Danish company AC Sun recently made news with the “invention” a new solar-powered air conditioning system.The new systems are pollution-free, low-noise, and use only 10% of the energy of conventional systems. The only problem is they’ve already been invented, several times over.

Lars Stigel, director of Østjysk Innovation, an investor in AC Sun, spoke with enthusiasm about AC Sun’s design. “It is a groundbreaking technology in relation to renewable energy and energy savings,” he says.

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Don't touch that thermostat
The magic number is 78 degrees. In most climates this is a comfortable temperature setting. Each degree higher than that will save you 6 to 8 percent in cooling costs. You can also set it a couple degrees higher when you're not home.

Lowering the set temperature won't cool your place any quicker and will only wind up costing you more energy. Keep it at a constant temperature. The AC unit will regulate itself as designed.

Close the curtains
We love natural day light and keeping the lights off reduces the overall heat, but if no one is in a room close the curtains to keep out direct sunlight during the day. This will keep the house cooler naturally so the AC won't have to work as hard. Also, in the evening open the curtains back up to allow heat to escape. If you can't close the curtains consider installing awnings or outdoor landscaping such as trees and shrubs around these windows to provide shade.

Switch on the ceiling fan
When used properly, ceiling fans can help circulate the cool air throughout the house, and can even provide comfort on cooler days if you're able to turn the AC off.

Proper sizing and placement
Make sure your AC unit is properly sized. A bigger air conditioner does not translate into a cooler room and will end up costing you more in the end.

If possible, place your AC unit on the north side to keep it out of the heat of the day. Otherwise look to create landscaping to shade it with trees or shrubs.

Make sure the air flow is not blocked with furniture or other items, and change the filter regularly. If your AC unit is fairly old, consider replacing it with an energy star model. newer units use up to 40% less electricity.

These things will ensure your AC unit is working at maximum efficiency.

Amy says: Last summer my roommate and I bought a window unit for our apartment. Luckily our place is on the ground floor and is shaded on the outside by a few trees, but it can get hot and stuffy in the summer with successive 90 days in New York City. We turn it off on days that aren't as hot and try to create a cross breeze with open windows and a fan. So far this year I haven't put it back in the window just yet and I'm waiting until the last possible moment to do so.

Check out these links for more tips on getting the most from your AC and staying cool:

About.com
Energy Star
Department of Energy
Air-ConditionerStore.com