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“ Traditional super-cool materials work by having very high reflectivity and emissivity , making them ideal for cities that only require heat mitigation . However , they can cause overcooling in cities that also need heating during cooler periods ,” Santamouris says . “ They also can ’ t be used in low-level streets or vertical façades because of the glare , so they can only really be used on roofs of highrise buildings – not in walls or pavements .”
Santamouris ’ team added new layers to the conventional super-cooling materials to help modify their solar reflectance and emissivity during colder periods without compromising the cooling efficiency .
The first layer is composed of a ‘ phase change ’ material which uses transitional metal oxides to modulate the reflectivity and emissivity during the seasons . A second fluorescent layer then increases the cooling capacity of the material .
“ We have integrated a new layer into the materials which changes the reflectivity and emissivity as a function of the ambient temperature ,” Santamouris says . “ We have also decreased the reflectivity of the materials to decrease glare by integrating [ another ] new layer that increases heat losses through fluorescence . It ’ s an intelligent material that is adaptable to any climate , can be used at a low level , and can be of any colour , and does not create any glare .”
Fluorescent materials absorb solar radiation but immediately re-emit it as fluorescent radiation at a lower wavelength . Because the material can emit more than it absorbs , it compensates for the reflectivity loss and can be used without causing glare .
The result is a material that , during the summer , has a surface temperature below the ambient temperature , providing cooling to the building , and then much above the average temperature during winter , providing heating .
“ In the recent study , we were not only able to overcome the overcooling issue , but we were able to decrease the peak summer ambient temperature up to five degrees and increase the peak winter temperature by 1.5 degrees ,” Santamouris says .
LEVELS OF APPLICATION Because the new materials rely less on reflectivity to reduce heat , they can also be used on any level of a building . “ It is also durable , non-toxic , and will be affordable when produced at scale ,” says Santamouris .
Santamouris concluded saying the team will continue to test the materials in new locations around the world with a view to making the materials commercially available . “ This technology has the potential to be used in all cities worldwide , which would reduce energy costs and help combat the impacts of climate change .” RACA
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RACA Journal I April 2022 www . hvacronline . co . za