Calculate required ventilation rate and duration based on greenhouse volume, temperature difference, and target humidity.
Calculate greenhouse ventilation rate, air changes per hour, and recommended ventilation duration based on greenhouse volume, temperature difference, and humidity. Input floor area, height, inside/outside temperature and humidity, and vent opening area. Prevent overheating and high humidity that cause disease.
You closed your greenhouse vents at 6 PM to retain heat overnight. By 8 AM, humidity was 95% and temperature was 22°C — perfect for botrytis. You opened vents at 9 AM, but by then gray mold had already infected 15% of your strawberry flowers. The critical window was 6-8 AM, when humidity peaks and temperature rises. Ventilating for just 15 minutes at dawn would have prevented the outbreak. Humidity management is more important than heat retention in most greenhouses.
Proper ventilation controls temperature, humidity, CO2, and disease pressure.
A: Minimum: 1 air change per minute (60/hour) during summer for cooling. Typical: 0.5-1 air change/minute. Winter: 0.1-0.2 air changes/minute (just enough to control humidity). The ventilation rate depends on: temperature difference (stack effect), wind speed, vent area, and greenhouse height. Natural ventilation (roof + side vents) is cheaper but less controllable than fan ventilation.
A: Short, frequent ventilation: open vents for 10-15 minutes when outside temperature peaks (midday), then close. This removes moist air without losing too much heat. Avoid long ventilation in cold weather — it drops temperature too much. Use horizontal air flow (HAF) fans to circulate air and reduce humidity stratification. Maintain minimum night temperature 2-3°C above dew point to prevent condensation on leaves.
A: Natural (roof vents + side vents): zero energy cost, works with wind and thermal buoyancy. Best for mild climates, simple structures, and organic production. Limitation: less control on calm, hot days. Mechanical (exhaust fans + intake louvers): precise control, works in any weather, can handle larger greenhouses. Cost: electricity, fan maintenance, initial investment. Combination: natural for most of the year, mechanical backup for extreme heat. For greenhouses >500 m², mechanical is recommended.