Selection Data
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 York DX piping guide form
YORK ASSUMES NO WARRANTY RESPONSIBILITY FOR SYSTEM OPERATION OR FAILURES 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, refrig- erant 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 give to:
1)Suction line pressure drop due to refrigerant flow.
2)Suction line refrigerant velocity for oil return.
3)Liquid line pressure drop due to refrigerant flow.
4)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 allow- ances 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 40 psi (276 kPa). Refrigerant vapor in the liquid line will measurably reduce valve capacity and poor system performance can be expected.
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 evapora- tor, 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 hold- ing charge. The remaining operating charge for the con- densing 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
REFRIGERANT PIPING REFERENCE
For more details, refer to ASHRAE Refrigeration Hand- book, Chapter 2.
10 | YORK INTERNATIONAL |
