BERC Engineers: Passive Radiative Cooling

BERC-E held a lively discussion of a new cooling technology detailed in a recent Nature paper, “Passive radiative cooling below ambient air temperature under direct sunlight.” The new cooling method uses panels to passively cool by sending heat out to deep space. This technology is currently being studied by a team in the Cleantech to Market class.

The cooling panels are specially designed to emit infrared radiation very strongly in a range of wavelengths that the atmosphere will transmit.  Thus, this energy escapes to space, rather than being absorbed by the atmosphere and re-emitted to the cooler. Simultaneously, the panels are very reflective of most other radiation, especially sunlight. The net effect of these emission/reflection characteristics, summarized below in the diagram from Figure 1 of the paper, is that the panels are able to be cooler than ambient temperatures, even in direct sunlight.
Device Schematic
Cooling is achieved without any energy input and without any moving parts. Moreover, the cooling power increases as things heat up.  However, to work well, the panels must face the sky with as few obstructions as possible, and the air must be of low humidity. As long as they are facing a clear sky, they are cooling, even when it is cold outside. Thus, this cooling method is really meant for warm, dry climates.
The cost of this cooling method will be driven entirely by the manufacturing of the panels, which involves the precise deposition of thin (10s-100s of nanometers) layers of material. The total surface area of panels needed for a specific cooling application will be set by the total heat load that needs to be chilled. Given the strengths and weaknesses of the cooling panels, there were wide-ranging opinions about the applications in which they would be useful.  Stay tuned to hear about what the C2M team comes up with.
Interested in the latest energy-related science and technology?  Want to discuss it with others who share that interest?  Come out to BERC-E. We have a new topic to discuss over pizza every other Monday at LaVal’s. For more information, see:
http://berc.berkeley.edu/programs/berc-communities/berc-e-berc-engineers/
Paper referenced:
A. Raman, et al. Nature 515, 540–544 (27 November 2014)