Experimental investigations on a transcritical CO2 refrigeration plant and theoretical comparison with an ejector-based one

The paper presents the development of an experimental research facility based on a transcritical single stage vapour compression refrigeration cycle with CO₂ as the working fluid. The experimental setup includes instrumentation and controls which enable tests in a broad range of operating conditions. The measurements presented refer to external temperatures between 21.0°C and 33.5°C; in this latter operating point, energy and exergy analysis allowed the breakdown of irreversibilities. In particular, the gas cooler contributes to the 42.6% of the total exergy losses while the share due to the high-pressure expansion valve is 27.2%. In order to improve the performance of the refrigeration system, a theoretical model was developed including an ejector as the replacement of the expansion valve. The results show that the Coefficient of Performance (COP) is strongly dependent on the entrainment ratio; a value of greater than 0.6 seem to lead to higher COP values, even at low external temperatures.