ICESQUARE / Piping design
Refrigerant piping velocity and pressure drop
Check pipe diameter at both ends of the load range. At minimum load, suction gas must carry oil back to the compressor. At maximum load, pressure drop must stay within the design allowance.
- Minimum and maximum flow
- Inside diameter
- Velocity and pressure drop
- Check each section
Calculate velocity using the inside diameter
For single-phase flow, divide mass flow by local density and internal cross-sectional area. The formula is v = ṁ/(ρ × A). With a 20 mm inside diameter and vapor density of 8 kg/m³, 0.020 kg/s gives about 8.0 m/s. At 0.008 kg/s and the same density, velocity drops to 3.2 m/s. The example shows the effect of modulation. Acceptance criteria depend on the refrigerant, oil and geometry.
Add losses along the actual route
Include straight pipe friction, losses through elbows, valves and filters, and elevation effects. Use equivalent lengths or loss coefficients for fittings and manufacturer data for components. For suction lines, also express the drop as an equivalent saturation-temperature change where the operating regime allows it. This shows how much pressure is lost before the compressor inlet.
Use criteria specific to each line
For suction lines, verify oil transport, especially in risers and with the lowest-flow compressor combination. In liquid lines, check that friction and elevation leave enough subcooling to avoid flash gas before the valve. For discharge lines, check pressure loss, velocity and vibration. Each line operates at a different density.
Document a calculation that can be checked
Identify each section, service, inside diameter, length, elevation, fittings and operating conditions. Record velocity at minimum and maximum flow, pressure drop in the critical case and the acceptance criterion. If the route changes in the field, update the review before finalizing the drawing.
Guide for trained technicians. Follow the manufacturer’s procedure and limits for the refrigerant and equipment model being serviced.
Technical references
- Copeland · Refrigeration Manual, Part 4 · AE-104, System Design · “Refrigerant Piping”
- Danfoss · Application Guidelines · AB250386497483EN-000701 · “Design Piping”