Exploring Low-GWP Alternatives for Heat Pumps: A Drop-in Comparative Study of R1234yf/R600a and R134a

Abstract

The progressive phase-out of high-GWP refrigerants as mandated by the Kigali Amendment to the Montreal Protocol and the EU F-gas Regulation necessitates the exploration of sustainable alternatives within the HVAC&R industry. A recent proposal by the Council and the European Parliament aims to significantly reduce Hydrofluorocarbons (HFCs) consumption by 2050, including specific bans on high-GWP fluorinated gases in heat pumps and small air conditioning units. Heat pumps, pivotal in mitigating climate change, are expected to see a significant rise in residential applications. However, R134a, widely employed in these systems, has a high GWP of 1530, highlighting the need for more eco-friendly substitutes. Hydrofluoroolefins (HFOs) and natural fluids, particularly hydrocarbons (HCs), have emerged as promising fourth-generation refrigerants due to their negligible ozone depletion potential (ODP) and very low global warming potential (GWP). Despite the potential of these new refrigerants, an optimal replacement for R134a in heat pumps has yet to be found. In this regard, this study investigates the potential of the low-GWP HFO/HC mixture R1234yf/R600a (0.85/0.15) as a drop-in replacement for R134a in water-to-water heat pumps. The research conducts a comparative analysis between R134a and the nearly-azeotropic mixture, assessing their performance under identical heating conditions across 20 different combinations of heat sink and heat source temperatures, ranging from 35 °C to 70 °C and from 10 °C to 20 °C respectively. The R1234yf/R600a mixture exhibited a lower pressure ratio and higher mass flow rates compared to R134a. Additionally, the mixture showed favorable performance in terms of power consumption and compressor outlet temperatures, with slightly lower COP compared to the baseline fluid. These findings suggest that with proper optimization, the R1234yf/R600a mixture could be a viable and sustainable alternative to R134a in residential heat pump applications.