Does magnetic bearing variable-speed centrifugal chiller perform truly energy efficient in buildings: Field-test and simulation results

The Magnetic Bearing Centrifugal Chiller with variable-speed control (MBCC), also known as an oil-free chiller, is highly recommended as a remarkable energy-efficient solution for space cooling in buildings by manufactures. However, MBCCs have to work coordinately with cooling demand of buildings as well as local climate. The energy performance of MBCCs rather than rated value from factory must be evaluated in operation for future applications. This paper examines actual performance of MBCCs in different buildings and cities through whole year and compares the results to conventional screw chillers and centrifugal chillers. It was disclosed clearly that MBCCs performed much efficiently especially at part load ratio of cooling demand as well as part compression ratio demand. Thus, to fully taking advantage of MBCCs for truly energy efficient in operation, one must optimize MBCCs design and operation based on annul hourly simulation of cooling demand and compression ratio demand rather than just thinking of nominal rated conditions of chillers. Based on time-series operational data log, an empirical model of MBCC was conducted which can help optimizing chiller plant design and operational strategy through annual hourly simulation of energy performance of MBCCs.