More Efficient Air Conditioning for Cars

In order to squeeze more mileage out of a gallon of gas, researchers at the National Renewable Energy Laboratory in Golden, Colorado are working to improve the efficiency of a critical but often overlooked piece of automotive equipment: the air conditioner.

According to N.R.E.L.’s findings, seven billion gallons of gasoline – a volume representing nearly six percent of total fuel consumption in the United States – are used annually to run the air conditioners of passenger vehicles. Beyond fuel use, the Environmental Protection Agency reports that refrigerant leaks from auto air conditioning units add an additional 50 million metric tons of carbon emissions to the atmosphere each year.

The overall goal, said N.R.E.L.’s senior engineer and project head, John Rugh, is to improve the efficiency of conventional car air-conditioners by 33 percent.

While the approach is piecemeal, Mr. Rugh sees his work as critical to the larger effort to increase the fuel efficiency of American-built cars. New fuel efficiency standards, announced last month by President Obama, call for American auto manufacturers to achieve an average fuel efficiency of 35.5 miles per gallon.

The plan, which will cover cars built between 2012 and 2016, is projected to save 1.8 billion barrels of oil and reduce greenhouse emissions by 900 million metric tons, according to White House estimates.

E.P.A. credits for greenhouse gas reductions will also “encourage more efficient air conditioning systems,” said Mr. Rugh. “There is increasing attention on our work because of that.”

N.R.E.L. is testing will test an alternative air conditioning system that uses thermoelectrics, a kind of semiconductor that produces a hot and cold side when an electrical current is passed through it.

Small thermoelectric modules placed throughout the car, said Mr. Rugh, could potentially replace augment the power-robbing pumps and condensers of conventional air conditioners. It would also eliminate the potential for refrigerant leaks, he said.

One drawback to the use of thermoelectrics, however, is the scarcity of the material – bismuth telluride – that is used to manufacture the modules.

Beyond the wholesale re-engineering of air conditioning systems, the N.R.E.L. team is looking at simpler ways to reduce air-conditioning use. By installing solar-reflective glass and paint, for example, the N.R.E.L. team reportedly reduced interior air temperatures in a passenger car by 34 percent and seat temperatures 35 percent.

The research team, part of N.R.E.L.’s “Vehicle Ancillary Load Reduction” group, will be partnering later this summer with the Ford Motor Company, which, in December, was awarded $4.2 million by Energy Department to improve conventional air conditioning efficiency and develop a thermoelectric air-conditioning system.