Shared Loop Field For 2 Geo Units

Discussion in 'Vertical and Horizontal Loops' started by rkinmoval, Apr 10, 2018.

  1. rkinmoval

    rkinmoval New Member

    Looking for some advice. I found an old thread from 2012 in this forum but unfortunately could not find the answer I'm looking for.

    I have two outbuildings that I'm installing GHPs in and want to install a shared loop field between them. I should clarify that one building has an air to air HP on it now and will remain that way until the system fails. However, the other building is new and therefore I'm putting in a geo unit to start. So in reality, the system will have a significantly oversized loop field for now but I want to be prepared for the future since I'm having the contractors here now to "dig everything up".

    The buildings sit about 100' apart and will both have 5 ton systems in them. My question is in relation to how do you plumb the loop so both systems can benefit? Is it possible to do it with one flow center with a signal wire coming from the other building to call the pumps? Is there a better way? Any suggestions would be greatly appreciated. Thanks in advance!
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Yes and yes. Flow center would be located in geo building now. Supply lines capable of flowing 15gpm to other building as well as control wire installed to air to air building for use down the road.
  3. rkinmoval

    rkinmoval New Member

    Good deal. But how do you plumb it so when both systems are calling for heat/cooling that each gets enough flow from the loop? Isn't there a risk that more flow will go to one system over the other? Thanks again!
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    It is all a matter of friction loss and throttling valves. The throttling valves can be set so that if the head loss is greater on one system or the other you can adjust the flow rates to satisfy both units. The industry term is " balancing the system ".
  5. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

  6. rkinmoval

    rkinmoval New Member

  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Multiple heat pumps on single loopfield.

    There are two ways to handle the problem.

    1) You can install a variable speed pump in the new building and then pump the water via a 100' line (200' both ways) to the old building.
    2) To have a variable speed pump in each building, and simple T-off outside at the header. This might be more challenging to get the air out of the loopfield without the old building operational. So lets focus on option 1.

    The challenge is 2 fold. Higher pressure drop with the 100' pipe, requiring more pumping power. That pipe should be 2" HDPE to keep the flow resistance as low as possible. Each heat pump has a motorized valve, shutting off the flow through the heat pump when not needed. The pump in the new building would be a pressure driven pump, meaning it senses a loss in pressure when only one or more heat pumps come online, and increases the rpm automatically to keep the pressure (and therefore the flow through the heat pump) constant.

    Now the complexity increases since when both heat pumps are running, the flow through the common loop field increases, which significantly increases the pressure drop in the loop field exponentially. Which is why the most efficient way now is to select a pump which not only can increase the pressure constant no matter how many heat pumps are online, but also increases the pressure with increasing flow requirements.

    I like to avoid balance valves, why would you pay for increased pumping power only to throttle back the flow again? But it requires skillful pressure drop calculations and understanding on the impact of different pipe lengths to the heat pumps on the flow of source fluid through the heat pump.

    Variable pumping power with variable flow requirements is the way to go. The amount of money you pay for constant speed pumps is not justifiable anymore, in my opinion.

    Here is another example of 29 heat pumps on a single loop field. (2) circulation pumps, only 1 is needed, but we have 2 for redundancy, since they have 27 tenants. While all are in the same building, some are right next to the flow center, and some are 150' away. So technically it is the same problem solved then what you have, with one heat pump right next to it, and the others further away. No balancing valve in the whole building, just different pipe sizes going to each heat pump, which all have different flow requirements.

    Yours is easy, since both heat pumps are the same size, and there are only 2 of them.

    At the end of the day you need to understand pressure drop and fluid dynamics, and the impact of pipe size, antifreeze concentrations, type of antifreeze, fluid temperature etc.

    Pumping efficiency is the holy grail of system efficiency.
    Last edited: Apr 13, 2018
    rkinmoval likes this.

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