Warm humid air in ducts

Discussion in 'Maintenance and Troubleshooting' started by ChrisJ, May 29, 2012.

  1. ChrisJ

    ChrisJ Active Member Forum Leader

    I have a 4-ton dual compressor GSHP, it makes on-demand DHW. The first summer it was used I noticed a trickle of warm air coming from the duct when it was set on cooling, mentioned it to the installer, we thought maybe the high return that runs in vented attic was to blame. This is the 3rd cooling season, noticed it 2nd season a little also. Now I know it's not the return duct in the attic. The warm humid air is in the ducts when the unit is not cooling(obviously), but has switched to heating DHW.

    I don't know a lot about the refrigerant but seems to me there is hot/warm refrigerant getting to the air coil. Does the reversing valve control this, could it be stuck part way between modes?

    ChrisJ RI
  2. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I don't know what system you have but it is possible that in DHW you are heating the fan coil and getting some heat by convection (air warmed by coil rises up through ducts).
  3. ChrisJ

    ChrisJ Active Member Forum Leader

    My system is a Hydro-Temp combination heat pump, almost embarrased to say, overall very happy with system. I got sucked in by the hype 3 yrs ago, do all unit air, radiant and DHW.

    What you say makes sense, convection air is so humid I get condensation in the 2 supply ducts that come off the top of the plenum. Gone pretty quick when a/c comes on. Just a little counter productive for humidity.

    I think another reason for this is while a/c is running loop pump is off, DHW pump is running, like a huge DSH, topping off my DHW storage tank. Causing higher pressures in compressors. It's like running a ground loop at 120*F.

  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Since RH is constant

    ..in a conditioned space I am more concerned about the moisture source than the latent heat.

  5. ChrisJ

    ChrisJ Active Member Forum Leader

    Moisture source would be humidity collecting on air coil, have been keeping an eye on indoor RH. When thermostat is satisfied, air coil dripping w/ moisture, then the DHW calls for reheat, some warm/hot refrigerant is causing humid convection.


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