Humidification Made Simple:
What is a Condensation Dehumidifier?
A condensation dehumidifier is a dehumidifier that draws water vapor out of the air through the natural principle of condensation.
Condensation dehumidifier operation
The colder air is, the less moisture it can hold. At 20°C, the maximum amount would be 14.7 grams of water per kilogram of dry air. At 5°C, the corresponding maximum is just 5.4 grams of water per kilogram of dry air.
For example, let’s consider air at a temperature of 20°C with an absolute humidity of 10 grams per kilogram of dry air and a relative humidity of 69%. As the air is cooled, it reaches the dew point at 14°C, meaning that the air would then contain the maximum amount of water vapor it could hold. If the air were then cooled to 5°C, a total of 5 grams of water per kilogram of dry air would condense out of the cooled air.
Anyone who wears glasses is familiar with how water condenses when air is cooled rapidly. In wintertime, when you walk into a warm room when your glasses are cold, the air near the glasses is suddenly cooled, and water condenses out of it. Your glasses fog up instantly. In a condensation dehumidifier, this natural effect of moisture condensation onto cold surfaces is generated mechanically through the use of a cooling circuit. A fan or blower forces the air to be dehumidified over a cold surface consisting of numerous plates onto which water condenses out, and then drips into a condensate receptacle.
The low temperature of the cooling plates is generated by a closed cooling circuit in accordance with the heat pump principle. The cooled and dehumidified air is then warmed back up in the condenser, at which point the warmer air can then absorb moisture from the environment again. The use of condensation dehumidifiers is especially advisable for applications involving high relative humidity levels and moderate to high temperatures, such as indoor swimming pools.
After the required dehumidification procedure for the specific application has been determined on the basis of calculations, the appropriate dehumidifier can be selected through its corresponding performance diagram. The performance and degree of effectiveness of condensation dehumidifiers increase as the temperature goes up, and decrease as temperatures go down. In the technical documentation, with respect to performance, generally only standard values at 30°C and 80% RH, sometimes also at 27°C and 60% RH are provided. In many cases, only the maximum possible dehumidification performance at 35°C and 80% RH is stated. With respect to the specific application concerned, these specifications are often insufficient to enable an estimation of the selected system’s capability to actually provide the required dehumidification performance under the conditions for which it was designed. Most manufacturers also supply performance diagrams to facilitate a sufficiently precise determination of the actual dehumidification capacity under the design conditions. Example: a condensation dehumidifier is stated in the documentation as having a dehumidification performance of 40 l / 24 h at 30°C and 80% RH. In accordance with the calculation, at 20°C and 60% RH dehumidification of 20 l / 24 h should occur. The actual dehumidification capacity at the required conditions is shown in the adjacent manufacturer’s performance diagram as follows:
Check application limits
Generally speaking, condensation dehumidifiers are suitable for operation up to approx. 45% RH and a temperature of approx. 5–36°C. For conditions other than these, contact the manufacturer or use a desiccant dryer.
Temperature increase: All condensation dehumidifiers release the waste heat of the cooling circuit, fan motors and internal electricity back into the ambient air, which can lead to a minimal increase in ambient temperature or to an enormous additional thermal load — depending on the size of the system. In many applications, this effect may be totally negligible or even desired (e.g. In the area of swimming pools), but in certain applications may lead to problems. In particular, with large facilities and temperature-sensitive applications, the temperature aspect must therefore be taken into account in the planning.
Ambient air quality
Condensation dehumidifiers are generally suitable for operation under normal ambient air conditions, e.g. not for aggressive air or air which is carrying toxic substances. Substances such as chlorine and ozone can attack parts and quickly destroy the systems. Therefore, swimming pool dehumidifiers are already protected from chlorine as standard using special measures. Some manufacturers are in a position to supply industry clients with special systems that have special protective coatings, e.g. to protect against acids or salty air.
Condensation dehumidifiers are available in either a mobile or a stationary version. Mobile systems are almost always operated with exhaust air released into the open, while large industry dehumidifiers can also be attached to a network of ventilation ducts. In this case, it is important to ensure sufficient available compression.