Refrigerated air dryers use mechanical refrigeration to lower the air temperature of the compressed air. This results in a lowering of the dew point that causes the moisture in the air to condense into liquid and be removed from the compressed air stream. Refrigerated air dryers can produce air with a dew point as low as 33-39F. They cannot operate below this range because the condensing water will freeze on the cooling coil of the dryer. These dryers are designed to operate under all conditions.
Refrigerated dryers use two heat exchangers in series to condense entrained moisture and reheat the outlet air. Most dryers of this type precool the incoming air before it reaches the refrigeration chiller. Precooling reduces the load on the chiller so that smaller, less-expensive heat exchangers and compressors can be used.
Types of Refrigerated Dryers
- Cycling Dryers - Cycling dryers use thermal
storage, and cycle the refrigeration compressor on and off depending
on the compressed air flow. They are ideal for systems with
fluctuating airflow and moisture content.
- Non Cycling Dryer - The dryer runs continuously regardless of the dryer load indicated by moisture content in the compressed air.
- Tube-in-Tube Refrigeration Dryers - These
dryers operate by cooling a mass of aluminum granules or bronze
ribbon that in turn cools the compressed air. During the process, a
thermometer in the granule mass senses its temperature. As the
temperature rises, a switch turns on the refrigeration unit and vice
- Water-Chiller Refrigeration Dryers - These
dryers use a mass of water for cooling. An extra heat exchanger is
needed to maintain chilled water flow through the condenser, as well
as a water pump.
- Direct-Expansion Refrigeration Dryers - These dryers use a refrigerant-to-air cooling process to produce pressure dew points of 35° F below standard operating conditions.
- Smoother and faster running
- Less downtime
- Less product spoilage
- Lower energy cost