A CU MANUAL
IOM-14 10 of 46 Feb 06 R4
PIPING CONNECTION SIZES
Refrigerant piping must be selected to meet the conditions required for your specific installation. The
tubing connection sizes on the condensing unit and/or evaporator may or may not be the correct size for
your specific application.
DO NOT select tubing sizes based on the size of the connection stubs.
The correct tubing size for your installation must be checked and selected for each and every
job.
Traps
It is recommended that traps be installed on all suction or discharge gas risers.
Suction Line
The temperature penalty is a measure of capacity loss due to pressure drop in the tubing. Select the
suction line to have a maximum temperature penalty of 2°F (1°C). Higher temperature penalties will
reduce both system capacity and efficiency. See Refrigeration Table 3.
Use Refrigeration Table 2 Piping Guidelines to select the suction line size. Suction lines are selected at
design load conditions, and must be rechecked at minimum load conditions to ensure oil return. Tandem
compressor systems and systems with unloaders must be re-checked at the unloaded condition to ensure
oil return.
Should a compromise be required between oil return and pressure drop, oil return must always have
priority.
• Slope the suction line down with a 1:200 grade in the direction of flow to help oil return.
• Suction lines should be insulated to prevent unnecessary heat gain.
• Install oil traps at the bottoms of all risers.
Liquid Line
Select the line size using piping tables.
Liquid lines should have a maximum refrigerant velocity of 350 feet per minute (1.78 m/s) to avoid liquid
hammer.
Select pressure drop for a temperature penalty of less than 2°F. (1°C)
If a liquid line travels through a warm area, such as a boiler room, insulate the line to prevent heat gain.
Ensure the temperature penalty does not exceed the subcooling provided by the condensing unit.
A sight glass should be installed at the TX valve to ensure the valve is receiving a solid column of liquid if
adequate subcooling is a concern. An EngA Intercooler may be ordered and installed to help reduce the
effects of inadequate subcooling.
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