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  1. #1
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    Static pressure calculation for aircon duct



    Hi i am new here.
    can anyone provide me the formula to calculate the static pressure for the aircon ductwork.


    Thanks



  2. #2
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    Re: Static pressure calculation for aircon duct

    Measure static pressure with a u-tube manometer
    static pressure = density x gravity x height

    if water in manometer
    density = 1000 kg/m3
    gravity = 9.81 m/s2
    height = difference in manemeter levels, meter


    typical static pressures in aircon duct
    0 to 400 Pascals

    Pressure drop due to friction

    The correct equation to use is Darcy-Weisbach.

    dP = (1/2) density f L V^2 / d
    density of air at sea level = 1.2 kg/m3
    f = friction factor (typical f = 0.019 )
    L = duct length, m
    V = air velocity, m/s (typical = 5m/s)
    d = equivalent diameter, m

    This pressure drop due to friction results in a drop in static pressure.

    For your info:

    Dynamic pressure = (1/2) density V^2

    note the similarity to the dp equation.

    Duct Fitting Pressure Drop

    pressure loss = C (1/2) density V^2

    C is the loss coefficient for the fitting
    note that it is just a factor on the dynamic pressure

    Simple lookup

    There are many table published that give a simple lookup. If you can get hold of the ASHRAE Fundamentals Handbook, you will find a good one.

  3. #3
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    Re: Static pressure calculation for aircon duct

    There's s not such a thing as a simple formula.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  4. #4
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    Brian_UK is offline Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
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    Re: Static pressure calculation for aircon duct

    Quote Originally Posted by sparo View Post
    Hi i am new here.
    can anyone provide me the formula to calculate the static pressure for the aircon ductwork.


    Thanks
    A couple of questions to help us with your query.

    What is the airflow rate?

    What is the duct size?
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

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