Stronger than aluminum, a heavily altered wood cools passively
Boiled in hydrogen peroxide and compressed, the wood can passively manage heat
' Most of our building practices aren't especially sustainable. Concrete production is a major source of carbon emissions, and steel production is very resource intensive. Once completed, heating and cooling buildings becomes a major energy sink. There are various ideas on how to handle each of these issues, like variations on concrete's chemical formula or passive cooling schemes. But now, a large team of US researchers has found a single solution that appears to manage everything using a sustainable material that both reflects sunlight and radiates away excess heat. The miracle material? Wood. Or a form of wood that's been treated to remove one of its two main components.
But rather than simply being structurally useful, the wood has some properties that could make it extremely useful as cladding, covering the exterior of a building. While most of the cellulose fibers are aligned along the grain of the wood, that alignment is very rough—there's plenty of variability in their orientation. That means light that strikes the processed wood will bounce around within a dense mesh of cellulose fibers, scattering widely in the process. The end result is a material that looks remarkably white, in the same way a sugar cube looks white even though each sugar crystal in it is transparent. As a result, the material is really bad at absorbing sunlight, and thus it doesn't capture the heat in the same way regular wood does.
But it gets better. The sugars in cellulose are effective emitters of infrared radiation, and they do so in two areas of the spectrum where none of our atmospheric gasses is able to reabsorb it. The end result is that, if the treated wood absorbs some of the heat of a structure, wood can radiate it away so that it leaves the planet entirely. And the wood is able to do so even while it's being blasted by direct sunlight; the researchers confirmed this by putting a small heater inside a box made of the treated wood and then sticking it in the sunlight in Arizona.
In the heat of the day, a square meter of the wood could radiate away about 16W of power. At night, that figure shot up to 63W, for a 24-hour average of 53 Watts per square meter. At mid-day, if there was no source of heat in the box, its ambient temperature was over 4°C lower than the surrounding air. This is all the result of the fact that the treated wood emits energy in the infrared more efficiently than it absorbs energy in thee visible wavelengths.'
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