Since the signing of the Montreal Protocol in 1987, the developed and developing countries have been steadily working to replace conventional hydrochlorofluorocarbon (HCFC) refrigerants, such as R22, with hydrofluorocarbon (HFC) refrigerants that have zero ozone depletion potential (ODP), such as R410A. The deadlines for phase-out of HCFC refrigerants were set for the years 2020 and 2030, respectively. In 1994, the Kyoto Protocol identified HFC refrigerants with high global warming potential (GWP) as a crucial environmental issue, and one that necessitated an immediate shift to low-GWP alternative refrigerants in order to achieve the greenhouse gas reduction targets.
The various proposals for next-generation alternative refrigerants include natural refrigerants, such as carbon dioxide (CO2) and hydrocarbons (HC), and chemical compounds, such as hydrofluoroolefins (HFO). Unfortunately, safety concerns have also been raised for low-GWP refrigerants because of their short atmospheric life and high flammability. Among HFC refrigerants, R32 has distinguished itself as an alternative refrigerant for air conditioners because of its especially low GWP of 675, which is one-third that of R410A at GWP 2,090. The air-conditioning industry has advocated the use of refrigerant R32 as the best choice at this time to satisfy all of the various factors of the environment, energy-savings, safety, and economic viability and successfully obtained the full support of the Japanese Ministry of Economy, Trade and Industry (METI).