Plant Sizing – Duct Sizing - Page 1 2 3 4 5 6 7 8 
Duct Sizing Table
The duct sizing table
shown below is an aid to duct sizing.
The explanation for use is
given in the table below.
A blank table is included
in this section at the end.
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Duct Sizing Table |
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1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
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Section |
Length (m) |
Flow Rate (m3/s) |
Pressure drop per metre (Pa/m) |
Duct Size (mm) |
Velocity (m/s) |
Velocity Pressure (Pa) |
Fittings pressure loss factor or z
(zeta) factor |
Pressure Loss |
Total
Pressure Loss (Pa) |
Cumulative Pressure Loss (Pa) |
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Fittings (Pa) |
Straight Duct (Pa) |
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Divide System into sections |
Measure lengths of each section from drawing |
From Drawing or from grille outputs |
Normally 1.0 |
From FIG 1 For circular Ducts. Convert to Rectangular if necessary |
Use
formula: Velocity = Volume flow rate / Cross sectional area (CSA) |
From Calculation or Table C4.33 V.P = 0.5 x r x v2 Where r = air density 1.2 m3/kg. v = air velocity from col.6. |
From (EXAMPLES OF z zeta FACTORS) or Table
C4.35. e.g. Radiused
Bend z = 0.67 Contraction
on one side (b)
with q = 600 gives z = 0.4 If more than one fitting, add all z factors to get total. |
Velocity pressure from column 7 x total fittings factor from column 8. |
Multiply Columns 2 by 4 |
Add Columns 9 and 10. |
Add new Pressure loss for each section to give total at end of system. |
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Blank
table below.
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Duct Sizing Table |
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1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
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Section |
Length (m) |
Flow Rate (m3/s) |
Pressure drop per metre (Pa/m) |
Duct Size (mm) |
Velocity (m/s) |
Velocity Pressure (Pa) |
Fittings pressure loss factor or z
(zeta) factor |
Pressure Loss |
Total
Pressure Loss (Pa) |
Cumulative Pressure Loss (Pa) |
|
|
Fittings (Pa) |
Straight Duct (Pa) |
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Plant Sizing – Duct Sizing - Page 1 2 3 4 5 6 7 8