Construction Corner: The science of the incredibly small heating things up

Counter-intuitive discoveries by researchers seem to be in season just now.

Last week, we learned about the possibility that the sun could be an air-conditioner, thanks to a high-tech paint that cools when exposed to sunlight.

This week, we get news that thanks to nanotechnology, we could soon have passive solar windows that heat up in cold weather.

Nanotechnology can be described as the science of the extremely small.

But how big is a nanometre?

It’s a billionth of a metre. But that might be as abstract to many as the size of the national debt. So, in the real world, think of a nanometre (nm) as one millionth of a millimetre, and a millimetre is about the thickness of the lead in a wooden pencil.

A human hair is about 75 microns (75µm), or about 75,000 nm in diameter.

At the nanoscale, particles of matter behave in unexpected ways, and to a researcher, the possibilities are both exciting and endless.

Which brings me back to windows that heat up in cold weather.

Windows are a major cause of thermal discomfort as the inner glazing of an office window during cold days can be several degrees colder than the indoor air. Turning up the heat helps, but inevitably leads to heat loss.

Now researchers at the University of Gothenburg in Sweden, along with researchers from schools in China, Iran and the U.S., have developed a way to transform ordinary windows into solar-powered heaters that use the sun’s energy to increase the window temperature by a bit more than 9 C when the weather gets cold.

These new surfaces are another application of nanotechnology since the main functional components are called plasmonic nanoantennas. These tiny antennas are elliptical sandwiches made of nickel-aluminum oxide and arranged in a grid on the surface of the glass. These nanoantennas absorb a great deal of light, which heats the entire surface.

The researchers have shown when sunlight hits the surface, light is absorbed more efficiently from the front side (the side with the antennas) than the back side. That makes the surfaces attractive for use in windows.

The surfaces are highly transparent, appear colourless and almost completely preserve the colour spectrum of sunlight.

The researchers say cold windows have a larger impact on heating a building than might be expected. That’s because when people sit next to a cold window they radiate their body heat toward the window and the window acts as a heat sink.

To compensate, the indoor temperature needs to be increased in order to maintain an adequate comfort level.

As these new window surfaces can increase the window temperature by more than 9 C, they offer the building owner large energy savings.

Alexandre Dmitriev, the lead scientist of the research project, says the team has "developed a surprisingly simple, cheap and effective way to transform regular glass windows into solar-powered heat-screens that could significantly change the thermal balance of living and working spaces, especially if one thinks of the ever-increasing amount of huge glass surfaces used in modern architecture."

Dmitriev says he expects the new surface may have other applications beyond windows.

The nanoantennas can be "painted" onto any surface and can be "tuned" to absorb light of different wavelengths, which changes their colour.

These advantages could lead to applications for such things as radiative cooling, he says. The tiny antennas might also be "coupled to molecular systems that are able to store sunlight as heat and release it on demand."

Still to come is work on achieving even greater temperature increases by enabling the surfaces to absorb ultraviolet and near-infrared radiation, both of which make up a significant share of solar radiation.

These new surfaces and the advantages they offer are just one more example of how the science of the incredibly small can affect all of us.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com.