In 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 →