Mirror to replace air cooler?
A mirror that sends heat into the frigid expanse of space has been designed by scientists to replace air-conditioning units that keep buildings cool on Earth.
Researchers believe the mirror could slash the amount of energy used to control air temperatures in business premises and shopping centres by doing away with power-hungry cooling systems.
Around 15% of the energy used by buildings in the US goes on air conditioning, but the researchers' calculations suggest that in some cases, the mirror could completely offset the need for extra cooling.
In a rooftop comparison of the device in Stanford, California, scientists found that while a surface painted black reached 60C more than ambient temperature in sunlight, and bare aluminium reached 40C more, the mirror was up to 5C cooler than the surrounding air temperature.
“If you cover significant parts of the roof with this mirror, you can see how much power it can save. You can significantly offset the electricity used for air conditioning,” said Shanhui Fan, an expert in photonics at Stanford University who led the development of the mirror. “In some situations the computations say you can completely offset the air conditioning.”
The Stanford mirror was designed in such a way that it reflects 97% of the visible light that falls on it. But more importantly, it works as a thermal radiator. When the mirror is warmed up, it releases heat at a specific wavelength of infrared light that passes easily through the atmosphere and out into space.
“The cold darkness of the universe can be used as a renewable thermodynamic resource, even during the hottest hours of the day,” the scientists write in Nature. In tests, the mirror had a cooling power of 40 watts per square metre at ambient temperature.
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