Total Environmental Warming Impact (TEWI) Calculations for Alternative Automotive Air-Conditioning Systems

The Montreal Protocol phase-out of chlorofluorocarbons (CFCs) has led manufacturers to develop refrigeration and air-conditioning systems that use refrigerants that do not damage stratospheric ozone. Most refrigeration industries have adapted their designs to use hydrochlorofluorocarbon (HCFC) or hydrofluorocarbon (HFC) refrigerants; new automobile air-conditioning systems use HFC-134a. These industries are now being affected by scientific investigations of greenhouse warming and questions about the effects of refrigerants on global warming. Automobile air-conditioning has three separate impacts on global warming; 1) the effects of refrigerant inadvertently released to the atmosphere from accidents, servicing, and leakage; 2) the efficiency of the cooling equipment (due to the emission of CO₂ from burning fuel to power the system); and 3) the emission of CO₂ from burning fuel to transport the system. The Total Equivalent Warming Impact (TEWI) is an index that should be used to compare the global warming effects of alternative air-conditioning systems because it includes these contributions from the refrigerant, cooling efficiency, and weight.

This paper compares the TEWI of current air-conditioning systems using HFC-134a with that of transcritical vapor compression system using carbon dioxide and systems using flammable refrigerants with secondary heat transfer loops. Results are found to depend on both climate and projected efficiency of CO₂ and flammable refrigerant systems. Performance data on manufacturing prototype systems are needed to verify the potential reductions in TEWI. Extensive field testing is also required to determine the performance, reliability, and “serviceability” of each alternative to HFC-134a to establish whether the potential reduction of TEWI can be achieved in a viable consumer product.