Ground loops with no heat pump

Discussion in 'Geothermal Loops' started by Brent Brod, Aug 18, 2016.

  1. Brent Brod

    Brent Brod New Member

    Would it be reasonable to install ground loops and simply circulate water through radiators in a building or greenhouse?

    I have a building that I need to maintain between 50 and 80 deg F. Most of the time in the winter the building requires no additional heat other than what radiates from the foundation and sunshine on the exterior. I'm wondering if I could adequately cool the building in the summer, or if the thermal transfer to the ground would be insufficient due to a low differential. I expect the water returning to the loop would be something less than 80F (since my goal is max 80 inside) and the soil temperature is probably 70F. With <10F differential, my gut tells me it would require a huge amount of loop piping.

    I know there is no such thing as free lunch, but a cheap one might be good enough :)

    Thanks in advance.
     
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    There have been heat pumps that can do passive cooling - running the fan coil but not the compressor type deal. A lake loop system works well in this regard. And passive heating exists in Iceland and such. The compressor does work both as a check valve (driving the heat in one direction) and as a motor (bumping up the temperature differential), and you would lose those benefits. The other negative is finding a radiator rated for the temperatures you're looking at - a fan convector would give you a better range.
     
  3. Brent Brod

    Brent Brod New Member

    Thanks, Crhis. It makes sense to use a lake loop positioned below the thermocline. I don't have that luxury. I'm wondering how much heat can be moved with such a low temperature differential. Is it even worth considering.

    Is there an easy way to estimate the heat transfer. I'm no mathematician. My concern is the heat won't dissipate to the surrounding rock quickly enough to do me any good with two or three 150' vertical loops.
     
  4. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    I'm pointing you to the load side being the limiting factor - how are you going to absorb heat or shed it? At what rate? It will depend on the heat exchanger approach temperature.
     
  5. Brent Brod

    Brent Brod New Member

    I hadn't considered the load side being the issue, but now that you mention it...I have work to do. Thanks again.
     
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The only thing I could see is an open system in the north providing a unlimited amount of water in the upper 40F/lower 50F range. A close loop would heat up quickly and not provide and a large enough temp difference, thus being self limiting.
     
  7. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    I can't see how a closed loop would "heat up" in this situation.
     
  8. Brent Brod

    Brent Brod New Member

    Chris, if I understand correctly, the ground loop(s) would be far more efficient than the relatively small surface area of the inside exchanger. Absorbing the heat becomes the problem, especially since air in less conductive. The size and number of exchangers in the building would become prohibitive unless a heat pump is employed to improve the temperature difference on both ends.
     
  9. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    You got it.
     
  10. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Depending on your ground temp you will take some heat out of the building. Not much, but some. That heat you will put into the loop, which will warm up slightly, now reducing the delta T between the air inside the building and the fluid circulating in the loop. So a passive system is self limiting, that was my point.
     
  11. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I don't see the location of this application in the thread, but BB's profile location is near Austin, TX. Without checking a deep ground temp map I suspect deep ground temp is indeed around the 70*F stated in BB's initial post. Passively cooling to 80*F would be a challenge.

    How bout a nice minisplit?
     

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