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4.0 INSTALLATION
4.4 Refrigerant Line Set Selection (cont.)
4.4.5 Long Line Set
Considerations
Long line set applications are defined as
applications that require accessories or alternate
construction methods. The following are things that
should be considered when selecting and installing
a long line set:
• Additional refrigerant charge
• Fitting losses and maximum equivalent length
considerations
• Refrigerant migration during the off cycle
• Oil return to the compressor
• Capacity losses
• System oil level adjustment
4.4.5.1 Determining if Long Line
Set Length Requirements Apply
Table 2 is used to determine if the application is
considered to have a long line set. A column is pro-
vided that shows the linear line length where long
line length requirements apply.
4.4.5.2 Oil Return to Compressor
Small amounts of compressor crankcase oil is
picked up and carried out of the compressor by the
moving refrigerant and is circulated through the
system along with the refrigerant before it returns to
the compressor crankcase. It is critical to the life of
the compressor for the oil to be able to return to the
compressor to maintain an adequate level of oil in
the compressor crankcase. Oversized suction lines
result in inadequate refrigerant velocities to carry
the oil along with the refrigerant and will cause the
oil to accumulate in the low spots in the vapor line
instead of being returned to the compressor crank-
case. This is especially true for long line lengths.
Only use the suction line sizes listed in Table 2 to
assure proper oil return. Do not oversize the suction
line.
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4.5.5.3 Refrigerant Migration
During Off Cycle
Long line set applications can require a consider-
able amount of additional refrigerant. This addition-
al refrigerant needs to be managed throughout the
entire ambient operating envelope that the sys-
tem will go through during its life cycle. Off-Cycle
migration is where excess refrigerant condenses
and migrates to the coldest and/or lowest part of
the system. Excessive build-up of refrigerant at the
compressor will result in poor reliability and noisy
operation during startup. Long line applications
require an EXV or TXV on both the indoor coil and
outdoor unit and a crankcase heater. (See Section
7.4 and 9.3 for crankcase heater information.)
4.4.5.4 Maximum Liquid Pressure
Drop
The total liquid line pressure drop must not exceed
50 psig [345 kPa] to assure a solid column of liquid
at the metering device and stable control of super-
heat. Be sure to account for vertical separation,
elbows, filter driers, solenoid valves, sight glasses,
and check valves when calculating liquid line pres-
sure drop.
4.4.5.5 Liquid Line Refrigerant
Flashing
Excessive pressure drop and heat gain in long
liquid lines can result in the refrigerant flashing into
a vapor before it reaches the metering device which
will dramatically reduce the capacity and efficiency
of the system. For this reason, the liquid line must
be sized properly using the table in Table 2 and
must be insulated in unconditioned spaces.
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