R744 refrigeration technologies for supermarkets in warm climates

Energy efficiency, covering of AC load & full heat recovery and cost efficiency of commercial refrigeration systems still have a large development potential when systems applying R744 as the only refrigerant. The system architecture has to be adapted to the working fluid properties, especially with respect to the maximizing of the system efficiency when these units are operated at elevated ambient temperatures. The objective of this study was to investigate the energy required for different R744 commercial refrigeration systems at various global locations. The most promising system configurations were described and performances were modelled for high ambient temperature operations based on experimental results from laboratory investigations and pilot shops in various countries. The energy consumption of these R744 system configurations were compared with measured values for H(C)FC supermarket refrigeration systems. It was shown that the efficiency level of R744 systems may be increased to exceed the baseline HFC system even at ambient temperatures up to 35-40°C by applying ejector supported parallel compression. This means that the systems may be energy competitive at peak power even in the hottest climates of the world. At lower ambient temperatures, the efficiency of the R744 systems is always superior, resulting in seasonal efficiency of the R744 systems that clearly outperforms the H(C)FC systems.