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Thread: exhust fan

  1. #1
    Join Date
    Jun 2006
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    308
    i was working on an exhust fan, but unit pulling to many amps, so i dicieded t go with a hire horse power, hire rpm, and hire fla from 7.5 to 10 amp, ater all breaker is a 20 amp, i cleaned the blades bearing are fine, working fine, any commmernts

  2. #2
    Join Date
    Feb 2005
    Location
    Miami, Fl.
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    3,559
    I used to do the same thing as you, wrong, until I took this class (NCI) and learned.
    There is a reason that it is pulling too many amps. Did you check the ducts?
    When you replace an exhaust fan or make up air fan, you must know the cfm and static pressure that was there.
    Rpm, voltage, it looks the same, etc do not cut it.
    If you do not replace it with the same you are then changing what the fan was designed to do, and will effect the building envelope of the space, ac and/or heat, the overall comfort level of the space.

  3. #3
    Join Date
    Nov 2005
    Posts
    575
    please do not forget the moor S.F. rating, perhaps someone adjusted the pulley past the S.F. number thinking they could draw more airflow. The only way to adjust is with an amp meter.

  4. #4
    Join Date
    May 2004
    Posts
    11,999
    I think if you tested that you would find the majority of exhaust hood fans running 100% and the building in a negative pressure. With increased HP you lay the ground work for a sheave change and even higher rpm.

    Exhaust hood fans should not run 100%, more like 70 to 85%. Use the OAD's and make up fans to correct a negative air situation after checking all duct work (ac's too) for leaks.

    Although it is the American way.. Bigger is better or more is best... I am not a fan of oversizing. (no pun intended)




  5. #5
    Join Date
    Jun 2006
    Posts
    308
    by the way , the employees, do not want the airmake-up system running , becouse thay say that the air pushes the heat towrds them , , and the exhust is not is efficient,, not pulling air is it should.

  6. #6
    Join Date
    May 2004
    Posts
    11,999
    Then, without the make up running there is little to no air for the exhaust to pull out of the building. You must have make up air to replace the exhausted air or your building will be in a negative pressure and will not pull out smoke and grease.

    If the make up air pushes heat toward them you may want to concentrate on resolving that issue first. Start with adjusting your AC outside air dampers to 20% open. Fix the make up air so it is comfortable to the employees and slow down your exhaust fans.

    If you walk through a door from the outside does the air rush in with you or push against you to the outside? To properly set up a balance you should have the building slightly negative thus when opening an outside door the air should gently push its way to the outside.




  7. #7
    Join Date
    Nov 2005
    Location
    Milwaukee, WI
    Posts
    68
    is the motor turning in the right direction if it is running wrong you can draw high amps, but move little air, you need to know direction of fan.

  8. #8
    Join Date
    May 2001
    Location
    Kansas City
    Posts
    2,729
    I wouldn't listen to the cooks, they learn early on that if they turn off the make up air that the exhaust hood pulls cool air conditioned air to them.

  9. #9
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    May 2004
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  10. #10
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    Jul 2000
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    Guayaquil EC
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    10,326

  11. #11
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  12. #12
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    Feb 2005
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    OK<

    Counterclockwise, so "true"


    What I win?

  13. #13
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,326
    I checked an ILG upblast that I have at the shop and it's CW. I also found CW rotation secified in a Greenheck I&O manual.

    I've worked on a bunch of those you pictured....but never really paid much attention to CW vs CCW. What brand is that one?

    So far I've found two CW to your one CCW....what else you got Dave?

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