Simulation on performance and regulation strategy of centrifugal refrigeration compressor with gas bearings in water chiller

Abstract

The centrifugal refrigeration compressor is a key equipment of chiller and using gas bearing instead of traditional bearing is an important development direction. The optimized regulation strategies based on the performance of the compressor are necessary to improve system efficiency. In this paper, the mathematical model of a two-stage compressor with gas bearings and refrigeration system is established and verified to simulate the performance of the compressor under variable operating conditions, and the regulation process by rotating speed is provided. The results show that the regulation by rotating speed changes the work process of the compressor, and the various combinations of pressure ratio and mass flow rate can be obtained. For the different refrigerating capacity at the same evaporating and condensing temperature, the rotating speed and power of the compressor and the mass flow rate of the cooling motor increase with the increase of refrigerating capacity, but the isentropic efficiency and COP increases at first and then decreases. The maximum COP is 7.11 which appears at the refrigerating capacity of 358.22 kW and rotating speed of 21000 rpm. When the same refrigerating capacity is needed, the rotating speed and power of the compressor and the mass flow rate of the cooling motor increase with the condensing temperature, and the COP gradually decreases. The compressor speed should be increased from 16000 rpm to 22330 rpm if 25%-100% of the refrigeration load is needed, but the compressor can achieve high isentropic efficiency at only 50%-75% of the refrigeration load.