The temperature and the rate of humidity of a greenhouse depends on its ventilation. This complex process involves the exchange of heat between the inside and the outside of the greenhouse. Controlling this is essential if your greenhouse is to function properly, as ventilation determines the temperature, the humidity rate and the concentrations of gas like CO² in the greenhouse.
The health of your plants depends on a good ventilation (breathing, photosynthesis, transpiration). Ventilation also provides good sanitary conditions for them.
Two types of ventilation exist : natural or artificial ventilation.
This is the most economical system for regulating the microclimate in the greenhouse. It consists of openings built into the structure of the greenhouse. These openings should represent 20% of the ground surface and have an opening angle big enough to let the air cirulate properly. It is recommended to have openings in the roof facing north, as these will allow the air to mix correctly in the greenhouse.
Openings on the sides at the level of the plants are also important, as these increase the efficiency of the roof openings and help modulate the ventilation. This gives the best ventilation, creating a self-regulating internal circuit of air : the cool air sucked in by the side openings is heated up in the interior of the greenhouse, before rising and exiting through the roof openings.
In spring and in summer, you can obviously open the doors as well, thus bringing down the temperature inside the greeenhoudse.
This type requires a specific electrical installation in the greenhouse : electric boxes with protected circuits, starters, lines, electrical channels, etc.. Having installed these, you can then set up your ventilator. The most common types are helicoidal ventilators with shutters, which work like air extractors.
These extractors change the air inside the greenhouse and remove the CO², thus rebalancing the general climate inside.
Their outflow can be prgrammed, most ventiators having three or four levels of ventilation. They should be installed at the end opposite to the dominant winds.
This type of installation may be used as a back-up to the natural ventilation of the greenhouse. It is useful for ventilating places which contain plants with specific needs, guaranteeing ventilation at particular moments when conditions aren’t suited to their development (when heavy snow or strong winds prevent the openings being opened, for example).