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November 27, 2014

This new rooftop mirror material can beam heat from buildings out into space

By Barbara Speed

It seems today’s materials researchers are intent on weaning us off air conditioning. First there were bobbled walls which use pockets of hydrogel to cool the air around them. Now, a team of Stanford engineers have invented a thin material which can send heat into space.

The material’s secret is that it’s multi-layered, which allows it to both radiate and reflect heat and light. One layer channels infrared radiation away from the building and into space; another reflects away 97 per cent of the sunlight that hits it. The Stanford team have called this two-layer process “photonic radiative cooling”. 

Both processes reduce the heat retained by the building, and therefore the need for air conditionoing. They also don’t require any power to work, which could make the process especially useful in off-grid areas. 

Image courtesy of Stanford University. 

The material could even help the mitigate the effects of global warming. The reflective layer prevents sunlight from being absorbed by buildings as heat; the infrared rays are mediated to a different frequency by the material so they travel upwards into space, rather than being absorbed by the air molecules around the building: thus, less global warming.

The project as a whole is a contribution to a relatively new field, which views space as a handy reservoir for our unwanted heat. The Stanford team have christened this concept the “cosmic fridge” or “heat sink” method (further kitchen-based suggestions welcomed). Shanhui Fan, the leader of the project and a professor of electrical engineering, said in a press release:

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Every object that produces heat has to dump that heat into a heat sink. What we’ve done is to create a way that should allow us to use the coldness of the universe during the day.

According to the team, two challenges remain. One is finding a way to channel a building’s heat to its roof, so the material can do its magic. The second is transforming the prototype into a functional building material: at the moment, the prototype is the “size of a personal pizza”. 

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