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Thread: VFD Savings

  1. #21
    Join Date
    Dec 2016
    Location
    Royal City, WA
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    199
    I do the well pumps for a 6,000 head dairy. They have 4 wells all about 600 ft deep. It pumps 500 gpm max. We have a 40 hp submersible on a Yaskawa drive, a 20 hp submersible on a drive, and a 10 hp submersible on a drive. The 40 hp is the primary pump and pretty much runs continuously between 55 and 50 hz. It is set to 60 psi. If it can’t keep up with demand, then the 20 hp sub comes when the system drops to 50 psi and then holds it at 55 psi. The 10 hp sub takes care of the half dozen residences and can be added to the feetlot drinking water system. This water system also provides the makeup water for the sewage system.

    The cattle’s water is also routed thru the plate chiller for cooling the milk. It takes about 50 Gpm for the plate coolers. I’ve also got a fourth well at the milking parlor. It was originally drilled to provide the employee drinking water. But it is just a backup well now. The only time it is used is if there is a power outage.the milking parlor had an backup generator to keep the milking process going. Then this well is run off the generator to provide cooling water to the plate coolers. Cows have to be milked regardless of the power working or not.

  2. #22
    Join Date
    Jun 2003
    Location
    NE (9.1 miles @5.07 Degrees from Winged Horses)
    Posts
    9,942
    FWIW

    The motor is running at 30.3 KW with a PFC installed and corrected to .93. Motor label indicates a PF of .84. The two 6" Clay valves dump into a 12" line. They can use fresh water to flush with if they have to. My SEWAG then would be that a 40 HP would be close to meeting the day to day needs.

    I installed a 100 HP VFD last year. There is no room for that size of equipment in this building. No room for the existing PP for that matter.

    Thank you to all.
    Tom
    TBLO

  3. #23
    Join Date
    Apr 2006
    Location
    Springfield, MA, USA
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    3,231
    If I understand things, you have a 100 Hp motor running at about 40 Hp, pumping with an output pressure of 96 psi, followed by pressure reducing valves that get the pressure down to 53 PSI.

    Making the motor smaller might give you a little bit of savings; if you have a same speed motor, than a 50 Hp motor would sill use 40 Hp and pretty much use the same power input, possibly _slightly_ more efficiently.

    Changing the pump or pump speed so that the output pressure drops will give you more savings. The pressure reducing valves are converting mechanical power into heat, and if you can reduce the pressure on the input side of the valves you will reduce this heat production. If you have 40 Hp of mechanical power upstream of the valves then you only have about 23Hp of mechanical power downstream of the valves, with 17 Hp going into heat.

    -Jon

  4. #24
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    Jan 2016
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    Quote Originally Posted by winnie View Post
    If I understand things, you have a 100 Hp motor running at about 40 Hp, pumping with an output pressure of 96 psi, followed by pressure reducing valves that get the pressure down to 53 PSI.

    Making the motor smaller might give you a little bit of savings; if you have a same speed motor, than a 50 Hp motor would sill use 40 Hp and pretty much use the same power input, possibly _slightly_ more efficiently.

    Changing the pump or pump speed so that the output pressure drops will give you more savings. The pressure reducing valves are converting mechanical power into heat, and if you can reduce the pressure on the input side of the valves you will reduce this heat production. If you have 40 Hp of mechanical power upstream of the valves then you only have about 23Hp of mechanical power downstream of the valves, with 17 Hp going into heat.

    -Jon
    the 40 hp includes the pressure drop losses
    which are substantial

    valve drop 43 psi ~ 100 ft hd
    if we assume piping losses at 25 ft hd and assume pump eff at 0.7
    40 = Q x 125 x 8.34)/(33000 x 0.7)
    Q ~ 900 gpm

    if valve drop is gone
    P = (900 x 25 x 8.34)/(33000 x 0.7) = <10

    so removing the valves (reducing their drop) changes hp from 40 to 10
    huge savings 200 kwh/yr

    need pump curve
    need system curve

    pump should be sized for ~ 1000 gpm at system losses and valves used to trim 10 ft hd or so vs the current 100

  5. #25
    Join Date
    Sep 2008
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    UK
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    Quote Originally Posted by ptonsparky View Post
    FWIW

    The motor is running at 30.3 KW with a PFC installed and corrected to .93.
    The question is about VFD savings. You can't normally add PFC to the motor side of a VFD.
    Si hoc legere scis nimium eruditionis habes.

  6. #26
    Join Date
    Jun 2003
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    Quote Originally Posted by Besoeker View Post
    The question is about VFD savings. You can't normally add PFC to the motor side of a VFD.
    We added the PFC a few years ago to help with utility billing. That PFC unit will disappear if a VFD is ever installed. This thread is related to another I had about power readings on my Fluke 43B. The trick, as you have suggested in the other, will be to add PFC and make it all work with whaterever harmonics I have or will introduce.
    Tom
    TBLO

  7. #27
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    Sep 2008
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    Quote Originally Posted by ptonsparky View Post
    We added the PFC a few years ago to help with utility billing. That PFC unit will disappear if a VFD is ever installed.
    Good man!

    Quote Originally Posted by ptonsparky View Post
    This thread is related to another I had about power readings on my Fluke 43B. The trick, as you have suggested in the other, will be to add PFC and make it all work with whaterever harmonics I have or will introduce.
    Yes. Detuning is, in my experience, is generally required. To somewhat lower than fifth harmonic.
    Si hoc legere scis nimium eruditionis habes.

  8. #28
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    are the valves automatic?
    what controls them?

    what is the avg gpm?

    it looks like the pump can be turned way down
    maybe to 10-20 hp
    to reduce pressure from 125 to 25 ft hd (same flow)
    sqrt(25/125) = new/60
    new = 27 Hz, you may have issues that low

    need pump and system curves before anything is done
    it appears poorly engineered now, you do not want the same result after the changes

  9. #29
    Join Date
    Dec 2016
    Location
    Royal City, WA
    Posts
    199
    In post #22, Ptonsparky indicated that the valves were clay valves. I’m going to assume he meant that they are Cla-Val brand automatic control valves.

    https://www.cla-val.com/waterworks

    I have used Cla-Val, Singer, and Nelson automatic control valves. Depending upon the pilot controls, they can be a simple on-off, pressure reducing, ordsure sustaining, flow control, or a number of other function control valves.

    it sounds like in this application, the Cla-Val is being used as a pressure reducing valve, however we Do not know that for a fact. We do know that because the Cla-Val is introducing a restriction in the discharge, the Pump curve is moving to the left, and consuming less horsepower than FLA.

    Motor FLA, can be reduced mechanically by restricting the discharge of the Pump, or it can be reduced electrically be changing the speed of the pump. Either method changes where on the Pump curve the pump is operating.

    my SWAG is that there might be a maximum amperage savings of 10% by installing a VFD and eliminating the control valves, it would make much more sense in the long run to replace the pump and motor with a more properly sized one.

  10. #30
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    what we don't know is everything
    flow or pressure control?
    manual or automatic?
    pump curve
    system curve
    flow?
    valve position? 0% open 50? 100?

    really all the stuff we need

    they could be throttling the valve to regulate flow
    he says in the op that they are prv's, imo self regulating
    the high dp is just a consequence of poor sizing
    if the valve is fully open a vfd won't help

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