How do dehumidifiers work?

How do dehumidifiers work?

Tuesday, September 27th, 2011

How do dehumidifiers work? Firstly you need to understand what humidity is. The air around us contains water vapour in our homes it comes from our breathing, drying clothes, baths, showers and many normal activities. It is also naturally present in the environment. The water is in gas form so cannot be seen or felt, but can be sensed – you could describe it as felling close or muggy.

Relative Humidity

The amount of water vapour in the air is measured as a percentage – when it reaches 100% then the air cannot hold any more moisture so liquid water forms as condensation. It is relative humidity because the amount of water vapour that can be supported by the air depends on the temperature. As air cools down then it can hold less moisture, which is why condensation forms of cold objects and surfaces. A comfortable relative humidity is considered to be between 40% and 60% which is why most dehumidifiers are set to keep relative humidity levels at about 50%.


Some extreme examples of relative humidity are in rainforests where even though it is very warm levels approach 100% and condensation can form on any solid object. An example of extreme low humidity would be in an aeroplane where the effect of the low pressure means that the air cannot support much humidity – this is why you often get dry, cracked lips on long flights.

How do dehumidifiers work?

If you imagine a cold glass of beer with beads of condensation forming on the outside – this is effectively what a dehumidifier does. It cools the air to reduce the capability of it to hold humidity then as the water vapour is transformed to liquid it is collected. The dry air is then pushed out of the dehumidifier.
So there are five stages to the process
1. A fan draws air into the unit
2. The air is passed over a refrigerated coil where the water vapour condenses and can be collected
3. The dry, cold air is warmed back up again
4. The dry, warm air is blown out of the dehumidifier. The idea is to blow he air out at the same temperature that it arrived at.

more info can be found here