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Air conditioning and indirect emissions go together in the sense that when a vehicle's air conditioning system is in use, fuel economy declines. When more petroleum fuel is burned, more pollution and greenhouse gases are emitted.
An additional, "direct" source of greenhouse gas emissions is the refrigerant used in air conditioning. Called HFC-134a, this pressurized gas tends to seep through tiny openings and escapes into the atmosphere. It can also escape during routine service procedures such as system recharging.
NREL's Vehicle Ancillary Loads Reduction team applied its vehicle systems modeling expertise in a study to predict fuel consumption and indirect emissions resulting from the use of vehicle air conditioning. The analysis process was presented to the U.S. Environmental Protection Agency (EPA), for potential use in foreign countries where such knowledge is less prevalent, ultimately to help control greenhouse gas emissions. For more information about this study check out the presentation on Significant Fuel Savings and Emission Reductions by Improving Vehicle Air Conditioning (PDF 2.12 MB). Download Acrobat Reader.
An NREL study showed that the United States uses 7 billion gallons (26.4 billion L) of fuel per year for light-duty vehicle air conditioning, equivalent to 5.5% of the total national light-duty vehicle fuel use. It would take 9.5% of the U.S. imported oil to produce this much gasoline. The fuel use percentages are based on a total annual light-duty vehicle fuel use of 125.9 billion gal (477 billion L) and imported oil of 73 billion gallons (276 billion L).
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In related work, NREL is participating in an Improved Mobile Air Conditioning (IMAC) project intended in part to select components for the "next generation" of air conditioning systems. The project entails extensive modeling to predict fuel use and carbon dioxide tailpipe emissions due to air conditioning use. Project partners include DOE, automotive original equipment manufacturers and suppliers, the U.S. EPA, the Society of Automotive Engineers, and the Mobile Air Conditioning Society. The technical goals of the project are to reduce the thermal load by 30%, increase the coefficient of performance by 30%, and reduce emissions by 50%. View a presentation (PDF 921 KB) to learn more about this project. Download Acrobat Reader.
Learn more about the VALR team's other research and development areas.
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