Wood windows are cooler than glass

Study shows wood windows are cooler than glass
A wood composite as an energy efficient building material: Guided sunlight transmission and effective thermal insulation. Credit: University of Maryland and Advanced Energy Materials

Engineers at the A. James Clark School of Engineering at the University of Maryland (UMD) demonstrate in a new study that windows made of transparent wood could provide more even and consistent natural lighting and better energy efficiency than glass.

In a paper just published in the peer-reviewed journal Advanced Energy Materials, the team, headed by Liangbing Hu of UMD's Department of Materials Science and Engineering and the Energy Research Center lay out research showing that their transparent wood provides better thermal insulation and lets in nearly as much as , while eliminating glare and providing uniform and consistent indoor lighting. The findings advance earlier published work on their development of transparent wood.

The transparent wood lets through just a little bit less light than glass, but a lot less heat, said Tian Li, the lead author of the new study. "It is very transparent, but still allows for a little bit of privacy because it is not completely see-through. We also learned that the channels in the wood transmit light with wavelengths around the range of the wavelengths of visible light, but that it blocks the wavelengths that carry mostly heat," said Li.

The team's findings were derived, in part, from tests on tiny model house with a transparent wood panel in the ceiling that the team built. The tests showed that the light was more evenly distributed around a space with a transparent wood roof than a glass roof.

The channels in the wood direct visible light straight through the material, but the that still remains bounces the light around just a little bit, a property called haze. This means the light does not shine directly into your eyes, making it more comfortable to look at. The team photographed the transparent wood's cell structure in the University of Maryland's Advanced Imaging and Microscopy (AIM) Lab.

Transparent wood still has all the cell structures that comprised the original piece of wood. The wood is cut against the grain, so that the channels that drew water and nutrients up from the roots lie along the shortest dimension of the window. The new transparent wood uses theses natural channels in wood to guide the sunlight through the wood.

As the sun passes over a house with glass windows, the angle at which light shines through the glass changes as the sun moves. With windows or panels made of transparent wood instead of glass, as the sun moves across the sky, the channels in the wood direct the sunlight in the same way every time.

"This means your cat would not have to get up out of its nice patch of sunlight every few minutes and move over," Li said. "The sunlight would stay in the same place. Also, the room would be more equally lighted at all times."

Working with transparent wood is similar to working with natural wood, the researchers said. However, their transparent wood is waterproof due to its polymer component. It also is much less breakable than glass because the cell structure inside resists shattering.

The research team has recently patented their process for making transparent wood. The process starts with bleaching from the wood all of the lignin, which is a component in the wood that makes it both brown and strong. The wood is then soaked in epoxy, which adds strength back in and also makes the wood clearer. The team has used tiny squares of linden wood about 2 cm x 2 cm, but the wood can be any size, the researchers said.

Explore further

Transparent wood made stronger than glass by applying epoxy

More information: Tian Li et al, Wood Composite as an Energy Efficient Building Material: Guided Sunlight Transmittance and Effective Thermal Insulation, Advanced Energy Materials (2016). DOI: 10.1002/aenm.201601122
Journal information: Advanced Energy Materials

Citation: Wood windows are cooler than glass (2016, August 16) retrieved 21 October 2019 from https://phys.org/news/2016-08-wood-windows-cooler-glass.html
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Aug 18, 2016
Non-transparent. Be like living in an integrating sphere. Also, wood burns, glass doesn't.

Aug 18, 2016
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Aug 18, 2016

Look it up. It's transparent.

Also, wood burns, glass doesn't.

Gets my vote for the most pointless comment today.

Aug 20, 2016
Maybe if they would replace the epoxy with something cheaper and nonflammable (sodium glass comes on mind here), it would be commercially more interesting.

The original invention was based on acrylic resin, which isn't particularily expensive.

The main problem against glass is that the fibers are all arranged against the plane, so you get no strength benefit from them. The whole material is brittle like a veneer cut from the endgrain - which it basically is. It's butt-cut veneer which is washed with lye and then impregnated with plastic.

It's like cutting up short sections of drinking straws and gluing them side by side to form a sheet. The straws are strong, the glue is strong, but the interface between the two is prone to peeling.

Look it up. It's transparent.

Translucent, not transparent.

"translucent medium allows the transport of light while a transparent medium not only allows the transport of light but allows for image formation"

Aug 20, 2016
Of course it's possible to laminate additional sheets of plastic on top of the wood to deal away with the brittleness issue. The continuous sheet of plastic on the outside would take the stress of bending much like the surface compression in tempered glass.

Or, you could laminate the wood on glass.

Or you could just use regular frosted glass with an IR filter on one side and roughed up surface on the other, that does the same thing much cheaper.

Aug 20, 2016
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Aug 20, 2016
Maybe this is the reason, why they switched from acrylics to epoxy resin, which adheres on material with hydrogen bridges better

Could well be, however it is never going to be as tough as solid plastic with the polymer fibers, or a composite with the glass fibers, laid along the plane instead of perpendicular to it.

With certain kinds of woods where the cellulose matrix is highly intertwined and gnarly, the result might be different. How much would that help in a very thin slice, I don't know.

A mighty good alternative could be glass wool impregnated with epoxy. It would have roughly isotropic properties and it would be translucent as well.

Aug 20, 2016
Re. the transparent vs. translucent thing and the photos on the internet about the transparency of the new material.

Imagine a wall made out of short sections of copper pipes polished from the inside. It lets light through, but you can't see what's on the others side because the internal reflections in the pipes scatters the light every which way and scrambles the image.

If something is brought right up to the wall, you can see a rough image because the object blocks the tubes, but if the object is removed, the view through the wall becomes a blur. That's what happens with the "transparent" wood as well - it's really translucent wood.

Aug 20, 2016
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Aug 20, 2016
The wood is cut against the grain....

Know what else is against the grain?
This ridiculous creation.
Turning wood into the worse thing, plastic, while dissolving away all its aesthetic value. Is this thing even recyclable?

Aug 20, 2016
Cement is a silicate too, so it perfectly adheres on glass.

Not always


Unlike water and oil, glass and concrete do mix and can marry well under the right circumstances. On the other hand, the union may not remain solvent if the chemistry isn't there to deter the main reason this coupling would meet its demise: alkali-silica reaction (ASR).

combining glass aggregate with portland cement may trigger ASR. What happens is the silica in the glass reacts with calcium hydroxide (a powerful alkali with a pH of 12) in the portland cement and forms a siliceous gel.

This gel within the cement paste absorbs water and swells. If the swelling is sufficient, the pressure can cause microcracking, expansion and ultimately the deterioration of the surrounding concrete.

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