Energy savings of multi-chiller systems comprising hybrid-type compressors combined with thermal energy storage technology: Focusing on compressor isentropic efficiency

Compressors account for over 50 % of total energy consumption in refrigeration systems, making operational efficiency improvements vital for energy savings. This study optimizes a large-scale food industry refrigeration system by integrating hybrid type compressor selection, cooling capacity management, and thermal energy storage (TES). The optimization focusing on the collaborative improvement of chillers' coefficient of performance (COP) and the isentropic efficiency (η_is) of compressors. A hybrid multi-chiller system combines variable-speed and variable-displacement compressors, where the former enables wide-range capacity regulation and the latter operates preferentially at full load. Cooling capacity is optimized by regulating primary chilled water flow and secondary return water temperature to maintain chillers’ PLRs within their optimal COP ranges, while compressor displacement adjustments ensure η_is remains maximized. TES integration facilitates “load shifting”, reducing parallel operation time of three chiller from 550 to 93 min and eliminating frequent on-off cycles. By coordinating TES charging/discharging with compressor control, variable-displacement chillers avoid low-load conditions while maintain the capacity regulating capability of variable-speed compressors, enhancing partial-load efficiency. Implemented in a milk production facility, this strategy achieves 32.2 %–33.0 % energy savings and reduces the peak-to-valley energy consumption difference by 44.8 %–47.4 %.