- (01-33) -
4-6. DUCT DESIGN
4-6-1. CALCULATION OF PRESSURE LOSSES DUE TO VENTILATION
THROUGH DUCT




       

PROCEDURES FROM DUCT
CALCULATION TO MODEL
SELECTION
Equal Pressure Method Simplified Method
Calculation of Required Ventilation Quantity
Duct Design (Duct Diameter, Duct Type, Piping Route,
Length, Bending)
Simplified Method based on “Straight Duct
Equivalent Length”
Method based on “Frictional Resistance
Dia
g
ram”
To determine
ressure loss in the
straight duct with
“Frictional Resis-
ance Diagram.”t
t
To determine the “straight
duct equivalent length” for
he entire duct by using the
straight duct equivalent
length table for the
com
p
onent.
p
To determine the
local pressure loss
with the “local loss
coefficient.
To determine the intersec-
tion by plotting the “loss
resistance curve” in the
“Static Curve - Quantity
Characteristic Curve.
To determine the
pressure loss of the
entire duct system.
The required static pressure is determined by adding
10-20% tolerancesto the obtained pressure loss.
To select a model satisfying the characteristics with the
“Static Curve - Quantity Characteristic Curve.
Fig. 7-1
CALCULATION BASED ON
EQUAL PRESSURE METHOD
 
(1)

 

 

g: Gravitational Acceleration (9.8m/sec2)
3) 1.20kg/m3
L: Duct Length (m)
d: Duct Diameter (m)

v = 3600π
4
d
Q
2×
 3/h)
 = 0.02 (Galvanized Steel Pipe) = 9.8 = 1.2 is

P (Pa) = 0.02 9.80665
2
3600π
4
2
d
Q
d
L
9.82
1.2
××××
×

(references)
Duct Materials
 0.03-0.04
PVC pipe 0.01-0.02
Galvanized steel pipe 0.016-0.025
 
Frictional Loss Calculation Chart for Circular Ducts
(Part)

Quantity (Q, Airflow Volume) [m
3
/h]
3
Friction Loss Rate ( ) [Pa/m]
Friction Loss Resistance Chart for Galvanized Steel Pipe
Fi
. 7-2

(Conditions) Ceiling-Mounted Ventilation Fan
3/h
Duct Diameter: ø15cm
Duct Length: 5m
Quantity (Q, Airflow
Volume) [m3/h]
3
Fig. 7-3
Wind Velocity ( )
(m/s)
A
Friction Loss Ratio(Pa/m)
B
(1)
To determine the intersection (A) of the duct diameter (d)


3
/h).
(2)

(3)

it with the duct length (5m) to produce 11 Pa.