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29-03-2007, 04:56 AM #1
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
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29-03-2007, 07:06 AM #2
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.
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29-03-2007, 08:58 PM #3
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.
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29-03-2007, 11:28 PM #4