Does anyone use a Positive displacement pump?

Discussion in 'Geothermal Loops' started by Designer_Mike, Feb 24, 2011.

  1. Designer_Mike

    Designer_Mike Member

    I've seen a lot of discussion lately about flow rates, pumps etc.

    It seems no-one uses a positive displacement pump for loop water which is somewhat understandable.

    Pros to PD:
    --With a VFD, I could easily control my flow rate and keep my pumping efficiency much higher than a centrifugal circulator pump.
    --Simple linear relation between frequency and flow will make control easy.
    --efficiency is almost always better than a centrif....best centrif I saw was about 60%

    Cons:
    --Marginally more expensive to purchase depending on the pump.
    --Maintenance will be more expensive, but again depends on the pump and the size.

    Few of the curves you can download will indicate the power consumption for the circulator pumps so it's hard to tell how efficient they are.

    and YES> it's kind of splitting hairs but I'm just curious.
     
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I wouldn't expect a PD pump to compete on efficiency, but I'm often wrong.

    Can you post a link to a pump you are considering?

    VFD's are generally not indicated for geo systems since required flow rate varies little. There might be an argument for slower pumping in low stage but just mentioning that will kick the Reynolds anthill.

    I'm looking at a potential project where ~50 units would share an open loop / reinjection system.That may well call for a freq drive.
     
  3. Designer_Mike

    Designer_Mike Member

    I'm not exactly sure if it would be of any benefit right now. I'm still trying to "optimize" my design for added flexibility with alternate heat sources somehow combined with my ground loop. I think it will make more sense to have a couple different pumps.

    Your multi-unit from a single loop will be challenging to keep the pumping costs down.
    It might make more cents to have a number of loop pumps to keep line pressures consistent and flows equalized without significant power usage.
     
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    I was hesitant to comment earlier, but. A pd has a lot of benifits that really do not equate to circulation of loop fluids.

    ability to generate high pressures
    ability to move copious ammounts of air/ and everything else

    All of the pd's I have experiance with : diaphram,piston,progressive cavity May have a better efficiency for the pump end than a centrifigal, but the power that drives the pd is where you will lose all that you gain. I also have not ever seen a well built small pd pump. For a residential application the flow rate and pressure required is relatively small in comparison to "market ready pd's"
    The flow centers readily available for a residential application are allready variable drive compatible, or static power at 1/25 of a horsepower. It would be my position that the electric consumtion or efficency of a 1/25 of a hp circulator pump is allready form following function.
    Eric
     
  5. Designer_Mike

    Designer_Mike Member

    I was considering one for controlled flow to my solar panels or a wood boiler and be able to throttle the flow precisely.
    The more I think about it, with a standard loop or through the heat pump there would be no advantage since pumping too much water doesn't really hurt anything.

    Incorporating some aux solar or wood heating may lend itself to flow control only to try and maintain some thermal segregation but that is off topic and I still need to convince myself of the benefits before I try to convince anyone else:eek:
     

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