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A
ir always contains a certain amount of water in the air in the form of water vapour.
This amount of moisture is commonly known as the humidity.
As the air warms up more moisture can be held so the level of moisture is relative to the
temperature.
This is why people talk about relative humidity expressed as a percentage.
When the weather is very hot and damp a relative humidity at 30°C can be perhaps 85%, yet
on a cold foggy day the air can be 5°C, again with a relative humidity of 85%.
In both cases it is possible to think of the air as being 85% full of water vapour, near to saturation.
In our homes, when temperatures drop, the water vapour held in the air condenses on cold
surfaces such as windows and walls, causing condensation and damp.
The purpose of a dehumidifier is to remove the excess moisture from the air, to control
condensation within the home.
Experts have established that the optimum environmental conditions for our well being and
preserve objects are obtained between 40% and 60% relative humidity. Below these levels the
air can feel too dry and may cause skin complaints and even static electric shocks.
The amount of water collected in the tank will be higher at times when outside air
temperatures are warm and high humidity prevails, than in the middle of winter when the air is
cold with high humidity. This is due to the fact that cold air is capable of holding less water
vapour than warm air.
If temperatures in the home are lower than 10°C for prolonged periods low level heating will
be necessary to allow the condensate to evaporate into the air before dehumidification can
take place. The air will however be slightly warmed by the dehumidifier as the dry air leaving
the dehumidifier is about 1°C higher than normal room temperature.
B r i e f n o t e s o n h u m i d i t y
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DE220GB 22-10-2002 13:35 Pagina 11
