There are several types of compressed air dryers on the market, and many different applications for drying compressed air. Many industrial and commercial applications for compressed air will be for hand tools or the operation of pneumatic cylinders and valves in an indoor applications. These are referred to as “power” applications. For the most part, these applications require the air to be free of condensate (free liquid), which will impede the tool’s performance and cause corrosion, shortening the life of the tool. Refrigerant air dryers are usually selected for these applications. They remove water vapor from the compressed air by means of cooling the incoming air to a level within the design dew point range, separating the condensate, and then draining it off.
Dew Point Requirement in Power Applications
In most refrigerant dryers (usually 15 CFM capacity and larger), the compressed air is re-heated after the separation stage, providing a temperature buffer between the ambient temperature and dew point temperature. Theoretically, the air temperature would have to decrease to below the dew point level before any condensate could form. As a minimum requirement, the compressed air should have a pressure dew point which is lower than the lowest ambient temperature that the compressed air line will be subjected to. If all air lines and tools/devices are being used in heated areas with temperatures above 60º F (16 ºC), the pressure dew point of the compressed air should be at least 10-15º F lower, which will mean an air dryer should provide a 45 to 50º F pressure dew point.
Points to consider when sizing a Refrigerant Air Dryer
It should be considered that as air passes through fittings, piping restrictions, regulators, orifices in tools and other devices, expansion can take place. When air expands, cooling takes place, which can result in cold spots in which condensate may still form, even though room temperature may be higher than the pressure dew point rating of the air dryer. For these applications, a refrigerant air dryer is normally sized to provide a “pressure dew point” in the range of 35 to 50º F. (2-10ºC). It should be considered that as the refrigerant air dryer ages, the heat exchangers will start to scale internally, and the air-cooled side will accumulate dirt and debris. These factors will affect the dryer efficiency, and dew point elevation can be expected as the dryer ages. For these reasons, a good buffer (difference between the coldest ambient temperatures to be encountered as opposed to dryer dew point rating for the volume to be dried) should always be allowed when sizing your refrigerant air dryer. Standard refrigerant air dryers cannot be used for dew point requirements close to, or below freezing, as the condensate may freeze in the air lines at those levels.