AC alternative could slash electricity use in cooling by 50%

Source: By Miranda Willson, E&E News reporter • Posted: Wednesday, August 26, 2020

Researchers have developed a way to cool people without chilling or dehumidifying the air around them, a development that they say could lead to significant energy savings in the coming decades as global air conditioning demand increases.

Environmental scientists and architects from Princeton University; the University of British Columbia; the University of California, Berkeley; and the Singapore-ETH Centre created a cooling system that absorbs heat from people via thermal radiation, making them feel pleasantly cool even when surrounded by hot, humid air.

The technology was tested in Singapore and succeeded in making 79% of test subjects feel “satisfactorily” cool, despite being in temperatures exceeding 85 degrees Fahrenheit and in relative humidity above 65%, according to a study from the team published last week in Proceedings of the National Academy of Sciences.

“This is the first demonstration that shows that you can make people comfortable without doing anything to the air and only using thermal radiation,” said Eric Teitelbaum, the study’s lead author and a former Ph.D. student in architecture at Princeton.

The cooling system, which consists of a pavilion-like structure that the researchers call a “Cold Tube,” functions similarly to radiant cooling systems, which absorb heat from indoor spaces using special panels containing chilled, circulated water, according to the Department of Energy.

However, existing radiant cooling systems can only operate effectively in dry conditions, such as in the arid Southwest, or when coupled with dehumidification systems that increase energy use. Otherwise, condensation forms.

“People don’t like it to rain inside,” said Forrest Meggers, co-author on the study and an assistant professor of architecture at Princeton, about the limitations of earlier technology.

What makes the Cold Tube unique is its inclusion of a membrane in the water-filled panels that allows radiation from human bodies to pass through, while preventing condensation from forming on surfaces such as walls or ceilings. In addition, the system works without reliance on convection, a process used in traditional and existing radiant air conditioning systems to cool the air, the researchers said.

While the Cold Tube consumes some power to cool the recirculating water, it could reduce electricity consumption by up to 30% to 50% by eliminating the need to cool and dehumidify the air itself, Teitelbaum said.

“As long as you’re supplying water to this cooling panel that is colder than a person, they’ll lose heat and feel cold,” he said.

‘Really promising’

If the technology is commercialized and distributed widely, the carbon emissions reductions could be significant, according to the researchers. Global demand for cooling is projected to overtake heating demand for the first time in 2070, the study said.

The International Energy Agency estimated in 2018 that air conditioning will be one of the biggest drivers of electricity demand worldwide over the next 30 years, with significant implications for carbon emissions unless cooling systems become more efficient.

“It’s just not a sustainable trajectory,” Teitelbaum said.

While the Cold Tube is not the first radiant cooling technology, it represents an impressive advancement in these systems by reducing the risk of condensation, said Steffen Lehmann, a professor of architecture at the University of Nevada, Las Vegas, who was not part of the study. In addition to the fact that most air conditioning systems use energy for dehumidification, traditionally air conditioning is inefficient because of the distances that cool air must travel in order to chill large buildings, Lehmann said.

“The common systems are so inefficient, so if we can do other things that are not dependent on air conditioning, that’s really promising,” he said.

An additional benefit of the Cold Tube, particularly during the global pandemic, is its ability to use fresh air instead of air-conditioned air, even if the temperature outside is hot, researchers said. The Centers for Disease Control and Prevention recommends maximizing exposure to fresh outdoor air to reduce one’s risk of contracting COVID-19 in indoor settings.

“Right now, there are tons of places that have AC in the middle of the summer, but we could in theory have the windows open if we could cool people with [these] radiant panels,” Meggers said.

One challenge that could limit applications of the Cold Tube is its size, Lehmann said. The pavilion contains 10 panels — eight vertical panels supporting two horizontal panels in a cube-like structure — that are each 4 feet by 8 feet, which Lehmann said would be better suited for public outdoor spaces rather than in buildings.

However, the design could “easily” be incorporated into indoor spaces, Meggers said. The biggest challenge will be integrating it into existing air conditioning systems that use an “air-centric” cooling model, as opposed to one based on radiation, he said.

“The technology does not involve any novel material synthesis,” Meggers said. “It’s completely standard materials.”