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