Refrigerated air dryer recommendation

  • Thursday, March 04, 2021 11:59 AM
    Message # 10164090

    Looking for recommendations for a reliable refrigerated dryer mfg. We have a couple of customers who cannot go with desiccant at this time. Both are small, aprox 35 CFM units.

    If you have had good luck with a particular manufacturer/model, can you PM me?


    Bob W

  • Friday, March 05, 2021 7:01 AM
    Reply # 10166636 on 10164090
    Al Moon (Administrator)

    Well let the dominoes fall.

    1) amazon and the rest of the internet + mgpho

    2) research the understanding between cycling and non-cycling refrigerated dryers

    3) check your requirements of nfpa 99 2012 code

    i.e. :

    I m not talking about the alarm set point for +35 degree F at both master alarm panel. Its the requirement for the performance of the dryer to be below 32 at all times. This is not always easy without a constant major flow demand.  Medical Air Dryers.

    Medical air dryers shall meet the following requirements: 

    (1) They shall be designed to provide air at a maximum dew point that is below the frost point [0°C (32°F)] at 345 kPa to 380 kPa (50 psi to 55 psi) at any level of demand.


    From our corp. vendor list:



  • Saturday, March 06, 2021 7:56 AM
    Reply # 10169936 on 10164090


    I've had good luck with Powerex, or Hankison, and Wilkerson as manufacturers of refrigerated dryers. The problem that Al addresses is that a cycling (utilizing a thermal expansion valve or hot gas bypass valve) or non-cycling (thermal mass) are limited to a minimum of around 34-40 F pressure dew point at all levels of demand. About 30 years ago we came up with an easy fix for a client that didn't want the headaches that desiccant dryers offer. We simply put a membrane dryer in series behind a refrigerated. You only need about 10F dewpoint suppression, so it can be downsized. It's bullet proof, and actually gave us decades of trouble-free service.

    Be careful on the membrane filter manufacturer, some options will deplete O2 molecules.

    Scott Jussel

  • Saturday, March 06, 2021 10:00 AM
    Reply # 10170277 on 10164090
    Al Moon (Administrator)

    Now that's an answer / thanks Scott / see you in Philadelphia Sept 12-115 for annual MGPHO meeting

  • Sunday, March 07, 2021 8:43 AM
    Reply # 10173659 on 10164090

    God willing, I'll be there. I'll keep an eye out for you!


  • Monday, March 08, 2021 10:35 AM
    Reply # 10176506 on 10164090

    Not another one!

  • Tuesday, March 09, 2021 1:01 PM
    Reply # 10180009 on 10164090

    Thanks for the help from everyone. A few comments if I may...

    Scott, thanks so much for the idea on the membrane dryer. I am looking into it...

    As for the MFG's mentioned, I ran into the following:

    Powerex was mentioned but they now sell Hankison for this size dryer. I do not know if they private-labeled them in the past.

    The information I have seen for Wilkerson (website) shows a Parker dryer (victim of another merger, probably).

    I have not been a fan of refrigerated dryers for some time now. Way too finicky lately. Desiccant is the best way to go IMO.

    As for the comments from Al and Scott regarding "  Medical Air Dryers.

    They shall be designed to provide air at a maximum dew point that is below the frost point [0°C (32°F)] at 345 kPa to 380 kPa (50 psi to 55 psi) at any level of demand", I am familiar with this, and if I am not mistaken refrigerated dryers can achieve this. I believe Mark spoke of this maybe 10 years ago at a meeting. 

    Al mentioned:  "Its the requirement for the performance of the dryer to be below 32 at all times." I (respectfully) disagree with this interpretation. The code states that the dryer is to be "designed" to provide dew point below 32 degrees. I believe the word "performance" is different somehow, and would involve monitoring it as such (below 32). 

    Getting back to "designed", a refrigerated dryer can do this taking into account the pressure drop (80+ psi dryer inlet air pressure vs 50 psi line pressure where dew sensor is located).  If my dewpoint calculator is correct, if a dryer can get down to 40F pressure dew point (Scott's higher number) at 80 PSI (compressor cut-in) dew point downstream of regulator (50 PSI) would be registered at 30.6 F. Just below the code limit, but it can be improved upon slightly if the compressors cut in at a higher pressure or if the dryer was able to achieve a lower pressure dew point. 

    Anyway my post is getting too long, especially considering the prevalence of desiccant dryers now. I do welcome any feedback.


  • Wednesday, March 10, 2021 7:43 AM
    Reply # 10182124 on 10164090


    You are correct about the lower dew point in reference to the difference of re-expanding the air @ 50 psig vs 80 psig. The truth is that the air holds only a certain amount of grains of H2O. If you look at a psychometric chart, the re-expansion of the air @ 50psig will give you a pressure dew point of around +18F. The "at any level of demand" problem is not related specifically to that, but to another problem. We found out in the first years of the dew point monitoring, a situation called "re-entrainment of the moisture". This is what Mark talked about some 20 years ago in a seminar. The velocity of the air through the dryer separator at times is so slow that the cyclone style separators do not drop the water droplets out with any degree of efficiency and repeatability. He coined the phrase "bathtub curve" which simply meant that the re-entrainment phenomenon occurs at the opposite ends of the dryer performance curve. Too little flow=too slow and too much flow=too fast. I hope this helps. I wrote a blog about this about 20 years ago and I'll try to find it and send it to you.

    Scott Jussel

  • Wednesday, March 10, 2021 12:30 PM
    Reply # 10182936 on 10164090

    I remember it being a while ago, but am hoping it wasn't 20 years...

    If I recall he was speaking of how liquid sitting in the separator bowl (with a float drain) would cause moisture to re-enter the airstream. (Re-entrainment?), and how electric auto drains would minimize that effect.

    Thanks Scott,


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