This white paint could reduce the need for air conditioning by keeping surfaces cooler than surroundings
By Kayla Wiles, Perdue University
West Lafayette, Indiana, October 21,
2020 -- What if paint could cool off a building enough to not need air
conditioning?
Purdue University engineers have created
white paint that can keep surfaces up to 18 degrees Fahrenheit cooler than
their ambient surroundings – almost like a refrigerator does, but without
consuming energy.
According to the researchers, the paint
would replace the need for air conditioning by absorbing nearly no solar energy
and sending heat away from the building. Without the building heating up, air
conditioning wouldn’t have to kick on.
“It’s very counterintuitive for a
surface in direct sunlight to be cooler than the temperature your local weather
station reports for that area, but we’ve shown this to be possible,” said Xiulin Ruan, a Purdue professor of mechanical engineering.
The paint would not only send heat away
from a surface, but also away from Earth into deep space where heat travels
indefinitely at the speed of light. This way, heat doesn’t get trapped within
the atmosphere and contribute to global warming. A video about this project is
available on YouTube.
“We’re not moving heat from the surface
to the atmosphere. We’re just dumping it all out into the universe, which is an
infinite heat sink,” said Xiangyu Li, a postdoctoral researcher at the
Massachusetts Institute of Technology who worked on this project as a Ph.D.
student in Ruan’s lab.
Earth’s surface would actually get
cooler with this technology if the paint were applied to a variety of surfaces
including roads, rooftops and cars all over the world, the researchers said.
In a paper published Wednesday (Oct. 21)
in the journal Cell Reports Physical Science, the researchers show that
compared with commercial white paint, the paint that they developed can
maintain a lower temperature under direct sunlight and reflect more ultraviolet
rays.
Their proof is infrared camera images
taken of the two paints in rooftop experiments.
“An infrared camera gives you a
temperature reading just like a thermometer would to judge if someone has a
fever. These readings confirmed that our paint has a lower temperature than
both its surroundings and the commercial counterpart,” Ruan said.
Commercial “heat rejecting paints”
currently on the market reflect only 80%-90% of sunlight and cannot achieve
temperatures below their surroundings. The white paint that Purdue researchers
created reflects 95.5% sunlight and efficiently radiates infrared heat.
Developing this paint formulation wasn’t
easy. The six-year study builds on attempts going back to the 1970s to develop
radiative cooling paint as a feasible alternative to traditional air
conditioners.
The researchers considered over 100 different
material combinations, narrowed them down to 10 and tested about 50 different
formulations for each material. They landed on a formulation made of calcium
carbonate, an earth-abundant compound commonly found in rocks and seashells.
This compound, used as the paint’s
filler, allowed the formulation to behave essentially the same as commercial
white paint but with greatly enhanced cooling properties. These calcium
carbonate fillers absorb almost no ultraviolet rays due to a so-called large
“band gap,” a result of their atomic structure. They also have a high
concentration of particles that are different sizes, allowing the paint to
scatter a wider range of wavelengths.
According to the researchers’ cost
estimates, this paint would be both cheaper to produce than its commercial
alternative and could save about a dollar per day that would have been spent on
air conditioning for a one-story house of approximately 1,076 square feet.
“Your air conditioning kicks on mainly
due to sunlight heating up the roof and walls and making the inside of your
house feel warmer. This paint is basically creating free air conditioning by
reflecting that sunlight and offsetting those heat gains from inside your
house,” said Joseph Peoples, a Purdue Ph.D. student in mechanical engineering
and a co-author of the work.
Cutting down on air conditioning also
means using less energy produced by coal, which could lead to reduced carbon
dioxide emissions, Peoples said. The researchers have further studies underway
to evaluate these benefits.
The researchers are working on
developing other paint colors that could have cooling benefits. The team filed
an international patent application on
this paint formulation through the Purdue
Research Foundation Office of
Technology Commercialization.
No comments:
Post a Comment