Chameleon-inspired coating could revolutionize building energy efficiency

By Stephen Beech via SWNS

A new colour-changing coating inspired by a species of chameleon could cool and warm buildings cheaply all year round, according to a new study.

The search has intensified for alternative energy-saving technologies as traditional heating and cooling systems are energy intensive, and because they usually run on fossil fuels.

Now, by mimicking a desert-dwelling chameleon, Chinese scientists have developed a cheap energy-efficient, cost-effective coating.

They say the new material could keep buildings cool in the summer - or warm in the winter - without using additional energy.

Dr. Fuqiang Wang, of the Harbin Institute of Technology in China, said: "Many desert creatures have specialized adaptations to allow them to survive in harsh environments with large daily temperature shifts.

"For example, the Namaqua chameleon of southwestern Africa alters its color to regulate its body temperature as conditions change.

"The critters appear light grey in hot temperatures to reflect sunlight and keep cool, then turn a dark brown once they cool down to absorb heat instead.

"This unique ability is a naturally occurring example of passive temperature control - a phenomenon that could be adapted to create more energy-efficient buildings.

"But many systems, such as cooling paints or colored steel tiles, are only designed to keep buildings either cool or warm, and can’t switch between modes.”

Inspired by the Namaqua chameleon, Dr. Wang and his colleagues wanted to create a color-shifting coating that adapts as outside temperatures fluctuate.

To make the coating, the team mixed thermochromic microcapsules, specialized microparticles and binders to form a suspension, which they sprayed or brushed onto a metal surface.

When heated to 68 degrees Fahrenheit, the surface began to change from dark to light grey.

Once it reached 86F, the light-coloured film reflected up to 93 percent of solar radiation.

Dr. Wang said, "Even when heated above 175 degrees Fahrenheit for an entire day, the material showed no signs of damage."

The team then tested it alongside three conventional coatings - regular white paint, a passive radiative cooling paint and blue steel tiles - in outdoor tests on miniature, doghouse-sized buildings throughout all four seasons.

In winter, the new coating was slightly warmer than the passive radiative cooling system, though both maintained similar temperatures in warmer conditions

In summer, the new coating was significantly cooler than the white paint and steel tiles, according to the findings published in the journal Nano Letters.

Dr. Wang added: "During spring and fall, the new coating was the only system that could adapt to the widely fluctuating temperature changes, switching from heating to cooling throughout the day."

The researchers say that the color-changing system could save a "considerable" amount of energy for regions that experience multiple seasons, while still being inexpensive and easy to manufacture.