Advanced Centrifugal | Module 308

Magnetic Bearing Chiller Surge Mapping

Field Status: Magnetic bearing chillers (oil-free) utilize high-speed centrifugal compressors. Surge is a catastrophic aerodynamic stall where the pressure differential exceeds the compressor’s ability to maintain flow, causing gas to reverse direction violently. In oil-free machines, this event can cause the magnetic bearings to overload and potentially force the shaft onto the “touchdown” (auxiliary) bearings.

Surge mapping is the process of correlating the **Compressor Pressure Ratio** against the **Inlet Guide Vane (IGV) opening**. Low condenser water temperatures (which lower head pressure) can sometimes push the compressor into the surge zone if the cooling load is too light.

SYS AUDIT: Surge Boundary Vector
SURGE STATUS: —
—

Aerodynamic Surge Mechanics

The “Surge Line” is a physical boundary on the compressor map. If you drop the condenser water temperature too low while the building load is also low, the compressor creates a “dead zone” where it cannot pump against the discharge pressure, causing the gas to dump backward through the impeller.

Load ConditionSurge Risk ProfileMitigation
High LoadExtremely LowCompressor is stable at high flow volumes.
Low Load / Low CW TempHigh RiskInstall CW isolation valves or increase CW temp setpoint.

Diagnostic Gateway Challenge

You are troubleshooting a magnetic chiller that trips on “Surge” during nighttime operation (very low load). The condenser water is currently 60°F. What is the logic-based mitigation?

END OF MODULE 308

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