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Chameleon-Inspired Coating For Buildings Could Significantly Improve Energy Efficiency

A green chameleon sits on a wooden branch
Credit: Hasmik Ghazaryan Olson / Unsplash.
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Scientists have developed a new dual-purpose coating that can help to keep houses cool in summer and warm in winter, taking some unlikely inspiration from the skin of desert-dwelling chameleons.

As described in a new paper published in Nano Letters, the coating’s ability to absorb and reflect solar radiation under different conditions is an improvement on current passive temperature control technologies for buildings and may lead to significant energy consumption savings.

The need for temperature-adaptive coatings

Since houses are not 100% efficient at trapping heat in or keeping cold out (or doing the reverse when the seasons change), additional systems are required to keep most buildings at a comfortable temperature during certain parts of the year.

But powering these systems takes a lot of energy – buildings account for roughly 30% of global energy consumption, with heating and cooling systems making up the bulk of this energy demand. As the general public and industry stakeholders begin to become more aware of their energy consumption and how this impacts global sustainability, there is a renewed push towards developing solutions that can help cut down on excess energy use.

“The need for passive temperature control technologies arises from several factors. First and foremost is the growing concern over energy consumption and its environmental impact,” study author Yan Dong, a PhD student at the Harbin Institute of Technology, told Technology Networks.

“Traditional heating and cooling systems in buildings are often energy-intensive and contribute to greenhouse gas emissions. Passive temperature control technologies aim to reduce this energy consumption by using natural processes like radiation and convection to maintain comfortable indoor temperatures.”

In the natural world, desert-dwelling chameleons such as the Namaqua chameleon regulate their body temperature by changing the color of their skin. During the day their light grey skin reflects a significant chunk of the solar energy that is beating down on them, while they turn a dark brown color during the cold desert nights to absorb as much energy and warmth as possible.

In a similar fashion, engineers and architects will sometimes add paints or colored steel tiles to the external faces of buildings to regulate internal temperature. But short of re-tiling your house every season, these measures cannot maintain efficient passive temperature control year-round.

New coating outperforms current tech

In pursuit of a new multi-season coating for buildings, researchers at the Harbin Institute of Technology wanted to create a color-shifting material that could mimic the behavior of chameleon skin and change its color depending on the temperatures outside.

By mixing thermochromic microcapsules – particles that change their color based on temperature – with other microparticles, specialized radiative cooling components and binders, the researchers were able to form a suspension with a texture ideal for spraying or brushing onto metal surfaces. Testing revealed that at temperatures below 68 degrees Fahrenheit, the coating was a dark gray color. But when warmed above this limit, the coating would turn into a lighter gray that was capable of reflecting up to 93% of incoming solar radiation.

“In this study, we drew inspiration from the Namibian chameleon and developed a Temperature-Adaptive Radiative Cooling Coating (TARCC),” Dong said. “This material overcomes the drawback of conventional radiative cooling materials that increase heating energy consumption during the winter season.”

To more fully assess the properties of the new coating, the research team conducted an outdoor test using doghouse-sized buildings covered in either regular white paint, a traditional radiative cooling paint, blue steel titles, or the new TARCC material. The test occurred over multiple days in Weihai City during typical summer, winter and transitional season (spring/fall) days.

They found that in hot weather, the TARCC kept temperatures up to 6.5 Kelvin below ambient temperatures. In winter, the TARCC’s strong absorption of solar light resulted in a 4.3 Kelvin temperature rise. 

Comparing the TARCC’s performance to the other solutions, the team found that the TARCC maintained slightly warmer temperatures in winter conditions compared to the traditional radiative cooling system, and matched its performance during summer temperatures. The TARCC was also significantly cooler than the white paint and steel tile options in hot conditions.

Additional computational model analyses of the TARCC, using a combination of its experimental performance and historic temperature data, suggested that the coating would reduce heating energy consumption and average energy consumption in single-story prefabricated buildings.

“In light of the positive findings, it is indeed worthwhile to consider further studies on TARCC,” Dong told Technology Networks, suggesting that real-world tests of the TARCC’s performance and durability would provide valuable further insights. Additionally, analyses focusing on the cost-effectiveness of retrofitting TARCC materials onto existing houses or including it in new construction projects might also be considered, to demonstrate the economic viability of the new coating.

“Conducting these further studies will help validate TARCC's potential and provide valuable insights into its broader applications and impact,” Dong said.

Reference: Dong Y, Meng W, Wang F et al. “Warm in winter and cool in summer”: Scalable biochameleon inspired temperature-adaptive coating with easy preparation and construction. Nano Lett. 2023. doi: 10.1021/acs.nanolett.3c02733

Yan Dong was speaking to Alexander Beadle, Science Writer for Technology Networks.