Because two-stage compression technology is rarely used in small-scale and medium-scale chillers

a two-stage compression water-cooled screw chiller with a nominal cooling capacity of 615.48 kW was designed in this study. A two-stage variable-frequency screw refrigeration compressor was developed by adopting a new rotor profile and structural design. An experimental test was also conducted on the developed screw compressor and chiller according to national standards. The results show that the volumetric efficiency of the two-stage variable-frequency twin-screw refrigeration compressor developed in this study is generally higher than 96% and the maximum isentropic efficiency reaches 84.4%. The coefficient of performance (COP) of the chiller reaches 7.01 under the nominal operating condition in which the outlet temperature of chilled water is 7 ℃. This value is16.83% higher than the first-degree energy efficiency specified in GB 19577—2015 standard. The integrated part-load value is 10.45

which is 39.33% higher than the first-degree energy efficiency specified in GB 19577—2015 standard. Furthermore

the two-stage compression technology effectively improved the performance of the water-cooled screw chiller. Compared with those of the case without intermediate cooling

the cooling capacity and COP of the chiller with intermediate cooling increased by more than 11% and 8%

respectively.