REFRIGERANT PIPING
GENERAL GUIDELINES
Many service problems can be avoided by taking adequate pre-
cautions to provide an internally clean and dry system and by using
procedures and materials that conform with established standards.
Use hard drawn copper tubing where no appreciable amount
of bending around pipes or other obstructions is necessary.
Use long radius ells wherever possible with one exception—
short radius ells for the traps in all suction risers. If soft copper
is used, care should be taken to avoid sharp bends which may
cause a restriction.
Pack fiber glass insulation and a sealing material such as
permagum around refrigerant lines where they penetrate a wall
to reduce vibrations and to retain some flexibility.
Support all refrigerant lines at minimum intervals with suitable
hangers, brackets or clamps.
Braze all copper to copper joints with Silfos-5 or equivalent
brazing material. Do not use soft solder.
Insulate all suction lines with a minimum of 1/2" ARMAFLEX or
equal. Liquid lines exposed to direct sunlight and/or high tem-
peratures must also be insulated.
Never solder suction and liquid lines together. They can be taped
together for convenience and support purposes, but they must be
completely insulated from each other.
A filter-drier MUST be installed in the liquid line of every system
to prevent dirt and moisture from damaging the system. A prop-
erly-sized filter-drier is shipped with each condensing unit for field
installation near the evaporator coil. The filter-drier is shipped
inside the unit control box.
NOTE: Installing a filter-drier does not eliminate the need for
the proper evacuation of a system before it is charged.
A moisture indicating sight-glass may be field installed in liquid
line(s) between the filter-drier and the evaporator coil. The
moisture indicating sight-glass can be used to check for excess
moisture in the system or used as visual means to verify
refrigerant charge.
LINE SIZING
When sizing refrigerant lines for a split-system air conditioner,
check the following:
1. Suction line pressure drop due to friction at full capacity,
2. Liquid line pressure drop due to friction at full capacity,
3. Suction line velocity for oil return at part capacity, and
4. Liquid line pressure drop due to static head.
NOTE: Never base refrigerant line sizes on the OD of the
suction and liquid connections on the unit.
Tables 4 and 5 list friction losses for both the suction and liquid
lines on the system. Table 6 shows the amount of refrigerant
charge required per foot of refrigerant line.
When the evaporator coil is below the condensing unit, the
suction line must be sized for both pressure drop and for oil
return. For certain piping arrangements, different suction line
sizes may have to be used. The velocity of the suction gas must
always be great enough to carry oil back to the compressor.
When the condensing unit is below the evaporator coil, the
liquid line must be designed for the pressure drop due to both
friction loss and vertical rise. If the total pressure drop exceeds
40 psi, some refrigerant may flash before it reaches the thermal
expansion valve. This flashing will not only cause erratic valve
operation and poor system performance, but could also dam-
age the expansion valve.
SERVICE VALVES
These condensing units have service valves on the compres-
sor suction line and on the liquid line leaving the condenser coil.
The liquid and suction line service valves are shipped from the
factory front-seated and closed with the valve stem in the
maximum clockwise position.
The liquid and suction line service valves have a 1/4" male flare
access port for evacuating, charging and pressure checking the
system.
NOTE: Never remove a cap from an access port unless the
valve is fully back-seated with its valve stem in the
maximum counter-clockwise position because the re-
frigerant charge will be lost. ALWAYS USE A REFRIG-
ERATION VALVE WRENCH TO OPEN AND CLOSE
THESE SERVICE VALVES.
Model
Designation
Nominal
Capacity
(Tons)
Refrigerant
Flow Rate
3
(Lbs./Min.)
Type L
Copper Tubing
(Inches O.D.)
Refrigerant
Gas
Velocity
(FT./Min.)
Friction
Loss
4,5
(PSI/100 Ft.)
180 Mbh
Full
Capacity
15
45
1-5/8
2-1/8
2300
1360
2.5
0.6
Part
Capacity
8-1/2
25.5
1-5/8
2-1/8
1150
770
6
0.7
0.2
240 Mbh
Full
Capacity
20
60
1-5/8
2-1/8
2-5/8
3120
1800
1200
4.3
1.2
0.4
Part
Capacity
10
30
1-5/8
2-1/8
2-5/8
1560
900
6
600
6
1.2
0.3
0.1
1All horizontal suction lines should be pitched at least 1 inch every 20 feet in the direction of the refrigerant flow to aid the return of oil to the compressor.
2
Every vertical suction riser greater than 25 feet in height should have a “P” trap at the bottom to facilitate the return of oil to the compressor. Use short radius fittings for these traps.
3
Based on Refrigerant-22 at the nominal capacity of the condensing unit, a suction temperature of 40
°
F and a liquid temperature of 105
°
F.
4
Although suction lines should be sized for a friction loss equivalent to a 2
°
F change in saturation temperature (or approximately 3 psi), sizing the lines for the proper return of oil
is more important.
5
These friction losses do not include any allowances for valves or fittings.
6
Since the refrigerant gas velocity may be too low to maintain good oil return up a vertical riser, use the next smaller size. The larger size may be used for horizontal runs for a smaller
pressure drop.
TABLE 4 - SUCTION LINES
1,2
550.23-N6Y
Unitary Products Group
7
