page_title: Compressed air dryer
section_title: Refrigerated dryers
hierarchical_section_title: Compressed air dryer / Refrigerated dryers
caption_attribution_description: English: Two-stage air compressor equipped with a JT type refrigerated compressed air dryer.
context_page_description: Compressed air dryers are special types of filter systems that are specifically designed to remove the water that is inherent in compressed air. The process of compressing air raises its temperature and concentrates atmospheric contaminants, primarily water vapor. Consequently, the compressed air is generally at an elevated temperature and 100% relative humidity. As the compressed air cools, water vapor condenses into the tank, pipes, hoses and tools that are downstream from the compressor. Water vapor is removed from compressed air to prevent condensation from occurring and to prevent moisture from interfering in sensitive industrial processes.
  Excessive liquid and condensing water in the air stream can be extremely damaging to equipment, tools and processes that rely on compressed air. The water can cause corrosion in the tank and piping, wash out lubricating oils from pneumatic tools, emulsify with the grease used in cylinders, clump blasting media and fog painted surfaces. Therefore, it is desirable to remove condensing moisture from the air stream to prevent damage to equipment, air tools and processes.
context_section_description: Refrigerated dryers are the most common type of compressed air dryer.  They remove water from the air stream by cooling the air to approximately 3 °C (38 °F) and effectively condensing out the moisture in a controlled environment.  3 °C (38 °F) is the realistic lower limit for a refrigerated dryer because a lower temperature runs the risk of freezing the separated water.  They are typically specified as primary dryers and generally produce air quality that is appropriate for approximately 95% of all compressed air applications.
  Refrigerated 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 and R-410a for smaller air dryers up to 100 cfm. Older and larger dryers still use R-22 and R-404a refrigerants. 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.
  Some 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 1.5 °C - 4.5 °C (35 °F – 40 °F) range. When selected with the optional "cold coalescing filter", these units can deliver compressed air with lower dew points. Non-cycling dryers use a hot gas by pass valve to prevent the dryer from icing up.
  Some manufacturers produce "cold coalescing filters" that are positioned inside of the air dryer at the point of the lowest air temperature (the point at which maximum condensation has occurred),
  Refrigerated dryers are generally manufactured in one of two different ways, Freon based units and Joule-Thomson based units.
caption: Two-stage air compressor equipped with a JT type refrigerated compressed air dryer.
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