Creating "Cool" Cars

Operating the air conditioning is the largest auxiliary energy drain on cars. In December 2008, DOE announced a project to study and develop thermoelectric heating and cooling systems. As partners in the project, NREL will team up with Ford to research efficient ways of cooling vehicles.

This collaboration is possible through a Cooperative Research and Development Agreement (CRADA). The National Renewable Energy Laboratory (NREL) has been working for years to understand how cooling techniques affect fuel use, as well as thermal comfort. A 2002 NREL analysis discovered that the U.S. uses 7 billion gallons of fuel per year for light-duty vehicle air conditioning.

NREL's Vehicle Climate Control Laboratory (VCCL) was developed to simulate the heating that takes place as the passenger cabin is exposed to sunlight, changing temperatures, and humidity - all while the cabin interior is cooled using an air conditioning system monitored by sensors linked to a computer.

ADAM - ADvanced Automotive Manikin - is the VCCL's most sophisticated test subject. ADAM is basically a human-sized sensor that measures heat at 120 independently controlled zones. As ADAM "sweats" or "shivers," corresponding data go into a computer model that simulates human responses.

The physiological model that controls ADAM is linked to another NREL computer model that predicts human comfort in various temperature settings. Working with researchers at University of California, Berkeley, NREL developed a way to translate data into corresponding human comfort levels.

NREL's Vehicle Ancillary Load Reduction team has previously evaluated technologies that reduce the amount of fuel used for air-conditioning. With no moving parts except the air blower, thermoelectric heating or cooling is achieved by providing an electric current to a thermoelectric unit. Heat can be generated or removed from the passenger compartment depending on the direction of the current. Researchers believe this type of system has the potential to augment the traditional air-conditioning unit and reduce vehicle fuel use.

One critical benefit of reducing thermal loads is that occupants experience lower temperatures when entering a heated vehicle and therefore feel more comfortable. NREL's research has shown that certain technologies, such as solar-reflective glass and parked-car ventilation, can significantly reduce thermal loads and fuel use. Cooling occupants through ventilated, cooled, or low-mass seats also shows the potential for energy savings.

Senior Engineer John Rugh says, “All of these pieces - from our past research in load reduction, to the VCCL and ADAM - make NREL a strong partner in this CRADA, and we are excited to be helping move this research forward and hopefully someday change the way we cool our cars."

This summer, according to Rugh, the research teams will be analyzing overall thermal loads with respect to vehicle cooling, and looking at how the number of thermal electric devices in a car can be reduced to help reduce costs. The researchers will also look into how to cool the people in the car rather than the car itself, possibly through strategic vent placement.

(Federal Laboratory Consortium for Technology Transfer)

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