Study of very low-GWP refrigerants for HVAC&R applications

This PhD thesis investigates the potential of alternative low Global Warming Potential (GWP) refrigerants as sustainable replacements for traditional high-GWP fluids in medium and high temperature applications. The study focuses on two refrigerants: the ternary blend R1234yf/R1243zf/R600a (and the binary mixtures composing it), as sustainable replacement for R134a in residential heat pump systems, and the hydrochloroolefin R1130E, as component of the binary mixture 514A for Organic Rankine Cycles (ORC), centrifugal chillers and high temperature heat pumps. For the ternary mixture R1234yf/R1243zf/R600a, an all-encompassing approach is proposed, starting with a comprehensive literature review on low-GWP refrigerants to inform the selection of the mixture based on its favorable thermophysical properties and low environmental impact. Experimental characterization of key thermophysical properties, including vapour-liquid equilibrium and speed of sound, was conducted for the binary mixtures comprised in the ternary blend. Given its similarity with the blend R1234yf/R1243zf/R600a, the performance of the R1234yf/R600a binary mixture was tested in two water-to-water heat pump systems under typical operating conditions, demonstrating comparable system efficiency and reduced compressor stress as a drop-in replacement for R134a. Additionally, this study investigates the thermophysical properties of R1130E. The research includes detailed experimental measurements on its vapor pressure, density, and thermal conductivity. Overall, the thesis presents viable, environmentally friendly alternatives to traditional refrigerants, aligning with global sustainability goals. It emphasizes a holistic approach to developing and optimizing low-GWP refrigerants for medium and high-temperature systems, ensuring environmental responsibility and high performance in real-world applications.