Fujitsu FO2416RTJNAA - Page 15

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
DVIROORZV
• The total amount of suction line needed
 $GGDOORIWKHHTXLYDOHQWOHQJWKVDVVRFLDWHGZLWK
DQ\ÀWWLQJVRUDFFHVVRULHVXVLQJWKHWDEOHRQ
previous page.
 $GGWKHOLQHDUOHQJWKDQGWRWDOÀWWLQJHTXLYD-
OHQWOHQJWK7KLVZLOOHTXDO\RXUWRWDOHTXLYDOHQW
length.
• Reference Table 2 to verify that the calculated
HTXLYDOHQWOHQJWKIDOOVZLWKLQWKHDFFHSWDEOH
region of the chart.
 9HULI\WKHFDSDFLW\GLIIHUHQFHLVFRPSDWLEOHZLWK
the application using the multiplier in Table 2.
• Use only vapor line sizes listed in Table 2.
4.4.5 Long Line Set
Considerations
/RQJOLQHVHWDSSOLFDWLRQVDUHGHÀQHGDVDSSOLFD-
tions that require accessories or alternate con-
VWUXFWLRQPHWKRGV7KHIROORZLQJWKLQJVVKRXOGEH
FRQVLGHUHGZKHQVHOHFWLQJDQGLQVWDOOLQJDORQJOLQH
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-
YLGHGWKDWVKRZVWKHOLQHDUOLQHOHQJWKZKHUHORQJ
line length requirements apply.
4.4.5.2 Oil Return to Compressor
6PDOODPRXQWVRIFRPSUHVVRUFUDQNFDVHRLOLV
SLFNHGXSDQGFDUULHGRXWRIWKHFRPSUHVVRUE\WKH
moving refrigerant and is circulated through the
V\VWHPDORQJZLWKWKHUHIULJHUDQWEHIRUHLWUHWXUQVWR
WKHFRPSUHVVRUFUDQNFDVH,WLVFULWLFDOWRWKHOLIHRI
the compressor for the oil to be able to return to the
compressor to maintain an adequate level of oil in
WKHFRPSUHVVRUFUDQNFDVH2YHUVL]HGYDSRUOLQHV
result in inadequate refrigerant velocities to carry
WKHRLODORQJZLWKWKHUHIULJHUDQWDQGZLOOFDXVHWKH
RLOWRDFFXPXODWHLQWKHORZVSRWVLQWKHYDSRUOLQH
LQVWHDGRIEHLQJUHWXUQHGWRWKHFRPSUHVVRUFUDQN-
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-
WHPZLOOJRWKURXJKGXULQJLWVOLIHF\FOH2II&\FOH
PLJUDWLRQLVZKHUHH[FHVVUHIULJHUDQWFRQGHQVHV
DQGPLJUDWHVWRWKHFROGHVWDQGRUORZHVWSDUWRI
the system. Excessive build-up of refrigerant at the
FRPSUHVVRUZLOOUHVXOWLQSRRUUHOLDELOLW\DQGQRLV\
operation during startup. Long line applications
UHTXLUH7;9VRQERWKWKHLQGRRUFRLODQGRXWGRRU
XQLWDQGDFUDQNFDVHKHDWHU6HH6HFWLRQIRU
FUDQNFDVHKHDWHULQIRUPDWLRQ
4.4.5.4 Maximum Liquid Pressure
Drop
The total liquid line pressure drop must not exceed
SVLJ>N3D@WRDVVXUHDVROLGFROXPQRIOLTXLG
at the metering device and stable control of super-
heat. Be sure to account for vertical separation,
HOERZVÀOWHUGULHUVVROHQRLGYDOYHVVLJKWJODVVHV
DQGFKHFNYDOYHVZKHQFDOFXODWLQJOLTXLGOLQHSUHV-
sure drop.
4.4.5.5 Liquid Line Refrigerant
Flashing
Excessive pressure drop and heat gain in long
OLTXLGOLQHVFDQUHVXOWLQWKHUHIULJHUDQWÁDVKLQJLQWR
DYDSRUEHIRUHLWUHDFKHVWKHPHWHULQJGHYLFHZKLFK
ZLOOGUDPDWLFDOO\UHGXFHWKHFDSDFLW\DQGHIÀFLHQF\
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.)