Dehumidifers - How They Work


Ever wondered exactly how a dehumidifier works? Our guide explains in detail the inner workings of the most common type of dehumidifier.

The Principle

Although there are several different ways in which dehumidifiers work, the most common type is that which makes use of the vapor-compression refrigeration cycle. This technique removes the moisture by passing the air over a cold surface onto which the moisture condenses. The condensed moisture then drips into a collection tank which is emptied when full. Anyone who has poured an ice cold beer into a glass will have seen this effect taking place, the outside of the cold glass quickly becomes wet with moisture from the air.


Compressor - It's normally a black rounded metal object a bit smaller than a football that can sometimes be seen at the bottom of the unit. As the name suggests it compresses the refrigerant gas in the system.

Condenser - normally painted black it is the part similar in appearence to a small radiator. When the unit is running this part will get warm.

Evaporator - also similair in appearence to a radiator this part tends to be made of a series of aluminium fins. When the unit is running this part will get cold.

Fan - the fan is used to move the air over the condenser and evaporator coils.

Collection tank - many units will have a tank to collect the water. They have a sensor that turns the unit off if the tank becomes full.


When the unit is switched on the compressor starts to compress the refrigerant gas. As the gas is compressed it gets hots and passes into the condenser where it cools down. Next the gas passes into the evaporator where it expands, as it does so it gets cold and cools the the evaporator. A fan then passes the air over the cold evaporator where the air is cooled and the moisture collects on the evaporator and then drips down into a collection tank. The air then passes over the condenser where it is warmed up again before going back out into the room.