oversized pumps
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Thread: oversized pumps

  1. #1
    Join Date
    Feb 2010
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    Michigan
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    24

    oversized pumps

    I have several B&G 1510 series pumps 7.5hp and up. Most of them have a triple duty valve restricting the discharge by as much as 60%. What do you think would be more efficiant, turning down the impeller or adding a VFD to slow the motor.

  2. #2
    Join Date
    Feb 2010
    Location
    Cal
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    1,596
    Payback? The turndown of impeller will beat trying to recapture the install cost of a vfd without doubt. Your B&G can give you an exact analysis.

  3. #3
    Join Date
    Mar 2003
    Posts
    7,321
    really? i buy 7.5 horse vfd for significantly less than a g. you could put it in, set it up to recieve the start signal that is now starting the pump, and then run at a preset frequency. this would give you better energy use, and allow for future needs in the form of additional load required for a new unit, or for compensation of scaling of the piping. to me its a no brainer on these little pumps. to pull it apart, either cut the impeller or buy a smaller one would probalby cost damn near the same with a lesser result. maybe if we were talking 75 horse pumps, but even then, i doubt it. of course, i could be a complete idiot too, who knows? so, for example you buy the drive, remove the magnetic starter, install drive in its place, and set vfd to 40 htz. motor runs more efficiently. now you need to add a unit for a tenant space on that loop. you cut the impeller, and you got nothing. with the vfd, maybe you ramp it up to 48 hertz and call it a day. hmmm....

  4. #4
    Join Date
    Feb 2010
    Location
    Michigan
    Posts
    24
    I've also been leaning to the vfd. I like the soft start and flexability. I'm sure I can install a drive with a presure sensor to control it for less than $2000. Factor in the $500 rebate from the power company and it looks like the way to go. I've never considered the question before so I thought I'd ask before getting in a discusion with an engineer and a been counter. I had not thought of calling our B&G rep. for some numbers.

    Thank you

  5. #5
    Join Date
    Mar 2003
    Posts
    7,321
    dont need a pressure sensor to control it if you are doing constant circulation. what controls your pump now? you run it all the time, and choke back flow with the triple duty valve. take a reading of your delta p at the valve, and then open it up after you install the drive. set up the drive to go to a given frequency when enabled. the frequency will be set by you after you run the drive in hand to get to the desired flow. if you want to get fancy, you can install a dp station later if you are concerned about two way valves closing off.

  6. #6
    Join Date
    Feb 2008
    Location
    canton, ohio
    Posts
    26

    hdl

    i would go with a vfd,you save money on the power you use and you get better control.

  7. #7
    Join Date
    May 2004
    Location
    Rapid City, SD
    Posts
    7,414
    I'll throw another vote on the VFD. With out going too far into pricing here, but if you can throw a vfd in for $2k, that's cheap enough, and better for a multitude of reasons down the line.
    "If you call that hard work, a koala’s life would look heroic."

  8. #8
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,366
    What is this pump being used for:

    Chilled water?

    Hot water?

    Primary or Secondary loop?

  9. #9
    Join Date
    Feb 2010
    Location
    Michigan
    Posts
    24
    I can think of about 10 pumps off hand that are oversized. The smallest being 7.5hp largest at 40hp. Mostly constant volume, cooling tower, chilled primary and hot water primary. I only consider the presure control to cover myself for future variables. It can be tough around here to get aproval to modify something that has already been improved. Does not always make sense but I do not make the rules. (bummer)

  10. #10
    Join Date
    Mar 2003
    Posts
    7,321
    these kinds of actions, if properly applied will give your facility better performance, and increase energy efficiency, a win-win.

  11. #11
    Join Date
    Feb 2006
    Location
    SouthEastern Virginia
    Posts
    1,075
    Make sure the motors are vfd rated before putting a drive on them. If they are not, you are gonna spend some dough to do the whole package. Impeller trim may be more feasable if that is the case.
    It might get loud!

  12. #12
    Join Date
    Jul 2009
    Location
    Michigan
    Posts
    103

    VFD Everything

    If it is a pump or fan over 1hp and your application "at times" can use a controlled speed reduction for any reason by all means VFD it. If your application can handle a speed reduction near the 45hz range for a majority of the operating time the drive will pay for itself within the 1st year or 2 of operation.

  13. #13
    Join Date
    Jun 2004
    Location
    Milwaukee, WI
    Posts
    258
    VFD is will give you better payback as when you trim the impeller the pump will operate well below the rated HP. Whn you fall below 80 of the motors load the PF and efficency drops fast. This can cause other issues within the facility if you are being pentalized for poor PF.

    As for the motor type and age. IF you truely want to operate a motor safely o a VFD it must be stampoed NEMA MG1 P 31 rated. Inverter duty and/or rated does not mean a thing. There is no current criteria for tose naming conventions. Keep your wire lengths from the VFD to the motor as short as possible and you will be safe. Follow proper grounding practices for yoyur VFD installation and this will hjelp further. If you are concerned about bearing flutting goto WWW>Aegis-EST Dot Com. for a grounding ring.

    MTC
    Jeff F.
    www.vfdhelp.com
    VFD, HVAC Motors and Manufacture Assistance.

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