A Guide to Compressor Dehumidifiers

Compressor driven dehumidifiers provide, in the right environment, an extremely simple and efficient method of removing mositure quickly and economically.

Working on the same principle as domestic refrigerators; through the refrigeration process the evaporator in the unit becomes extremely cold. A fan draws air into the machine which passes over the evaporator unit and, as the air temperature drops, 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 small reservoir tank or is fed off through a drain hose. 
Compressor dehumidifiers work best at higher temperatures and are generally rated in test conditions at a temperature of 30 degrees centigrade and a relative humidity of 80%.
The performance of a compressor driven unit tends to vary depending on different envionmental variables. This is referred to as the sensible capacity. It is important to note than in more realistic working environments the actual sensible performance of a compressor driven dehumidifier will be much lower than the nominal rated performance under test conditions.
For example, in a more real world scenario of 27 degrees centigrade temperature and 60% RH (relative humidiity), as opposed to the rated test condition of 30 degrees and 80% RH a unit with a rated capacity of 10 litres per day will in reality tend to only draw 5.6 litres; a unit rated at 16 litres will draw 8 litres; and a unit rated at 50 litres will draw 30 litres. As the temperature drops further then the performance of a compressor driven unit will tail off significantly.
Ultimately in cooler temperatures below around 12 degrees centigrade basic compressor dehumidifiers will stop working as the evaporator plates are likely ice up and they will stop extracting moisture. In contrast desiccant units tend to be rated in a test condition of 20 degrees centigrade and 60% RH and are unaffected by temperature until it reaches zero degrees centigrade.
Different units solve this problem in different ways:some switch off; some switch off the compressor but continue to run the fan, passing ambient air over the plates until they thaw and more advanced models have a reverse hot gas defrost cycle.

Our best selling compressor dehumidifier is the BROLIN BR20C, a 20 litre per day extraction and has a large 3.5 litre holding tank which is best in class. Only £159 including VAT and delivery.