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Researchers scale up cooling film technology to rooftop size

Universities of Colorado at Boulder and Wyoming collaborate on cooling material which could provide air conditioning with ’almost no consumption of electricity.’

Researchers at the Universities of Colorado at Boulder and Wyoming say they have successfully scaled up an innovative water-cooling system capable of providing continuous day-and-night ’radiative cooling’. The development of the hybrid organic-inorganic radiative cooling film or ’metamaterial’ could increase the efficiency of power generation plants in summer and lead to more efficient, environmentally-friendly temperature control for homes, businesses, utilities and industries, they claim.

The new research demonstrates how the film, which was demonstrated in 2017, can be scaled into a 13 sq m array, which is small enough to fit on most rooftops. The significant benefit, the researchers say, is that the film can ’act as a kind of natural air conditioner with almost no consumption of electricity.’ 

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

The researchers’ film-like material reflects almost all incoming sunlight while still allowing an object’s stored heat to escape as much as possible, keeping it cooler than ambient air, even in the midday sun.

“The material, which we can now produce at low cost using the current roll-to-roll manufacturing techniques, offers significant advantages.” said Associate Professor Xiaobo Yin of the Mechanical Engineering department.

Associate Professor Gang Tan of the University of Wyoming’s Department of Civil and Architectural Engineering added: “We can now apply these materials on rooftops, and even build large-scale water cooling systems like this one, with significant advantages over the conventional air conditioning systems, which require high amounts of electricity to function,” said 

The researchers tested their system outdoors in a variety of weather conditions, including wind, precipitation and humidity. In experiments conducted in August and September 2017, their proprietary RadiCold module kept a container of water covered by the metamaterial 20 deg F cooler than the ambient air between 12:30 pm and 3 pm, the most intense summer sunlight of the day.

The researchers proved that a cold storage unit could be used for load shifting, using a heat transfer fluid such as water, which could then be retrieved at a later time.

Co-author, Professor Ronggui Yang of the Mechanical Engineering department said: “We have built a module that performs in real-world, practical situations. 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 many applications, from houses to data centres, Mr Yang added. The US Department of Energy’s Advanced Research Projects Agency – Energy (ARPA-E) provided funding for the research. Startup company Radi-Cool Inc holds an exclusive option to the technology through March 2019.

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