The Art of Dryer Sizing

By: Michael Camber

Compressed air dryers are commonly rated to achieve a specific moisture level (e.g. 40°F pressure dew point) for a certain volume of air flow (cfm). This nominal flow rating is typically based on a set of standard conditions (100 psig, 100°F inlet temperature, and 100°F ambient temperature). In practice, your actual conditions can change from day to day and are rarely the standard conditions, and the dryer may be over or undersized depending on how it is selected.

When sizing a dryer, it’s important to understand how temperature and pressure affect water content in the air. The water vapor content of air varies directly with temperature—if temperature increases, the air’s ability to hold water increases. As a rule of thumb, every 20°F rise in inlet air temperature may double the water load on a dryer. Pressure is the opposite. The water vapor content of air varies inversely with pressure—if pressure increases, it squeezes moisture out. Because of these two relationships, compressed air dryers have correction factors (supplied by the manufacturer) to help determine how much air a dryer can actually handle for specific conditions.

We have updated our website to include sizing correction factors and provide a sizing example using one our SECOTEC refrigerated dryer series: How to size compressed air dryers

4 thoughts on “The Art of Dryer Sizing

  1. Very easy to understand and nicely done.

    Kind regards,

    Werner Rauer
    Product Manager Compressors, Technical Department
    US Headquarters
    Ext. 266

  2. How the over sized refrigerant air drier drawing more power. Compressor is 1100 CFM . What should be the dryer capacity . ?

    1. Bigger the dryer, bigger the refrigerant compressor. A bigger refrigerant compressor consumes more electricity. The refrigerant compressor is the largest electricity consuming component and therefore is the determining factor in the cost to operate. There are two kinds of refrigerant dryers, cycling and non-cycling. A cycling dryer (our Secotecs) reduces the power consumption by loading and unloading the refrigerant compressor when it’s needed. A non-cycling (our Kryosec) dryer’s refrigerant compressor is always loaded, so it’s power consumption is constant.
      To size the dryer, we need to know three things:
      1. Operating pressure
      2. Max room temperature where the dryer is located
      3. The temperature of the compressed air as it enters the dryer. The discharge temperature of the compressor is a good approximation. If you don’t have a discharge temperature reading on the compressor, it can be estimated by knowing the temperature of the air entering the compressor and adding the temperature rise inside the compressor (the compressor manufacturer can provide this information).

      Send us an email ( telling us where you are and we’ll connect you with the local rep who can assist you.

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