Handbook of air conditioning and refrigeration / Shan K

Piping Design for Reciprocating Refrigeration Systems
REFRIGERATION SYSTEMS: RECIPROCATING, ROTARY, SCROLL, AND SCREW 11.13
TABLE 11.1 Correction Factors for Suction, Discharge, and Liquid Lines for HCFC-22
or T suc Other than 40°F and T con Other than 105°F
Correction factors for T suc other than 40°F
Tsuc, °F 50 40 30 20 10 0 �10 �20
Fsuc,s 1.20 1.00 0.84 0.70 0.58 0.47 0.38 0.30
Fdis,s 1.01 1.00 0.99 0.97 0.96 0.95 0.93 0.91
Correction factors for T con other than 105°F
Tcon, °F 80 90 100 105 110 120 130 140
Fsuc,c 1.11 1.07 1.03 1.00 0.97 0.90 0.86 0.80
Fdis,c 0.79 0.88 0.95 1.00 1.04 1.10 1.18 1.26
Fliq,c 1.12 1.07 1.02 1.00 0.98 0.93 0.88 0.83
Note: F liq,s � F dis,s
Packaged units with factory-assembled and -integrated refrigeration systems have become more
popular, and air-cooled reciprocating packaged units or chillers contain a reciprocating compressor,
liquid coolers, air-cooled condensers, expansion valves, and controls all in one package. However,
many field built-up or split systems need proper refrigeration piping design to provide adequate
cooling for air conditioning and industrial applications.
A proper refrigeration piping design must satisfy the following requirements:
● Transport the required amount of refrigerant to the evaporator, compressors, condenser, and throttling
devices.
● Provide optimum pressure drop in the refrigeration lines, i.e., the most economical maximum
pressure drop in the suction, discharge, and liquid lines. Current practice limits the maximum
pressure drop in suction, discharge, and liquid lines corresponding to a change of saturated temperature
�T sat as follows:
�Tsat, °F HCFC-22 pressure drop, psi (kPa)
Suction line
Discharge line
Liquid line
2
1
1
2.91 (20) at Tsuc � 40°F (4.4°C)
3.05 (21) at Tcon � 105°F (40.6°C)
3.05 (21) at Tcon � 105°F (40.6°C)
● For halocarbon refrigeration systems, oil should be miscible with liquid refrigerant, and oil
entrained in the refrigerant should be returned to the crankcase of the compressor to maintain an
adequate level for proper lubrication. Refrigerant piping design must accommodate the flow of both
refrigerant and oil. Oil does not mix with gaseous refrigerant. Transportation of entrained oil in hot
gas or vapor refrigerant is accomplished by ensuring a minimum refrigerant velocity not less than
500 fpm (2.5 m/s) in horizontal refrigerant lines and not less than 1000 fpm (5 m/s) in vertical
refrigerant risers. Horizontal refrigerant lines must be pitched in the direction of refrigerant flow.
● Flashing of liquid refrigerant must not occur before the expansion valve. Adequate subcooling
should be provided to offset the pressure drop of the liquid line and its accessories.
● Piping design should be configured to prevent liquid slugging, in which liquid refrigerant, oil, or a
combination of both floods back to the compressor.
● Maintain a clean and dry refrigeration piping system.