Greenhouse ventilation is as important as keeping greenhouse warm. It prevents slow growth, low produce and spread of diseases. Also, it plays an important role in the temperature control even in winter.
Why to ventilate a greenhouse in winter?
- If you don’t ventilate, then musty and warm air accumulates which significantly impacts the growth of the plants. Eventually the plants can die.
- Artificial heating can increase the humidity levels inside the greenhouse which is also harmful to low humidity plants. Humidity over 90 per cent provokes a quick development of mold on the leaves. Also, it can accelerate the rot of fruit and stem.
- Plants need carbon dioxide for photosynthesis or they will die off.
- Oxygen is required for respiration and plant transpiration at nights.
- Poor ventilation can result in condensation which damages the frame of either wooden or metal greenhouse. Moreover, condensation provokes fungus diseases and creates damp and uncomfortable environment.
- Air is required to cool down gas heaters. Many gas heaters have a built in security sensors which turn off the heater once the oxygen levels in the air drop significantly.
Greenhouse ventilation rate
Sometimes greenhouse needs speedy air changes. For example, when temperature is higher than 80 degrees F or the humidity levels are almost at 100%. Then the ventilation rate has to be 40-60 air changes per hour.
One air change is equal to the volume of the greenhouse. Then, the volume of air which moves is calculated from the air changes per minute or hour.
To calculate the volume of the greenhouse you just need to time the length of greenhouse by the area of one end wall.
Ventilation rate in winter
When ventilation rate increases, the heating requirements increase too. Greenhouse ventilation in winter exhausts moist air and replaces it with the heated outside air to lower humidity levels.
So, it is very important to find the ventilation rate that allows to keep the optimal humidity levels (less than 70 per cent) and maintain the heating requirements to a minimum.
The ventilation rate in winter is two to three air changes per hour. Apart from controlling humidity, this ventilation rate removes the gases of combustion resulting from leakages around the heater.
So, you can either do three complete air changes per hour or shoot one air change every 20 minutes.
How to ventilate a greenhouse in winter?
You can use two systems to mix cold air from the outside with the warm air of the greenhouse before it reaches the plants.
First system is cheap to install and uses fan on a low speed setting to get rid off the warm air from the greenhouse.
A perforated plastic tube installed in the ridge of the greenhouse and connected to louver. The tube should be punched to discharge the air horizontally into the greenhouse.
Second system of greenhouse ventilation in winter uses a fan suspended in the ridge of one end wall to inflate the adjacent perforated tube.
Attached louver lets the air in. So, a continuously operating fan provides ventilation air when the louver is open and circulated air when it’s closed.
How do you vent a greenhouse in the winter? More tips!
Tip #1 – You need to make sure that the freezing cold air entering the greenhouse is heated. Otherwise the leaves and fruit bodies will freeze.
To do that you need to install the ventilation pans high up, preferably under the roof. You can use fan heaters to warm up the air entering the greenhouse.
Tip #2 – Use fan heaters to create air circulation – the warm air will flow through the greenhouse filling the entire structure. It also prevents air stagnation when the greenhouse doors are shut.
Tip #3 – To save on the heating consumption in winter you need to monitor the temperature and humidity levels constantly.
Rather than spending extra money on permanent heating, you can invest into greenhouse thermometer and hygrometer systems.
That way you can ensure that you ventilate and heat the greenhouse when it is needed.
Tip # 4 – Use Circulation Fans
Circulation fans not only help to keep the temperature inside the greenhouse stable in summer but, also, in winter too.
Moreover, ideal greenhouse ventilation in winter involves the use of circulation fans at all times. Why?
Circulation fans keep the temperature consistent by keeping the hot air from going up and the cold air from staying close to the ground.