I told you about it a while ago: at Purdue University they have developed a white paint… which overcomes the limits of white.
In October last year, Ruan and his team revealed their discovery to the world. At the time, they said the white paint reflected up to 95,5% of light and its equivalent infrared heat signature.
Super white paint? What is it about?
It is a white paint that is so reflective that coating a building inside can reduce the need for air conditioning. explain the engineers in a press release.
“If we used this white paint to cover a roof area of approximately 1.000 square feet (92 square meters), we could achieve 10 kilowatts of cooling power. It's more powerful than the central air conditioners used by most homes,” he says Xiulin Ruan, Purdue professor of mechanical engineering and project leader.
Today this paint has been further improved, and reflects 98,1% of the light.
And not only is this new paint whiter, it also reflects more heat away from surfaces, the researchers say. It is not a trivial matter: Average commercial white paint, researchers say, heats rather than cools surfaces because it absorbs light. Even paints designed to reflect heat typically reflect 80-90% of sunlight and do not cool surfaces, the team says.
Test for 'widest spectral spread'
To design their ultra-white paint, engineers at Purdue University considered over 100 different materials, before narrowing the list to 10. For each of these, they tested around 50 different formulations.
The researchers ultimately opted for an extremely high concentration of a chemical compound called barium sulfate, which is used to make cosmetic whites and photo paper.
Importantly, barium sulfate particles come in a variety of different sizes in the paint. Different particle sizes scatter light from a wider range of the color spectrum, so more size means more light reflected outward.
A high concentration of particles even of different sizes gives the paint the widest spectral dispersion, which contributes to the maximum reflectance
Joseph Peoples, Ph.D., Purdue University
It could still be improved, but...
The team say they can add an even higher concentration of the compound, but they also warn that adding too much of it could cause the paint to crack or peel off the walls.
Yes, but how cool is the super white paint?
In an outdoor demonstration of their white paint's cooling ability, the researchers used high-precision temperature reading equipment called thermocouples to demonstrate that they can keep surfaces 19 degrees Fahrenheit (7 degrees Celsius) cooler than the environment surrounding during the night.
Under strong sunlight, however, the paint can cool surfaces by 8 degrees Fahrenheit (13 degrees Celsius) beneath its surroundings.
Radiative cooling to combat climate change
Purdue's white paint employs a process called radiative cooling in which an object loses heat via thermal radiation, even in direct sunlight.
It's not the only technology currently being developed to take advantage of this process. Last year, researchers at Stanford University announced the development of “anti-solar panels” that used radiative cooling to harvest energy at night.
Another research development sees “cold tubes” cool interior spaces via radiative cooling, reducing the need for air conditioning systems and allowing users to keep windows open on hot summer days.
Although more work is needed, Purdue University's super white paint has the potential to greatly reduce our dependence on air conditioning systems.
This would be a great advantage in the fight against climate change: It is estimated that various air conditioners emit millions of tons of CO2 worldwide every day. According to the IEA, without rigorous policy intervention, energy demand from air conditioners will triple by 2050.
An unsustainable situation, if we want to stop the ongoing climate crisis.
