Radiant and AC combination

Discussion in 'Radiant Heating and Cooling' started by DavidCraig, Jul 25, 2012.

  1. DavidCraig

    DavidCraig Member

    Have radiant floor heat, currently heated from oil boiler. Also, a broken 2-ton AC system in attic.

    Will use a 3-ton water-to-water unit for both functions (with added water coil for AC)

    Water geothermal pumps require buffering tank to reduce cycling frequency. Am concerned about having ‘tons’ of water buffered when switching between heat and AC.

    Any thoughts, experiences, or recommendations?

    For a start, this might argue for poorly insulating the buffer tank, lol.

    Perhaps a temp sensor on tank to not allow switching modes until tank has cooled/warmed to ambient temp. This is a residential application so this shouldn't be hardship -- and have young grandkids that love to play with thermostats, etc.
    Last edited: Jul 25, 2012
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    This is a common layout. I'm not too sure what you're asking?

    It is generally a seasonal layout. Especially since you have radiant. A summer/winter type layout, but outdoor reset can automate it.

    The insulated buffer tank functions effectively in both modes.
  3. DavidCraig

    DavidCraig Member

    My concern, for example, is to prevent the scenario where 'AC mode' starts up with a 80 gallon buffer tank at 100 F due to recently being in 'heating mode'. This could be more likely problem if domestic water heating was assisted by 'heating mode' rather than having a DSH.
  4. zacmobile

    zacmobile Guest


    You can get controls that have an adjustable sample period that it will use to read an average outdoor temperature to base the heat/cool switchover off of. But it has been my experience problematic rapid heat/cool switchover only occurs in either really old or poorly designed homes with bad insulation and/or big solar gains. Regardless, it only takes about 15-20 minutes to completely transition a warm tank to cold and you are in effect just sending the heat back into the loop field with only a small parasitic cost involved in the transfer, not something you want to be doing on a regular basis however.

    What i usually do is have a permanent heating demand on the control and have the cooling enabled by a call from the air handler or cooling device of choice with a 5 degree C deadband in between the warm weather and cold weather shut down settings. Say warm weather shut down set at 17C (63F) and cold weather shut down set at 22C (72F). Seems to work well in most cases.
  5. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    There isn't the conflict you suggest. A domestic water heat usage will be a seperate tank than the radiant buffer. The radiant buffer will be switched once from heating to cooling per season. This is simply a control setup. Granted you could short cycle your tank back and forth between heating and cooling, but that would be a poor installation job.

    If it helps, you can use three tanks: one hot, one cold, one domestic.
  6. DavidCraig

    DavidCraig Member

    Thank you for responses. Am probably being too 'paranoid' about efficiency.

    If short cycling was needed, then the additional tank (circulator/zone) would make sense. Or separate geothermal units. One would think that large commercial buildings could have all sorts of wild-stuff going on.
  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Again the other choice is to just switch from summer to winter modes. That's what many of these systems do.
  8. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    You should have enough deadband, thermal mass (and thrift) to avoid daily switches between heating and cooling modes.

    Heating setpoints are typically 65-70 and cooling setpoints 74-78. Configure your setpoints suitably far apart so as to avoid heating in the AM and cooling in the PM.

    Many thermostats allow auto changeover with configurable deadband. I usually set them for manual changeover, requiring user intervention to change modes.
  9. zacmobile

    zacmobile Guest

    another thing

    Another thing that is done is to just pipe your air handler directly off the heat pump before the buffer tank, your air handler should be generously sized to pull this off though, it would have to be rated for more output than the heat pump so as to take all (or give back) all the heat that the heat pump produces.

    I'm a big fan of a manual seasonal heating/cooling switchover switch too, guaranteed no heat/cool flip flopping then.
  10. DavidCraig

    DavidCraig Member

    Manual intervention is probably the best for my app.

    On sunny days the solar gain is significant. Plus the livingroom is open to the second floor so upstairs is 10-15 degrees warmer (and that is where the AC thermostat currently is). Another thing would to have the fan running low continuously ... but that is contrary to the philosophy of radiant floor heat.

    Interesting solution.

    I had thought of an 'interseasonal' solution of adding an H2O coil that was connected to the actual ground loop. A dehumidification mode, so to speak.

    However, the additional cost of 2 coils is one concern. But the worry on having Methanol antifreeze in an air coil inside a home greatly concerns me - a small leak (which seems inevitable over time with coils) could cause neurological damage. Overall, decided to abandon this approach. Creative thinking can be dangerous, lol

    In upstate New York, AC is minor compared to heating. And with an actual quote I got last year, they said it was much cheaper to just replace the equipment rather than run a dual system. That may be true but there are additional pluses for the dual system.
    Last edited: Jul 30, 2012
  11. ACES-Energy

    ACES-Energy Member Industry Professional Forum Leader

    where in upstate NY are you?
  12. DavidCraig

    DavidCraig Member

    Near Saratoga Springs
  13. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Sounds like a common problem. You probably do not want an automatic change over but a manual one, otherwise you indeed risk that the buffer tank needs to be switched from heating to cooling. It is a hige stress on the compressor to deal with incoming load temps of over 100F in cooling mode.
    You have a water-water heatpump which is reversible, a hydronic air handler, and you want to make your domestic hot water all year around. You can make this all off one heatpump, have a seasonal changeover for the a/c, and run the hot water tank as a zone for full time hot watr alll year around. Check our website, we have a couple systems on there similar to this setup.
    Controls are a bit complex, your best bet is the new tekmar 406. Give John Manning a call, at phoenix energy supply in Auburn, NY. He has the controls palns for such a setup, and can premount everything on a panel for you.
  14. DavidCraig

    DavidCraig Member

    Will look up the new Tekmar controler, thanks.

    You can make this all off one heatpump, have a seasonal changeover for the a/c, and run the hot water tank as a zone for full time hot watr alll year around

    With seasonal changeover, how can I run the how water tank as a zone for full time hot water all year around?
  15. ChrisJ

    ChrisJ Active Member Forum Leader

    I think Doc is suggesting 2 tanks, one that does the seasonal switch, the other stays hot all the time. The reversing valve on the heat pump would switch from making hot water to cold water. The tekmar would control it.

  16. zacmobile

    zacmobile Guest

    They don't seem to be there, are they in a hidden file?

Share This Page