11
Tubing
4.4.3 Line Set Length and Fitting Losses
Refrigerant tubing is measured in terms of actual length and equivalent length. Actual length is used for
refrigerant charge applications. Equivalent length takes into account pressure losses from tubing length,
fittings, vertical separation, accessories, and filter driers. The table below references different commonly
used equivalent lengths.
Table 5: Equivalent Length for Fittings: ft [m]
Line Size
in [mm]
90° Short
Radius
Elbow
90° Long
Radius
Elbow
45°
Elbow
Solenoid
Valve
Check
Valve
Sight
Glass
Filter
Drier
3/8 [9.53] 1.3 [0.40] 0.8 [0.24] 0.3 [0.09] 6 [1.83] 4 [1.22] 0.4 [0.12] 6 [1.83]
1/2 [12.71] 1.4 [0.43] 0.9 [0.27] 0.4 [0.12] 9 [2.74] 5 [1.52] 0.6 [0.18] 6 [1.83]
5/8 [15.88] 1.5 [0.46] 1 [0.30] 0.5 [0.15] 12 [3.66] 6 [1.83] 0.8 [0.24] 6 [1.83]
3/4 [19.05] 1.9 [0.58] 1.3 [0.40] 0.6 [0.18] 14 [4.27] 7 [2.13] 0.9 [0.27] 6 [1.83]
7/8 [22.23] 2.3 [0.70] 1.5 [0.46] 0.7 [0.21] 15 [4.57] 8 [2.44] 1 [0.30] 6 [1.83]
1-1/8 [28.58] 2.7 [0.82] 1.8 [0.55] 0.9 [0.27] 22 [6.71] 12 [3.66] 1.5 [0.46] 6 [1.83]
4.4.4 Liquid Line Selection
The purpose of the liquid line is to transport warm sub-cooled liquid refrigerant between the outdoor unit to the
indoor unit in the cooling mode. In the heating mode, the liquid line returns sub-cooled liquid from the indoor unit
to the outdoor unit. It is important not to allow the refrigerant to flash into superheated vapor prior to entering the
expansion device of the indoor coil or outdoor unit. Flashing of refrigerant can occur for the following reasons:
• Low refrigerant charge
• Improperly selected liquid line size
• Absorption of heat prior to expansion device
• Excessive vertical separation between the outdoor unit and indoor coil
• Restricted liquid linear filter drier
• Kinked liquid line
The total pressure drop allowed for the liquid line is 50 PSI [345 kPa]. The procedure for selecting the proper liquid
line is as follows:
• Measure the total amount of vertical separation between the outdoor unit and indoor coil.
• Measure the total indoor length of liquid line required.
• Add all of the equivalent lengths associated with any fittings or accessories using Table 5.
• Add the linear length to the total fitting equivalent length. This will equal your total equivalent line length.
• Reference Table 6 to verify the calculated equivalent length is acceptable with the required vertical separation
and diameter of liquid line.
Example: A 3-ton heat pump unit is installed 25’ below the indoor unit, requires a 75’ of 1/2” diameter liquid line,
3/4" vapor line, 4 90° LR elbows and a filter drier.
• Fitting Equivalent Length (ft.) = 4 × .9' + 6' = 9.6’
• Total Equivalent Length (ft.) = 75’ + 9.6' = 84.6’
This application is acceptable because the 25’ vertical rise is less than the maximum rise of 50’ for this application.
Example Table (Excerpt from Table 6A)
Unit Size
Allowable
Liquid Line
Size
Allowable
Vapor Line
Size
Outdoor Unit ABOVE or BELOW Indoor Unit
Equivalent Length (Feet)
< 25 26-50 51-75 76-100 101-125 126-150
Maximum Vertical Separation / Capacity Multiplier
3 Ton
5/16" 5/8" 25 / 0.99 50 / 0.97 50 / 0.95 50 / 0.93 36 / 0.91 NR
3/8" 5/8" 25 / 0.99 50 / 0.97 50 / 0.95 50 / 0.93 50 / 0.91 NR
5/16" 3/4" 25 / 1.00 50 / 0.99 50 / 0.99 50 / 0.98 36 / 0.97 20 / 0.96
3/8" 3/4" 25 / 1.00 50 / 0.99 50 / 0.99 50 / 0.98 50 / 0.97 50 / 0.96
1/2" 3/4" 25 / 1.00 50 / 0.99 50 / 0.99 50 / 0.98 50 / 0.97 50 / 0.96
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