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Light-Filtering Paint can Cool down your Room when Exposed to Sunlight

Posted May 27, 2018

As soon as ambient temperatures start climbing above comfortable levels in the summer, people turn on the air conditioning, jacking up the energy bill and stretching the grid thin in the process.

To address this problem, Yaron Shenhav and colleagues from SolCold, a firm based in Herzliya, Israel have developed a special paint that actually cools when exposed to hot mid-day sun. “It’s like putting a layer of ice on your rooftop which is thicker when there is more sun,” said Shenhav.

According to the research team, the new technique is based on laser cooling ­– a highly counterintuitive principle of shining a laser beam on specially designed materials, causing them to lose heat.

Laser cooling works because molecules in these materials absorb photons of one frequency while simultaneously re-emitting higher-frequency photons which contain more energy, resulting in net heat loss.

The trick for Shenhav and his team was to figure out how to adapt laser cooling to ambient sunlight, so that “heat from a building could be absorbed and re-emitted as light”.

To achieve the desired result, the researchers developed a two-layer paint which filters out some of the sun’s rays and then performs the heat-to-light conversion, cooling itself in the process.

Preliminary tests showed that premises using the new paint on their rooftops can be up to 10°C cooler than otherwise, with metal roofs producing better results than concrete ones. The team hopes to commence pilot testing within the next two years.

As opposed to light-coloured rooftops which reduce ambient heating, roofs covered in the new paint can actively cool buildings while exposed to sunlight. Image credit: Acroterion via, CC BY-SA 3.0.

While the paint is currently quite expensive — costing around $300 per 100 square metres — it can reduce energy consumption by as much as 60 percent, making it an excellent choice for large commercial buildings.

Furthermore, Shenhav and his team are looking to space for potentially even more significant and lucrative applications – the lack of air in space makes cooling difficult, while the new paint developed by SolCold does is magic by light alone.

“With our technology, heat is transferred through light,” said Shenhav. “Space applications are a big market for us”.

The first presentation of the team’s work will take place this month at the Hello Tomorrow summit in Paris.


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