Pump Selection for Non-Pressurized System

Discussion in 'General Discussions' started by Cadman, Dec 5, 2018 at 10:37 AM.

  1. Cadman

    Cadman New Member

    Hey Guys,

    I'm at the point of selecting a flow center for my DIY geo install and wanted a gut check before pulling the trigger.

    I have a 5 ton, single stage Bard HP, and just finished backfilling 6 horizontal slinkies (6x 600' 3/4" loops in parallel).

    The HP literature recommends a minimum of 15 GPM, and has a drop of 18.7 Ft of Hd at that rate.
    With 20% methanol, the CM worksheet puts me at 10.8 Ft of Hd for the loops. All six loops come through my slab and are headered mere feet away from the HP and planned FC location.

    My preference is for a non-pressurized FC, and I really like the B&D QT setups. I was hoping to get away with one 26-99 pump but I think that'll be too marginal (the Reynolds number is right at 2500). I'm now leaning towards a two pump unit with a pair of 26-99's. I see I can get one of these for just shy of $1k; a few hundred bucks more than the single pump. Think that'll do the job?

    Incidentally, I do have a good-used pressurized FC I was given that has a pair of 26-116's, but I've read they're power hogs. Perhaps I could sell that to raise a few bucks towards the QT.

    Any thoughts or advice appreciated.
     
  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    yes, non pressurized is the way to go, and the goal is 1 pump, and to make it a 26-99. Whenever I see a 26-116 in a geo system, I know that the designer/installer was clueless about efficiency and not evolved.

    WHAT IS YOUR ANTIFREEZE?
     
  3. Cadman

    Cadman New Member

    Hi Doc, anti-freeze is 20% methanol.
     
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome!
    If a single 26-99 is marginal I would buy the twin 26-99 and see how it performs with a slightly lower reynolds number. If it works you are home free with a 100% back up pump. If not run both and you are covered.
    Eric
     
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You get about 12 gym with a single 26-99, 16 gpm with a dual 26-99 flow center.
     
  6. Cadman

    Cadman New Member

    Eric, that's what I was thinking, too, though I was worried about the drag of a second pump. However, since these are both 3-speed units, I could always dial both down in tandem and play around a bit.

    Doc, thanks for the numbers. Always good to have a second set of eyes on the figures.

    It looks like both the Geo-Flo and QT centers are priced about the same, and use the same pumps. (QT 2-230QFC-G, for example) Anyone have experience on choosing one over the other?
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    We are using variable speed pumps (Groundfos 32-140) even on single or dual stage compressor units, since they run much more efficient, and their pressure curve is right between the 1 and 2 pump 26-99 solution. More expensive, but worth it for me. A single 32-140 would get you about 13.5 gpm, and use about 190 watts running at full speed.

    With dual stage heat pumps, the 32-140 would slow down when the compressor is in 1st stage (about 90% of the time) and then use between 35-50 watts.
    On the upper end, I rather "starve" the heat pump and use less flow, then overpaying for pumping power.

    Thus in my own house, I have a single 26-99 for a 6 ton w-w heatpump. requiring 18 gpm, is happy with 12 gpm. All relative.
    I know, the shoemaker runs around barefoot! Did not have time to change it out. Customers first....
     
    Cadman and waterpirate like this.
  8. Cadman

    Cadman New Member

    Well guys, I guess we'll see how it goes; thanks for the advice. I scored a deal last night on a QT FC with cosmetic defect- dual 26-99's. Planning on getting the system online by the end of the month if all goes well. Now to build the manifolds....
     

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