Heating and cooling households and buildings is an energy-intensive process primarily driven by fossil fuels. As our modern society looks for ways to reduce carbon emissions, there is also a need to develop more efficient systems that can work through the seasons.

Demand for Temperature-Adaptive Coatings

Conventional houses and buildings are not 100% efficient at trapping heat in or keeping cold out during summer and doing the reverse when the seasons change. Additional systems are needed to keep most buildings at a comfortable temperature during certain parts of the year.

However, a lot of energy is required to power these systems. While buildings account for almost 30% of global energy consumption, heating and cooling systems comprise the bulk of this energy requirement. Conventional heating and cooling systems in buildings are usually energy-intensive and significantly contribute to greenhouse gas emissions. In recent years, there has been a renewed push towards passive temperature control strategies to help reduce excess energy use.

In the natural world, there is a type of desert-dwelling chameleon, such as the Namaqua chameleon (Chamaeleo namaquensis), which can regulate its body temperature by changing the color of its skin. During the daytime, their skin appears light grey to reflect the chunks of solar energy that beat down on them. Meanwhile, it turns into a dark brown color during the cold nights to absorb as much energy and warmth as possible.

Getting inspiration from these reptiles, engineers and architects sometimes add paints or colored steel tiles to the building's facade to help in regulating the internal temperature. However, retiling the building every season is impossible, so this measure cannot maintain efficient passive temperature control year-round.

READ ALSO: The Secret To a Chameleon's Color Change-It's Crystals


Temperature-Adaptive Radiative Cooling Coating

At the Harbin Institute of Technology, researchers developed a color-shifting material that can mimic the behavior of chameleon skin and change its color depending on outside temperature. They aim to help homes and buildings drive down energy consumption year-round.

To make this possible, the research team mixed thermochromic microcapsules - particles with color-changing ability based on temperature - with other microparticles, binders, and specialized radiative cooling components. By doing so, they made a suspension with a texture that can be sprayed or brushed onto metal surfaces.

At temperatures below 68° Fahrenheit, the coating turns dark gray. When the surface is warmed above this limit, the layer turns into a lighter gray capable of reflecting up to 93% of incoming solar radiation.

The material is dubbed as Temperature-Adaptive Radiative Cooling Coating (TARCC). According to study author Yan Dong, their material can overcome the drawback of conventional radiative cooling materials, which increases heating energy consumption during the winter season.

To further evaluate the potential of the new coating, the experts conducted an outdoor test using doghouse-sized buildings. The models were covered in regular white paint, traditional radiative cooling paint, blue steel tiles, or the new TARCC material. The test was carried out over multiple days in Weihai City during typical summer, winter, spring, and fall.

Their study revealed that during hot weather, the TARCC kept temperatures of up to 6.5 Kelvin below the ambient temperature, while a temperature rise of 4.3 Kelvin is observed in winter due to the TARCC's strong absorption of solar light.

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