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  1. #1
    Join Date
    Mar 2005
    Posts
    5

    Fan-powered VAV's with a ducted return

    Looking to put up a small office building. We are looking at fan-powered VAV's (parallel type) and the tenant is requesting a ducted return.

    Question... since fan-powered VAV's grab plenum air for reheat.... will this work with a ducted return? Our plenum depth will be in the range of 6-8'. I've seen this work well in plenum returns but never with a ducted return system.

  2. #2
    Join Date
    Mar 2005
    Posts
    5
    sorry..i guess a bit more detail would help...

    I generally see fan-powered VAV's in a plenum return where the VAV's grab "tempered" plenum air (70F or so) in the heating mode before going through the coil. In lieu of VAV's without fans where the boxes heat 100% of the non-tempered air from the supply duct (55F or so).

    the ducted return would grab air direct from the office space via return grilles and be ducted directly back to the RTU.

    I'm a bit worried about pressure issues since the fan-powered VAV's are still grabbing plenum air even though the main RTU has a ducted return.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,058
    hvactech0, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

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  4. #4
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    Acoustical ceilings are not much of an air/ pressure barrier

    So they should work BUT why the ducted return in the first place?
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  5. #5
    Join Date
    Mar 2005
    Posts
    5
    Quote Originally Posted by genduct View Post
    So they should work BUT why the ducted return in the first place?
    good question.... we have a very large plenum in this building 6-7' and the user is concerned about keeping the air-stream clean. They also have a corp policy about only using ducted returns though we are working verifying this.

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