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SECTION 5. CALCULATIONS - TUBING EQUIVALENT LENGTH, TUBE SIZE AND REFRIGERANT
1.
In long line applications the “equivalent line length” is the sum of the straight length portions of the suction line plus
losses (in equivalent length) from 45 and 90 degree bends. Add the total straight (lineal) length of tubing to the
equivalent length of elbows and bends to get total equivalent length.
Equivalent length = Length
Horizontal
+ Length
Vertical
+ Losses from bends (see Table 5-1)
2.
Table 5-1 lists the equivalent length gained from adding bends to the suction line. Properly size the suction line to
minimize capacity loss.
3/4
7/8
1 1/8
90° short radius
1.7
2
2.3
90° long radius
1.5
1.7
1.6
45°
0.7
0.8
1
Type of
Elbow Fitting
Inside Diameter (in)
Table 5-1. Losses from suction line elbows (equivalent length, ft.)
3/4
7/8
1 1/8
90
° short radius
0.5
0.6
0.7
90
° long radius
0.5
0.5
0.5
45°
0.2
0.2
0.3
Type of Elbow
Fitting
Inside Diameter (in)
Table 5-2. Losses from suction line elbows (equivalent length, m)
Table 5-1. Losses from suction line elbows (equivalent length, ft.)
EXAMPLE: 3/4” suction line using 3/4” elbows
150 feet of straight (four short radius elbows x1.7) + (2 long radius elbows x1.5) =
150 + 3.4 + 3 = 156.4 equivalent feet
3.
Table 5-2 lists multiplier values to recalculate system cooling capacity as a function of a system’s equivalent line length
(as calculated from the suction line) and the selected suction tube size.
NOTE: Select the proper suction tube size based on equivalent length of the suction line
(see Tables 5-1 and 5-2) and recalculated system capacity.
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