Back up heat instead of aux heat

Discussion in 'Geothermal Loops' started by clockwalk, Dec 7, 2010.

  1. clockwalk

    clockwalk New Member

    My system is open loop using my well. WF Envision 049 4 ton water to air unit. I chose to not have an aux heat installed since I have a working oil furnace and 7 zones. I have set the oil furnace thermostats 2 degrees below the WF thermostat. Does this sound like an efficient plan for heating the house? Will the WF run for a long time and use alot of electricity before the oil furnace comes on. Does anyone have a better way to use this system?
    Thanks Ed in New England
  2. bobpietrangelo

    bobpietrangelo New Member

    Is your Geo zoned like your Oil
  3. clockwalk

    clockwalk New Member

    The geo system has one zone but we have it balanced so it is evenly distributed. The oil furnace is a hot water baseboard system on zones. The oil furnace thermostats are set 2 degrees below the geo thermostat. I guess what I want to know is will the geo system run for a long time while it tries to generate enough heat on very cold days when the auxiliary heat would have normally cut in. Even if I set the oil furnace thermostats only 1 degree below the geo system I have the same question. What can I look for to know that the geo syatem has maxed out? Look for very cold LWT ? Does the WF thermostat indicate that Aux heat is called for?
    Thanks Ed
  4. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Outdoor reset would be an option to figure this out. Basically at some outdoor design temperature you will be calling in additional stages of heat. We dont know what that is for your system, but if you can figure that out, then tie that in to your oil demand.

    In the meantime you are somewhat guessing as to when to call for oil. In almost all areas i can think of, you'll prefer running geo forever before calling for oil.

    If you start running setbacks on your geo, the issue gets further complicated. Holding 72f inside when it is 25f outside is a lot less of a demand on geo then bringing it up from 68f to 72f for example.

    I find similar setups require the homeowner to learn their system somewhat like playing a piano. Design helps to make predictions and controls help to reacte, but you'll need to verify.
  5. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Another I agree with urthboy.

    I would only let the oil come on if the geo is running constant and your house is getting colder.

    This is assuming that your loop temp does not drop too low, (less than 30°)

    Do you have a loop design report that tells you when back up heat is needed?
  6. clockwalk

    clockwalk New Member

    Urthbuoy and palacegeo, thanks for the input. I can watch the loop temp by watching the LWT and I can make sure the oil comes on if the Geo is running a long time without keeping up. I still wonder what triggers the Aux heat if I had it. It would be convenient if the Geo could trigger the oil furnace but the installer said this was the only way back up heat could be activated. If I was an engineer I would work on that one.
  7. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Aux heat is triggered by the thermostat. When it comes on depends on make of the tstat and how it is set up.

    I know that tstats can be set to fire a gas funace, so it seems it should be the same for a oil furnace. But I have never done it so I can't say for sure.
  8. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    Ditto. Calls for staging is always the thermostat, and yes you can trigger just about any other kind of heat with the 2nd or 3rd stages. I'm going to set mine up one day to make me a hot chocolate when it gets really cold:)

    Heat pumps are supposed to run a long time. You may have secondary concerns with it being open loop if you have limited water, but that is how they work.

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