Experience with R744 refrigerating systems and implemented multi ejectors and liquid overfeed.

Two CO2 refrigerating systems with parallel compression and ejectors have been designed, installed and commissioned in 2014 in a Swiss supermarket. Additional components and measuring instruments are installed, so that different operation modes and control strategies can be investigated. Recorded data from the first year of operation are analyzed. Since the end of 2014, the systems are running in the ejector operation mode. The ejectors recover expansion work which normally is lost. The recovered work is applied to return liquid and vapour from the MT suction accumulator downstream of the MT evaporators back to the medium pressure receiver. Due to the liquid ejectors and the MT suction accumulators, the MT suction pressure of system A was raised from -8°C up to -2°C and of system B from -8°C up to -3°C. Further, the systems are equipped with an LT suction accumulator and two internal heat exchangers. Thereby, the LT suction pressure of system A and B was raised from -33°C up to -26°C. Switching from booster operation mode to ejector operation mode, the energy consumption of the systems has been reduced by 15 to 20%. Depending on the application, climatic region and the demand of the heat recovery, the annual energy efficiency improvement of ejector supported CO2 refrigerating systems compared to ordinary CO2 systems with parallel compression is between 15 to 25%.