How to Design Vertical Refrigerant Risers and Oil Traps

nexoradesign.net
1 day ago
2 min read

Vertical refrigerant risers are critical for proper oil return in DX, split AC, heat pump, and VRF/VRV systems. If the riser is too large, refrigerant velocity becomes too low and oil may not return to the compressor.

If it is too small, pressure drop increases and cooling performance can reduce. Key design rule: Maintain enough refrigerant velocity for oil return while keeping pressure drop acceptable.

Basic velocity equation:

v = m_dot / (rho x A)

Oil traps are usually installed at the base of vertical suction risers and sometimes at intermediate levels in tall risers.

A common preliminary rule is one trap every 6 m to 9 m of vertical lift, but manufacturer requirements must always be followed. For systems with wide capacity variation, double suction risers may be required to maintain oil return at low load and reduce pressure drop at high load.

Common mistakes to avoid:

- Oversized suction risers

- Too many oil traps

- Ignoring part-load operation

- Ignoring liquid line lift

- Poor pipe support

- Not following manufacturer piping limits (How to Design Vertical Refrigerant Risers and Oil Traps)