Coefficients of Resistance (for ductwork fittings)
| Fitting |
K |
Fitting |
K |
Sharp 90° Bend |
1.3 |
Exit to room |
1.0 |
90° Bend with vanes |
0.7 |
Entry from room |
0.5 |
Rounded 90° Bend (r/w < 1) |
0.5 |
Abrupt reduction |
0.5 - (V₂/V₁)² applied to V.H. of V₂ |
Rounded 90° Bend (r/w > 1) |
0.25 |
Abrupt enlargement |
(1 - V₂/V₁)² applied to V.H. of V₁ |
Sharp 45° Bend |
0.5 |
Tapered enlargement (α ≤ 8°) |
1.5 × (1 - V₂/V₁)² applied to V.H. of V₁ |
Rounded 45° Bend (r/w < 1) |
0.2 |
Tapered enlargement (α > 8°) |
(1 - V₂/V₁)² applied to V.H. of V₁ |
Rounded 45° Bend (r/w > 1) |
0.05 |
Tapered reduction |
0 |
Flow to branch |
0.3 applied to V.H. in the branch |
Grilles |
| Ratio of free area to total surface |
K |
| 0.7 |
3 |
| 0.6 |
4 |
| 0.5 |
6 |
| 0.4 |
10 |
| 0.3 |
20 |
| 0.2 |
50 |
|
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