Intelligent roof coating: it can reflect heat in summer and block heat loss in winter.

It is learned that engineers from Berkeley Lab have developed a roof coating that can keep buildings warmer or cooler according to weather conditions. When the weather is warm, the material will reflect sunlight and heat, but this radiation cooling will automatically turn off in winter, thus reducing the energy consumption of heating and cooling.

the working principle of radiant cooling system is to attract thermal radiation (that is, heat) from buildings and then emit it into the sky. Because the atmosphere is transparent to these wavelengths, heat escapes directly into space. Other versions use reflective surfaces such as ultra-white paint to reflect sunlight and heat and keep buildings cool.

however, although these systems may keep your house cool well in summer, they will also keep cool in winter. Therefore, in the new research, the team developed a coating that can automatically switch to capture heat when mercury drops. They call this material temperature adaptive radiation coating (TARC).

the key of this technology is a strange compound called vanadium dioxide (VO 2). In 217, the team discovered an unusual characteristic of VO 2-when it reaches 67 C, the material will conduct electricity but not heat, which obviously violates known physics.

now, the team has applied this quirk to their work. The idea is that when the weather gets warmer, the material will absorb and emit thermal infrared light, thus keeping it away from buildings. But when the weather is cool, this material is transparent to heat, which allows it to pass directly from the sun to the building.

The research team tested the equipment with a 2-square-centimeter TARC film patch and compared it with the samples of commercial dark and white roofing materials. Wireless devices are responsible for measuring direct sunlight and temperature changes.

sure enough, the effect of TARC is unexpectedly good. According to the measurement, TARC can reflect about 75% sunlight no matter what the weather is, and when the ambient temperature is higher than 3 C, it can dissipate up to 9% heat to the sky. When the weather cools below 15 C, TARC reflects 2% of the heat.

By using the collected data, the research team simulated the annual work of TARC in 15 different climate zones in the continental United States, and estimated that the average American family could save up to 1% of electricity bills by using TARC.

The researchers said that TARC can also be used as a temperature regulating material for automobiles, electronic products, satellites and even the fabrics of tents or clothes.

Next, the team will use a larger prototype of TARC to test its practicability as a roof coating.