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Location of Return Air Grille

Discussion in 'Commercial Mechanical Codes' started by north star, Nov 30, 2017.

  1. north star

    north star Sawhorse

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    @ ~ @ ~ @

    Greetings all !

    I have a small Occ. Group B - Office Addition to an existing bldg.
    I am reviewing plans for compliancy on a number of items.
    The plans ARE sealed & signed by an RDP.

    In this current set of plans, they have Supply Air Grilles in each
    of the rooms and spaces, but no Return Air Grilles [ in any room
    or space. ]........They DO however, have one 18" x 18" Return Grille
    shown to be installed in a small Supply Room.......This Supply Room
    DOES have a closeable \ latchable door with one 24" x 18" Return
    Air Grille in the door.

    I have never seen a design with Supply Air Grilles only to each room
    and essentially, ...no way for the Return Air to leave each "closed off"
    room.

    Comments ? Code Compliant ? Code Sections please !
    o_O

    @ ~ @ ~ @
     
  2. Builder Bob

    Builder Bob Sawhorse

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    stab in the dark from IMC -

    upload_2017-11-30_15-4-2.png
     
  3. north star

    north star Sawhorse

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    @ ~ @

    Thank you Builder Bob ! :D

    @ ~ @
     
  4. Paul Sweet

    Paul Sweet Sawhorse

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    A 3/4" gap below the door will transfer a little over 100 CFM. This might be adequate if the rooms are small.
     
  5. north star

    north star Sawhorse

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    & # & # &

    Thanks Paul for your input........The current set of plans do not indicate
    any "gaps below any doors"......Also, 3/4" sure does seem like very little.

    I have sent a Comment Letter requesting clarification of the design.

    # & # & #
     
  6. tmurray

    tmurray Sawhorse

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    The use of halls as a return air plenum is relatively common here. The only concern is that this approach can create dead air zones if the return air location is not centrally located.
     
  7. north star

    north star Sawhorse

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    $ * $ * $

    Thank you **tmurray** for your input as well !

    Another question for all:

    QUESTION: The current HVAC design is for all of the Return

    Air to go thru the Supply Closet Door and then thru a gypsum
    wall Return Air Grille back to the AHU.....Our staff has a
    concern of [ possible ] hazardous chemicals, cleaners, solvents,
    etc. being stored in the Supply Closet, and then being drawn
    in to the Return Air stream.


    Thoughts ? Comments ? Code violations ? Other ?

    Thanks !


    $ * $ * $

     
  8. Keystone

    Keystone Sawhorse

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    I would have the same concerns as North Star.

    System has to balance and without adequate return air from the supplied areas it's not going to be compliant.
    Options are; undercut doors to the design professionals requirement, wall or similar thru transfer grills to the common hall or provide ducted returns. While not the best approach from a comfort standpoint it will work when the balance calcs come back.

    The preference we see is undercut doors.
     
  9. tmurray

    tmurray Sawhorse

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    I would assume this system is designed for recirculation, but then again, that's only because it gets cold where I live and re-heating air is expensive. Is it just a supply closet or is there a mop sink/janitor's sink in there as well? If it's just for storing chemicals, I would not be overly concerned, but if the chemicals are used in that room, I would be concerned.

    As far as codes go, we use ASHRAE 62. This standard classifies air streams into four classes of 1 to 4 with one being the most clean. Offices have an air classification requirement of 1. A good example of a class 2 air is an elevator machine room. Generally you can recirculate any air stream to it's own classification or any higher classification. However, you can also recirculate class 2 air to class 1 spaces. I don't know that I've ever seen someone recirculate an elevator machine room into the regular air stream. I'm pretty sure these all are exhaust only, but someone could do it. The big driver here becomes indoor air quality through the workplace health and safety enforcement.
     
  10. Josh Koci

    Josh Koci Member

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    To expound on tmurray "chemical storage closets" per ASHRAE 62.1 are strictly exhaust and classified as class 4 air. However, if it is a "Janitors closet" it is class 3 air and can be recirculated as long as it does not exceed 5% of the outdoor air intake.

    I also agree with Paul on this. I don't have the drawings in front of me so I cannot speak directly to them, but from what it sounds like to me the doors could be undercut. We do this in smaller office spaces (<5-10 tons) as common practice. We do however, have a symbol specified for undercuts and a coded note specifically calling it out.
     
    tmurray likes this.

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