Advances in Eco-Friendly Refrigerants for Vapour Compression Refrigeration Systems

The refrigeration and air-conditioning sector play a central role in food preservation, thermal comfort, healthcare, and industrial processing, but the working fluids historically used in vapour compression refrigeration (VCR) systems — chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) — contribute significantly to ozone depletion and global warming. International agreements such as the Montreal Protocol and its Kigali Amendment have accelerated the phase-down of high Global Warming Potential (GWP) refrigerants, driving research toward low-GWP alternatives including hydrofluoroolefins (HFOs), hydrocarbons (HC), ammonia (R717), and carbon dioxide (R744). This paper reviews the thermodynamic, safety, and environmental characteristics of conventional and eco-friendly refrigerants, compares their coefficient of performance (COP) and energy efficiency in VCR systems, and discusses the technical, safety, and regulatory challenges associated with their adoption. The review finds that natural refrigerants and HFO blends offer substantial reductions in GWP with competitive or improved energy performance, though flammability, toxicity, and system-redesign requirements remain key barriers to widespread implementation. The paper concludes with recommendations for future research directions, including refrigerant blend optimisation, safety engineering for mildly flammable fluids, and integration of renewable energy with next-generation refrigeration systems.