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With the passage of the Kigali Amendment to the Montreal Protocol, HFC-134a refrigerant will be phased down in all markets worldwide, including those where automotive companies have been slow to embrace HFO-1234yf. Engineers are currently being challenged to design MAC systems using alternate low GWP refrigerants that are allowed by regulations, and are simultaneously cost-effective to manufacture, energy efficient, safe, reliable, affordable for consumers, and also suitable in electrified vehicles. This paper documents the latest international research and developments on: 1) refrigerants that satisfy the Montreal Protocol and national environmental regulations; 2) secondary loop MAC (SL-MACs) that achieve lower refrigerant emissions and higher energy efficiency in cooling-only and cooling and heating (heat pump) applications; 3) progress in Europe, North America, and Asia on heat pump systems for electric and hybrid vehicles optimized for safety and energy efficiency, and 4) the latest SAE standards for the emerging use of HFC-152a in SL-MACs. The authors of this paper are an interdisciplinary team from organizations based in China, Germany, India, Italy, and the United States, including experts from vehicle manufacturing, AC component and system suppliers, and non-government environmental organizations.
