The U.S. expends roughly 185 billion kilowatt-hours of energy each year on home cooling, the most by any nation in the world. Air conditioner sales are growing globally by roughly 20 percent per year, with the newly affluent in China and India leading the way. How do we beat the heat without increasing that heat through global warming caused by burning fossil fuels to power the air-conditioner? The U.S. Advanced Research Projects Agency for Energy, ARPA–E, hopes to cut this hot forecast by reducing the energy required for air-conditioning.
Conventional air-conditioners employ refrigerants such as chlorofluorocarbons to absorb heat from the room to be cooled. That heat is then expelled outside, requiring electrically powered pumps and compressors. One idea to conserve energy is to replace coolant fluids and gases—which are often super-powered greenhouse gases capable of trapping more than 1,000 times more heat than CO2—with solid materials, such as bismuth telluride.
A new device uses electricity to change a thermoelectric solid to absorb heat, and could lead to cheaper air-conditioners or refrigerators. Such refrigerators, which lack moving parts and are therefore less likely to break down, can be lifesavers in remote, rural areas for keeping medicines cool or food fresh.
Another approach is to employ specialty membranes to cool air by condensing water. These technologies are being developed by companies and now have acquired backing from the U.S. Navy, which requires efficient air-conditioners and dehumidifiers for both troops and equipment in hotspots such as Iraq and Afghanistan. "A 30 percent improvement in efficiency means 30 percent less fuel to drag to the front," Martin notes, adding that the Navy program aims for units that use 20 to 50 percent less fuel.
More efficient air-conditioners can provide cooling that could prove vital for people trying to adapt to more extreme heat waves in the future, whether in the U.S. or India. Meanwhile, a simple approach to cut down the HVAC bills would be to keep the knob a level higher than freezing temperatures - a practice in many places!