Experimental evaluation of low-GWP refrigerants R513A, R1234yf and R436A as alternatives for R134a in a cascade refrigeration cycle with R744

This work presents an experimental analysis of the energy and environmental performance of low-GWP re-frigerants R513A, R1234yf and R436A as alternatives for R134a in a cascade refrigeration system that operates with R744 in low-temperature cycle. An apparatus was built using a well-insulated room, where tests were carried out in a steady state condition. In addition to the typical components of a cascade cycle, an intermediate heat exchanger was used to thermally communicate the low and high temperature cycles, thus providing additional superheating and subcooling, respectively. The cooling capacity of the system ranged from 2.2 to 3.8 kW, the evaporation temperature varied from-34 to-24.5 degrees C and the air temperature inside the cold room ranged from-23.1 to-9.4 degrees C. The results revealed that the alternative refrigerants are potential substitutes for R134a in cascade refrigeration systems, showing an average increase in the CRC coefficient of performance of 3.1% for R436A, while R1234yf and R513A exhibited a reduction of 3.7% and 4.4%, respectively. The environmental impact analysis considered the scenarios of Chicago (USA) and Curitiba (Brazil), the latter being a southern Brazilian city with a wet climate throughout the year, a warm and mostly cloudy summer, and a short and cold winter. Total TEWI values, compared to those obtained with the originally designed R134a system, showed reductions in CO2 equivalent emission of 46%, 42.1% and 22.5% for refrigerants R436A, R1234yf and R513A, respectively, for the Curitiba scenario, while the values for Chicago were increments of 0.3%, 2.4% and 5.8%, respectively.