7AC Technologies, a start-up from Boston, is creating a commercial prototype of an air conditioner it claims will be able to cut cooling costs by 50-75 percent, and heating costs by about 50 half. How does it work? It uses a combination of salt water and high-tech plastic to help the air conditioner remove humidity from the air. In traditional air conditioners, this is accomplished by way of a condenser. Condensers do a good job of removing moisture, but at a significant energy cost. To save energy, the 7AC air conditioner uses a set of plastic plates covered with a proprietary membrane licensed from the National Renewable Energy Laboratory. As water flows inside each plate, salt water is sprayed onto the surface – and attracts moisture from the air as it runs down. The salt water is then collected, sprayed onto another set of plates that heat the solution and exhaust the hot air and water vapor. The salt solution is then returned to the system. 7AC Technologies’ CEO, Peter Vandermeulen, described the polypropylene membrane:

It's made using the same process they use to make garbage bags. Except if you saw it under a microscope, the plastic sheet would look like netting.

Because the operating temperature of the system is a relatively low 100 degrees Fahrenheit, i's possible use a range of heat sources including solar, natural gas and waste heat. Efficient, but there is a trade-off – the 7AC Technologies system is a net user of water.