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Home » Glossary

Hot Gas Defrost (HGD)
An internal automatic defrosting process that is built into refrigerent dehumidifiers to allow cold temperature operation. Below about 10C moisture from the air condenses out as frost inside a refrigerent dehumidifier. If left to build up the machine will slowly turn to a block of ice. To overcome this HDG equipped machines periodically reverse the flow of refrigerent inside the coils, actively heating the cold condensing coil and melting any frost or ice build up. The process typically happens about once an hour,lasts 2-3 minutes and is totally automatic in operation. This allows HGD machines to operate down to near freezing point ambient temperature. (NOTE: Machines with HGD fitted do NOT require any external gas supply or a gas bottle to operate - it is a totally in-built function of the refrigeration circuit and nothing to do with 'gas' as such!).
Adsorption Dehumidifier
A method of moisture extraction from the air where the moisture is retained on the surface of a dessicant rotor rather than condensed from the air on a refrigerated coil. The moisture laden rotor is then dried out via a heated and separate airflow. Adsorption machines will work efficently at lower temperatures than refrigerent machines and can get the air much drier.

Relative Humidity (RH)
When we talk about a target environment we usually express it in terms of RH%. The % RH is the proportion of moisture in the air compared to the maximum that air can hold before saturation at a given temperature. SO, to lower the RH% you can either RAISE the ambient temperature or remove the moisture with a dehumidifier. The latter is usually the much more economical solution.

Dew Point
The temperature at which the RH reaches 100%. Any surface that is at or lower than the dew point temperature will produce condensation. If you can lower the RH% for any given temperature then you also lower the dew point. If you dry the air enough then the dew point temperature becomes so low as to be never reached in normal day to day life - result - no condensation.