Thermodynamic and economic seasonal analysis of a transcritical CO2 supermarket with HVAC supply through ice thermal energy storage (ITES)

A real case of a supermarket where a CO2 refrigerating plant also supplies heating, air conditioning and hot water is considered. Ice thermal energy storage (ITES) is used both as latent storage in summer and as sensible thermal energy storage (TES) in winter to partially cover the space cooling/heating load of the supermarket. In particular, it allows to reduce peaks in the electrical power use, when the refrigeration and HVAC systems are running at full power together with ovens and heaters for meals. A thermodynamic analysis, including a detailed theoretical model of the formation and melting of ice on the coils, is carried out to predict the behaviour of ITES during the charging and the discharging phases. A daily energy analysis for both a winter and a summer typical day, and an annual analysis are carried out for the whole system. In summer, two cases are evaluated, i.e. supplying the whole AC demand in the morning or partially covering the AC demand to reduce the design capacity of the reversible heat pump. In all cases, the use of ITES aimed at shaving electrical peaks leads to a higher electrical energy use, also on an annual basis. However, the cost analysis reveals significant benefits, including a reduction in the required capacity of the reversible heat pump, better exploitation of tariffs and the avoidance of installing an electrical transformer in a dedicated room. This results in savings €58,699 over 10 years €47,888 over 15 years, making the choice of ITES more economically advantageous within the typical lifetime of these systems