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  1. #1

    Constant Air Volume Basics

    New to the field, I want to confirm my understanding of a Constant Air Volume (CAV) system. If an air handler is not attached to a VFD, then it is safe to say it must be CAV? What if I say there are no VAVs/VVTs downstream?

    The system I am picturing has a packaged unit ahu with supply air ducted directly into the conditioned space which is a warehouse. Likewise, a return duct brings the air back to the AHU.

    Thanks!

  2. #2
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
    Posts
    4,531
    you are correct.

    no drive or igv's (inlet guide vanes) or some other 'air restictive device' and you have a constant volume system.
    "If you pull one more stunt like you just pulled with Tommy, you won't have to get on a plane because I will personally kick your ass from here to Korea!" - Best of the Best

  3. #3
    Join Date
    Aug 2009
    Location
    hazzard county md
    Posts
    173
    i beleive on some large commercial rtu's that are cav you can have turning vanes on 90's. also i have seen freq drives(vfd) on some. i may be wrong tho. always thought cav was fans always run and has reheats/vav's to condition spaces or area's. just my 2 cents tho.
    I need some free-zone in my compensate line.
    I am just a cog in the wheel.

  4. #4
    Join Date
    Mar 2003
    Posts
    7,326
    Its about the air delivered to the conditioned spaces. No vav boxes, mod motors or whatever control you think of as modulating, its constant volume, UNLESS it uses some sort of pressure reference and a vfd. VAV is what it is, Variable Air Volume delivered to the space. in some systems, vav uses a constant volume air handler and a bypass. in some constant volume systems, they use vfd's and airflow stations to measure airflow and keep it constant, while ramping the fan to account for things like filter loading, or belt loosening.

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