Are white roofs a climate solutions? Yes! White roofs reflect sunlight back into space as opposed to absorbing the light, decreasing building temperatures and lessening the call for energy-intensive air conditioning.
Although the technology for reflective paint is known, it should be enhanced. Scientists are still in search of the Holy Grail — a paint so white that it reflects the sun’s rays, devising a surface that’s cooler to the touch than the air surrounding. And now, a team of researchers from Purdue University in Indiana claim to have achieved it.
Xiulin Ruan, the professor of mechanical engineering who guided the research, stated that the average white paint on the market reflects 80-90 percent of the sunlight that strikes its surface, absorbing the remainder. Their paint reflects a whopping 98.1 percent.
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All surfaces, including roofs, radiate heat at an outward angle. This is deemed thermal radiation, or emissivity. With this new paint, the heat lost through radiation exceeds the heat garnered from the sun, said Ruan. Ruan and his colleagues discovered that a surface coated with the paint maintained a temp between 8 and 18 degrees Fahrenheit lower than the air during the day. They assert that for a 1,600-square-foot building with an average air conditioning system and electricity rate of $0.10 per kilowatt-hour, their paint could mean a savings of $36 monthly on air-conditioning.
Sarah Schneider, deputy director of the Cool Roof Rating Council, a nonprofit that rates roofing products according to their cooling properties, informed Grist that the new formula sounded very cool.
Ruan’s team created the paint with a common brightening material known as barium sulfate, used to make cosmetics, paper, and standard white paint. The innovation comes in the size and distribution of particles in the paint to increase its reflectivity.
As with the majority of scientific developments, this research is an improvement on yesterday’s designs. Other researchers have attained similar results with barium sulfate. Jyotirmoy Mandal, a postdoctoral researcher at the University of California, Los Angeles, was part of a team that printed an advance in barium sulfate–based paint a year ago that also claimed 98 percent reflectivity. Mandal said the researchers advanced the concept by improving the paint’s viscosity and resistance to abrasion.
Another “cool roofs” researcher, Ronnen Levinson of Lawrence Berkeley National Laboratory’s Heat Island Group, did say that barium sulfate paint reflects ultraviolet light, which can quicken smog production.
When used across a neighbourhood, cool roofs can lower the ambient temperature on the street, combatting the heat island effect that affects concrete-lined cities and prompts heat-provoked illness and deaths.
That’s why U.S. cities have imposed “cool roof” requisites as a part of their building codes. Los Angeles set a cool roof mandate on all new buildings and roof replacements in 2014. New York City started mandating reflective coatings on new low-slope roofs in 2009, began encompassing roof replacements in 2012, and increased the reflectivity requirement in 2019. A city-sponsored program instituted in 2009 painted 10 million square feet of roofs white in New York City over a 10-year period. Austin, Chicago, Dallas, Denver, Houston, Miami, Philadelphia, and Washington, D.C., have intermingled cool roofs into their building codes.
But, as not all of them are white, even they don’t match the effectiveness of pure white paint.
For Ruan, the whitest white also could facilitate a passive cooling or refrigeration system that sends water or air through outdoor pipes painted ivory, since the paint would keep the pipes cooler than the air surrounding.
Ruan stated that the group is partnering with a “large corporation” to offer the technology on a commercial market, and testing it via more practical metrics, such as resistance to dust and water. The product should hit the market in a year or two.