
- Optimise energy efficiency
Controller and automation:
Temperature-controlled:
- Switch on fans in the event of overheating
- Step-by-step speed control
- Hysteresis function
- Day/night profiles
- Alarm functions
*Humidity