Loop length and dept differences, route of least Resistance

Discussion in 'Vertical and Horizontal Loops' started by Reef, Nov 21, 2013.

  1. Reef

    Reef New Member

    Hey guys..

    We have a contractor working on our geo thermal system, new installation.

    The plan was to run 2 trenches at pretty much the same depth and length for both loops.

    Now they bumped into rock layers they can get through, so one loop is shorter than the other, plus to make up for the part lost loop, they added another small loop higher up closer to the house.

    My common sense tells me this will cause problems, the coolant will be pumped from a large tube, and than split up to 3 small loops, all with different resistance.

    I'm afraid the small loop with the least resistance will get most of the volume now, not utilizing the full ground heat exchange.

    Can anybody say something about this from experience ?Is my thinking off here ?

    I do hope so cause they will fill up the trenches tomorrow, after that it will be a guess in the dark what happens below the ground
  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You are right on the money here. Need more info about pipe size, length, depth, size of the heatpump etc. Stop them from closing the trenches!
  3. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Yes, you want the same pressure drop across each circuit. I could see two of the loops being hooked in series and then tied in parallel to the other one?
  4. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    We know that loop balancing is hog wash however all our training demands we make sure loops are evenly sized to balance pressure drop across each circuit. Our training also demands turbulent flow though that is not 100% necessary if field is large enough. We also have been taught rules about spacing yet jobs don't always allow us to follow those rules and systems are in place with enough loop too close together.

    What is most important is having enough loops in the ground. Is there a consequence to uneven sized circuits. Perhaps as much as 10% pumping power, but little else if you have enough loop overall.......

    Of course it is not industry standard and many will squawk, but the proof is there is a lot they could do to improve performance that we haven't looked at. For instance why only 2 trenches, 4 would be more efficient. Is the flow center PSC? Variable speed is more efficient. Is the duct work adequately sized........on and on.
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The description here suggests that one loop is at least 50% of the length of the first loop, perhaps less. Yes, this should be corrected. Running the 2 shorter loops in series is not a bad idea. While Joe is correct, the overall performance might not be that much impacted, since the increased flow through the shorter loop will also increase the pressure drop through the shorter loops until all the loops are balance again having the same amount of pressure drop. You will get less performance out of the longer loops now, since the lower flow will warm up the pipes more and it will have a lesser delta T between the pipes and the ground.
    So the most flow will go through the pipe with the lowest heat exchange area, not picking up much heat after a while. One thing will add to another, and soon you will see some impact on your loop performance.
  6. Calladrilling

    Calladrilling Member Industry Professional Forum Leader

    I would like to see a diagram of the proposed install before i let them bury the trenches if this was my house.
    I agree that the loops should be the same length to balance the flow...it may not be completely mandatory but if its possible then why not?
  7. wcpresley

    wcpresley New Member

    In our area all loops must be under 10% variance.. (90% of our loops are 200ft/ ton) We always keep loops as close as possible in our residential heat exchangers.
  8. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I have not typed in a few days, sooo....DON'T let them do this. As above flow is everything.

  9. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Why the hub bub? I see this as a field change order that CAN be easily overcome with the correct piping schedule. Hows about they run all the loop tails into the mech. space and we correct for balancing inside?

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