A Guide to Dehumidifier Jargon

Our dehumidifier jargon buster is here to help explain key points and features of dehumidifiers and how they work and the problems that they combat !

Humidistat - pretty much the same as a thermostat monitors temperature, a humidistat measures relative humidity and switches the machine on and off automatically at certain levels pre-determined by the user.

Relative humidity (RH) - humidity is a measure of the amount of water vapour contained in the air. Relative humidity is the ratio between the amount of water vapour in the air compared with the maximum it could hold at that temperature. The higher the temperature, the more water air will absorb.

Dew point - when hot, humid air cools down it reaches its dew point, the temperature where the water then starts to condense out of the air, and may appear as droplets on cool surfaces (eg mirrors and windows).

Auto restart - after a power failure or power cut the unit will start back up automatically and continue to run at the same setting it was running at prior to the cut in power rather than going into standby and having to be manually reset.

Continuous drain off - rather than just collecting the extracted moisture in a holding tank there is option to drain off the moisture through a small hose which can be fed into a sink, drain point or seperate holding tank.
Resevoir tank - the inbuilt tank on unit that is used to collect the condensate (moisture) that has been removed from the air.
Compressor dehumidifier - work on the same principle as domestic refrigerators. A compressor raises the pressure of a refrigerant when it is in gas form. The gas is then led to a heat exchanger (condenser) which cools the gas, changing its state to liquid. The liquid is then forced through a small valve into a low pressure region where it evaporates back into gas. It is the evaporation process which cools the gas.
A fan draws the surrounding air over the evaporator unit, the temperature is lowered and the water held in the air reaches its dew point and condenses onto the evaporator surface. This water then runs off to be collected in a reservoir or through a pipe. The cold dry air is then directed over the condenser coil where it assists in the condensing process. This warms the air, which then exits the dehumidifier.

Desicccant absorption dehumidifier - these machines use a desiccant material, typically Zeolite, which absorbs water vapour in much the same way as silica gel (a packet of which you would often find in a pair of new shoes). A fan draws air into the dehumidifier and passes it through a section of a slowly rotating wheel which holds the desiccant. The material draws the moisture out and dries the air. The moisture is then extracted from the desiccant, this is done by heating the portion of the wheel not being used to dry the air. The water then evaporates from the desiccant, is passed over a cold plate where it condenses, runs off and is collected in a resevoir or a permanent feed.

Hot gas defrost - a hot gas, usually freon, is used to prevent the compressor in compressor driven unit from icing up when used in cooler environments.


Did we miss something? Please let us know if you would like us to explain any dehumidification jargon in the comment box below!