BACKGROUND: Researchers at the Department of Energy's National Renewable Energy Lab are working with industry to try to reduce fuel consumption from air conditioning use in cars and trucks, by improving the comfort level inside the cars in a variety of new ways. The team at NREL has already demonstrated that car seats with a little fan inside can improve a vehicle's fuel economy while improving passenger comfort. That's because ventilated seats keep drivers and passengers cooler, so they need less air conditioning to be comfortable. The NREL estimates that if all passenger vehicles had ventilated seats, it would result in a 7.5 percent reduction in the use of fuel by the air conditioning system, saving an estimated 552 million gallons of fuel each year.
OTHER STRATEGIES: The researchers are also testing such options as reflective glass insulation, different seat materials, and modifying the angle of the air flow. They are conducting the tests with a "human thermal comfort manikin" named ADAM. ADAM is a surface sensor shaped like a human body that measures heat loss. ADAM is a test dummy that can "sweat" and "shiver" to simulate the internal heat systems in the human body and how a body changes in response to heat or cool. This data is fed into a computer, which can use it to predict human thermal comfort based on these simulated "skin temperature" measurements.
HOW A/C WORKS: An air conditioner works on the same principle as a refrigerator, without the insulated box. Freon gas (or a similar refrigerant) is compressed, causing it to heat up and its pressure to rise. The hot gas runs through a set of coils, dissipating its heat so that it condenses into a liquid. The now-liquid Freon runs through a special valve that causes it to evaporate back into cold, low-pressure gas, and this cold gas runs through another set of coils. Because heat always flows from a hotter to a colder region or object, the gas will absorb heat and thereby cool down the surrounding air.
COOL CARS: All cars come with a built-in cooling system. That's because gasoline engines are quite inefficient at converting chemical energy into mechanical power. Most of that energy (70 percent) is converted into heat. The cooling system keeps the engine from overheating by transferring the heat into the air.