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  1. #14
    Join Date
    Jul 2008
    Location
    Denver, CO
    Posts
    4,207
    I have heard of companies running motors without loads on them just to bring their PF down. But depending on if your PF is lagging or leading you may need a capacitive load rather than an inductive load to correct the PF.

  2. #15
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    Quote Originally Posted by Tiger93rsl View Post
    I have heard of companies running motors without loads on them just to bring their PF down. But depending on if your PF is lagging or leading you may need a capacitive load rather than an inductive load to correct the PF.
    What you are referring to is called a "synchronous condenser" It is a synchronous motor with an overexcited field and no load. They improve power factor like a capacitor. They were used in large industrial settings to do power factor corrections to a large system. I remember down at Bethlehem Steel (when they existed in Bethlehem) they had several substations with synchronous condensers. Looked funny seeing a 10' high open frame motor with no shaft coming out of the bearing blocks. Very effective but large and relatively high maintainance (brushes and all).

    http://en.wikipedia.org/wiki/Synchronous_condenser

    paul

  3. #16
    Join Date
    Feb 2007
    Posts
    999
    I've reconciled myself to the fact that a PF corrector is not a cost-effective way for me to save energy re my HVAC system.

    So, can anyone comment on how my existing PF (whatever it is) will affect my 2000 CFM ECM blower motor which will run mostly at about 1100 CFM on cooling, and about 800 to 1000 on heating (thinking in terms of longevity)?

    Likewise, how about a 4 ton Copeland scroll compressor running mostly on first stage.

    AM

  4. #17
    Join Date
    Jun 2006
    Posts
    294
    Quote Originally Posted by ampulman View Post
    Thanks everyone for your replies. Bottom line is---I forgot about it.

    I remember studying Ohm's Law in Physics class and all of the conversions including I^2 * R, but can't remember the specific reference.

    That being said, since we are dealing with AC rather than DC, Ohm's law per se doesn't apply; rather, inductive or capacitive reactance is substituted for pure R (resistance).

    So going back to my original post, can anyone explain what if any relationship exists between power factor and circuit reactance?

    Thanks.

    AM
    Power factor is, FYI, the cosine of the arctangent of the reactive impedance over the resistance.And the impedance Z is the vector sum of the resistance and the reactance

    Moreover, contrary to what you learned, OHMS law does apply to AC power, where

    I=V/Z

    AND I^2R losses are heating losses which are also valid for AC systems.

    Finally, stop worrying about longevity vs power factor. The Mfr of the equipment has already accounted for it in the design so that improving the PF would have a negligible affect on it . Moreover , to add to longevity ,your ECM will seldom work at the "design" full power condition anyway

  5. #18
    Join Date
    Jan 2008
    Posts
    85
    If you want to save on HVAC run costs with a modulating or multiple stage furnace or A/C, insulate the ductwork running through unconditioned or semi-conditioned areas. The losses there can be substantial.

    http://www.pubs.bnl.gov/documents/25288.pdf

    The duct delivery efficiency and loss graphs on the last several pages are a real eye opener.

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