High-speed turbocompressors for natural fluid heat-pumps: from integrated design to digital-twin.

Compressors for commercial and industrial heat-pumps in the 100kW-load range are currentlydominated by positive displacementmachines. In the context of refrigerant phaseouts andchanging regulations, natural refrigerants are seen as a compelling alternative by a growingnumber of policy makers and industrial players. The excellent thermodynamic properties ofammonia in heat-pump applications, combined with oil-free, high-speed centrifugal compressorsrunning on gas lubricated bearings offer the possibility of significant COP improvementsover a wide operating range. In addition, increased safety by refrigerant charge reduction,system compactness and increased planned maintenance intervals are major advantageswith respect to the state-of-the-art. Novel solutions andmethods associated with the turbomachinerydesign, thermal management, high ND numbers (product of the rotor speed tothe bearing diameter), material selection,motor design, design integration and optimizationhave been implemented in order to achieve first experimental data of the two-stage prototyperunning in ammonia at a maximum rotor speed of 90 krpm and with isentropic efficiencies inexcess of 80%.