Dropwise condensation reduces selectivity of sky-facing radiative cooling surfaces

Authors: E. Simsek, J. Mandal, A. Raman, L. Pilon

Journal Link: Int. Journal of Heat and Mass Transfer, 198, 123399

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Summary: It is well-known that sky facing surfaces, including radiative coolers, can collect dew at night, but the impact of dew on the optical/spectral properties of radiative coolers, and by extension, their cooling capability, has not really been explored.

We show that dew formation turns sky-facing selective LWIR emitters into broadband emitters, reducing their ability to reach deeper sub-ambient temperatures. This is not so much the case for vertically oriented emitters, which can maintain their optical properties more easily.


* Despite claims in the literature, it is probably not that beneficial to use selective emitters on building roofs for cooling. For vertical facades, that may be a different story.

If you are making radiative coolers that harvest dew, it is best to have dew not form on the sky-facing side as it will reduce cooling capability. If that is not possible, it may be best to make/let it run off.

While the momentum on radiative cooling research has largely been towards materials development, for effective designs, we must also think about the environment in which radiative coolers operate.