White Paint Considered for Cutting Emissions
One year after engineers from Purdue University created a new ultra-white paint, reports are now considering how the coating could slash carbon emissions and, in some cases, replace air conditioning units.
Detailing how white paint can keep buildings cool, the researchers’ study was recently published in Cell Reports Physical Science.
The ‘Whitest White’ Cooling Paint
According to PaintSquare Daily News, the research team from Purdue University initially created an ultra-white paint in October 2020. Since then, the team has been pushing to reformulate it for even “cooler” properties.
In 2021, the team published a paper about its findings in the journal ACS Applied Materials & Interfaces.
At the time, researchers went as far as to say that their white paint was the closest thing available to an equivalent of “Vantablack,” which absorbs up to 99.9% of visible light. On the flip side, the new whitest paint reflects up to 98.1% of sunlight, compared to 95.5% in the researchers’ previously developed ultra-white paint. Typically, white coatings expect to reflect 80-90% of sunlight.
Revolutionary White Paint Could Cool Greek Island Buildings Better than AC - Greek Reporter https://t.co/hk30Ucv3o8— Air Conditioning LV (@AirConditionLV) May 8, 2022
“If you were to use this paint to cover a roof area of about 1,000 square feet, we estimate that you could get a cooling power of 10 kilowatts. That’s more powerful than the central air conditioners used by most houses,” said Xiulin Ruan, a Purdue professor of mechanical engineering, at the time.
There is one key element on achieving the white coating: barium sulfate.
“We looked at various commercial products, basically anything that’s white,” said Xiangyu Li, a postdoctoral researcher at the Massachusetts Institute of Technology, who worked on this project as a Purdue Ph.D. student in Ruan’s lab. “We found that using barium sulfate, you can theoretically make things really, really reflective, which means that they’re really, really white.”
But it’s not just the high concentration of barium sulfate, it’s also that those particles are deliberately different sizes in the paint. How much light each particle scatters is directly dependent on its size, and a wider range of sizes allows the paint to scatter more of the light spectrum.
However, if there is too high of a concentration, the durability of the paint is negatively affected.
“Although a higher particle concentration is better for making something white, you can’t increase the concentration too much. The higher the concentration, the easier it is for the paint to break or peel off,” Li said.
To test the cooling traits of the paint, researchers used thermocouples to demonstrate outdoors that the paint can keep surfaces 19 degrees Fahrenheit cooler than the ambient surroundings at night, and 8 F below their surroundings during high noon. Reportedly, the paint even works in winter climates.
Patent applications for this paint formulation were filed through the Purdue Research Foundation Office of Technology Commercialization. The research was supported by the Cooling Technologies Research Center at Purdue University and the Air Force Office of Scientific Research through the Defense University Research Instrumentation Program. The research was performed at Purdue’s FLEX Lab and Ray W. Herrick Laboratories and the Birck Nanotechnology Center of Purdue’s Discovery Park.
Recently, several reports have brought the idea of utilizing Purdue’s white paint back to light. The reports have not only praised the coating for its potential to save energy, but also that the coating scatters the sunlight’s wavelengths so that it can exit through an atmospheric window.
A key feature in the coating development, the ability to send the sunlight's ray heat into deep space would create an infinite “heat sink,” according to Li. This is important not only in fighting the effects of global warming, but when air conditioners are used, they remove the heat and humidity from indoors and transfer it outdoors, increasing the overall heat sink effect of a city or town.
“Air conditioners can cool your house, but they move the heat from inside the house to outside—the heat is still in the city, it’s still on the Earth, in our air,” Ruan said.
“So even if you don’t care about the power bills you pay, it’s going to warm up the Earth anyway. Our paint does not use any power but, more importantly, it sends the heat to space. The heat doesn’t stay on the Earth, so that really helps the Earth to cool down and can stop the warming trend.”
If applied on several surfaces, apart from buildings and other structures, researchers believe that we could witness a significant global cooling effect. According to the researchers at Purdue, their ultra-white paint could reduce air conditioning by up 70% in desert cities such as Reno, Nevada, and Phoenix, Arizona.
In a separate study published in Nature Geoscience, researchers found that by creating lighter surfaces by painting structures, roads and unused land, among other things, up to a 3 C decrease in temperatures could be witnessed during the summer months. The effort would improve public health and lower both electricity usage and carbon emissions.
“It’s a lot of area, but if one day we need to use this approach to help reverse the warming trend, it’s still affordable—the paint is not expensive,” Ruan declared.
Purdue scientists have already applied for a patent on the ultra-white paint and are committed to clarifying its durability in in residential and commercial use.
Recent Cool Coating Research, Projects
Israeli startup SolCold recently begun testing a new type of coating designed to help keep buildings—among other structures and industries—cool in the presence of sunlight.
SolCold reports the coating was developed after researchers contemplated the idea of harnessing the sun's radiation in a reverse method—meaning, instead of radiation heating up buildings, it would actually help to cool them down.
Made up of four layers, the coating includes: a reflective IR emission layer at its base; a flexible, transparent, and thermal conductive layer; a layer of active cooling particles; and a confidential top layer. The company adds that the cool roof coating also utilizes an anti-strokes fluorescent patent technology.
The resulting combination reportedly creates an active cooling effect with zero implementation and maintenance.
According to reports, the coating works by reflecting most sunlight, but allows some particles of light to breakthrough. The second layer of material then reacts to the specific radiation let in and emits particles of light at a higher frequency, thus causing the material to lose energy and get cooler.
The company recently applied the coating to car roofs for concept testing. In its study, SolCold found that a white car covered with the coating was as much as 25 F cooler than a non-coated white car sitting in the sun in the middle of the day. A black car was reported to be 34 F cooler.
Earlier this year, scientists from the Lawrence Berkeley National Laboratory announced their development of an all-season smart-roof coating, designed to keep homes warm during the winter months and cool throughout the summer without consuming natural gas or electricity.
According to Berkeley Lab, the problem with current cool roof systems, most notably reflective coatings, membranes, shingles or tiles that have light-colored or darker “cool-colored” surfaces, is that they still naturally emit some of the absorbed solar heat as thermal-infrared radiation. Because of this, heat is also radiated in the winter months and can lead to increased heating costs.
To find a more effective alternative, researchers looked to metals, as the material is typically a good conductor of electricity and heat.
Results from the study revealed that the average household with TARC installed on the roof could save up to 10% in electricity usage and reflected around 75% of sunlight year-round. The thermal emittance of the material, however, was high (about 90%) when the ambient temperature was warm (above 25 C or 77 F), promoting heat loss to the sky. In cooler temperatures, the thermal emittance switched to low, and further promoted the retention of heat from solar absorption and indoor heating.
The coatings research has since been published in the journal Science and was primarily supported by the Department of Energy Office of Science and a Bakar Fellowship.
Most recently, beer brand Coors Light created 12 new, energy-efficient rooftop billboards, dubbed “Chillboards,” that utilize reflective white acrylic roof coating systems.
According to reports, the Chillboards were created atop 12 apartment buildings in Miami with A-300 Finish, a reflective white topcoat from Mule-Hide Products Co. Inc.’s acrylic roof coating system.
The coating in noted to have an initial solar reflectance of .85, meaning that a newly coated roof reflects 85% of solar radiation. In addition, the A-300 Finish is noted to be durable, flexible in low-temperature environments and has a high resistance to the effects of ultraviolet light.
Mule-Hide adds that the coating is Cool Roof Rating Council-rated and ENERGY STAR-listed.
For the project, more than 36,000 square feet of black roof surface—the equivalent of 90 average-size billboards—was coated with the reflective acrylic paint. In keeping with Coors’ goal of highlighting the benefits of cool roof coatings, the Chillboards used a typeface called “coolest.”
Intended for short-term display, the 12 apartment roofs have since been coated in full with A-300 Finish. In a test conducted on one of the Chillboards, the coating was noted to have lowered the surface temperature of the roof by as much as 50 F.