Waste heat utilization: Energy and economic benefits from multi-ejector chiller sub-cooling R744 supermarket refrigeration systems

This study investigated the energy and economic benefits of a novel sub-cooling technique using a heat-driven multi-ejector chiller (HDEC) in R744 supermarket refrigeration systems. Two configurations were evaluated: a conventional booster system with HDEC (CBEC) and a parallel compression system with HDEC (PCEC). Among various natural refrigerants, R717 was identified as most suitable for the HDEC. Various multi-ejector combinations were examined to assess the potential for waste heat utilization and energy savings in the R744 refrigeration system. The CBEC system provided effective operation only at ambient temperatures above 31 degrees C, whereas the PCEC system was effective above 24 degrees C. Performance of the proposed configurations were compared with a conventional R744 booster system (CB) and a parallel compression system (PC) both devoid of HDEC. The PCEC system showed improvements in the coefficient-of-performance ranging from 4.2 % to 23.9 % at ambient temperatures between 28 degrees C and 40 degrees C compared to the baselines. In various warm-climatic zones, including India, the Middle East, Thailand, and the USA, energy savings of approximately 2.1 %-9.5 % were observed compared to the PC system. Economic analysis indicated a reasonable payback period of 2.1-2.7 years for the additional investment required for deploying the PCEC system in Phoenix.