Light-Duty Vehicle Thermal Management
National Renewable Energy Laboratory (NREL) researchers are focused on improving the thermal efficiency of light-duty vehicles (LDVs) while maintaining the thermal comfort that drivers expect. Recognizing that reaching fuel efficiency goals will require a full spectrum of transportation options, the lab is working to optimize the thermal management of both electric-drive and conventional vehicles.
Fuel economy has improved considerably in recent years, but there is still a long way to go before reaching the 2025 target of 54.5 mpg. There are currently 232 million passenger cars, sport utility vehicles, vans, and light trucks in use on U.S. roads, and the average American drives 11,300 miles per year. NREL researchers estimate that the nation consumes approximately 7 billion gallons of fuel per year just to air-condition these LDVs.
NREL testing and analysis evaluates the effectiveness of thermal management strategies including:
- Thermal load reduction, using technologies and methods such as advanced window glazing, heat-pipe cooling systems, parked-car ventilation, and insulation
- Occupant thermal comfort optimization, using technologies and methods such as zonal climate control and heated, cooled, and ventilated seats
- Intelligent heating, ventilating, and air conditioning (HVAC) controls that automatically adjust to conditions to provide optimum fuel efficiency and comfort
- Thermal preconditioning to achieve comfortable cabin temperatures and preheating or precooling the battery while the vehicle is still plugged in.
Researchers use a wide range of NREL test facilities and tools to evaluate LDVs. Thermal manikins add another dimension to these evaluations, allowing researchers to gauge the impact of technology solutions on driver and passenger thermal comfort. Analogous to crash-test dummies, these manikins measure heat loss and skin temperature through numerous sensors, making it possible to efficiently and accurately predict responses to climate control adjustments.
Electric-Drive Vehicle Thermal Management
Energy needed for climate control can significantly reduce electric-drive vehicle (EDV) range—in some cases by as much as 68%. The lack of engine waste heat, combined with an electric-drive system's greater thermal management requirements, make balancing power needs and cabin comfort in electric-drive vehicles difficult. NREL research explores technologies to improve thermal efficiency and EDV range while maintaining thermal comfort.
An initial goal is to increase EDV range by 10% with improved thermal management during operation of the climate control system. This will help reduce drivers' range anxiety and, ultimately, will help increase customer acceptance of EDVs. Improving thermal comfort may also improve safety through reduced driver thermal distraction.
NREL collaborates with automotive industry partners to research and develop techniques that will reduce cooling and heating loads on EDVs to improve driving range. Related research is exploring the benefits of combining thermal management systems in vehicles with electric powertrains. By decreasing the number and weight of fluid loops, NREL researchers at the Vehicle Thermal Management Laboratory are working to reduce climate control energy consumption and increase EDV range.
Conventional Vehicle Thermal Management
Although EDVs continue to grow in popularity, they currently command only 3% of the automotive market. The power required to cool passenger compartments also lowers the fuel economy of conventional LDVs with gasoline engines. About 5.5% of total national LDV fuel use can be attributed to cooling systems. Even though a large number of passenger vehicles now get 30–40 mpg, improvements to climate control systems can make petroleum-powered vehicles even more fuel efficient. NREL researchers have examined the potential of improved cabin insulation, advanced window systems, advanced cooling and venting systems, and waste heat utilization.
Read more about NREL's conventional vehicle thermal management research in the Vehicle Ancillary Load Reduction Project Close-Out Report.