York YLUA Series Operation Manual page 10

Selection Data - continued
REFRIGERANT PIPING
General – When the unit has been located in its final
position, the unit piping may be connected. Normal instal-
lation precautions should be observed in order to receive
maximum operating efficiencies. System piping should
conform to the Johnson Controls DX piping guide form
050.40-ES2 or ASHRAE refrigeration handbook guide-
lines. All piping design and installation is the responsibility
of the user.
JOHNSON CONTROLS ASSUMES NO WARRANTY
RESPONSIBILITY FOR SYSTEM OPERATION OR FAIL-
URES DUE TO IMPROPER PIPING OR PIPING DESIGN.
Filter driers and sight glasses are shipped loose for field
installation on each refrigerant circuit. Field refrigerant
piping can be connected to the condensing unit.
All expansion valves, liquid line solenoid valves, refrigerant
and refrigerant piping are supplied and installed by others.
Table 4 lists refrigerant line connections sizes per unit
model number.
REFRIGERANT LINE SIZING
Refrigerant piping systems must be designed to provide
practical line sizes without excessive pressure drops,
prevent compressor oil from being "trapped" in the refrig-
erant piping, and ensure proper flow of liquid refrigerant
to the thermal expansion valve. Considerations should
be given to:
• Suction line pressure drop due to refrigerant flow.
• Suction line refrigerant velocity for oil return.
• Liquid line pressure drop due to refrigerant flow.
• Liquid line pressure drop (or gain) due to vertical rise
of the liquid line.
Table 5 provides the pressure drops for given pipe sizes
for both liquid and suction lines. The pressure drops given
are per 100 equivalent ft. (30.5 m) of refrigerant piping.
These friction losses do not include any allowances for
strainer, filter drier, solenoid valve, isolation valve or fittings
Nominal pressure drop for solenoids, sight glass, and
driers are shown in Table 2.
Table 1 includes approximate equivalent lengths for
copper fittings.
To ensure a solid column of liquid refrigerant to the expan-
sion valve, the total liquid line pressure drop should never
exceed 50 psi (3.4 bar). Refrigerant vapor in the liquid line
will measurably reduce valve capacity and poor system
performance can be expected.
10
To allow adequate oil return to the compressor, suction
risers should be sized for a minimum of 1000 FPM (5.08
m/s) while the system is operating at minimum capacity
to ensure oil return up the suction riser. Refer to Table
5 under column labeled Nominal Tons (KW) Unloaded.
Evaporator Below Condensing Unit
On a system where the evaporator is located below the
condensing unit, the suction line must be sized for both
pressure drop and oil return. In some cases a double
suction riser must be installed to ensure reliable oil return
at reduced loads. Table 3 indicates when a double suc-
tion riser should be used for listed pipe sizes to provide
adequate oil return at reduced loads. The calculated
information was based on maintaining a minimum of 1000
fpm (5.08 m/s) refrigerant vapor velocity.
Condenser Below Evaporator
When the condensing unit is located below the evaporator,
the liquid line must be designed for both friction loss and
static head loss due the vertical rise. The value of static
head loss of 5 PSI/ft.(3.4 kPa/30 cm) must be added to
the friction loss pressure drop in addition to all pressure
drops due to driers, valves, etc.
OIL TRAPS
All horizontal suction lines should be pitched at least 1/4"
per foot (2 cm/m) in the direction of the refrigerant flow to
aid in the return of oil to the compressor. All suction lines
with a vertical rise exceeding 3 feet (.91 meters) should
have a "P" trap at the bottom and top of the riser. Suction
lines with a vertical rise exceeding 25 feet (7.6 meters)
should be trapped every 15 feet (4.6 meters).
REFRIGERANT CHARGE
The condensing unit is charged with a dry nitrogen holding
charge. The remaining operating charge for the condens-
ing unit, evaporator coil, and refrigerant piping must be
weighed in after all refrigerant piping is installed, leak
checked, and evacuated. Final adjustment of refrigerant
charge should be verified by subcooling values (refer to
section on Pre-Startup for checking subcooling).
REFRIGERANT PIPING REFERENCE
For more details, refer to ASHRAE Refrigeration Hand-
book, Chapter 2.
FORM 150.63-EG4 (1012)
JOHNSON CONTROLS