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A lick of paint helps keep the heat in

by Mark Cantrell
Scientists at Stanford University have developed colourful paints that can keep buildings cooler in summer and warmer in winter

Scientists at Stanford University in the United States have come up with a new kind of paint that helps insulate homes and properties.

The paint is claimed to help keep homes and buildings cooler in the summer and warmer in the winter. As a result it helps reduce energy use – and therefore costs – as well as cut carbon emissions.

Space heating and cooling accounts for about 13% of global energy use and about 11% of greenhouse gas emissions, according to the team behind the invention.

The new paints were found to reduce the energy used for heating by about 36% in experiments using artificial, cold environments, according to a study published in the journal, Proceedings of the National Academy of Science.

Furthermore, the energy needed for cooling was found to be reduced by almost 21% in artificial warm conditions.

In simulations of a “typical” mid-rise apartment building located in different climate zones across the United States, with the new paint on exterior walls and roofs, total heating, ventilation, and air conditioning energy use declined 7.4% over the course of a year.

The study’s senior author is Yi Cui, professor of materials science and engineering, and of photon science, at SLAC National Accelerator Laboratory.

Cui, who directs the Precourt Institute for Energy and the Sustainability Accelerator, both within the Stanford Doerr School of Sustainability, said: “Energy and emissions from heating are forecast to continue to fall due to energy efficiency gains, but air conditioning use is rising, especially in developing economies in a warming world.

“For both heating and air conditioning we must reduce energy and emissions globally to meet our zero-emissions goals. How to reduce heat exchange between human living and work spaces and their surroundings is getting more attention, and new materials for enhanced insulation – like low-emissivity films for windows – are in demand.”

Adding a little colour

Current low-emissivity paints usually have a metallic silver or grey color, the aesthetics of which limit their use, according to the Stanford team.

However, the newly invented paints have two layers applied separately: an infrared reflective bottom layer using aluminium flakes and an ultra-thin, infrared transparent upper layer using inorganic nanoparticles that comes in a wide range of colours.

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

For keeping heat out, the paint can be applied to exterior walls and roofs. Most of this infrared light passes through the colour layer of the new paints, reflects off the lower layer, and passes back out as light, not being absorbed by the building materials as heat.

On the flipside, to keep heat inside, the paints are applied to interior walls where, again, the lower layer reflects the infrared waves that transfer energy across space and are invisible to the human eye.

Up to about 80% of high mid-infrared light is reflected by the paints, doing most of the work of keeping heat inside during cold weather, and outside during hot weather.

The colour layer also reflects some near-infrared light, which is said to enhance the reduction in air conditioning.

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

Main image: Objects of different materials in various shapes coated with the new paints. Credit: Yucan Peng

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