Patent ID: 7412841

Claim:
A turbo chiller comprising: an evaporator, a condenser, an expansion valve opening control device which controls a degree of opening of an expansion valve provided between the condenser and the evaporator, and a compressor of comprising: an inverter-driven electric motor which is driven by an inverter and subjected to rotation speed control; a turbo compressor unit which is rotated by the inverter-driven electric motor to compress an intake refrigerant; and a rotation-speed control device which controls the rotation speed of the turbo compressor unit by means of a control signal transmitted to the inverter; wherein the rotation-speed control device is provided with an aerodynamic feature map indicating a rotating stall line at which rotating stall occurs, on a map represented by a first parameter reflecting a volume flow based on an output thermal capacity of the chiller and by a second parameter that reflects a head based on an evaporator pressure, a condenser pressure, and the output thermal capacity; and wherein the rotation-speed control device includes: a minimum rotation speed obtaining unit that obtains a minimum rotation speed from the second parameter and the rotating stall line on the aerodynamic feature map at a current operating state; and a rotating speed instructing unit for instructing the inverter to drive at a rotation speed greater than or equal to the minimum rotation speed obtained in the minimum rotating speed obtaining units, wherein the expansion valve opening control device controls the expansion valve to be in a speed-of-sound reduction transition region, from a liquid phase state to a vapor-liquid two-phase state, where a rate of decrease of the speed of sound of the refrigerant is reduced.