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  1. #1
    Join Date
    Sep 2019
    Northern Ontario
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    Return fan needed on meeting room AHU?

    Existing rooms were converted to our main meeting room in the 1980's. Approx 30' x 40' seats 180 people. It is an indoor ahu (Sheldons 4LP-2000) that consists of a supply fan and a heating coil and a cooling coil. Looks to be around 4000 cfm. There are 3 sets of dampers. Outdoor air inlet, mixed air and return air exhaust to outside. Original plans don't show a return fan.

    Fast forward to today. There is a return fan in place now, installed in 80's or 90's. The ducting at this return fan, seemingly do to limited space issues, is way undersized. 3 x 10" round flex ducts for that 4000 cfm. This is causing lots of noise and slow temperature response.

    Generally speaking, when would you install one or not? I ask because it was not originally spec'd and our cafeteria has almost the same system but no return fan.

    Thank you for any responses,

    Currently looks like this setup
    Name:  AirHandlingUnit_FreeCooling-700x650.png
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    Last edited by Gdh33; 09-20-2019 at 08:02 PM. Reason: Added photo

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