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Water source mini split?

Post in 'The Green Room' started by peakbagger, Oct 2, 2012.

  1. peakbagger

    peakbagger Minister of Fire

    Joined:
    Jul 11, 2008
    Messages:
    1,631
    Loc:
    Northern NH
    Has anyone seen a source for a water source mini split heat pump?. It sort of makes sense that a water source unit would make sense for both winter heating and summer cooling. Obviously I could cut up an air source unit and replace the coils with a heat exchanger but that would obviously ruin any warranty. I dont have much experience with AC but when I worked in a industrial plant, all the AC units were water cooled as the atmosphere was damp and dirty.

    I have an old well that would make a nice winter and summer source with two pipes already running from my well to the basement. The well is 17 feet deep and was built with a couple of truck loads of crushed rock at the base for addtional storage. I have soft water so I dont really have to worry about scale buildup but worst case is I could put a coil in the well and have an intermediate loop.

    With the exception of making sure I dont overcool or overheat the well am I missing anything on why these units arent available except in 3 ton or larger sizes?

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  2. EatenByLimestone

    EatenByLimestone Minister of Fire

    Joined:
    Jul 12, 2006
    Messages:
    4,848
    Loc:
    Schenectady, NY
    It's only a guess, but maybe the costs of production outweigh the benefits on the smaller unit. If your abandoned well has water in it I don't see why you couldn't do it with a radiator and attached electric fan/shroud out of a car. The water in the ground would be around 55 degrees and I'd love to have a nice 55 degree breeze in my house all summer. It wouldn't be bad to heat from 55 degrees in the winter either.

    Matt
  3. DickRussell

    DickRussell Member

    Joined:
    Mar 1, 2011
    Messages:
    97
    Loc:
    central NH
    The first thing that comes to mind is the size of that well and it's ability to provide heat over the long haul of a winter. When using a water well as a heat source, in a more conventional standing column well (SCW) design, a conventional 6" bored well needs about 80 feet of water column per ton of heat load. The ground becomes a large heat exchanger, with both sufficient area and tapping the heat content of a large enough mass of rock to provide long term heat without being cooled to the point of freeezing. The (presumably) larger diameter of that old well gives more surface area per foot of depth. If the well is, say, three feet in diameter (dug well?), the area of ground contact is roughly six times that of a drilled well of the same depth. If there is 14-15 feet of water in the well, then you'd think you have the equivalent of one ton worth of steady heat withdrawal. However, the six inch well bore is tapping the heat from rock for some distance around it, and over an 80 foot depth. This means you likely wouldn't be able to withdraw long-term heat from the shorter wider well at the same rate as you could from the deeper narrower well. That's my take on it.

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