Transcritical CO2 refrigeration plants: Experimental campaign and model-based evaluations of new technologies

The paper copes with a transcritical CO2 refrigeration plant: R744 (CO2) is an economic and natural refrigerant with a negligible impact on the environment and with good thermodynamic and safety properties compared to synthetic ones, and it is a sustainable alternative in commercial refrigeration of retail food. A specific 18 kWt test bench is available and under testing in the lab of the University of L'Aquila. Experimental tests were performed at different external temperatures between 8 °C and 33 °C: first results showed that COP (Coefficient Of Performance) decreases when external temperature grows up. Experimental data made it possible to calibrate a mathematical model of the test rig, useful to evaluate the effect of the possible introduction of new technologies: variation of receiver pressure, intercooled two-stage compression and expander in place of the high pressure throttling valve. All these technologies may be useful to improve plant efficiency and to promote new "green" installations in warmer climates, where food conservation standard in terms of goods cold-chain are increasingly demanding, especially considering EU and Global goals on HFC reduction targets (e.g. EU F-gas regulation - 2014 and Kigali amendment to the Montreal Protocol - 2016).