Cooling off, with no guilt

Air conditioning that’s environmentally friendly? And cheap?

Patrick H. Corkery

After a long hot summer, homeowners are opening electricity bills that are sky-high thanks to months of air conditioning—and higher electricity rates in several provinces. Add to that the guilt, felt more deeply by some, of heating the globe while cooling your home. But relief, both financial and moral, is on the horizon. Scientists at the U.S. government’s National Renewable Energy Laboratory (NREL) have created a new method of air conditioning that could use up to 90 per cent less energy than today’s high-tech units. The new units rely on an environmentally friendly saline solution without using conventional refrigerants that can contribute significantly to global warming.

The idea for the desiccant-enhanced evaporative air conditioner, or DEVap—clearly the science is further along than the marketing—came to co-inventor Eric Kozubal about three years ago. In a nutshell, it uses thin membranes, a liquid desiccant salt solution and water to produce cold-dry air that works in both humid and dry climates.

Despite its clunky name, DEVap is an elegant and simple way to merge the best features of two existing, lesser-known cooling systems. The first is evaporative cooling, which can be as simple as cooling air by blowing it across water. While its operating cost is lower than the ubiquitous refrigerant system, it either creates or can’t eliminate humidity, which confines its use to drier climates such as Salt Lake City, Utah, and Tucson, Ariz. The second system uses a drying agent, known as a desiccant. Since desiccants can be complex to use and maintain, the process has been largely restricted to the industrial sector, as Kozubal, a mechanical engineer at the lab in Golden, Colo., explains.

Though Kozubal isn’t the first scientist with the idea of using desiccants to fix the humidity problem of an evaporative system, his solution—membranes that keep the desiccant solution and water separated from air flow—is the first that will work for residential and commercial markets. Using the membranes also means the desiccants aren’t difficult to maintain. And since desiccants need only a modest amount of heat to dry, the energy consumption of air conditioning could be dramatically slashed. If that energy comes from solar power or a building’s waste heat, the savings would help not only pocketbooks but the overtaxed electricity grid.

The green cred of the new unit extends beyond energy-saving. NREL estimates the chemicals in a typical residential air-conditioning unit are the equivalent of up to 12,000 kg of carbon dioxide. “And refrigerants leak out of air conditioning units all the time,” Kozubal points out. “The idea is to revolutionize cooling, while removing millions of metric tonnes of carbon from the air,” he explains.

Kozubal is now working on a small prototype to show interested industrial manufacturers. Several large firms have inquired about the method. He’s also trying to make DEVap smaller and simpler, though currently it is around the same size as today’s air conditioners. Its cost, too, is similar. “The materials are not exotic, and the manufacturing methods are not complicated,” Kozubal shrugs.

While the research lab holds patents on the DEVap, a fortune in royalties won’t be flowing into the lab’s coffers or to Kozubal, since he’s a government employee. “The main goal is to make it very attractive for industry to take the technology,” he explains matter-of-factly. “We’re doing it for the benefit of society.”

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