53
RTAA-IOM-3
Suction Line Sizing
This example uses the unit installation
shown in Figure 31 and assumes a 100
ton circuit. As in the liquid line sizing
example, the equivalent pipe length
must first be determined. It must also
be determined what portion of the pipe
is “horizontal and/or downflowing”
and what portion is “horizontal and/or
upflowing.”
In Figure 31, the actual length of field
installed piping is 100 feet (20 + 5 + 75).
Using the factor of 1.5, the equivalent
line length is 150 feet. The suction line
has an elevation of 20 feet and consists
of horizontal and vertical (upflowing)
sections, which must be sized
separately.
The two vertical sections are separated
by a small horizontal section. The total
distance is 25 feet (20 +5). The first
approximation of equivalent pipe
length is 37.5 feet (1.5 times 25).
Referring to Table 6 for a horizontal
and/or upflow suction line on a 100 ton
circuit with 37.5 feet of line, the pipe
O.D. should be 3 1/8 in.
Add the 75 feet of horizontal and/or
downflow line to the 45.4 feet of
horizontal and/or upflow line, resulting
in 120.5 of equivalent pipe length. Table
7 at 125 feet (use the dimension closest
to the calculated dimension) indicates
the use of 4 1/8 in. O.D. pipe. Therefore,
the 4 1/8 in line will have to be reduced
for the vertical sections of the line and
expanded again for the horizontal
sections.
There are four long-radius elbows in
this section of piping. Using Table 5
and the pipe OD of 3 1/8 in., these
fittings represent 20.4 feet (4 elbows @
5.1 feet each). Therefore our new
equivalent line length is 45.4 feet (25 +
20.4). Table 6 indicates that 45.4
equivalent feet still permits the use of 3
1/8 in. O.D. pipe.
In sizing the horizontal and/or
downflow portion of the suction line, it
is necessary to account for the total
equivalent length of the line.
Note: In this example, the horizontal
line is pitched downward in the
direction of flow
Using Table 7 and 150 feet of
equivalent pipe length for a 100 ton
circuit, a pipe O.D. of 4 1/8 in. is
specified. There are no fittings in the 75
foot horizontal run, so no equivalent
fitting lengths need to be determined.
Table 6
Suction Line Size for Horizontal and/or Upflow Lines
Circuit Size: Suction Line Size (OD”)
Total Vertical Equiv. Length (Ft) 100 Ton 85 Ton 70 Ton
50': 3 1/8 3 1/8 2 1/8
75': 3 1/8 3 1/8 2 1/8
100': 3 1/8 3 1/8 2 1/8
Table 7
Suction Line Size for Horizontal and/or Downflow Lines
Circuit Size:
Total Equiv. Length (Ft) Suction Line Size (OD”)
(Including vertical section, if any) 100 Ton 85 Ton 70 Ton
50': 3 1/8 3 1/8 2 5/8
75': 3 1/8 3 1/8 2 5/8
100': 3 1/8 3 1/8 3 1/8
125': 4 1/8 3 1/8 3 1/8
150': 4 1/8 3 1/8 3 1/8
175': 4 1/8 4 1/8 3 1/8
200': 4 1/8 4 1/8 3 1/8
225': 4 1/8 4 1/8 3 1/8
250': 4 1/8 4 1/8 3 1/8
275': 4 1/8 4 1/8 3 1/8
300': 4 1/8 4 1/8 3 1/8
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