| Summary: | The objective of this work is the comparison of the different cascade refrigeration systems with CO<sub>2</sub> in the low-temperature circuit. A total of 18 different cascade refrigeration systems are examined including the CO<sub>2</sub>/CO<sub>2</sub> cascade system. The analysis is performed for four different evaporator temperatures (−35, −25, −15 and −5 °C), while the condenser temperature is ranged from 10 up to 45 °C. The systems are compared energetically, as well as using the total equivalent warming impact (TEWI) for yearly operation at the weather conditions of Athens (Greece). The final results show that all the examined cascade systems are more efficient than the CO<sub>2</sub>/CO<sub>2</sub> cascade system. The natural refrigerants (NH<sub>3</sub>, R290, R600, R600a and R1270) seem to be the most appropriate choices according to the energy and the TEWI criteria. Moreover, the refrigerant R152a is a promising choice for achieving high performance with a relatively low TEWI.
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