Chill out the easy way: science can cool you down

The Mediterranean way to chill: Paint it white and keep it cool. Image: By Heidi Kaden on Unsplash

There’s more than one way to chill out. White paint and watery windows could help. So could the deep blue sea.

LONDON, 21 December, 2020 − It’s getting simpler and cheaper to chill out: US scientists have developed an ultra-cool white paint that can reflect more than 95% of the sun’s rays and keep the house cooler on the hottest days.

Across the Pacific in Singapore, researchers have developed a “smart window” clever enough to block the incoming sunlight and regulate the building’s internal temperature. It’s pretty good at blocking the noise from the streets, too.

And people who live on tropical islands and find the heat a bit much can cool their homes with a steady flow of cold seawater from the ocean depths.

Austrian researchers calculate that a cubic metre of water from 700 metres below the ocean surface can deliver the same cooling power as 21 wind turbines, or a solarpowered-farm the size of 68 football fields.

Prototypes tested

None of these developments is anywhere near commercial scale exploitation. But two have been tested in prototype and each is a reminder of the ingenuity and imagination at work in the world’s laboratories in bids to confront the energy crisis, limit climate change and find new and carbon-free ways to solve the planet’s mounting challenges.

One of the biggest of those challenges is the soaring thermometer: as global heating driven by profligate fossil fuel use steadily drives up the mercury, yet more and more people, if they want to chill out, are being forced to invest in air-conditioning, a technology that demands even more energy use and heightens the temperature in the city streets.

So the case for passive, or sophisticated, or simply new ways to turn to stay cool is irresistible. Researchers from Purdue University in Indiana in the US write, in the journal Cell Reports Physical Science, that they have developed a technology that could be used in commercial paints, that could be cheaper to make, and that could reflect so much sunlight back into space that the surface of the property could be cooler than the air around it. And it used calcium carbonate − think chalk, or limestone − rather than the more difficult-to-find titanium dioxide to do the trick.

Tests in West Lafayette, Indiana found that when the sun was at its zenith the paint surface stayed 1.7°C cooler than the atmosphere around it. At night, the paint temperature dropped to 10°C below the ambient surroundings.

“Scientists in Singapore have developed a liquid sandwiched between two glass panes that in tests can cut 45% of the energy needed to heat, ventilate and air-condition a property”

Windows are vital in building design, but they can be the least energy-efficient part of any construction. Scientists at Nanyang Technical University in Singapore report in the journal Joule that they have developed a hydrogel-based liquid sandwiched between two glass panes that − in tests − can cut 45% of the energy needed in heating, ventilation and air-conditioning a property.

This could be big business: buildings account for 40% of global energy usage, and half of that goes out of the world’s windows. With savings on that scale possible, all will be able to chill out.

So researchers have been experimenting with glass coatings that cut down the infra-red traffic − the waves that carry heat − from within and without the building, but which do not regulate visible sunlight, which heats the interior as it shines through the glass.

The Singapore scientists found that their micro-hydrogel could respond to temperature change, and turn opaque when exposed to heat. So it could block incoming sunlight, and return to clear glass when things got cooler. At the same time, the trapped hydrogel water stored a lot of thermal energy rather than let it into the building during the heat of the day, but gradually released it at night.

District cooling

In midsummer noonday tests in Beijing, when a normal glass window registered 84°C, the smart window glass stayed at 50°C and saved 11% of the energy required to maintain the same indoor air temperature.

They tested the smart glass in Shanghai in China, Las Vegas in the US, Riyadh in Saudi Arabia and in Singapore: in each case, it performed better than regular glass or low-emission windows. It also reduced noise 15% more efficiently than normal double-glazing.

And rather than cool indoor air, and pump the hot air back into the streets with an electric motor − the basis of most air-conditioning − scientists at the International Institute for Applied Systems Analysis in Austria report in the journal Energy Efficiency that for those who live on tropical or subtropical coasts, a short distance from the deep ocean, in places where electricity costs are high, it might be much cheaper to cool whole districts − universities, airports, data centres, hotels and resorts and so on − with pumped deep ocean water at temperatures of around 3°C to 5°C.

Stored tanks of cold seawater could even make chiller facilities more efficient, and reduce the costs of food storage. But, the IIASA team warns, there might be problems with the impact on coastal wildlife while returning the used seawater to the ocean surface. − Climate News Network