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posted by CoolHand on Tuesday May 28 2019, @07:54PM   Printer-friendly
from the sawing-logs dept.

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 has 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 gases 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.


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  • (Score: 2) by engblom on Wednesday May 29 2019, @05:04AM (1 child)

    by engblom (556) on Wednesday May 29 2019, @05:04AM (#848785)

    I'm thinking of painting my house a dark color so it can absorb a little heat rather than reflect it.

    Black is simply just more efficient in transmitting heat as the heat is not reflected back. Thus the sun radiation is absorbed rather then reflected. It also works the other way. After sunset a black house would be cooler because the heat is not reflected back into the house but radiated out into the environment.

    As a side note if you want to stay as cool as possible in a hot climate: if you are inside or in shadow, you will have it less hot with black clothes. Only when you are in direct sunlight you benefit from having white colored clothes.

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  • (Score: 1, Insightful) by Anonymous Coward on Wednesday May 29 2019, @02:33PM

    by Anonymous Coward on Wednesday May 29 2019, @02:33PM (#848910)

    There is black, and then there is black. At visible wavelengths, black is a good solar absorber. At the long wavelengths radiated (at night, or anytime really) by a warm surface, the same visible black color may or may not be "black" for infrared wavelengths. This varies all over the map with different surface materials.

    This is part of the cleverness of the invention in tfs -- it happens to re-radiate at useful IR wavelengths for cooling.