Passive Radiative Cooling Moves Out Of The Lab & Into The Real World

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In August of 2017, we brought you news of a new hybrid material that can lower the temperature of a building without the use of electricity, using a process known as passive radiative cooling. The challenge was creating a material that can reflect incoming solar rays back into the atmosphere while still providing a means of escape for infrared radiation. The researchers embedded glass micro-spheres into a polymer film. The spheres scatter visible light while allowing infrared radiation to escape. Then they added a thin silver coating underneath in order to achieve maximum spectral reflectance.

The glass and polymer sheet is only 50 micrometers thick — slightly more than aluminum foil — and can be manufactured using conventional roll-to-roll production techniques. Other products that use roll-to-roll technology include cylindrical lithium ion battery cells. Roll-to-roll was originally invented to make magnetic recording tape.

At the time of our original story, the researchers were focused on how to move their invention out of the laboratory and into the real world. They constructed several 140 square foot units and mounted them outdoors on the roof of a building at Colorado University at Boulder. There they tested them over a range of wind, temperature, and humidity conditions for a year.

During experiments conducted in August and September last year, the new material — dubbed RadiCold — kept a container of water 20º F cooler than the ambient air between 12:30 pm and 3 pm, the part of the day when summer sunlight is most intense.

“You could place these panels on the roof of a single family home and satisfy its cooling requirements,” Dongliang Zhao, lead author of the study and a postdoctoral researcher in CU Boulder’s Department of Mechanical Engineering, tells Science Daily.

RadiCold radiative cooling systems
Image courtesy CU Boulder

“We can now apply these materials on building roof tops and even build large scale water cooling systems…..with significant advantages over conventional air conditioning systems, which require high amounts of electricity to function,” adds professor Gang Tan of the University of Wyoming’s Department of Civil and Architectural Engineering, who participated in the study.

“We have built a module that performs in real world, practical situations,” professor Yang says. “We have moved quite far and fast from a materials level to a system level.” The RadiCold module could become a viable solution for supplemental cooling for single-family homes, businesses, power plants, municipal utilities, and data center facilities among other potential applications, Yang adds.

Earlier this year, professor Toby Peters of the University of Birmingham suggested the need for cooling as global temperatures rise could gobble up virtually all renewable energy at some point in the future. Keeping people and things cool will become hugely important as average temperatures soar, especially in places that are already overheated, such as Phoenix, Arizona. RadiCool could become an important part of the cooling process without consuming terawatts of electricity to get the job done.

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Steve Hanley

Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else The Force may lead him. He is proud to be "woke" and doesn't really give a damn why the glass broke. He believes passionately in what Socrates said 3000 years ago: "The secret to change is to focus all of your energy not on fighting the old but on building the new." You can follow him on Substack and LinkedIn but not on Fakebook or any social media platforms controlled by narcissistic yahoos.

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