The importance of good ventilation in a greenhouse
Ventilation has several benefits. As well as offering greater control over the internal temperature and humidity, it also increases airflow which is crucial for effective photosynthesis and pollination and reduces the likelihood of disease.
In order to ensure that proper ventilation in the greenhouse is achieved, gardeners must install either a passive or powered ventilation system.
Passive Ventilation System
We are huge fans (hoho) of automatic ventilation systems as they use solar energy to automatically open the vents.
A passive ventilation system is a ventilation system with no mechanical components. In other words, there are no powered fans involved with a passive ventilation system. Instead, the greenhouse is ventilated via convection (hot air becomes less dense and rises). No electrically required, and 100% environmentally friendly!
In addition to the ridge vents, a passive ventilation system needs intake vents to allow cool air to enter the greenhouse and displace the hot air as it rises.
Powered Ventilation System (PVS)
A powered ventilation system for a greenhouse is a ventilation system with a powered fan and intake vents. The cubic feet of the greenhouse space will be the determining factor for sizing a fan system. The minimum goal is to get the cubic volume of air turned over in less than two minutes.
The fan should be installed on the top section of the wall opposite of the intake vents and screen door. In other words, the intake vents should be installed on the same wall as the door and the fan should be installed on the top of the opposite wall. This ensures that the fresh air entering the greenhouse travels across the greenhouse before being evacuated.
Powered ventilation systems are usually set up with a thermostatic control that will turn on the fan when the set-point temperature is reached. The intake vents are synced with the fan so they will open at the same time the fan is activated.
In addition to the cooling/exhaust fan of a PVS, a greenhouse should also be equipped with a circulating fan which provide continuous air movement within the greenhouse which helps to maintain uniform temperatures and humidity while also increases the structural integrity of the plants (much like the wind strengthens plants in nature).
In summary
Whether you choose a passive or powered ventilation system, making sure a greenhouse is properly ventilated is crucial to creating an ideal growing environment for plants.
A greenhouse’s temperature, humidity, and ambient CO2 levels are all determined by the ventilation system. In other words, the ventilation system is one of the most important determining factors over the way plants will perform in a greenhouse and should be contemplated by every potential greenhouse gardener.