Cooling buildings conventionally calls for an air conditioning system, which requires a lot of energy. For this reason, Stanford engineers have developed a new material that could be a game changer as it can cool buildings by ejecting the unwanted heat into space.

Shanhui Fan from the Ginzton Laboratory at Stanford University's department of electrical engineering, together with colleagues, developed an ultrathin and multilayered material that can lower a building's temperature by stopping the heat before it even comes in and sucking it out when the building's temperature becomes too hot.

The revolutionary material, which is described in the journal Nature on Nov. 27, works like a rooftop mirror that reflects up to 97 percent of the sunlight that strikes it. It also works like a kind of thermal funnel that sucks the heat from inside the building up through the roof and sends it into space as infrared radiation.

The two-in-one process called photonic radiative cooling, which involves reflecting sunlight that could warm the building while funneling out infrared heat from the building, results in cooler buildings that would need less air conditioning.

What makes the process more interesting is that it does not require a volt of energy. Although the material won't cool the building on its own, it can help in reducing heat and lead to significant electricity savings. The researchers believe that the technology could reduce the demand for electricity as well as the associated cost in the future.

In the U.S., up to 15 percent of the energy that buildings use goes to air conditioning systems. The researchers pointed out that given the dangers posed by global warming, there is a need for cooling technologies that do not require power.

"Across the developing world, photonic radiative cooling makes off-grid cooling a possibility in rural regions, in addition to meeting skyrocketing demand for air conditioning in urban areas," said study researcher Aaswath Raman, also from Stanford University.

The research team likewise sees the project as an initial step towards utilizing space as a resource. The coldness of the universe can serve as a nearly unlimited expanse that can serve as a heat sink.

"These results demonstrate that a tailored, photonic approach can fundamentally enable new technological possibilities for energy efficiency," the researchers wrote. "Further, the cold darkness of the Universe can be used as a renewable thermodynamic resource, even during the hottest hours of the day."

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