Conventional coatings are typically designed for a specific purpose, such as cooling or warming a building. While reflective coatings are used to cool a building by reflecting sunlight away from the surface, insulative coatings are used to warm a building by trapping heat inside.
Heating and cooling buildings is an energy-intensive process, so we need more efficient systems that can work around the year.
Coatings that can cool a building in hot climates and warm it in cold climates.
Researchers at the Harbin Institute of Technology in China have developed a new color-changing coating for buildings that can change properties in both winters and summers.
The coating is inspired by the temperature-adaptive skin color of chameleons.
Deserts undergo drastic temperature shifts within a day, with daytime temperatures soaring and plummeting rapidly once the sun sets, resulting in chilly nights.
The Namaqua chameleon in southwestern Africa changes color to manage its body temperature in response to these extreme conditions. During the sunny daytime, it turns grey to reflect sunlight and stay cool. As night falls, it shifts to a dark brown to absorb heat and remain warm.
How effective was the coating?
Researchers created the coating by mixing microcapsules of thermochromic material, specialized binders, and microparticles into a suspension. They applied it to a metal surface either by spraying or brushing.
When exposed to sunlight, the coating shifted from dark to light grey at 68°F (20°C) and began reflecting 93% of solar radiation at 86°F (30°C). Even at 175°F (80°C), the material remained undamaged.
The coating performed better than passive radiative cooling in winter for warmth. It outperformed tiles and white paint in summer for cooling. Additionally, it smoothly transitioned between heating and cooling in spring and fall.