Cooling Without Electricity

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Cooling Without Electricity

Today, it’s estimated that worldwide electricity costs total roughly $2.5 trillion a year and that cooling systems consume 15% of that electricity. With experts forecasting demand for cooling to grow ten-fold by 2050, that means electricity expenditure for cooling alone could rise to nearly $4 trillion per year. Therefore, improving the efficiency of cooling systems is a critical part of the twenty-first-century energy challenge.

Fortunately, there appears to an extremely clever and cost-effective way of doing just that. Here’s how it works.

All objects give off heat in the form of thermal radiation. But the air around them, mainly because of water molecules, absorbs and radiates back most of that heat. However, a sliver of those emissions in the mid-infrared range, can slip past these compounds, enabling surfaces that emit radiation at those wavelengths to become cooler than the surrounding air. A team of Stanford researchers developed a thin film tuned to radiate infrared heat in exactly this band. Then, in an even bigger advance, they coupled those radiative properties with reflective ones, enabling the materials to throw back nearly all the heat in sunlight. That’s crucial because without this reflective capability, the sun would more than offset the radiative cooling effect during the daytime.

Recently, the team demonstrated that retrofitting radiative panels to an office building could cut its cooling electricity needs by 21 percent in summer. Extrapolated to the expected global electricity demand for cooling in 2050, that amounts to roughly $800 billion a year.

To commercialize this technology, team members Shanhui Fan, Aaswath Raman and Eli Goldstein, founded a company called SkyCool Systems.

The underlying scientific phenomenon called “radiative sky cooling” is a natural process that everyone and everything does, when their molecules release heat. You can witness it for yourself in the heat that comes off a road as it cools after sunset. This phenomenon is particularly noticeable on a cloudless night because, without clouds, the heat we and everything around us radiates can more easily make it through Earth’s atmosphere, all the way to the vast, cold reaches of space.

If you have something that is very cold, like outer space, and you can dissipate heat into it, then you can do cooling without any electricity or work. The heat just flows! For this reason, the amount of heat continuously flowing off the Earth into the universe is enormous.

But on a hot, sunny day, radiative sky cooling doesn’t work that well for the human body or for most other objects...

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