15
Tubing
4.4.4 Vapor Line Selection
Purpose of the vapor line is to return superheated
vapor to the condensing unit from the evaporator
in the cooling mode and hot discharge gas to the
indoor coil in the heating mode. Proper vapor line
sizing is important because it plays an important
role in returning oil to the compressor to prevent
potential damage to the bearings, valves, and scroll
sets. Also, an undersized vapor line can dramatical-
ly reduce capacity and performance of the system.
The procedure for selecting the proper vapor line is
DVIROORZV
• The total amount of suction line needed
$GGDOORIWKHHTXLYDOHQWOHQJWKVDVVRFLDWHGZLWK
DQ\ÀWWLQJVRUDFFHVVRULHVXVLQJWKHWDEOHRQ
previous page.
$GGWKHOLQHDUOHQJWKDQGWRWDOÀWWLQJHTXLYD
-
OHQWOHQJWK7KLVZLOOHTXDO\RXUWRWDOHTXLYDOHQW
length.
• Reference Table 2 to verify that the calculated
HTXLYDOHQWOHQJWKIDOOVZLWKLQWKHDFFHSWDEOH
region of the chart.
9HULI\WKHFDSDFLW\GLIIHUHQFHLVFRPSDWLEOHZLWK
the application using the multiplier in Table 2.
• Use only vapor line sizes listed in Table 2.
4.4.5 Long Line Set
Considerations
/RQJOLQHVHWDSSOLFDWLRQVDUHGHÀQHGDVDSSOLFD
-
tions that require accessories or alternate con-
VWUXFWLRQPHWKRGV7KHIROORZLQJWKLQJVVKRXOGEH
FRQVLGHUHGZKHQVHOHFWLQJDQGLQVWDOOLQJDORQJOLQH
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-
YLGHGWKDWVKRZVWKHOLQHDUOLQHOHQJWKZKHUHORQJ
line length requirements apply.
4.4.5.2 Oil Return to Compressor
6PDOODPRXQWVRIFRPSUHVVRUFUDQNFDVHRLOLV
SLFNHGXSDQGFDUULHGRXWRIWKHFRPSUHVVRUE\WKH
moving refrigerant and is circulated through the
V\VWHPDORQJZLWKWKHUHIULJHUDQWEHIRUHLWUHWXUQVWR
WKHFRPSUHVVRUFUDQNFDVH,WLVFULWLFDOWRWKHOLIHRI
the compressor for the oil to be able to return to the
compressor to maintain an adequate level of oil in
WKHFRPSUHVVRUFUDQNFDVH2YHUVL]HGYDSRUOLQHV
result in inadequate refrigerant velocities to carry
WKHRLODORQJZLWKWKHUHIULJHUDQWDQGZLOOFDXVHWKH
RLOWRDFFXPXODWHLQWKHORZVSRWVLQWKHYDSRUOLQH
LQVWHDGRIEHLQJUHWXUQHGWRWKHFRPSUHVVRUFUDQN
-
case. This is especially true for long line lengths.
Only use the vapor line sizes listed in Table 2 to
assure proper oil return. Do not oversize the vapor
line.
4.4.5.3 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-
WHPZLOOJRWKURXJKGXULQJLWVOLIHF\FOH2II&\FOH
PLJUDWLRQLVZKHUHH[FHVVUHIULJHUDQWFRQGHQVHV
DQGPLJUDWHVWRWKHFROGHVWDQGRUORZHVWSDUWRI
the system. Excessive build-up of refrigerant at the
FRPSUHVVRUZLOOUHVXOWLQSRRUUHOLDELOLW\DQGQRLV\
operation during startup. Long line applications
UHTXLUH7;9VRQERWKWKHLQGRRUFRLODQGRXWGRRU
XQLWDQGDFUDQNFDVHKHDWHU6HH6HFWLRQIRU
FUDQNFDVHKHDWHULQIRUPDWLRQ
4.4.5.4 Maximum Liquid Pressure
Drop
The total liquid line pressure drop must not exceed
SVLJ>N3D@WRDVVXUHDVROLGFROXPQRIOLTXLG
at the metering device and stable control of super-
heat. Be sure to account for vertical separation,
HOERZVÀOWHUGULHUVVROHQRLGYDOYHVVLJKWJODVVHV
DQGFKHFNYDOYHVZKHQFDOFXODWLQJOLTXLGOLQHSUHV
-
sure drop.
4.4.5.5 Liquid Line Refrigerant
Flashing
Excessive pressure drop and heat gain in long
OLTXLGOLQHVFDQUHVXOWLQWKHUHIULJHUDQWÁDVKLQJLQWR
DYDSRUEHIRUHLWUHDFKHVWKHPHWHULQJGHYLFHZKLFK
ZLOOGUDPDWLFDOO\UHGXFHWKHFDSDFLW\DQGHIÀFLHQF\
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.
4.0 INSTALLATION
4.4 Refrigerant Line Set Selection (cont.)
