Keep your cool

Summer temperatures can leave us feeling like Goldilocks. It's either a little too hot or a little too cold, but rarely just right.

Enter the humble air-conditioner. Ripping through hundreds of square feet of hot air, it rescues us from the swelter, so we can lounge around in a predictable, air-purified, 72 degrees.

Traditional refrigerants, of course, have also helped eat a hole in the ozone layer and push up the global temperature gauge. Now the whole world is a little hotter.

But some cool technology is on the way. And interestingly, it's mostly old technology. Since many synthetic coolants are either banned or being phased out, scientists are revisiting thermoacoustic refrigeration that cools using sound waves, solid-state devices that cool through semiconductors and have no moving parts, and carbon-dioxide systems that use compression.

All three were largely abandoned for lack of efficiency, says James Braun, professor of mechanical engineering at Purdue University.

But engineers at Purdue are experimenting with carbon dioxide again, he says, despite its global-warming reputation, because its impact is miniscule compared to that of conventional refrigerants. Hydroflurocarbons, for instance, cause 1,400 times more warming than the equivalent amount of CO2.

In the early 20th century, CO2 was a common coolant. The drawback was the high pressure required to make it work. New materials and compact ways to keep the high-pressure liquid under wraps are making the CO2 look attractive again – particularly to the automotive industry (cars are notorious for leaking coolant). But commercial application is a year or two away.

So before you turn on that air conditioner, crack a window and try nature's coolant: a summer breeze.