Dictionary of Environmental Health
Liquid returned from gaseous, via vapour, to liquid form (also known as condensate) or the process whereby this is achieved. It is a natural phenomenon, although many commercial and industrial processes (such as the separation of petroleum and the DISTILLATION of spirits) employ the technique. Clouds, mist and fog are natural examples of this phenomenon whilst the vapour remains suspended in the air when the liquid in question is water.
Condensation can be a problem in buildings as the water can cause damage and lead to events (such as providing conditions suitable for DUST MITES) that can adversely affect health. The air naturally contains water that has evaporated. The amount of evaporated water the air can hold is finite. The air can however hold different amounts of water at different temperatures.
As a general rule, the higher the air temperature, the more evaporated water can be held.
The amount of water the air holds at any given time compared to the maximum it could hold at that temperature is a measure of the HUMIDITY. When air cools, for example by contact with a cool surface, the humidity increases, possibly beyond the limit (or ABSOLUTE HUMIDITY) for that temperature – this is known as the dewpoint. At this stage the water vapour reforms (or condenses) and condensation results.
Most condensation in buildings occurs on the surface of either the inside structure or on items contained therein. It is also possible for condensation to occur within the fabric of the structure, for example within the internal structure of brickwork. This is known as ‘interstitial condensation’.
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