Refrigerants are used in a wide variety of HVAC&R equipment. The first generation of refrigerants included substances such as hydrocarbons, ammonia, and carbon dioxide. The second generation of refrigerants included chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which became widely used because they were efficient, non-flammable, and non-toxic. In the 1980s, CFCs and HCFCs were determined to play a major role in depleting the stratospheric ozone layer. Beginning in the 1990s, the industry phased out CFCs and HCFCs in favor of a third generation of refrigerants: hydrofluorocarbons (HFCs). HFCs have zero ozone depletion potential; however, when released to the atmosphere, they have significant global warming potential (GWP)4.

The growing international emphasis on global warming mitigation has stimulated interest in a fourth generation of low-GWP refrigerants.

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