If you've ever visited Vegas in the summertime, you know the American West gets hot. Insanely hot. But air-conditioning all those casinos (and hotels and restaurants and shopping malls) takes a lot of energy. Which is why a group of scientists, engineers, manufacturers, and industrial air-conditioning users have teamed up to find ways to seriously scale up air-conditioner efficiency.

One participant in the "Western Cooling Challenge," a program being run by the Western Cooling Efficiency Center, at the University of California, Davis, has already developed a rooftop air-conditioning-unit retrofit that uses 65 percent less energy than a conventional unit.

Most air-conditioners use electric motors to compress refrigerants (such as Freon) and cool the air surrounding refrigerant coils. But all of the designs submitted to the Challenge have also incorporated what's known as "evaporative cooling." By drawing air through water-soaked pads, evaporative coolers lower ambient temperature by evaporation (much the way a sweating human body does).

This type of cooling works best in areas with low humidity, but hybrid rooftop units (combining compressive and evaporative cooling) may prove applicable in a range of arid and semi-arid environments. Which means production levels could go up and prices come down -- leaving all those casinos to pass on the savings to gamblers. Or not.