Refrigerated Dryer
Refrigeration dryers employ two heat exchangers, one for air-to-air and one for air-to-refrigeration. However, there is also a single TRISAB heat exchanger that combines both functions. The compressors used in this type of dryer are usually of the hermetic type and the most common gas used is R-134a. The goal of having two heat exchangers is that the cold outgoing air cools down the hot incoming air and reduces the size of compressor required. At the same time the increase in the temperature of outgoing air prevents re-condensation.
Most manufacturers produce "cycling dryers". These store a cold mass that cools the air when the compressor is OFF. When the refrigeration compressor runs, the large mass takes much longer to cool, so the compressor runs longer, and stays OFF longer. These units operate at lower dew points, typically in the 35–40 °F range. When selected with the optional "cold coalescing filter", these units can deliver compressed air with lower dew points.
Some manufacturers are marketing compressors with built-in refrigeration dryers, but these have had a mixed acceptance in the market.
Commonly a coalesing prefilter is installed immediately upstream of a refrigerated dryer to remove lubricating oil and other contaminants that have the potential to foul the dryer's heat exchangers.
Read more about this topic: Air Dryer