Air Conditioner Ready to Change Industry
Award-winning air-conditioning cycle cools with a fraction of air conditioner's energy.
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NREL engineers Jason Woods, left and Eric Kozubal conduct research on a DEVAP prototype at the HVAC Systems Laboratory.
Credit: Dennis Schroeder
When National Renewable Energy Laboratory (NREL) scientist Eric Kozubal began pondering an evaporative and desiccant cooling system in 2006, the concept wasn't new. After all, desiccants are used to create very dry air, ideal for cooling with evaporative techniques. Desiccants, which can be liquids or solids, had been deployed in heat-exchange cooling systems before. There were, however, limits to their effectiveness.
In looking for something better, Kozubal envisioned combining desiccant and evaporative cooling into an innovative "cooling core." This would marry the desiccants' capacity to create dry air using heat and evaporative coolers' capability to turn dry air into cold air. If it worked, it could be nearly twice as efficient as conventional heating, ventilation, and air conditioning (HVAC) systems. However, the path wasn't clear cut.
Kozubal, who was joined on the quest by Jason Woods and Jay Burch under program manager Ron Judkoff, noted significant challenges.
"What we thought was far removed from what it evolved into," Kozubal said.
Judkoff added, "We'd investigated evaporative and desiccant cooling technologies for many years, but could not find a way to combine them in a cost-effective manner. The recent availability of new materials, and the creativity of our researchers resulted in a major breakthrough with great potential for the future."
The researchers found out that they couldn't just use off-the-shelf components to build the technology they envisioned. In addition, they discovered that they needed to use liquid desiccants in close contact with the airflow in the cooling system. This need created problems in early desiccant systems, however.
The first desiccant systems were plagued by a problem called "carry-over", in which desiccants can get into the airflow and corrode the rest of an HVAC system's ductwork and components. Kozubal said that they needed to find a way to create positive separation between desiccant and air. This led to the invention of an air conditioner that uses an innovative membrane that is permeable to water vapor, but not the liquid desiccant.
Proof-of-Concept Shows Potential for Every Climate
In early 2008, NREL constructed a proof-of-concept prototype and showed that the air conditioning cycle worked as expected and could be built using inexpensive materials. Unlike an evaporative cooler, which is only effective in dry climates, the Desiccant-Enhanced Evaporative (DEVAP) Air-Conditioning Cycle approach could function in any location.
Encouraged, the research team followed the path to full-scale development of the invention. NREL partnered with two industry experts, AIL Research and Synapse Product Development, who would help construct the two proof-of-performance prototypes. By the end of 2011, they had successfully built the working demo models and written a report that garnered industry interest. See the DEVAP technical report.
Unlike energy-intensive conventional systems, DEVAP requires neither a compressor nor environmentally harmful refrigerants, but instead uses a liquid desiccant cycle that removes humidity from the air, then uses thermal heat to evaporate water out of the desiccant in a component called a regenerator. Thus, energy is expended only to dehumidify the air, while evaporative cooling further amplifies the cooling effect.
The researchers expect that natural gas will provide the energy in most cases; however, DEVAP can also be integrated with solar and waste heat. The design eliminates much of the electricity needed to power a conventional air conditioner, because only fans and small liquid pumps are needed. As a result, a DEVAP air conditioner is expected to use 30% to 80% less energy than top-of-the-line refrigeration-based air conditioning.
"We're still evolving the idea," Kozubal said, with "a lot of science to make it smaller and cheaper."
The next phase, he explained, is to continue to refine the components to reduce size and cost. The next step for this project will be to build it into a prototype that will demonstrate a marketable air conditioner design. This could take another several years. Once completed, Kozubal expects the first application would be in the commercial cooling market, which has packaged air conditioners that will be easy to retrofit or replace with new technology. Residential cooling would certainly follow.
A Disruptive Technology in the Making
Kozubal sees DEVAP becoming a popular choice because of the likely savings in energy costs. These are key, because air conditioning currently consumes about 15% of the electricity generated in the United States and is a major contributor to peak electrical demand on hot summer days.
DEVAP has other benefits, including:
- Removing harmful refrigerants, which have a far greater global warming potential than CO2
- Better temperature and humidity control than standard AC because DEVAP treats each separately and effectively
- Better indoor air quality, because vast ventilation air is inherent in the DEVAP AC cooling cycle—gone will be the days of stuffy homes and sleepy co-workers.
"It could be a disruptive technology," he said, to describe this innovation that is poised to revolutionize embedded concepts about energy costs and consumption. And during times of heavy electricity use, that kind of disruption is welcome.
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— Ernie Tucker