Daikin VAM Series Engineering Data page 180

Appendix
17.5.2 Calculation of pressure loss for straight pipe duct
 In the Case of Circular Ducts
(1) Duct Resistance is Found by the Following Formula.
The following formula is generally used to find Pressure Loss rP at time air flows in the straight pipe duct.
Duct resistance P (Pa) = λ ×
λ: Friction coefficient of pipe for duct (0.01 to 0.25)
γ: Specific weight of air (kg/m
L: Duct length (m)
d: Duct diameter (m)
v: Air velocity inside duct (m/sec)
Q 4
v = ×
3,600 π
2
d
3
Q: Airflow rate (m /h)
Here when we substitute λ = 0.01 (in the case that the pipe is extremely smooth) γ = 1.2,
1.2 L Q
{
P = 0.01 × × ×
2
2 d d
 Airflow Resistance Coefficient for Main Duct
(2) Method that finds by Air Duct Flow Resistance Chart
 Circular Air Duct Flow Resistance Chart (Galvanized Steel Pipe)
178
γ
L
2
× × v
2 d
) ≈ 1.20 kg/m
3 3
2
4
}
×
3,600π
0.04 0.1 0.2
1000000
800000
600000
400000
200000
100000
80000
60000
40000
20000
10000
8000
6000
4000
2000
1000
800
600
400
200
100
80
60
40
20
10
0.04 0.1 0.2
0.4 1.0 2.0 6.0 10
0.4 1.0 2.0 6.0 10
γ
Friction loss coefficient (Pa/m)
Duct Flow Resistance Chart
EDMMT712101
20 40 60 80
20 40 60 80
VAM-HVE/HVLT Series