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  1. #1
    Join Date
    Jun 2005
    Location
    The Gray Northwest
    Posts
    661
    I have an air handler that needs more air flow. The capacity was reduced by the installing contractor becasue of noisy air complaints. Now there's not enough air flow to heat the space. I'm getting very high discharge temps and high return temps but a cold space. The unit serves a high bay area and I need more air. The fan motor has a fixed, 4 belt "B" section sheave. I know the fan curve has the capacity for more flow but what I don't know is how to figure out what size motor sheave I need to get a 25% increase in air flow.

    Any pointers?

  2. #2
    Join Date
    Nov 2005
    Location
    Texas
    Posts
    1,628
    The formula is:

    RPM1 over RPM2 = PD2 over PD1

    Where RPM1 is the motor
    RPM2 is the blower
    PD1 is the motor sheave
    PD2 is the blower sheave

    Solve for ratio then multiply for % increase.


    Regards.......

    [Edited by gonefishing on 01-09-2006 at 07:44 PM]

  3. #3
    Join Date
    Aug 2003
    Posts
    1,311
    gone fishing

    you not gonna tell him about wether or not the motor has the room for it? hehe!

  4. #4
    Join Date
    Nov 2005
    Location
    Texas
    Posts
    1,628
    Nope, gotta figure if he reads fan curves
    he has an ampmeter

  5. #5
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720
    Originally posted by gonefishing
    The formula is:

    RPM1 over RPM2 = PD2 over PD1

    Where RPM1 is the motor
    RPM2 is the blower
    PD1 is the motor sheave
    PD2 is the blower sheave

    Solve for ratio then multiply for % increase.


    Regards.......

    [Edited by gonefishing on 01-09-2006 at 07:44 PM]
    Or...in an easier to remember form....

    RPM1 X PD1 = RPM2 X PD2

    Jogas

  6. #6
    Join Date
    Jun 2005
    Location
    The Gray Northwest
    Posts
    661
    Thanks fellers, you've saved my bacon. What's an amp meter? (tee hee)

  7. #7
    Join Date
    Dec 2005
    Posts
    424
    I thought the formula for rpm to static pressure is rpm2 new divided by rpm old that ratio times itself then times original static pressure gives you new esp.

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