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Thread: Atrium

  1. #1
    Join Date
    Mar 2004
    Does anybody know how many cfm/person O.A. you need in an atrium (for a church) based on Ashrae Standard 62-2001?
    I am trying to figure it out but the calculation is so confusing...

  2. #2
    Are you looking at addendum N?

    I only have addendum N 2003 and ASHRAE 62 1999.

    Since the closest thing I have is ASHRAE 62 1999, I'll use that and hope they didn't change it too much,.. double-check.

    Is the church atrium a lobby-type space or an assembly-type space? Either way it's 15 cfm/person, but it changes ASHRAE's occupancy per 1000 sqft. That's OK though because ASHRAE allows you to use the anticipated occupancy load.

    Will this space be served by its own dedicated air handler?
    If so, you're done. If not, and the air handler that serves the atrium also serves other spaces, you will have to use the beloved "Z" formula for multiple spaces. Tell me if that is the case and I'll walk you through it.

    If you want to use ASHRAE 62 addendum N (the latest version),.. Throw all of this out and we'll tackle that.

  3. #3
    Join Date
    Mar 2004


    Thank you for your reply.
    If I look at ASHRAE 62-2001,, says for intermittent or variable occupancy, you can reduce the 15 cfm/pers. by half in your calculation, if the occupied time is less then 3 hours ( which is the case for this project). There is no mention of cfm per sqft.
    The atrium is an assembly type with 256 individual seats.
    When you say "but it changes ASHRAE's occupancy per 1000sqft" What do you mean?
    I want to put a dedicated AHU to be able to control this area separate from other areas.
    It all started with addendum "n". The calculation is confusing for variable occupancy... Can I just use above and just ignore "n"? Is "n" more restrictive or not?

  4. #4
    Most of the time N is more lenient actually, in terms of how much outside air you are required to bring in. But I'm still learning N as well and I'm not sure how intermittent occupancy affects N.

    Anyway, what I meant by "it affects the 1000 person per sqft" is that if you have no idea how many people are going to be in the space, ASHRAE provides you with an "occupancy per/1000 sqft" in their chart. Assembly rooms are estimated at 120 people per 1000 sqft and lobbies are estimated at 30 people per 1000 sqft. BUT, you don't need to use these since you have the seating layout.

    If you use 15 cfm per person and reduce the ventilation amount 50% due to intermittent occupancy, it sounds like you will be compliant with ASHRAE 62 2001.

    If the customer requires the very absolute latest addendums included,.. then we will both have to learn N... (grumble grumble,..stupid changes,...)

    Remember, ASHRAE is a standard, not a code. Usually ASHRAE standards exceed code, but don't let anyone force ASHRAE down your throat if it is above and beyond the International Mechanical Code.

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