A greenhouse is structure with a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building.
Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall.
These structures range in size from small sheds to a very large buildings.
The glass used for a greenhouse works as a selective transmission medium for different spectral frequencies, and its effect is to trap energy within the greenhouse, which heats both the plants and the ground inside it.
This warms the air near the ground, and this air is prevented from rising and flowing away, in addition to the fact that infrared radiation cannot pass through the greenhouse glass. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature drops considerably. This principle is the basis of the autovent automatic cooling system. Greenhouses thus work by trapping electromagnetic radiation and preventing convection.
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