During hot summer days when the heat becomes barely bearable, most of us seek refuge in air-conditioned indoor spaces. The trouble, though, is that all those air-conditioners use up vast amounts of power, which is driving up global carbon emissions.
In naturally hot climates, such as in the tropics, air-conditioners keep going at full blast pretty much all year round. Worse: as the climate warms, we’ll be needing even more air-conditioning. That hardly bodes well for our plans to reduce global carbon emissions.
Creative solutions can help us stay cool in greener ways, however. One such solution involves applying white paint on the outside of offices and homes. Not just any white paint, though.
A team of materials scientists at the University of California – Los Angeles has devised a new form of extra-white paint that reflects up to 98% of the heat coming from the sun. If applied to roofs and walls, the paint can significantly reduce the need for for indoor cooling, the experts say.
“When you wear a white T-shirt on a hot sunny day, you feel cooler than if you wore one that’s darker in color. That’s because the white shirt reflects more sunlight and it’s the same concept for buildings,” explains Aaswath Raman, an assistant professor of materials science and engineering at UCLA who led the research, whose findings have been published in the journal Joule.
“A roof painted white will be cooler inside than one in a darker shade. But those paints also do something else: they reject heat at infrared wavelengths, which we humans cannot see with our eyes. This could allow buildings to cool down even more by radiative cooling,” Raman elucidates.
The idea of applying white paint to the outsides of homes in hot climates to keep an ambient temperature inside isn’t radically new, of course. In fact, as far back as in ancient times people noticed the phenomenon. Yet even the most heat-reflecting white paints currently on the market can reflect around 85% of solar radiation. The rest is absorbed by the paint itself.
The UCLA researchers tweaked a commercially available paint’s chemical composition to boost its ability to reflect solar radiation. “Current white paints with high solar reflectance use titanium oxide. While the compound is very reflective of most visible and near-infrared light, it also absorbs ultraviolet and violet light,” the scientists explain. “The compound’s UV absorption qualities make it useful in sunscreen lotions, but they also lead to heating under sunlight – which gets in the way of keeping a building as cool as possible.”
In order to cause the paint to reflect UV light better, the researchers replaced the titanium oxide in it with other ingredients such as barite, a pigment widely used by artists, and powered polytetrafluoroethylene. The team then fine-tuned the paint’s formula further by lowering its content of polymer binders, which also absorb heat.
“The potential cooling benefits this can yield may be realized in the near future because the modifications we propose are within the capabilities of the paint and coatings industry,” stresses Jyotirmoy Mandal, a member of the research team.
“We hope that the work will spur future initiatives in super-white coatings for not only energy savings in buildings, but also mitigating the heat island effects of cities, and perhaps even showing a practical way that, if applied on a massive, global scale could affect climate change,” Mandal adds.
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