Technology 3 min read

Passive Radiative Cooling System for Crowded Places

A novel device uses radiative cooling to absorb heat from the air and release it into space, lowering the temperature of hot, crowded places.

Image courtesy of Shutterstuck

Image courtesy of Shutterstuck

To understand the phenomenon of radiative cooling, let’s take a “white hot” piece of metal as an example.

The glowing white light would shift to red as the part cools down until it is no longer emitting visible light. But that doesn’t mean the metal has lost all the heat energy trapped in it.

It’s just that the emitted light isn’t in the visible spectrum. Our naked eyes can’t see infrared, which the heated body would still be emitting for a while.

Everything on Earth, including our bodies, give off heat mostly in the form of infrared that goes into outer space. Because the sky is a lot cooler by night, objects can reach sub-ambient temperature.

Long before electricity was discovered, people in the Middle East and India noticed the phenomenon of radiative cooling and exploited it to cool their spaces and make ice.

Climate-Challenged Cities Need Passive Radiative Cooling

Today, engineers can make daytime radiative cooling devices that work under direct sunlight, and the need for such systems is more critical now than in the days of yore.

Passive radiative cooling is a very low-cost cooling technique because it doesn’t require energy input from an external power source or a battery.

As reported in a press release, an international team of researchers, led by electrical engineers from the University at Buffalo, created a passive radiative cooling system designed for crowded metropolitan areas.

This electricity-free radiative cooling device uses a unique film substrate made from polymer and aluminum to bring temperature lower than the ambient air.

Where ancient people used hay to insulate their rudimentary radiative cooling systems before leaving them out during the night, the Buffalo team used a “specially designed solar shelter.”

So, the concept is still pretty much the same.

This solar shelter contains the polymer/aluminum film installed inside a box. While the film absorbs heat from inside the box to keep the surroundings cool, the shelter blocks incoming sunlight.

The shelter also serves another purpose. It beams thermal radiation emitted by the film into the sky. According to the Buffalo researchers, this is where their system shines because it would be ideal for metro areas.

Qiaoqiang Gan, associate professor of electrical engineering at the University at Buffalo and lead researcher, said:

“One of the innovations of our system is the ability to purposefully direct thermal emissions toward the sky. Normally, thermal emissions travel in all directions. We have found a way to beam the emissions in a narrow direction. This enables the system to be more effective in urban environments, where there are tall buildings on all sides. We use low-cost, commercially available materials, and find that they perform very well.”

This passive radiative cooling is relatively small if we take the shelter size as a reference, measuring about 18 inches tall, 10 inches wide, and 10 inches long. But instead of a big system covering a building’s roof, the researchers think of a network of small units.

That’s more efficient of a system because small units, as numerous as needed, would fit any roof’s surface and shape.

Read More: Novel Device Harvest Waste Heat and Turn it Into Electricity

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Zayan Guedim

Trilingual poet, investigative journalist, and novelist. Zed loves tackling the big existential questions and all-things quantum.

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