Direct/DX cooling
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  1. #1

    Direct/DX cooling

    I have a new building which is currently cooled with a AHU containing direct/indirect evap. The unit was undersized and not cooling the rooms. Now the fix is to add a DX coil. Has anyone had any experience with this set up?

  2. #2
    Join Date
    Feb 2012
    Location
    New York City
    Posts
    106
    Where is this?

  3. #3
    New Mexico, this is a combination the engineers what to use more. Until now we use either one system or the other.

  4. #4
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    938
    depends if its undersized is the AHU undersized? and if you add another coil how will if effect the fan operation (air flow, static) are you bringing in a lot of outside air? when you say new, is it brand knew? and are these the same guys who installed it the first time, and who is trying to install this fix? overall i would get other bids or ideas and get the manufacture involved as well, to review the changes

  5. #5
    Join Date
    Feb 2012
    Location
    New York City
    Posts
    106
    The basis of design may be a different level of comfort than we typically design to with this kind of aystem, and the client might not have understood the implications. If the solution is adding mechanical cooling check the psychrometrics and coil selections for before and after the evaporative stuff. Depending on climate and comfort parameters a dry coil upstream of the evaporative equip uses less energy but if indoor humidity is an issue it won't solve your problem.
    I hope I helped!

    Feel free to contact me and other users here for more detailed assistance within the context of a contract. Advice and opinions are provided here "as-is" without any warranties, guarantees or acceptance of liability for use, misuse, or accuracy of advice given. (Gotta keep my legal team off my back at work.)

  6. #6
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    1,439
    If he's is new mexico, dryness is likely an issue.

    I imagine the load there is primarily sensible load only.

    I would not mix and match the systems as control becomes an issue.

    Dx works well, when controlled properly.

    I would be sure and look into a Rawal devices APR valve to add to the dx system if the loads are not consistent.

    Also, as others have pointed out, get a 2nd engineers opinion.

    After all, it may not be an issue with the current cooling, but the air handler, or duct work, etc...

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