Abstract
Energy efficiency, 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 in the focus with respect to increase the system efficiency when these units are operated at elevated ambient temperatures. The objective of this work is to investigate the energy required for different R744 commercial refrigeration systems at various locations in China. The most promising system configurations designed for high ambient temperatures as described by Hafner 2014 are taken into consideration, these are:
• Standard R744 booster cycle (R744 baseline)
• R744 booster cycle with a mechanical subcooler (MS) unit: working fluid MS: hydrocarbon
• R744 ejector supported parallel compression system
The energy consumption of these R744 system configurations are compared with measured values for HFC 404A supermarket refrigeration systems. It is shown that the efficiency level of R744 systems may be increased to exceed the baseline HFC system at all ambient temperatures up to 42'C either by utilizing mechanical sub-cooling or by 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 are always superior, resulting in seasonal efficiency of the R744 systems that clearly outperforms the HFC systems.
• Standard R744 booster cycle (R744 baseline)
• R744 booster cycle with a mechanical subcooler (MS) unit: working fluid MS: hydrocarbon
• R744 ejector supported parallel compression system
The energy consumption of these R744 system configurations are compared with measured values for HFC 404A supermarket refrigeration systems. It is shown that the efficiency level of R744 systems may be increased to exceed the baseline HFC system at all ambient temperatures up to 42'C either by utilizing mechanical sub-cooling or by 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 are always superior, resulting in seasonal efficiency of the R744 systems that clearly outperforms the HFC systems.
