Potential evaluation of water-cooled multiple screw chillers with serial water loops and development of ultra-efficient dual screw chillers

•An energy and exergy analysis is performed on multiple screw chillers.•The maximum potential of multiple screw chillers with serial water loops is recognized.•An ultra-efficient dual screw chiller with COP above 7.0 was developed.•The COP and IPLV of the developed dual screw chiller reached 7.22 and 9.50. Applying serial water loops in multiple screw chillers has the potential to improve the COP of screw chillers above 7.0. However, the maximum potential of this method hasn’t been identified and the ultra-efficient target hasn’t been achieved until now. Therefore, an energy and exergy analysis is performed on the water-cooled multiple chillers with serial water loops in this paper to recognize their maximum potential. Analysis results show that the water-cooled multiple screw chillers with serial water loops have the maximum potential to increase COP by 26.02% and exergy efficiency by approximately 22% relative to the single screw chiller under the normal operating condition. Adding one chiller based on the single chiller system could increase the COP by 11.38%, and it is not suggested to design multiple chillers with more than four chillers owing to the reduced additional improvement in COP with the increasing number of chillers. Moreover, both condensers and both evaporators should be designed with the equal area of heat exchange, respectively, aiming to set the equal temperature difference through both evaporators and both condensers. On basis of analysis results, the ultra-efficient dual screw chillers were developed and tested. The COP and IPLV of the chillers reached 7.22 and 9.50, which were higher than the minimum allowable value of the first-order energy efficiency for water chillers by 20.3% and 26.67%.