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Thread: CFM Question

  1. #1

    CFM Question

    Hi' friends I need some help with this'''' If I has three phase AHU with this? only one cooling coil'' (268 v 270 v and 270 volt) ( 7 amp 7 amp and 8 amp)and ( 25deg DT) I need to know the cfm. any help please'''
    juan clavell santiago

  2. #2
    Join Date
    May 2004
    Los Angeles, CA

    Please be a bit more clear on future posts........

    Dear Oly77,

    At best your posted question is vague. You seem to have an air handler system, your measured volts at A, B, and C are 268, 270, and 270 respectfully, your measured amps at A, B, and C are 7, 7, and 8 amps respectfully, and your delta T is 25 degrees F (educated guess). You now what to know what your CFM is.

    “IF” you have a resistance heater, and “IF” the amps on the heater ONLY are the measured 7, 7, and 8, and the heater has a heat rise of 25 degrees F, then:

    CFM = BTU/Hr / 1.08 x TD

    CFM = (7 + 7 + 8) x (268 + 270 + 270) x 1.73 x 3.41 / 1.08 x 25
    3 3

    CFM = 7.333 x 269.3 x 1.73 x 3.41 / 1.08 x 25

    CFM = 11,649 BTU/Hr. / 27

    CFM = 431.4

    “IF” on the other hand, ANY of the above prerequisites are not correct, then the above CFM calculation is not correct.

    Hope this helps…..and next time please be a bit more clear as to what the readings are.

    Respectfully Submitted,
    John J. Dalton CM

  3. #3
    what you need to help me ?Dalton
    juan clavell santiago

  4. #4


    measure your rpm on the blower pulley, take static preasure readings on supply and return duct near ahu. plot readings on manufactures data sheets.
    This is not as accurate as a duct traverse but it will get you in the ballpark.

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