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how much air cfm for 10 tons of AC cooling?

for a server room that's about 20' square and very well sealed - solid sheet rock all walls and ceiling. Has a bunch of computers, pulling ~ 20,000 watts. As such if the existing AC setup turns off, the room will go over 100°F no problem. Looking to understand and be sure of how much airflow is needed per ton of AC cooling? I thought it was 300-500 cfm per ton is that true? So about 4000 cfm in order to make use of my outside condensers that are rated 10-20 ton ?

For ~4000 cfm how large of a duct plenum (length x width or diameter) would/should be made up, and I'm assuming round with round bends is better that square with 90° bends? thanks.

Comments

  • ChrisJ
    ChrisJ Member Posts: 13,562
    edited August 23
    ron said:

    for a server room that's about 20' square and very well sealed - solid sheet rock all walls and ceiling. Has a bunch of computers, pulling ~ 20,000 watts. As such if the existing AC setup turns off, the room will go over 100°F no problem. Looking to understand and be sure of how much airflow is needed per ton of AC cooling? I thought it was 300-500 cfm per ton is that true? So about 4000 cfm in order to make use of my outside condensers that are rated 10-20 ton ?

    For ~4000 cfm how large of a duct plenum (length x width or diameter) would/should be made up, and I'm assuming round with round bends is better that square with 90° bends? thanks.

    It depends on many things.
    Your sensible load vs latent load.

    Duct work sizing depends on what static pressure the equipment can tolerate as well as expected noise levels etc. I believe most would also require low ambient controls in this situation as well.

    How are you doing refrigeration work if you do not know the basics?

    @pecmsg Thoughts?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,881
    Almost all of your load is sensible. You'd start by figuring how much heat is being put into the room with 20000 watts (68,240 btu's). Add that to what the room needs with no equipment. And use that btu cooling number to figure out CFM you need. Then you can size the ductwork.
    steve
  • ron
    ron Member Posts: 253
    how many cfm of air per ton of cooling?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,288
    If you are the type of technician that uses the beer can cold method of charging the refrigerant system, then you would also use the 400 CFM per ton duct sizing method. But if you were to do the proper engineering you might find that since there is less latent load and more sensible load that the average residence, you might find a different number is better. How far off of the 400/ton will it be. I can't tell you that... I'm a beer can cold type of guy. LOL

    Coors Light for me!
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

    bburdGGross
  • ratio
    ratio Member Posts: 3,292
    With that kind of load, it sounds like a company data center, I'd be a little leery of depending on homemade equipment.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,288
    edited August 23
    There are systems specifically designed for server rooms. I think they are called Leibert Systems. They are usually more expensive than the standard stuff. https://www.vertiv.com/en-us/products-catalog/thermal-management/room-cooling/liebert-pdx-compact-dx-cooling-system-11-29kw/
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

    ratio
  • ron
    ron Member Posts: 253
    you guys went off the deep end, i just wanted some quick numbers to satisfy curiosity.

    should i factor in reynolds number to distinguish between laminar and turbulent to go along with sensible and latent heat calculations?


    ima head out now
    EdTheHeaterManGGross
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,664
    @ron you need to know your sensible to latent heat ratio to figure out the cfm.

    Normal ac is 400/ton. that is usually 80% sensible 20% latent

    Server rooms are different. And have less latent load and more sensible load
    ChrisJ
  • pecmsg
    pecmsg Member Posts: 3,339
    ChrisJ said:
    for a server room that's about 20' square and very well sealed - solid sheet rock all walls and ceiling. Has a bunch of computers, pulling ~ 20,000 watts. As such if the existing AC setup turns off, the room will go over 100°F no problem. Looking to understand and be sure of how much airflow is needed per ton of AC cooling? I thought it was 300-500 cfm per ton is that true? So about 4000 cfm in order to make use of my outside condensers that are rated 10-20 ton ? For ~4000 cfm how large of a duct plenum (length x width or diameter) would/should be made up, and I'm assuming round with round bends is better that square with 90° bends? thanks.
    It depends on many things. Your sensible load vs latent load. Duct work sizing depends on what static pressure the equipment can tolerate as well as expected noise levels etc. I believe most would also require low ambient controls in this situation as well. How are you doing refrigeration work if you do not know the basics? @pecmsg Thoughts?
    Some one went cheap on there server room!
    1st rule is a 65 - 75% backup. 
  • ratio
    ratio Member Posts: 3,292
    ron said:

    you guys went off the deep end, i just wanted some quick numbers to satisfy curiosity.

    There really aren't quick numbers. A Ductulator is a real think, but it only works when the assumptions you make match up with the assumptions the calculations were made with—like sensible/latent split.
    ChrisJ
  • ChrisJ
    ChrisJ Member Posts: 13,562
    ratio said:

    ron said:

    you guys went off the deep end, i just wanted some quick numbers to satisfy curiosity.

    There really aren't quick numbers. A Ductulator is a real think, but it only works when the assumptions you make match up with the assumptions the calculations were made with—like sensible/latent split.
    They don't know how to do the work and they want us to do it for them.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,664
    If you don't start out right you will end up wrong. Hey, that sounds like a Yogi Berra. Did I just make a goodie up??
    ChrisJGGross