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Thread: VFD Savings

  1. #81
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    Quote Originally Posted by Ingenieur View Post
    most as in 20-25 as calculated
    Long way from 2 kW.
    Si hoc legere scis nimium eruditionis habes.

  2. #82
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    Quote Originally Posted by Besoeker View Post
    Long way from 2 kW.
    did you figure that out by youself?
    the vfd will need 2-3 hp more than a properly sized pump

  3. #83
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    Quote Originally Posted by winnie View Post
    Hmm. So you have at least 2 operating states. Normal where you are pumping via the pressure regulating valves to another tank, and 'flush' where you are pumping considerably more volume of water via much longer pipes.

    The pump and motor may be sized for the 'flush' operation. Then for normal operation the pressure regulating valves are used for control.

    The PRVs are in the system to provide control. The PRVs are analogous to linear voltage regulators. They function by creating a _variable_ resistance which gets adjusted to maintain the desired output. As linear devices any power not delivered to the load must be dissipated as heat in the device.

    As Ingenieur has calculated, if you replace the pump and motor appropriately, you could reduce the pressure 'upstream' of the PRVs, getting the same output simply with the valves more 'open' (lower resistance) dissipating less energy in the valves. This would save energy while keeping the PRVs for control.

    As has been pointed out, a VFD controlled motor could entirely replace the PRVs in terms of control. VFDs can be manually adjusted to get the required flow rate, or can be implemented with flow or pressure sensors to respond to changing conditions.

    The benefit to using a VFD is much greater flexibility. If you need higher pressure or flow for some operations, then you have that available. On the other hand, using the pump well below its design point might make the pump much less efficient. The losses in the VFD and motor will be small; the efficiency hit to the pump might be quite large.

    There are lots of issues here which could impact the end result...but you are talking some 20K of electricity used per year; getting an engineer involved is well worth your customer's money.

    -Jon
    the nice thing about the prv you can set them a few psi > desired output
    essentially no loss
    it does not sound like accuracy is critical

    I would have used 1/3 2/3 valves
    6" and 10" or 8"
    dp much lower
    set the 1/3 at 53 psi for control of the 420 gpm dp ~ 1 psi <1/3 hp
    when flushing press will drop, 1/3 goes full open, and the 2/3 will flow and control the balance ~1400 dp 2 psi 2 hp

    losses <2.5
    the vfd losses will be greater due to loss of eff
    how low freq for 420 gpm on a 2800 gpm pump?

  4. #84
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    Quote Originally Posted by Ingenieur View Post
    did you figure that out by youself?
    the vfd will need 2-3 hp more than a properly sized pump
    But those pesky energy wasting valves would be gone without the need to buy and install a new motor, new pump, new pipework, new cabling, new switchgear, and new protection devices.
    I'm sure you can figure it out
    Si hoc legere scis nimium eruditionis habes.

  5. #85
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    Quote Originally Posted by Besoeker View Post
    But those pesky energy wasting valves would be gone.
    sized properly 2.5 hp max for pump and valve

    and the vfd would lose at least 1/6 x 22 ~ 4 hp due to lower pump eff
    and another 1.5 hp running at < 20 Hz(may not move water)
    5-6 losses vs 2.5
    do the math

  6. #86
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    Quote Originally Posted by Ingenieur View Post
    sized properly 2.5 hp max for pump and valve
    Removed - zero.
    You are on a hiding to nothing.
    Si hoc legere scis nimium eruditionis habes.

  7. #87
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    Quote Originally Posted by Besoeker View Post
    But those pesky energy wasting valves would be gone without the need to buy and install a new motor, new pump, new pipework, new cabling, new switchgear, and new protection devices.
    I'm sure you can figure it out
    no new valves (would be better though)
    no new pipe
    no wiring only ol and cb
    no new swgr

    vfd
    wiring
    pressure xmtr
    pid controller

    100 hp vfd driving 100 hp pump running at 20-25 hp lol

    savings with pump vs vfd
    power 2-3k per year, possible more
    lower capital cost, 3-4k
    easier to operate and maintain

  8. #88
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    Quote Originally Posted by Besoeker View Post
    Removed - zero.
    You are on a hiding to nothing.
    vfd losses
    pump loss of eff
    >5 hp
    you have lost the plot
    one trick pony

    Quote Originally Posted by Ingenieur View Post
    sized properly 2.5 hp max for pump and valve
    Quote Originally Posted by Ingenieur View Post

    and the vfd would lose at least 1/6 x 22 ~ 4 hp due to lower pump eff
    and another 1.5 hp running at < 20 Hz(may not move water)
    5-6 losses vs 2.5
    do the math

  9. #89
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    I am closing this thread as the OP has indicated that they got the answers and information they were looking for and it was wandered far afield.
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