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Thread: diy geothermal for garage

  1. #1
    DIY Junior Member katherine1962's Avatar
    Join Date
    Jul 2011
    Fairfield, Ohio

    Default diy geothermal for garage

    I will be having a new furnace installed in my house. My old one has a fairly new replaced cooling coil heat exchanger in it (1.5 ton). i was considering running a couple hundred feet of cooling line buried approximately 5 ft in my backyard and having a glychol medium pumped through the line and through the cooling coil. i would have an appropriate sized fan to blow air across the coil. should something like this be sufficient for heating and cooling a 2 car garage that i use for woodworking. provided i have my garage adequately insulated. Thanks in advance for any information.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    If the a/c unit is not a heat pump, I don't think you would be able to get it to work. Also, a couple of hundred feet may not be enough volume/length to extract much heat. A ground source heat pump system can be quite efficient, but the setup costs can be fairly expensive and the engineering required to make it all work well are not trivial.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Senior Member Runs with bison's Avatar
    Join Date
    Aug 2009


    Since you aren't planning to have a refrigeraton loop (the normal geothermal heat pump arrangement) the best you can hope for is an approach (differential) to ground temperature. Fin efficiencies aren't all that great and I doubt you will want to use a high volume air source--further depressing the heat transfer coefficient. Plus this will be primarily a non-condensing mode. Condensation can increase heat transfer coefficients, but without refrigeration or a particularly cold source, this is an unlikely mode for the operation of your loop. Jim's comments about the length also are relevant as a cap--since the heat must be conducted away through the soil as source. The input power of the pump also comes into play, but I assume the pump would be before the ground coil so it's heat would be dissipated to the ground. (A monster pump would be a bad idea. I suspect a powerful fan/blower would also be bad as they might introduce more heat than can be removed or at least exceed the point of diminishing returns for their energy input.)

    To put it in easier to understand terms: don't expect much. It should give some cooling due to temperature differential. It will not give you any dehumidification. That might be all that you require, but I suspect that some dehumidification is what you really need in Summer in Ohio.

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