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All installations and services must be performed by qualified service personnel.
The pressure drops for the remaining branches of the system must be set. This
includes segment “G”; segments “I” and “J”; and segments “K”, “L”, and “M”. To
balance the system, the pressure drop for each branch must be approximately
equal to the pressure drops of the other branches. For example, segment “G”
must equal segments “D”, “E” and “F” combined. Thus,
.
FEDG
PPPP
Δ
+
Δ
+
Δ
=Δ
Likewise for the other branches,
....1.0
...1.0
GWinPPP
GWinPP
mlK
JI
=Δ+Δ+Δ
=
Δ
+Δ
Using the previous technique, duct sizes can be found for all the remaining
segments. The duct sizes adequate for the entire supply system are summarized
in Table 7, below.
Table 7: Required Duct Sizes for the Residence in Example 2
Duct
Segment
Air
Flowrate
(CFM)
Circular
Duct Dia.
(in.)
Air Velocity in
Circular Duct
(FPM)
Equivalent
Rectangular
Duct Dim.s
(in.)
A 120 7 449 6 x 6
B 235 9 532 8 x 8
C 350 11 530 10 x 10
D 392 10 719 9 x 9
E 196 7 733 6 x 6
F 742 14 694 13 x 13
G 56 3 1141 N/A
H 798 14 746 13 x 13
I 126 5 924 N/A
J 231 7 864 6 x 6
K 370 10 678 9 x 9
L 304 9 688 8 x 8
M 157 7 587 6 x 6
N/A - Not Applicable
69