Refrigerant Piping

Refrigerant piping is an process where heat is move from one location to another by the use of refrigerant in a closed cycle. A refrigeration cycle consists of oil management, gas and liquid separation, subcooling, superheating, piping of refrigerant in a liquid and gas, and two-phase flow in the condenser drain line.

Applications include air conditioning, commercial refrigeration, and industrial refrigeration.

Desired characteristics of a refrigeration system may include:

• Year-round operation, regardless of outdoor ambient conditions;
• Possibly wide load variations during short periods without serious disruption of the required temperature levels;
• Frost control for continuous-performance applications;
• Oil management for different refrigerants under varying loads and temperatures; and
• System efficiency, maintainability, and operating simplicity.

A successful refrigeration system depends on a good piping design and an understanding of the required accessories.

Refrigerant line velocities

Economics, pressure drop, noise, and oil entrapment establish feasible design velocities in refrigerant lines. These are:

Suction line – 700 to 4,000 fpm

Discharge line – 500 to 3,500 fpm

Condenser drain line – 100 fpm or less

Liquid line – 125 to 450 fpm

Higher gas velocities are sometimes found in relatively short suction lines on comfort air conditioning or other applications where the operating time is only 2,000 to 4,000 hrs per year and where the low initial cost of the system may be more significant than low operating cost.

Industrial or commercial refrigeration applications, where equipment runs almost continuously, should be designed with low refrigerant velocities for the most efficient compressor performance and low equipment operating cost.

The liquid line from the condenser to the receivers should be sized for 100 fpm or less to ensure positive gravity flow without incurring a backup of liquid flow. Liquid lines from the receivers to the evaporator should be sized to maintain velocities below 300 fpm, thus minimizing or preventing liquid hammer when solenoids or other electrically operated valves are used.