Results 1 to 10 of 10

Thread: Duct Size Help!

  1. #1
    Join Date
    Oct 2001
    Location
    New Jersey
    Age
    71
    Posts
    83
    Rep Power
    0

    Duct Size Help!



    I am installing a 5 ton package unit. The supply air duct size is 12X19. Evap fan 2000 CFM. I plan on using a 24' horizontal duct with 10" round takeoffs. I would like to use 7 of these. The recommended velocity is 1000 FPM in trunck duct and velocity in branches not to exceed 800 FPM. My question is, am I in the ballpark here? Thanks for any input!



  2. #2
    Join Date
    Jan 2002
    Location
    Austin, Texas
    Posts
    718
    Rep Power
    23
    In just a wink (I didn't particularly check it out) I found this online duct size calculator...


    http://www.aes.uconn.edu/tools/airductm.htm

  3. #3
    Join Date
    Oct 2001
    Location
    New Jersey
    Age
    71
    Posts
    83
    Rep Power
    0
    Thanks very much...I'll check it out right now!

  4. #4
    Join Date
    Oct 2001
    Location
    Nottingham UK
    Posts
    5,733
    Rep Power
    51
    Your 12" x 19" main duct will give you a velocity of 1263FPM which is in excess of the recommendations. To obtain the required maximum velocity your duct needs to be 12" x 24", or slightly larger to reduce resistance.

    The branch duct size of 10" will give you a velocity of 377FPM within each branch if you balance the system correctly.

    You do not say what the maximum external static resistance is for the fan so I can't say if the amount of ductwork you are planning is within spec.

    Hope this helps

    Frank

  5. #5
    Brian_UK's Avatar
    Brian_UK is offline Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
    Join Date
    Mar 2001
    Location
    Dorset
    Age
    76
    Posts
    11,192
    Rep Power
    60
    I find this question rather worrying....

    An installer of a ducted system who is unable to calculate the simple basic facts of his proposed system.

    Or am I wrong and he is fitting his own equipment and praying that it will do the job correctly?

    Call me fussy, but.....
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

  6. #6
    Join Date
    Oct 2001
    Location
    New Jersey
    Age
    71
    Posts
    83
    Rep Power
    0
    Your absolutely right Brian...I find it worrying myself. Please understand this is a factory which is under constant changes. Room sizes change, ceiling heights lower, newer equipment can run hotter or cooler depending on the technology. Equipment can be added in a heartbeat or the entire way we do things can call for equipment that we haven't even seen yet. With all this, I have to compensate for a 100 ton R-12 system that was shut down this year by me cause I refuse to pump R-12 through the building. This is what goes on in my world! It's something that takes a little more then a calculator to solve. I wish "simple basic facts" could be applied here, but they can't. Thanks for your replies guys.

  7. #7
    Brian_UK's Avatar
    Brian_UK is offline Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
    Join Date
    Mar 2001
    Location
    Dorset
    Age
    76
    Posts
    11,192
    Rep Power
    60
    I wish you all the luck in the world buddy, it sounds like you nedd it
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

  8. #8
    Join Date
    Feb 2001
    Location
    Tampa Florida
    Posts
    1,086
    Rep Power
    25
    If it is a factory, then I wouldn't worry about velocity limitations related to noise considerations... not on returns, supplies, nor registers. Be sure to check those requirements on your duct-a-lator, they may not apply.

    On the other hand, I would worry about delivery velocities required from the registers... and, of course, design total static pressure considerations. Depending upon your ceiling height, you may have to deliver the air at higher velocities.

    I think you might have been been precipitate in condemning an R12 central system. But I don't know your situation.

    It just doesn't sound like you have a simple package unit solution here, that stands a chance of adapting to what you are facing.

  9. #9
    Join Date
    Oct 2001
    Location
    New Jersey
    Age
    71
    Posts
    83
    Rep Power
    0
    Have been battling this situation for the last 25 years or so. Two phase motors on the old R-12 system is one of the deficiencies of the system not to mention open drives, one recip and one radial. I am really relieved that I have made the choice. Package units and splits have been added over the last 3-4 years and another this year is almost finished. I seem to hold temp okay except when the plant goes on 24 - 7...It never gets a chance to cool down. It's gonna be an interesting summer for me!

  10. #10
    Join Date
    Feb 2001
    Location
    Tampa Florida
    Posts
    1,086
    Rep Power
    25
    LOL! I understand. Good for you!

Similar Threads

  1. Tool for flexible duct
    By Peter_1 in forum Air Conditioning
    Replies: 10
    Last Post: 27-06-2011, 11:28 AM
  2. which is the correct size for this conenser
    By 27143721 in forum Fundamentals
    Replies: 4
    Last Post: 09-06-2006, 08:57 PM
  3. Evaporator design: minimal channel size.
    By DaBit in forum CPU Overclockers
    Replies: 9
    Last Post: 05-06-2003, 03:47 PM
  4. Urgent!!! S.O.S. - nozzle size
    By herefishy in forum Fundamentals
    Replies: 3
    Last Post: 25-05-2002, 10:29 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •