Refrigerant Line Size for Oil Return
The largest refrigerant line inside diameter that still meets the oil-return minimum velocity.
Example
You enter
- Mass flow (lb/hr) 600
- Specific volume (ft^3/lb) 0.5
- Oil-return minimum 1500
You get
- Max line inside diameter 0.781764
- Area (ft²) 0.003333
Details, formula, and sources
d = 12 sqrt(4 m sv / (pi 60 V)). 600 lb/hr at 0.5 ft^3/lb needs a suction riser no larger than ~0.78 in ID to hold 1500 fpm. Manufacturer line-sizing tables govern.
area_ft2 = (mass_flow_lb_hr * specific_volume_ft3_lb) / (60 * target_velocity_fpm); line ID_in = 12 * sqrt(4 * area / pi). The inverse of the line-velocity relation, solved for the diameter that meets the oil-return minimum velocity.
ASHRAE Refrigeration Handbook line-sizing and oil-return guidance, by name.
ASHRAE licensed; refrigerant specific volume is read from the manufacturer's P-T / property data (user-supplied).
Estimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
Field names used by the API: mass_flow_lb_hr, specific_volume_ft3_lb, target_velocity_fpm, line_id_in, area_ft2
- Oil-return window horizontal min ~700 fpm, suction-riser min ~1500 fpm (advisory)ASHRAE Refrigeration Handbook line-sizing guidance
- Specific volume refrigerant specific volume at the line condition is state-specific and user-suppliedmanufacturer refrigerant property data