Cost-effective optimization for charging/discharging cycles of thermal energy ice storages in transcritical R744 supermarket refrigeration systems

Abstract

Due to the low critical temperature of R744, supermarket refrigeration systems using this working fluid widely operate in transcritical operating conditions, causing severe penalizations on their energy efficiency. On the one hand, this study explored the economic benefits from integrating a thermal energy ice storage to cool down the R744 leaving the condenser/gas cooler to address the aforementioned performance disadvantages. On the other hand, the literature review brought to light the lack of an algorithm to cost-effectively and dynamically optimize the charging and discharging cycles of thermal energy ice storages in transcritical R744 refrigeration systems, thus limiting their spread in supermarkets. Therefore, an innovative algorithm tailored to different climate conditions was developed in this study with the goal of minimizing yearly electricity expenses by accounting for supermarket refrigeration demand, ambient temperature, and electricity price. The novel optimization method incorporated constraints that reflected realistic requirements for the thermal energy ice storage’s expected capacity, its selected compressor, and desired level of maximum charge/discharge rate. Simulations performed in Seville (Spain), Athens (Greece) and New Delhi (India) revealed a reduction in the annual electricity bill of the supermarket by 6.9 %, 5.7 % and 12.5 % compared to the case without thermal energy ice storage thanks to the new optimization strategy, respectively. The results obtained showcase the efficacy of the innovative algorithm, suggesting a promising approach to improve the energy efficiency and cost-effectiveness in the commercial refrigeration industry.