What is a condensation dehumidifier?

How a condensation dehumidifier works

The colder the air, the less moisture it can hold. At 20°C, this would be a maximum of 14.7 grams of water per kilogram of dry air. At 5°C, the corresponding maximum value is just 5.4 grams of water per kilogram of dry air.

Let us now take, for example, air conditions with a temperature of 20°C, an absolute humidity of 10g per kg of dry air and a relative humidity of 69%. As the air cools, the dew point line – and thus the maximum amount of water vapour that can be absorbed – would be reached from 14°C onwards. At a temperature of 5°C, the air would have released a total of 5 grams of water per kilogram of dry air, i.e. it would have condensed.

The phenomenon of water condensation caused by rapid cooling of the air is particularly familiar to spectacle wearers. If you enter a warm room in winter with cold spectacle lenses, the air cools down abruptly on contact and water condenses. The lenses fog up. In a condensation dehumidifier, the natural principle of moisture condensation on cold surfaces is mechanically generated by a cooling circuit. A fan draws the air to be dehumidified over a cold surface consisting of many fins, where water condenses and drips into a condensate tray.

The low temperature on the cooling fins is generated by a closed refrigeration circuit based on the heat pump principle. The cooled and dehumidified air is then reheated in the condenser and, due to the higher temperature, can once again absorb moisture from the environment. The use of condensation dehumidifiers is particularly recommended for applications with high relative humidity levels combined with medium to high temperatures, such as in indoor swimming pools.

Check operating limits

Condensation-type dehumidifiers are generally suitable for operation at relative humidity levels of up to approximately 45% and temperatures of approximately 5–36 °C. If conditions differ, contact the manufacturer or use an adsorption dehumidifier.

Rise in temperature

Temperature rise: All condensation-type dehumidifiers release the waste heat from the refrigeration circuit, the fan motors and the internal electrical components into the room air, which – depending on the size of the unit – can result in anything from a minimal rise in room temperature to an enormous additional heat load. This effect is completely negligible in many applications or even desirable (e.g. in swimming pool areas), but can lead to problems in certain applications. The temperature aspect must therefore be taken into account, particularly in the case of large systems and temperature-sensitive applications.

Indoor air quality

Condensation-type dehumidifiers are generally suitable for use under normal indoor air conditions; in other words, they are not designed for use with aggressive or pollutant-laden air. Substances such as chlorine and ozone can corrode components and cause the units to fail within a short space of time. Swimming pool dehumidifiers are therefore protected against chlorine as standard through special measures. Some manufacturers are also able to supply specialised units for commercial use, featuring special protective coatings against, for example, acid or salty air.

Installation

Condensation-type dehumidifiers are available in portable or fixed versions. Portable units are almost exclusively operated with free exhaust, whilst large industrial dehumidifiers can also be connected to a ventilation duct network. In this case, care must be taken to ensure that sufficient pressure is available.