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