The air-conditioning industry is starting to feel the heat, and not just from the scorching temperatures that are being felt around the world. It's getting tougher to squeeze more efficiency from today's cooling technology, offering little relief anytime soon for consumers fuming from summer electric bills.

(Related: Heat Wave: 2010 to Be One of Hottest Years on Record)

Century-old refrigeration technology is simply nearing its limits in energy efficiency. The focus now is on alternative technology, with potential breakthroughs on the horizon.

"Cooling systems in general have been a tougher nut when looking for efficiency," says Mark Modera, director of the Western Cooling Efficiency Center at the University of California, Davis.

For one, air-conditioning units don't get replaced as often