Darcy equation for friction loss

= Friction loss in Pa

= Friction factor (dimensionless)

= Duct length in meters

= Hydraulic diameter

= Velocity (m/s)

=

v =

Standard air, Re can be calculated by:

= Absoulute roughness factor of material

A =

P = Perimeter of cross section (mm)

Duct friction loss calculation for size outside range of friction loss table.

Density (kg/m3)

Kinematic viscosity (m2/s)

Duct area (mm2)

Δ pf=1000 fLDh

ρV 2

2

Δ pf

fL

DhV

ρ

Re=DhV

1000v

Re=66 .4 ⃗DhV

f=0 .11( εDh+68Re )0.25

Dh=4 A

P

ε

Supply air duct on C2-L1-AHU-67

Duct size 2100 x 600

Duct length 1 m

Air flow 8400 l/s

Velocity 6.67 m/s

Density 1.2046

A = 1260000

P = 5400 mm

= 933.3 mm

Re = 413156

= 0.1

= 0.01412

= 0.405

(L)

(V)

(ρ) kg/m3

mm2

Dh

ε

f

Δ pf