Lab develops A/C that cools homes using less energy

Air conditioning makes many parts of the tropics and subtropics — even temperate regions — more comfortable on those oppressively hot and sticky days of summers. But the technology that made metropolises like Miami and Las Vegas possible is also a big energy-guzzler, which is bad news for an increasingly carbon- and oil-constrained future.

Enter the US Department of Energy’s National Renewable Energy Laboratory (NREL), which has developed a new method of air conditioning that could use 50 to 90 per cent less energy than even the most energy-efficient A/Cs on the market today.

The new design combines membranes, evaporative cooling and liquid dessicants in a device its developers have dubbed DEVap (for “dessicant-enhanced evaporative air conditioner”).

“The idea is to revolutionise cooling, while removing millions of metric tons of carbon from the air,” said Eric Kozuba, a NREL mechanical engineer who co-invented the device. “We’d been working with membranes, evaporative coolers and desiccants. We saw an opportunity to combine them into a single device for a product with unique capabilities.”

The DEVap features a water- and liquid dessicant-based cooling core that draws in warm air and puts out cool, dry air. The combination of evaporative cooling and dessicant drying also provide better dehumidification than standard air conditioners, which helps to reduce energy use.

Traditional evaporative coolers, a more efficient alternative to regular air conditioners, function best in climates that are dry and warm, rather than oppressively hot. They work by running a fan over a wet mesh to blow out cool, humid air. However, the process doesn’t work in hot, humid climates, where the air is too sticky to absorb enough water to provide comfortably cool indoor temperatures.

The DEVap takes that strategy a step further by using both dessicants and evaporative cooling. The dessicants use heat to create dry air, while the evaporative cooler takes the dry air and makes it cold.

“By no means is the concept novel, the idea of combining the two,” Kozubal said. “But no one has been able to come up with a practical and cost-effective way to do it.”

In a place like Phoenix, the DEVap could provide cooling in all but the hottest months using fewer than two kilowatts, compared to a traditional air conditioner, which would consume at least 10 to 20 kilowatts.

Dessicant cooling is already used in some settings, such as industrial drying, but the technology up until now has been too complex to be practical for residential or commercial cooling. DEVap’s developers solved that problem by using thin membranes to streamline how air flow, dessicants and evaporative cooling work together.

The device also relies on salt solutions rather than refrigerants, eliminating concerns about climate-damaging substances like the chlorofluorocarbons or hydrochlorofluorcarbons used in standard air conditioners. A typical household A/C can have as much as 13 pounds of these chemicals … an amount that, released into the atmosphere, has as much warming effect as burning 1,300-plus gallons of petrol

The DEVap can also be powered by either natural gas or solar energy, as well as by electricity.

NREL has already patented the DEVap concept, and researchers now plan to continue refining the design to make it even smaller, simpler and more cost effective. Eventually, the laboratory plans to license the technology for commercial development.

“We’re never going to be in the air conditioner manufacturing business,” said Ron Judkoff, principle programme manager for building energy research at NREL. “But we’d like to work with manufacturers to bring DEVap to market and create a more efficient and environmentally benign air conditioning product.”