Variable Speed Flow Center

Discussion in 'General Discussions' started by TheGreenGoblin, Mar 3, 2018.

  1. TheGreenGoblin

    TheGreenGoblin New Member

    We will be installing a 4 ton Geocomfort closed loop in our home this summer in Green Bay, WI - heating dominant. We're going through all the details with our installer and I'm questioning if the variable speed flow center is worth the additional $1,900 vs a non-pressurized single-speed Grundfos pump The installer provided me with the wattages and it seems like over the life of the unit it would be a wash even though the operating cost is cheaper/mo with variable speed.

    Is being able to see entering/exiting water temps and set flow rates worth the variable speed? Are there other benefits of variable speed that I might not be thinking of?
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    IMHO a variable speed pump for a single 4 ton unit is not worth it. Variable speed pumps really shine in multiple unit, varying usage applications. Your ewt and lwt and flow rates are easily gathered on your alternate non pressurized unit.

    Hope this helps
  3. TheGreenGoblin

    TheGreenGoblin New Member

    I will likely go with a non-pressurized unit. I should also add, we get a discounted electricity rate of 4.9 cents/kwh through our electric cooperative year round, making the cost to run the pump that much less. We have no plans to add an additional geo unit in the future.

    The figures our installer gave me on the two pumps:

    Variable Speed - 45w on low, 180w on high but said it should run on low 70-80% of the time
    Single Pump - 320w

    Over 25 years (if a pump lasts that long) I don't think I would make the $1900 back at 4.9 cents/kwh
  4. ChrisJ

    ChrisJ Active Member Forum Leader

    The single pump wattage sounds like a 26-116 which is only 10% more powerful then the 26-99 Grundfos pump. Learned from Docjenser.

    Hopefully the loop field can be designed to use the 26-99 pump.
  5. arkie6

    arkie6 Member Forum Leader

    Regarding the Grundfos 26-99 pump mentioned above, it is a 3 speed pump with a watt rating of 150 W on low and 197 W on high. If you can design your loop to work with this more efficient pump rather than the 26-116 pump, you will be money ahead.

    If you can keep your total loop head loss under ~21 ft-hd, then the 26-99 can flow at least 12 gpm on high which would be sufficient for a 4 ton heat pump.

    Here is the Submittal sheet for the 26-99 pump:
  6. TheGreenGoblin

    TheGreenGoblin New Member

    I'll be honest, I know nothing about pumps. The spec sheet I was given says Grunfos Magna 32-140.

    One correction from above, it's actually a 3 ton geo unit with a 4 ton pond loop.
  7. ChrisJ

    ChrisJ Active Member Forum Leader

    That is the variable speed pump, the single speed is the 26-99 or 26-116.

    The 26-99 I believe can be had with 3 speeds.
  8. TheGreenGoblin

    TheGreenGoblin New Member

    Thanks for the replies, I’ll go back to the installer and ask some more questions.
  9. arkie6

    arkie6 Member Forum Leader

    If you only have a 3 ton heat pump, you only need ~9 gpm (3 gpm x 3 ton = 9 gpm). The 26-99 pump can provide this amount of flow on high speed provided your total loop head loss is less than 23 feet of head. If the total head loss is less than that, you may be able to change the pump to speed 2 or 1 and save even more energy. Things that reduce head loss are larger diameter pipe, shorter lengths of pipe, more pipe circuits in parallel, and fewer 90 deg bends.
  10. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    1) a 4 ton system can (should) or must be designed to use only a single circulation pump
    2) $1900 premium for is a heck of a premium for a 32-140
    3) every 3-5 ton system can run on on a single 26-99
    4) My own 6 ton unit runs on a single 26-99
    5) Having said that, all new units between 3-5 ton we install now we put in the 32-140 pump. The higher pumping power of other pumps continued to bother me.We adjust the variable speed pumps to use between 39 watts in first stage, and a max of 100 watts in second stage depending on the wattage and loop system.
    6) variable speed system operate between 6-190 watts.
    7) your electric rate is very low, your monetary value might be different
    8) which is why a single pump at low speed might save you well, but not one which uses 320 watts. A 3 speed 26-99 should be all you need. If requiring more pumping power, then the loop and piping should be redesigned.
  11. TheGreenGoblin

    TheGreenGoblin New Member

    I talked to our installer more and I misunderstood part of what he quoted. It’s not the pump that’s so much more $ but the variable speed panel mount flow center. Worth the additional $?
  12. arkie6

    arkie6 Member Forum Leader

    The Grundfos Magna 32-140 variable speed pump and associated controls, valves, etc., combine to make up the variable speed flow center. For a single 3 ton heat pump, the best cost vs. benefit option would likely be a single pump flow center using one (1) 26-99 pump. The newer 26-99 has three speeds that can be selected based on the flow needs of your loop, but it is not continuously variable speed like the 32-140.

    This is an example of the single 26-99 pump non-pressurized flow center:
  13. TheGreenGoblin

    TheGreenGoblin New Member

    Thanks for the explanation, that helps!
  14. TheGreenGoblin

    TheGreenGoblin New Member

    I’ve decided on the single pump and confirmed with the installer that he’s using the 26-99. At our current elec rate I can’t justify the added expense for the variable speed. Thanks again everyone for the info.

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