Fujitsu UTZ-BD035B Technical Manual page 37

[2] Conversion from Rectangular Duct to Circular Duct

How to use Fig. 7-4
Example: A rectangular duct measuring 40 x 200
corresponds to a circular duct having a diameter of 90.
1) To determine the intersection (A) of
2) Next, to determine the line (B) going
Short Side
[3] Local Pressure Loss in Duct
1) Local loss coefficient (also referred to as "local resistance
coefficient")
At bends or portions where cross sections change, losses
different in nature from those in straight potions will occur
due to eddy currents, etc. These pressure losses in places
other than straight portions can be expressed by the
following formula.
Where, : Local Loss Coefficient
V: Wind Velocity .......................................... [m/s]
* This is the velocity of the upper part of the local
area excluding the merging point.
Pv: Dynamic Pressure ...................................[Pa]
2) Calculation of pressure loss at a local area in a duct Example:
Consider a case in which the duct bends as follows.
[Conditions] R/d = 1.5 V = 5.0 (m/s)
From Table 7-1, = 0.15
From the above, P = (Local Loss Coefficient) x Pv (Dynamic
Pressure) = 0.15 x 15 = 2.25 [Pa]
The right side in Table 7-1 indicates the value of the local
pressure loss in this particular part converted to a duct
diameter. ( : Case in which PVC pipe is used)
le:Straight pipe corresponding length of the local resistance ... [m]
d: Straight pipe diameter ...[m]
: Local loss coefficient
De
Equivalent
Diameter
Short Side Fig. 7-4
the short side (40) and the long side
(200).
through the intersection (A), and
determine the intersection (D) with
the diagonal line (C).
The figure (D) indicates the corresponding
diameter, which is 90 in this case.
A round bend with the circular
cross section
<Set at 0.018>
: Duct friction resistance coefficient
Graphic
No. Name
Depiction
A round bend
1 with the circular
cross section
A square bend
2 with the circular
cross section
A round bend
3 with rectangular
cross section
 CALCULATION IN SIMPLIFIED
METHOD
 A case in which a model is selected, based on straight
pipe corresponding length and airflow quantity A model is
selected, based on the following conditions.
Required ventilation quantity: 120 [m
7-5 (60Hz)
(Example Problem)
Ceiling-Mounted
Ventilation Fan
(Case in which the galvanized steel pipe of = 0.02 is used)
Pipe Hood
Product Duct
Type
Number Diameter
FY-WKX042 ø100mm
Stainless Steel
(Rectangular)
FY-WKX062 ø150mm
FY-MCX042 ø100mm
Stainless Steel
(Round)
FY-MCX062 ø150mm
FY-MCXA042 ø100mm
Stainless Steel
(Accompanied by
a fire damper)
FY- MCXA062 ø150mm
FY-MCA042 ø100mm
Aluminum (Round)
FY-MCA062 ø150mm
Aluminum FY-MNA042 ø100mm
(Accompanied by
FY-MNA062 ø150mm
an insect net)
 Table 7-2 is used to convert
the resistance at each
component of the duct to
the straight pipe length.

Static Pressure - Quantity Characteristic Curve
3
Airflow Quantity (m
- (01-34) -
Conditions
Loss
Coefficient
H/W R/d
0.5 0.71
0.75 0.33
1.0 0.22
1.5 0.15
2.0 0.13
1.2
0.5 1.30
0.5
0.75 0.52
1.0 0.25
1.5 0.20
0.5 1.20
0.75 0.44
1
1.0 0.21
1.5 0.17
3
/h] Duct system: Fig.
Duct Diameter:
100mm
Material: Galvanized
Steel Pipe
( = 0.02)
Bent Cap
Straight Pipe Product Duct
Type
Corresponding Length Number Diameter
5m FY-VCX042 ø100mm
Stainless Steel
12m FY-VCX062 ø150mm
9m Stainless Steel FY-VNX042 ø100mm
(Accompanied by
13m FY- VNX062 ø150mm
an insect net)
FY-VCXA043
12m ø100mm
Stainless Steel
BL
(Accompanied by
FY-VCXA063
a fire damper)
13m ø150mm
BL
9m FY-VCA042 ø100mm
Aluminum
13m FY-VCA062 ø150mm
15m ø100mm
(R/d = 1.0) Elbow
32m ø150mm
Piping Length of Corresponding Straight
Portion Pipe (Diameter: 100mm)
I 0.5m
II 2m
III 0.5m
IV 2m
V 5m
VI 9m
Total 19m
 To select an appropriate model.
Case in which a model satisfying
the straight pipe corresponding
length: 19 [m] and the airflow
3
quantity of 130 [m /h]
A perpendicular line is dropped
from the intersection (A) made
by the resistance curve of the 19
[m]-pipe and the static pressure
- quantity characteristic curve to
determine the point (B), and the
/h)
model to be selected should satisfy
the value at the point, that is, 130
3
[m /h].
Table 7-1
Length
Corresponding
to PVC Pipe
39d
18d
12d
8d
7d
67d
72d
29d
14d
11d
67d
24d
12d
9d
Fig. 7-5
Straight Pipe
Corresponding Length
2m
4m
5m
7m
8m
7m
2m
3m
2m
3m
Table 7-2
Table 7-3