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The Next Great Thing: Part Two

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We left off last time mentioning two research reports, both of which discuss a functional material that might—someday—serve as a cooling device. No moving parts and no energy required to operate this device. Science fiction? Definitely not, but there is still much to be done before such a device becomes a commercial reality. But, for the moment, let’s not worry about such details.

At the 2015 CRRC Membership meeting, Aaswath Raman, Ph.D., from the Ginzton Laboratory at Stanford University, presented his work on sub-ambient cooling of sky-facing surfaces. To understand Dr. Raman’s work, picture a sheet of material with an exceptionally high solar reflectance (around 97%), mounted in a fixture on a roof in Phoenix. It has a shiny metal appearance. (Super-high reflectance is only possible with mirror-like materials.) Because the material has such a high reflectance, it will not absorb much incoming IR radiation, but it certainly will be heated by the surrounding hot desert air (convective heating). Since this shiny material is hot because of the desert heat, it is emitting plenty of IR radiation. Here is the actual installation. Continue reading

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The Next Great Thing: Part One

ImageforBlogPart1forwebIn the arena of university R&D, one often thinks, who cares? I certainly do. But in this and the next post, you will read about some fascinating work coming out of Stanford University. As a self-professed cynic, I would never mention “the next great thing” if I did not see some very real potential. There is, of course, a big valley between R&D and commercial reality, but from what I have heard and read … well, you be the judge.

One of these ideas that could fall into the “too good to be true” category is radiative cooling. Before you fear that I’ve taken leave of my senses, yes, I do understand that all objects radiate energy and will cool as a result. All cool-roofing codes contain an emittance requirement for this reason. Objects (such as painted metal roofing) with a high thermal emittance (>75%; a perfect emitter would be 100%) cool down faster than low-emittance materials such as shiny metal. When the sun sets, you want the roof to radiate as much heat as possible to the atmosphere as fast as possible. Of course, when the sun is beating down on the roof, you also want the roof to reflect as much heat as possible in the form of infrared radiation (IR), keeping the roof as cool as possible. That’s why both parameters—reflectance and emittance—are important in the cool-roofing arena. Continue reading