Liquid Line Selection; Vapor Line Selection - Rheem P17 Series Installation Instructions Manual

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 following Refrigerant Line Selection (Table 2)
lists the equivalent length per 25' [8 m] of liquid line at
various diameters up to 150' [46 m]. The total pressure
drop allowed for the liquid line is 50 PSI [345 kPa].
Allowable
Unit Size Liquid Line
Size
5/16"
3/8"
3 Ton 5/16"
3/8"
1/2"
(Excerpt from Table 2A)

4.4.5 Vapor Line Selection

The purpose of the vapor line is to return superheat-
ed vapor to the condensing unit from the indoor coil
in the cooling mode. While in the heating mode, the
vapor line transports discharge vapor to the indoor
coil from the outdoor unit. 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 improperly sized vapor line can dramatical-
ly reduce capacity and performance of the system.
The procedure for selecting the proper vapor line is
as follows:
Allowable
Vapor Line
< 25
Size
5/8" 25 / 0.99
5/8" 25 / 0.99
3/4 " 25 / 1.00
3/4 " 25 / 1.00
3/4 " 25 / 1.00
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 re-
quired.
• Add all of the equivalent lengths associated with any
fittings or accessories using Table 2.
• Add the linear length to the total fitting equivalent
length. This will equal your total equivalent line
length.
• Reference Table 2 to verify the calculated equiva-
lent 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' verti-
cal rise is less than the maximum rise of 50' for this
application.
Outdoor Unit ABOVE or BELOW Indoor Unit
Equivalent Length (Feet)
26-50 51-75 76-100
Maximum Vertical Separation / Capacity Multiplier
50 / 0.97 50 / 0.95 49 / 0.93
50 / 0.97 50 / 0.95 50 / 0.93
50 / 0.99 50 / 0.99 49/ 0.98
50 / 0.99 50 / 0.99 50 / 0.98
50 / 0.99 50 / 0.99 50 / 0.98
• Determine the total linear length of vapor line
required.
• Add all of the equivalent lengths associated with
any fittings or accessories using Table 1.
• Add the linear length and total fitting equivalent
length. This will equal your total equivalent line
length.
• Reference Table 2 to verify that the calculated
equivalent length falls within the compatibility
region of the chart.
• Verify capacity loss is acceptable for the applica-
tion.
4.0 INSTALLATION
101-125 126-150
31 / 0.91 NR
50 / 0.91 NR
31 / 0.97 14/ 0.96
50 / 0.97 50 / 0.96
50 / 0.97 50 / 0.96
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