Water storage to improve the efficiency of CO2 commercial refrigeration systems

Carbon dioxide is being more and more widely used in commercial refrigeration, due to its negligible environmental impact. However up to now its application as the only refrigerant is especially devoted to cold climates, which allow for the best exploitation of this refrigerant. Several solutions are being identified to extend a convenient application of CO2 also to mild climate conditions, through modifications of the refrigerating cycle and the adoption of various innovative configurations. Quite often such configurations require significant extra costs or involve the adoption of solutions not yet well established in the market. In some cases the promotion of interactions between the refrigeration systems and other systems available in the building could allow for the exploitation of simple solutions which could be easily adopted with low extra costs. In this paper a basic CO2 transcritical/subcritical commercial refrigeration system is considered, applied to cold rooms and display cabinets in a supermarket located inside a large shopping mall. Subcooling of the refrigerant is performed, taking advantage of a large fire prevention water tank. The whole refrigeration system has been modelled in Trnsys environment. Simulations have been carried out taking into account the hourly weather data and the daily profile of the cooling load demand from the refrigerated food storage equipment. Different configurations are examined, for the best exploitation of this cold storage. The technical feasibility of this solution is investigated.