Review on the trend of ultra-low-GWP working fluids for small-capacity vapour-compression systems

Small-scale vapour-compression systems for refrigeration, air conditioning, and heat pump (RACHP) applications guarantee several essential human needs. The global energy and environmental policies have compelled these solutions to take a new sustainable growth path, i.e., the adoption of low global warming potential (GWP) refrigerants. The working fluids with GWP below 150 as substitutions in vapour-compression systems across six main applications have been exhaustively reviewed, and focus is given to the aspects of system performance, environmental impacts, operating conditions, and cost. Due to the negligible environmental impacts, natural refrigerants are prioritized to be selected as alternatives to high-GWP synthetics. R744 and R290 are the two most popular natural refrigerants employed across all applications. Compared with using R134a, R744 systems can save energy consumption by up to 37% in commercial refrigeration units while R290 systems can provide higher efficiencies for space heating at low ambient temperatures. R600 and R600a are used in domestic appliances to decrease energy consumption by up to 18.6% and to reduce flammability risks while mixing with R290. R1234yf, as a hydrofluoroolefin (HFO) with negligible-GWP, has been widely used as a substitution in mobile air-conditioning (MAC), although it is under pressure as currently classified as per-fluorinated alkylated substance (PFAS).