Transcritical R744 refrigeration systems for supermarket applications: Current status and future perspectives

•Transcritical R744 supermarket refrigeration systems are exhaustively reviewed.•Multi-ejector concept is the driving force behind their proliferation worldwide.•“All-in-one” concept will further promote their adoption worldwide.•Nowadays the adoption of these technologies can even be extended to warm locations.•Their potential of enhancement is still considerable. Visible signs of climate change call for urgent actions on food retail industry, since such a sector is characterized by an abundant carbon footprint. Being CO2 (or R744) recognized across the world as the most promising working fluid for supermarket applications, commercial transcritical R744 refrigeration systems have emerged as leading hydrofluorocarbon (HFC)-free technologies. This study is intended to implement an in-depth review study covering the most important aspects related to the state-of-the-art pure R744 refrigeration plants for food retail applications, including the evolution of system architectures, some field measurements, the main available results from an energy, environmental and economic perspective as well as the indispensable future investigations. It could be concluded that, in spite of some persisting barriers which still prevent such technologies from a wider adoption, the usage of R744 as the only refrigerant in supermarkets is no longer open to dispute, even in warm locations.