Flow

Volume

1.200m³/h

Duct

Ø 307mm

Velocity

4,50m/s

Duct sizing covers straight ducts for dry air. Pressure loss follows Darcy–Weisbach, with the friction factor from the Prandtl–Colebrook equation. Round, rectangular and oval sections return velocity, friction and the equivalent diameter.

Calculated

Ø 307 mm

741 cm² · Internal size

Velocity

4,50

m/s

Friction

0,78

Pa/m

Standard sizes

0481216

Cross-section

Task

Target

Air and duct wallSpiral seam · k = 0,09 mm · 20 °C · 1,204 kg/m³

Absolute roughness k = 0,09 mm. For a custom value, choose “Custom”.

Run and fittings10 m · no fittings

ζ guide values, based on the dynamic pressure in this duct. The real fitting geometry can differ a lot.

Flow and pressure dropTotal 7,82 Pa
over 10 m
7,82 Pa
Fittings
0,00 Pa
Total
7,82 Pa
Cross-section
0,0741m²
Dynamic pressure
12,2Pa
Hydraulic Ø
307mm
Equivalent round Ø
307mm
Reynolds number
91.744
Friction factor λ
0,0197
Mass flow
1.445kg/h
Flow regime
Turbulent

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How it's calculated

Duct sizing is for straight ducts that run full. Pressure loss follows Darcy–Weisbach, and the friction factor follows the Prandtl–Colebrook equation. The calculation uses the hydraulic diameter, the air density and the dynamic viscosity at the chosen temperature and barometric pressure. The aim is the smallest common size within the target velocity or the target pressure gradient. Fittings enter only as a sum of ζ values, not as measured geometry.

Worked example

800 m³/h at 20 °C and 1,013.25 hPa, spiral duct k = 0.09 mm, 250 mm round: velocity 4.53 m/s, friction 1.02 Pa/m.

FAQ

What velocity is usual for comfort ventilation?
Often about 2 to 4 m/s in the duct for occupied rooms, and much less at the outlet. The tool flags high values, but it is not an acoustic design.
What is the equivalent diameter?
The round diameter that carries the same volume flow at the same friction pressure drop as the rectangular or oval section.
Is a bend included automatically?
No. The straight run is friction only. Bends, branches and outlets have to be added as ζ values.
Does this cover wet exhaust air?
No. Density is for dry air. Mist, high humidity and filter resistance are not included.