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  1. #1
    Join Date
    Jul 2005
    Location
    Steeler country
    Posts
    69

    Noise and Drafts

    I need some thoughts on this.
    We have an air handler thats designed to deliver 30K cfm.
    But we're having problems with noise and drafts.
    We had to bypass our speed drive on this unit, so we're delivering full volume
    as far as I know.
    What info do I need to gather to resolve the issue of noise and drafts or do we just let it go until our speed drive is back on line.
    Would like to know for future reference.

  2. #2
    Join Date
    Sep 2007
    Location
    Michigan
    Posts
    290
    Quote Originally Posted by techreptdh View Post
    I need some thoughts on this.
    We have an air handler thats designed to deliver 30K cfm.
    But we're having problems with noise and drafts.
    We had to bypass our speed drive on this unit, so we're delivering full volume
    as far as I know.
    What info do I need to gather to resolve the issue of noise and drafts or do we just let it go until our speed drive is back on line.
    Would like to know for future reference.
    If it's designed to move 30k with strictly VAV boxes I'm not sure where the excess air is going, a VAV will only pass what it's set to allow. If box set points were increased (overridden) to reduce static in the duct, you would then likely be exceeding the design values of diffusers, boxes, and the design amount of air flowing though mains/branches, it's probably flowing through the duct with the least resistance and exceeding the FPM design. Had an 11floor building where the static sensor was reading a few tenths off and system was generating noise just from that.

    There isn't much you can do besides put everything into full cooling, which brings in more problems. The reheat is not designed to give a comfortable discharge temp at the box with the full cooling CFM, and the reheat system probably won't support the whole building wanting heat at the the same time under a loss condition. If it has enough capacity, it's going to feel drafty because of the rise.

    With 30k summer you might only need 15k winter, that's a lot to get rid of, could install a temp bypass into the return. Connect the damper to the VFD output from your DDC control, and make the actuator Reverse acting. I'd get the VFD replaced/repaired ASAP. The customer is suck pretty much, just my two cents.
    "Yeah I can figure out whats wrong with it, but you were here first and there isn't room for two, plus it's cold up here, I'll be in the van"

  3. #3
    Join Date
    Oct 2001
    Posts
    6,966
    count up your filters and cut pieces of cardboard the same size for half of them to start.place them on every other filter(like a checkerboard) and check your amps and the air on the furthest box in full cool....remove/add one at a time to add/drop air till the VFD is back on-line...try to get 50% of your tagged rating on the motor(all the boxes in cooling MAX air calling)that would be almost satisfied with the boxes floating between minimum and going to cooling and more air with about 1" of duct static...i'll PATENT this one if it gives you temporary results for the...noise?
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  4. #4
    Join Date
    Jun 2003
    Location
    Cracker Country
    Posts
    62
    Slow down the Blower Wheel if u are going to be running in by-pass for sometime.If u have a V/P Sheave on the motor open it up a few turns and check your static.If the Sheave is fixed , figure out the pitch diameter u need for the original fan RPMS and swap it out for a smaller P/D. Is this unit an a BAS were u can see all the data u need.Like KEEP said, your boxes will be chocking back to heat CFM,s set point and your static and cfm,s will be too high.Hope this helps ya.

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