PCERT LEV COURSES
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MATHS REVISION For P602
Calculate Duct Diameters from Duct Areas
If you are not familiar yet with these equations then have a look at the Tutorial Sheet
“Areas of Circles/Ducts” before proceeding.
Area of a circle
A
=
πD2/4
Where π = 3.142
D = dia (m)
Or
A
=
πr2
Where r = radius in metres(!)
OK—so we are going to assume that you are comfortable working out how to
calculate the area of a Circle using the equations above?
In P602 however there is a critical part where you will know the Area of a Duct and
from that you need to work out what Duct Diameter.
For that we need to scramble the Area of a Circle equation to produce it in the
following format (it’s the same equation—again—just jumbled about a bit:-
Diameter, D =
4A
π
Where A = Area of duct and π = 3.142
Example:
As part of your P602 Design Exercise you find that you need to be able to choose a
duct which has an Area of 0.0491m2—so you will need to find out what Diameter of
duct gives that Area (as that will be the diameter of duct you will instal as part of your design)
Using the above Equation:Diameter, D =
4A
π
=
= 0.250m x 1000
© Oxyl8 2017
4 x 0.0491
3.142
=
=
√0.0625
=
0.250m
250mm Duct Diameter
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PCERT LEV COURSES
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Examples for you to Try:-
Duct Area
Duct Dia (m)
Duct Dia (mm)
0.0050 m2
0.0113 m2
0.0177 m2
0.0314 m2
0.0531 m2
0.0962 m2
0.1964 m2
Answers: 80mm, 120mm, 150mm, 200mm, 260mm, 350mm, 500mm
© Oxyl8 2017
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