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Construction Corner: New paint cools in sunlight, chilling buildings

Korky Koroluk
Construction Corner: New paint cools in sunlight, chilling buildings
Korky Koroluk

With Halloween almost here the problem of cooling indoor spaces is not at the front of most Canadians’ minds.

In most of the country, you can cover the unit that sits out on the patio, turn off the circuit breaker and wait for things to warm up six months from now.

By next July, enough people will have turned on and turned up their air conditioners to cause electricity consumption to soar and electricity bills to increase in lock-step.

But it is at least conceivable that the sun itself could soon become a low-cost air-conditioner. That’s because a high-tech paint that actually cools when exposed to sunlight can provide a better way to chill buildings.

Yaron Shenhav and his colleagues from SolCold in Herzlia, Israel, have hit upon an alternative that doesn’t require electricity to cool your home or office.

The technology is based on laser cooling, a counterintuitive principle that involves zapping specially designed materials with a laser.

The reason it works is because molecules in those materials absorb photons whose light is of one frequency but at the same time, they are spontaneously re-emitting higher-frequency photons that carry more energy. That means energy is lost, so the temperature of the material is cooled.

Shenhav says it’s "like putting a layer of ice on your rooftop which gets thicker when there is more sun."

Most of us wouldn’t particularly want a laser mounted on our roof, so Shenhav decided to see if he could come up with a system that used sunlight instead of lasers.

He says "heat from the building could be absorbed and re-emitted as light. As long as the sun is shining on it, it would be continuously cooled."

But sunlight’s spectrum is much broader than that of a laser light, which is a narrowly focused beam. That meant the team had to devise a material that could be cooled using several wavelengths of scattered light.

What the researchers came up with was a paint with two layers. The outer layer filters some of the sun’s rays and the inner layer handles the conversion of heat to light while cooling itself below the ambient temperature.

In recent years, using white paint to reduce the amount of heat buildings absorb has gained some currency.

But these "cool roofs" can’t actively reduce a building’s inside temperature.

The new paint has passed lab testing with flying colours. In the process, researchers found it’s more effective on metal roofs than on concrete and it works best when the roof is over rooms with low ceilings.

The team also ran computer simulations that showed a room on the top floor will feel as much as 10 C cooler when the new paint is used.

The paint isn’t cheap. It costs about $380 to coat 100 square metres.

At that price, Shenhav says he thinks early adopters will be large commercial installations like shopping malls and stadiums. In those applications, he says the coating could lower energy consumption by as much as 60 per cent, which would mean a major reduction in both bills and carbon emissions.

There could be other environmental benefits as well, Shenhav says. In places like Phoenix, Ariz., which is hot, continuous use of air conditioning creates urban heat islands, which are a major factor in increasing temperatures across urban areas.

The new paint would mean homeowners could get away with smaller air-conditioning units and commercial buildings would be able to install smaller chillers.

Don’t expect the new paint to be available anytime soon.

The researchers will conduct pilot tests on buildings during the next two years. Those tests, if successful, will prove the concept of the new paint.

They will also point out where improvements in the paint could be made.

All of that means it will be at least five years before the paint arrives in the marketplace.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to

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