How they work

Most dehumidifiers use a small refrigeration unit to first cool the room’s air (so it can condense the moisture) then reheat it. The water-removal rate reduces as the air temperature drops.

Desiccant dehumidifiers use a water-absorbing (desiccant) material such as a silica-gel. The air in the room is blown through a slowly rotating disc containing the desiccant – that’s what dries the air.

Next, the moisture-laden desiccant disc rotates into a chamber where a heated portion of the desiccant-dried air is blown through the disc. This dries the desiccant. The desiccant then rotates out of the drying chamber and repeats the cycle.

After this, the damp and warm air that’s resulted from the disc-drying process passes through a heat exchanger and is cooled by air coming in from the room. The result is that moisture in the previously warm air is condensed out and collected in a tank.

It sounds complicated, but it works – especially at low temperatures.

Warm and dry?

All the electricity a dehumidifier uses ends up heating the room. This is a good thing in our climate … but it gets even better.

Every time water is turned from a liquid to a gas, heat has to be added. This heat is called the “latent heat of evaporation”. The reverse happens when water vapour is condensed to a liquid – that latent heat is released.

So when a dehumidifier condenses the water vapour in the air back to a liquid for draining off, the latent heat in the water vapour is released. The dehumidifier both dries the air and delivers more heat to the room than it uses in electricity. Only a heat pump gives you more bang for your buck.