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  1. #1
    Join Date
    Oct 2002
    Posts
    970
    1.1 cfm per sq/ft..Am I far off for a typical office space?

  2. #2
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579

    Is that how you design duct systems? By the CFM/Sq foot method?

    Would it matter to you if the office space had no windows, single pane windows, double pane windows, blinds, tinted solar film or the windows faced south or perhaps north?

    That is just talking windows. There are many other factors that affect the heat load. I could post a rather long list here.

    What does the heat load have to do with the CFM? EVERYTHING! The load calculation for the Block Load determines the equipment size and total CFM. Then the load for each room determines how many CFM each room needs to handle that rooms load.

    If you perform the load calculation for each room and break it down to CFM/Sq foot it will vary all over the place for each room.

    Norm

  3. #3
    Join Date
    Oct 2002
    Posts
    970
    Would someone, other than Norm, tell me if 1.1 cfm/sq' is an acceptable RULE OF THUMB BALLPARK FIGURE to begin adjusting airflow to one freakin 10'x10' office with one 40 year old pencil-pusher with B/O and a drinking problem and no windows....thanks in advance














    Just kiddin, Normie

  4. #4
    Join Date
    Aug 2003
    Posts
    1,311
    if you have to ask....
    using rule of thumb is based upon your experience and judgement. 1cfm is typical for most aplications on interior zones but is the gentleman overweight? is there a high density of computers? etc. etc. i would say 1cfm per sq. ft. is typical of most interior zones but not all.

    for all you guys that bash the rules of thumb, of all the load calcs you've done computers rooms exempt. how many of them deviated drastically from the thumb rules? no one uses rules of thumb for system sizing, if they are a reasonable and prudent person. however the rules of thumb do work in many cases for small balancing and system checks, imo. if the rules of thumb were so far off base then there would be no rule of thumb. it would be nothing more than a wild a** guess.

    but back to the if you have to ask....then you probably should'nt be using the rule of thumb.

  5. #5
    Join Date
    Apr 2002
    Posts
    11,808
    Norm's right Sonc.

    The starting point is the CFM you get from the load calc. It is based on the sensible heat gain of the zone, and how cold the air out of the diffusers are.

    1.1 CFM per square foot IMHO would be a lot of air for an interior office space.

    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  6. #6
    Join Date
    May 2004
    Posts
    1,462
    Never mind.

    [Edited by plain spoken on 08-16-2004 at 04:25 PM]
    If all else fails....Try reading the directions!

    Tell it like it is and let the chips fall where they may.

    Any views or opinions stated here are strictly my own.


  7. #7
    Join Date
    Jul 2000
    Location
    Dallas,Texas
    Posts
    4,923
    It depends on a lot of variables. One is climate.

    1 cfm/ft² is pretty close for commercial office space in my area. It would probably not be sufficient for a church or restaurant.

  8. #8
    Join Date
    Oct 2002
    Posts
    970

    "but is the gentleman overweight?"

    Looks like a panda bear without the fur.

    Guys listen..I don't balance every building I get a service call in, and if I did I wouldn't be in service for very long, and as far as heat load, ya, I did that in trade school. The comp i work for has a division that takes care of that.. I'm just runnin' and gunnin'.. I didn't want to get into a "longest service wrench" contest (but I would win.. oh ya baby)



    [Edited by sonc on 08-16-2004 at 08:11 PM]

  9. #9
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579
    Originally posted by sonc

    "but is the gentleman overweight?"

    Looks like a panda bear without the fur.

    Guys listen..I don't balance every building I get a service call in, and if I did I wouldn't be in service for very long, and as far as heat load, ya, I did that in trade school. The comp i work for has a division that takes care of that.. I'm just runnin' and gunnin'.. I didn't want to get into a "longest service wrench" contest (but I would win.. oh ya baby)



    [Edited by sonc on 08-16-2004 at 08:11 PM]

    Actually Sonic, I have wrenches of various lengths so I have the right size for the job. In this case the correct wrench is a calculator.

    It is always best to use the right tool for the job.

    Norm

  10. #10
    Join Date
    Aug 2003
    Posts
    1,311
    see there you go Sonc..
    the gentleman is overweight, and has a drinking problem as you stated. i don't know about you guys but i get pretty warm when i've had a few. you can throw the rules of thumb out here. this guy sounds like his body could transfer much more btu's than the rest of us and still fell a bit on the warm side.

    anybody know where the ashrae tables are for the overweight folks at sedentary office work? is'nt it 250 sensible and 250 latent for normal folks. what about table for overweight office drinkers? even a calculation wouyld'nt work here, thats my take anyway. cause even the ashrae tables are based on those cursed typicals (rules of thumb). just giving you guys a ribbing here, not trying to start a mess.

    [Edited by hvac3901 on 08-16-2004 at 10:04 PM]

  11. #11
    Join Date
    Aug 2003
    Posts
    422

    As a rule of thumb......................

    .............. I don't use my thumb for a rule.
    For you guys that do "comfort balancing" as part of a service call or a design build concept where an independant balancer is not required, the rule of thumb doesn't matter.. (who holds you accountable?)
    As for me and my crew........ we'll get a P.E. to nail down the air changes per hour required. That's his job and if his pencil is dull he'll have to answer to it.

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