Monday, 28 January 2013

PRINCIPLES OF CONDENSATION


Warm air can hold more moisture than cold air.  If air in a building acquires additional moisture this increased moisture content will not be apparent in places where the air is also warmed.  But if this moist air comes into contact with colder air, or with a cold surface, then air is likely to be cooled to its dew point temperature and sample of air is likely to be saturated, and the excess water vapour condenses to a liquid.
This effect could also be achieved by the same body of air without the addition of moisture, being allowed to cool down until it reaches its saturation point  (dew point).

TECHNICAL BACKGROUND
Condensation in buildings is a form of dampness caused by excess water vapour in the air.  Among the effects of condensation are misting of windows, beads of water on non-absorbent materials and mould growth.

As a general principal it can be stated that:
        Condensation occurs whenever moisture laden air meets
 surfaces that are at or below the dew point of that air.
The two types of condensation can be classified into two main types:

 1.     Surface Condensation;
 2.     Interstitial Condensation.

Surface Condensation 
Surface condensation occurs on the surfaces of walls, windows, ceilings and floors.  The condensation appears as a film of moisture or beads of water on a surface and is most obvious on the harder, more impervious surfaces such as ceramic wall tiles.  An absorbent surface may not show condensation at first, although persistent condensation will eventually cause dampness.

Interstitial Condensation
Interstitial Condensation occurs within the construction of the building. Most building materials are, to some extent, permeable to water vapour (that is, they allow the passage of air containing moisture).  If this air cools as it passes through the structure then, at the dew point temperature, condensation will begin to occur inside the structure and can damage important structural materials, such as steelwork.

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