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  1. #1
    Join Date
    Feb 2006
    Posts
    114

    Trane chilled water fan coils

    What can be expected when the chilled water supply is piped into the coil outlet and the return to the coil inlet ? I have a number of these units from 2 to 4-1/2 ton capacities, and over half of them are piped in this fashion. I realize that coils are generally designed for counterflow operation (entering air enters the circuits of leaving water and the air leaving the coil contacts the entering water), but I'm not sure what to expect if it isn't piped properly. All I can tell you is that the areas served by these units are having humidity issues. 8 deg air TD, 10 deg water TD, CWV's are functioning, I'm getting flow through the coil but I can't verify the PD due to lack of test ports. Very little condensate off the coils, yet we're maintaining a 70 deg space temp, but the the rh% is around 70. This has been a problem from the beginning, 6 yrs). New acct for us. Thanks for any input. ---gman
    BTW - These are a mix of 4 row and 6 row coils.

  2. #2
    Join Date
    Feb 2006
    Location
    SouthEastern Virginia
    Posts
    1,077
    I believe the results you are seeing are the result of the backwards flow. I'm afraid they will need to be reversed if you want to see the problem go away. Coil efficiency is dependant on correct flow direction. No getting around it.

  3. #3
    Join Date
    Apr 2004
    Posts
    566
    Also i really wouldnt bother taking pressure drops on these coils,because most of these smaller coils have a very low delta p and if you use a standard pressure guage it may not give you good results,check the spec. on the coils some times they are as low as 5 feet wich is about 2 psi,i personally would try to repipe 1 of them correctly and see if the situation improoves it may take less time than taking a bunch of readings.

  4. #4
    Join Date
    Feb 2006
    Location
    SouthEastern Virginia
    Posts
    1,077
    Bobby M is right. You need a digital water pressure gage to get readings on these units.Dwyer makes them where they read in hundredths psi.

  5. #5
    Coils that are piped in the reverse fashion as in your example will yield exactly what you are finding. The sensible heat is being removed from the air, but the latent heat is not thus no dehumidification. Lowering the setpoint in the room will only cause the relative humidity to increase. Using a psychrometric chart will allow you to see what is happening with the air as it enters and when it leaves. Changing the pipe to the correct orientation is really the only fix.

  6. #6
    Join Date
    Jun 2007
    Location
    RI
    Posts
    121

    What's the water temp?

    I see so many coils piped backwards. lol You described exactly what happens to the coil output when this happens. Second most important thing, when I see a humid room, with chilled water is what's the temp of the water? Is it cranked up into the low fifties or is it closer to say 48 degrees? You might have a little adjustment there to squeeze out some of that humidity by dropping the water temp setpoint a couple of degrees.

  7. #7
    Join Date
    Feb 2006
    Posts
    114
    Thanks to all of you guys for taking the time to respond. I had a serious hunch that this was the problem, but wanted some other opinions. I hate getting into these situations, cause the customer then asks, "why wasn't it piped properly to begin with" ? Can we go back on them ? It's a gov't bldg about 7 yrs old, and of course everybody signed off on the job. I just don't understand how it got by the start-up and the test & balance. I hate pissin' people off, especially fellow contractors. It sorta makes me feel like a snitch or somethin'. ---gman

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