Avaliação experimental de fluidos refrigerantes alternativos ao R134a em um ciclo de refrigeração cascata com CO2

Abstract

This work evaluated the possible drop-in alternatives taking R134a as a fluid reference in the high temperature cycle, in commercial cascade refrigeration systems, using CO2 as the refrigerant fluid on the low temperature side. The aim of this work was to experimentally verify the best refrigerant pair for CO2 operating in tropical climates, under the energetic and environmental point of view, testing the main alternative fluids to R134a. Thus, the compatibility of the type of lubricating oil, as well as issues of safety, flammability, toxicity, chemical characteristics, stability and compatibility with materials, in addition to fluid availability were considered. The chosen refrigerants were R513A, R1234yf and R436A (mixture of R600a and R290), proposed to replace R134a in the high temperature cycle, operating under similar conditions in the cascade refrigeration system. The results for the Brazilian scenario, through a global analysis, aiming at energy efficiency and a lower environmental impact, showed that R1234yf and R436A fluids can be substitutes with better performance for R134a. R436A proved to be more energy efficient than R134a, while R1234yf presented values slightly lower than R134a, obtaining power consumption values around 5% higher and within a range of up to 10% in the reduction of COP values. Finally, R513A had similar energy values to those obtained by testing R1234yf. However, taking into account the TEWI, this refrigerant showed a 35% reduction, justified by the significantly lower GWP value. It is noteworthy that R513A, even with lower energy efficiency results, can be used in an R134a drop-in process, in addition to being classified as non-flammable.