Hermetic Compressor - Tecumseh

76 SERVICE HANDBOOK
Refrigerant Line Sizes
R-12, R-134a and R-404A Refrigerant Line Sizes for Remote Systems
Commercial Refrigeration
Refer to Tables 5-1 through 5-8. The recommended suction line sizes are based on a pressure
drop no greater than the equivalent of a 1.5°F change in saturation temperature. The
resulting pressure drop should provide sufficient refrigerant velocities necessary for proper
oil return for suction lines up to 100 ft in length.
Suction line sizes that provide a minimum 1500 ft/min velocity are provided as a reference
when sizing risers.
On heat pump systems, the lines serving as both a discharge line and suction line should
be sized as a suction line.
Refer to these installation considerations for good oil return on commercial systems.
• Slope horizontal suction line downwards in the direction of the compressor at least ½”
fall per 10 feet of line.
• For systems using a thermostatic expansion valve (TEV), the valve should be set to its
proper setting. A typical superheat setting for commercial refrigeration applications is
6°F to 8°F. For low temperature refrigeration, a superheat setting of 4°F to 6°F is usually
appropriate.
• In the case of a flooded type evaporator (bottom feed, top suction header, large internal
volume, low refrigerant/oil velocities), it is necessary to maintain a liquid spillover
into the suction line so as to return the oil with the liquid refrigerant and to minimize
oil trapping in the evaporator. If because of the spillover, the return gas is “wet” at the
compressor, a suction line accumulator should be installed adjacent to the compressor.
• Install a suction accumulator to prevent liquid refrigerant from entering the compressor,
particularly when long suction lines are being used.
• On multiple evaporator systems, prevent oil and refrigerant from collecting in an idle
coil. If the evaporator coils are to operate independently of each other, each should
have its own suction riser sized to the coil’s capacity.
• Insulate suction lines.
• Suction lines longer than 100 ft are not recommended.
The recommended discharge line sizes are based on a pressure drop no greater than the
equivalent of a 1.5°F change in saturation temperature. Discharge line sizes that provide a
minimum 1500 ft/min velocity are provided as a reference when sizing risers.
The recommended liquid line sizes are based on a pressure drop no greater than the
equivalent of a 1°F change in saturation temperature. Liquid lines sizes that provide a
minimum 100 ft/min velocity are provided as a reference.