U.S. Light-Duty Vehicle Air Conditioning Fuel Use and Impact of Solar/Thermal Control Technologies

To reduce fuel consumption and carbon dioxide (CO2) emissions from mobile air conditioning (A/C) systems, "U.S. Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy Standards" identified solar/thermal technologies such as solar control glazings, solar reflective paint, and active and passive cabin ventilation in an off-cycle credit menu._* National Renewable Energy Laboratory (NREL) researchers developed a sophisticated analysis process to calculate U.S. light-duty A/C fuel use that was used to assess the impact of these technologies, leveraging thermal and vehicle simulation analysis tools developed under previous U.S. Department of Energy projects. Representative U.S. light-duty driving behaviors and weighting factors including time-of-day of travel, trip duration, and time between trips were characterized and integrated into the analysis. In addition, U.S. weather conditions weighted based on light-duty vehicle registrations were generated and used for the analysis. Three representative vehicle types for the light-duty fleet were selected based on registration data containing vehicle size information. These key inputs were used to support a weighted parametric analysis that quantified vehicle thermal load, vehicle accessory load, and vehicle fuel use. This analysis estimates that 7.6 billion gallons of fuel a year are used in the United States for vehicle A/C, equivalent to 6.1% of the total national light-duty vehicle fuel use. This equates to 30.0 gallons/year per vehicle or 23.5 grams CO2 per mile (g/mi) for an average U.S. light-duty vehicle. A/C is a significant contributor to national fuel use; therefore, technologies that reduce A/C loads have an opportunity to reduce fuel consumption, reduce imported oil, and improve energy security. Implementing solar control glass reduced the CO2 emissions by 2.0 g/mi and the reduction due to solar reflective paint was 0.8 g/mi. The active and passive ventilation strategies as defined in this analysis only reduced emissions by 0.1 and 0.2 g/mi, respectively. This analysis shows the potential to reduce operational costs, A/C fuel use, and CO2 emissions by implementing advanced vehicle climate control technologies including the solar/thermal technologies.