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VFD pump versus bypass valve

Hvacman Member Posts: 159
Both will do the job but I think you will find the drive to be a more expensive way to go. Even though the cost of drives have dropped and you will see a modest energy savings from using a drive I think the BP valve is the way to go.


  • Jack Smith
    Jack Smith Member Posts: 53
    VFD pump versus bypass valve

    Just wondering what your opinions are on versus the other. 24 unit apartment house, constant circ., zone valves on baseboard, mod/cons, outdoor reset, supply and return temp. sensors, one space sensor for reset. More information needed? Pump is 1 1/2 hp B&G.
  • Jack Smith
    Jack Smith Member Posts: 53

    Cost is always a concern. Not so much as reliability. If reliability is comparable, would electrical savings make up initial instalation costs?
  • Brad White_203
    Brad White_203 Member Posts: 506
    Cost Versus Value

    Most VFD applications below code threshold are rebate eligible at least here in MA. Your local utility would have more information.

    You have to know and crunch the numbers, what your current actual draw is (brake HP or kW, not nameplate HP). How many hours of operation at what settings.

    VFD's are way down in cost these days but if you are going to install a VFD, the motor of the pump has to be inverter-compatible which means a motor change if not a pump change.

    This is what I would do: Figure out your actual flow rate and head which satisfies the building load. Be as accurate as you can. If you have a current pump curve, figure the amps, delta-P and know the impeller size (dead-head the pump momentarily to determine the no-flow, maximum head. This will tell you the pump impeller size if you have a good curve from the manufacturer.)

    Then, select an ECM motor pump, such as by Wilo or Grundfos. These have, as features on the right models, integral Delta-P sensors. Dial-in and enjoy the savings.

    I would hope that your control valves are two-way and not three way. If three-way, the use of Delta-P becomes moot.
  • Hvacman
    Hvacman Member Posts: 159
    I forgot...

    I forgot the VS pumps now available... Others can tell you application info, I peeked at the Wilo site but the range of products is enormous. I've not used them but are an interesting option to me vs. a "normal" pump with separate VFD. See post below for payback ideas, will depend on many factors.
  • tim smith
    tim smith Member Posts: 2,738
    I am with Brad, Wilo or Grundfos, Delta p. 3 way valves will

    mess up the savings so forget it if 3 way valves. I think perfect application. Other way is 3 phase 1.5 hp motor and maybe Danfoss vfd but this gets expensive along with a pd transducer. Go the ECM route and will be a winner.
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