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  1. #1
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    Cooling tower fan minimum speed

    In general, on a forced draft cooling tower application, do you need to set a minimum speed in drive for motor cooling purposes?
    For example, newer tower and sealed motor run off of drive's PID control on 100 ton chiller.

    I worry that a minimum speed might throw the PID off due to the delay and hope that the PID will keep it from staying at low speed. Low load, low ambient would be a worst case scenario I imagine.

  2. #2
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    I'm not an expert on the subject, but its my understanding that all motors have a minimum speed you need program in the drive.

  3. #3
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    X2 and sometimes on tower inverter duty motors, it might be on the motor label.
    UA Local 32

  4. #4
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    Quote Originally Posted by RezAtDorsia View Post
    In general, on a forced draft cooling tower application, do you need to set a minimum speed in drive for motor cooling purposes?
    For example, newer tower and sealed motor run off of drive's PID control on 100 ton chiller.

    I worry that a minimum speed might throw the PID off due to the delay and hope that the PID will keep it from staying at low speed. Low load, low ambient would be a worst case scenario I imagine.
    Look up break out speed, thermal load, carrier frequency, stall speed and start load.

    Typically we never run a tower fan slower than about 12hz, this is a moving target for some systems.

    Give the PID plenty of integration time. you'll be fine. Don't forget to search for critical frequencies if the tower is on islation bases.

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  5. #5
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    You need a minimum speed so the motor will cool it's self. If it isn't on the motor the maker or seller should be able to tell you.

  6. #6
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    Thread Starter
    I watched the drive run at mild ambient, medium load conditions and it didn't stay under 12hz for very long and never stayed low at all. The condenser temp went up fast enough to keep the fan going at a good clip.
    I may set a 12hz min and adjust PID.
    Also need to check for resonance freq, thanks

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