Piping, Tubing, Fittings, and System Layout
The Piping, Tubing, Fittings, and System Layout domain covers how a refrigeration circuit is physically built: material selection, sizing for pressure drop and oil return, brazing, support, and testing. Items are practical - which filler to use, where a trap belongs, and how to keep oxide out of the lines.
Materials and joining
- ACR copper is cleaned and capped; use refrigeration-grade tubing only. Soft temper suits small sizes, hard drawn suits larger lines and headers.
- Braze copper to copper with 5% silver-phosphorus filler and no flux; use 15% silver with flux for copper to brass or steel.
- Flow dry nitrogen while brazing, a low trickle vented to atmosphere, to prevent carbon and copper oxide scale inside the line. That scale later plugs driers, EEV screens and compressors.
- Cut square, ream and deburr; a burr restricts flow and sheds debris into the circuit.
Sizing and layout
- Suction lines are sized for low pressure drop while keeping velocity high enough to return oil.
- Slope horizontal suction lines toward the compressor about 1 in 100 (1/4 in per 10 ft) when the compressor sits above the evaporator; add an inverted trap at the top of a riser and oil traps at the base of risers over roughly 3 m.
- Double risers allow oil return at part load.
Support and movement
Support horizontal runs every 1.8–2.4 m and near changes of direction, using hangers rather than the insulation to carry weight. Allow for expansion on long runs and fit vibration eliminators and flexible connections at compressors.
Worked example
A 12 m copper run heats from 10°C to 40°C. The expansion coefficient of copper is about 0.0000168 per °C: ΔL = 12 × 0.0000168 × 30 = 0.0060 m, or 6 mm. That is the movement an expansion loop or offset must absorb; a fully clamped straight run of that length will bow or crack a joint.
Traps
- Skipping the nitrogen purge and blaming a plugged screen on the manufacturer.
- Placing a suction trap where it creates an oil-logged low point.
- Using soft solder on a high-side joint.
- Leaving an open line overnight in a damp building.