USA: Scientists at Stanford University claim to have invented a new kind of paint that can keep homes and other buildings cool in summer and warm in winter.

A paint that can be produced in a wide range of colors is said to be able to reduce the need for both heating and air conditioning in buildings and other spaces such as trains and refrigerated trucks.

According to a study published in the Proceedings of the National Academy of Sciences, the new paints have reduced energy consumption for heating by about 36% in experiments using artificial cold environments  .

In addition, they reduced the energy required for cooling by almost 21% in artificially warm conditions. In a simulation of a typical mid-rise apartment building in various US climate zones with new paint on exterior walls and roofs, total energy consumption for heating, ventilation and air conditioning decreased by 7.4% during the year.

two layers

The researchers argue that modern low-emissivity paints are typically metallic silver or gray in color, an aesthetic that limits their use. The newly invented paints consist of two layers applied separately: an infrared reflective bottom layer using aluminum flakes and an ultra-thin, infrared-transparent top layer using inorganic nanoparticles, which is available in a wide range of colors.

The infrared spectrum of sunlight causes 49% of the planet’s natural heating when it is absorbed by surfaces.

To preserve heat, paint can be applied to exterior walls and roofs. Most of this infrared light passes through the color layer of the new paints, reflects off the underlying layer, and returns as light without being absorbed by the building materials as heat. To keep the heat inside, the paints are applied to the interior walls, where, again, the bottom layer reflects infrared waves that transmit energy in space and are invisible to the human eye.

In particular, up to about 80% of the high-frequency mid-infrared light is reflected by paints, doing most of the work of keeping warm inside in cold weather and outside in hot weather. The color layer also reflects some near infrared light, enhancing the reduction in air conditioning.

The research team tested their paints in white, blue, red, yellow, green, orange, purple and dark gray. The researchers found that they were 10 times better than conventional paints of the same colors at reflecting high mid-infrared light.

Other applications

The possibilities of applying paints are not limited to buildings. For example, they may cover trucks and train cars used for refrigerated transport, where refrigeration costs can take up to half of the transport budget.

“Both layers can be sprayed onto a variety of surfaces of various shapes and materials, providing an additional thermal barrier in many different situations,” said Yukang Peng, co-author of the study.

The researchers also evaluated how practical their paints would be in different situations. Both layers are water-repellent, which should increase stability in wet environments. The researchers report that painted surfaces can be easily cleaned with a damp cloth or water.

In addition, the performance and aesthetic performance of the paints did not deteriorate after one week of continuous exposure to high temperature (176ºF), low temperature (-320.5ºF), and high and low acid environments. The paint actually increased AC usage slightly in some US3 cities, but no increase in overall HVAC load was recorded in any location.

“Our team continues to work on improving paint formulations for practical applications,” said another co-author of the study, Jian-Cheng Lai, a postdoctoral fellow who was advised by Zhengan Bao, professor of chemical engineering. “For example, water-based solutions would be more environmentally friendly than the organic solvents we use. This can facilitate the commercialization of paints.”