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  1. #1
    Join Date
    Feb 2007
    Posts
    999

    Power factor converter

    It has been suggested by my contractor (they don't install them) that a PFC would save on energy costs associated with heating/air conditioning systems and other household, motor driven appliances.

    Information on the web is highly technical so I couldn't get too good of a grasp on their workings.

    Basically, as I understood it, PFCs tend to deal with the reactive component of current, rather than the resistive part.

    Other than that, I'm kind of in the dark.

    Hoping the PROs can address this in terms of savings, effect on startup vs continuous run, and degree of surge protection (if any).

    Thanks.

    AM

  2. #2
    Join Date
    Jul 2008
    Posts
    53
    I've been reading up on your PFC question. As far as savings go, it would depend on what the power factor of your electrical service is. The lower your power factor the less efficient the electricity usage. The PF is rated between 0 and 1. Electrical companies want to see a PF of .95 or better.

    It seems that the biggest usage is in industrial complexes. For a homeowner, I'm not sure that there would be huge savings. But, it does seem that it would help reduce electrical "noise" that affects electronics. Also, the motors in your home would be more efficient. It will also help control voltage spikes from the transmission lines.

    Hope this helps, and if I've made any errors, someone will correct me.

  3. #3
    Join Date
    Jun 2006
    Posts
    294
    The "savings" to you would be infinitesimal; it only the reduces heating loss in the house wires leading to the unit, called the "I squared R " loss. So your benefit would be almost zero since the wiring resistance is negligible to begin with and decreasng the current by, say 15% would decrease this tiny loss a fraction.

    The only one to benefit would be the power company who has to drag that current over great distances.

    So bottom line DON"T DO IT unless you have stock in the power company and/or want to further enrich them.
    Last edited by sskzekeman; 08-02-2008 at 11:30 AM.

  4. #4
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    The only real savings is if you power company charges you for power factor, which I believe is not done anywhere for residential customers.

    paul

  5. #5
    Join Date
    Jul 2008
    Posts
    53
    Am I off on the electrical "noise" that can affect electronics? This is definitely a new subject for me.

  6. #6
    Join Date
    Feb 2007
    Posts
    999
    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

  7. #7
    Join Date
    Jul 2008
    Posts
    53
    This is a link to Reducing Power Factor Cost. It is a US Dept of Energy document. It does a good job explaining what the Power Factor is. Also, how "real" power, "apparent" power and "reactive" power are related.


    http://www1.eere.energy.gov/industry...fs/mc60405.pdf
    Last edited by S_Helton; 08-02-2008 at 02:44 PM. Reason: Link didn't show

  8. #8
    Join Date
    Feb 2007
    Posts
    999
    Quote Originally Posted by S_Helton View Post
    This is a link to Reducing Power Factor Cost. It is a US Dept of Energy document. It does a good job explaining what the Power Factor is. Also, how "real" power, "apparent" power and "reactive" power are related.

    Thank you. That was very interestiing reading. It explained PF with a very simple illustration.

    Two things that I got from the article, were:
    (1) operate motors near full load conditions.

    Interesting, since many motors in HVAC systems, whether multi or variable speed, operate partially or totally below their maximum rating. I'll make an assumption that ECM motors handle PF better. Right?

    (2) Install capacitors to reduce reactive effects.

    Since HVAC motors/compressors have beefy capacitors, I'm assuming that improves PF practically ($). Would most of the 'improving' occur during starting of motors? I wonder if any circuit boards in use utilize any components to improve PF.

    So, as has been stated re: PF: Forget about it.

    AM





    [URL]http://www1.eere.energy.gov/industry/bestpractices/pdfs/mc60405.pdf[/URL

  9. #9
    Join Date
    Aug 2003
    Posts
    225
    Wont make a difference – and it wont pay back (Cost / etc)

    Not unless your a heavy commercial or Industrial customer ? Or have “Super” Dirty Power and below .96? (I would check this first) before you make some china man a mint (well a few bucks) of money

  10. #10
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,031

    Mfg'ers ought be required to always list the PF

    Mfg'ers ought be required to always list the PF on the equipment tag, the power factor of their OEM motors. PF should be listed on all motors.

    My old Thermo Pride oil furnace has a split phase blower belt-drive motor with a high Service Factor (SF), I believe its SF rating is 1.25 or 1.35 above its full load amp rating, yet it operates well below its FLA rating. Meaning that it has a low PF!

    I wonder how the PF's compare on the Scroll compressors compared to the piston compressors, starting usually requires less force on a Scroll. Can anyone provide us with the PF Ratings on our present day HVAC compressors & blower motors.

    My old 1979 ARI text book says condensing units PF will be between 0.86 & 0.94, however we need the mfg'ers actual rating to more accurately figure the motor heat input for the ARI's condenser BTUH output rating method, that I occasionally use. - Darrell

  11. #11
    Join Date
    Aug 2007
    Location
    Atlanta, Ga
    Posts
    213
    We had one installed where I work...All I can say is I'm glad it has a money back guarantee......

  12. #12
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    since the power factor for a motor depends upon its load, how do you propose that the motor mfgr determine this?

    thousands of dollars for them to send a tech to measure for one!!!!
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  13. #13
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,031

    The Power Factor would be listed at a specific nominal load

    Quote Originally Posted by cem-bsee View Post
    since the power factor for a motor depends upon its load, how do you propose that the motor mfgr determine this?

    thousands of dollars for them to send a tech to measure for one!!!!
    The Power Factor would be listed at a specific nominal load. There would be a ratio from the rating in relationship to the actual load.

    A lot of ratings that are listed depend on a specific load condition: SEER; BTUH; amp draw; EER; RLA; FLA; Service Factor, & more.

    It would be of value to me to know what the base PF is.

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