A greenhouse, also called glasshouse, or, if with sufficient heating, a hothouse, is a structure for the cultivation of plants, it is totally closed to protect crops from excessive cold outside at certain times of the year. The outer cover is made of a transparent material (glass or plastic) to let the sun rays pass, which warms the environment (high temperature) and the plants inside.
Within the greenhouse several factors must coexist in their proper measure so that the growth of the crops is correct: temperature, humidity, light, oxygen and CO2 concentration. Ventilation will be essential to maintain the right climate in the greenhouse.
Depending on the country concerned, there are large differences in climatic conditions and therefore in the interior climate of the greenhouse. These differences are marked even within the same country and the needs of the North can be very different from those of the South.
For the regulation of the temperature inside the greenhouse, mainly in summer, it is advisable to provide it with a ventilation system on the roof. The ventilation allows the hot air to be expelled to the outside, but also the recirculation of the air inside the greenhouse to avoid plagues and plant diseases. When expelling the hot air, the interior air is replaced by a mass of cold air from the outside and so the excess temperature is lowered and the humidity and concentration of gases are modified.
It must be taken into account that both an excess of temperature (more than 70ºC) and cold (sub 0ºC) would be totally harmful for the crop. The fans intended for this application must be resistant to moisture, so they must be fans protected against corrosion or made of aluminum or plastic.
The use of greenhouses extends to the cultivation of vegetables, both green leaves (chard, celery, spinach, lettuce, parsley) and brassicas (broccoli, cauliflower, turnip and radish). Also for tomato, pepper, zucchini, melon, cucumber, strawberry, bean, cabbage, pea, baby leaf, etc.
A totally different crop, but for which ventilation is also required, is that of the mushroom in caves, cellars, mines, tunnels, or any dark and cool place that meets the appropriate environmental conditions (constant temperature of 12-14ºC and relative humidity close to 75-80%). Ventilation fans will be placed in such a way that the air flow does not arrive directly to the crop, and others for the extraction to renew the air of the room 3 or 4 times a day.