Super Cool

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So, yesterday, I spoke about titanium dioxide– memories that were triggered by this new article.  Research performed by Drs. J. Mandal (he earned his PhD in Applied Physics at Columbia; now he is a postdoc at UCLA), Y. Yang and N.Yu (Columbia), as well as A.P. Raman (UCLA).  Their paper, Paints as a Scalable and Effective Radiative Cooling Technology for Buildings, was published in the journal, Joule.

As we discussed yesterday, many rooftops have been painted white to reflect the sun and heat.   These solar reflecting paints are based upon titanium dioxide (TiO2 )  at the base, which reflects most visible and some near-infrared light- but absorbs UV and violet light.  (Titanium dioxide is also the substance that  is used in sunscreens to protect our skin.)  But, as I said, the pigment only reflects 85% of incoming solar radiation.  These four folks have formulated what they call a ‘super-white’ paint- one that reflects 98% of the incident heat coming from the sun.  That’s a major difference.

Reflective Coatings for Super Cool Buildings

The team reduced the amount of polymeric binders in paint (which absorb the heat), and replaced the titanium dioxide with (relatively cheap) barite (artist’s pigment) and PTFE (PolyTetraFluoroEthylene, which you know as Teflon®, a product of DuPont).   These coatings not only reject heat from visible light, but also at the infrared and ultraviolet ranges.

https://youtu.be/YZz1lrrEAK0

The team also dreams that this development of theirs, passive daytime radiative cooling, can be part of the arsenal against climate change.  As opposed to using this willy-nilly among all the buildings, they want to map those sites where the changed pigment could yield the biggest difference.

After all,  natural environments are exceptionally good at dissipating heat (via evapotranspiration), but cities, with their paved streets and buildings, normally form what is called a “heat-island”.   That is a region that is considerably hotter than the surrounding communities. This phenomenon is why the State of California and the City of New York are pushing “cool-roof” technologies for all new structures.

 

 

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18 thoughts on “Super Cool”

  1. I had no idea because I never considered that heat could be entering the building via my roof. Of course here in Mexico our roofs are poured concrete a few inches thick so I am not sure if it would do any good. Living in an area where 90+ degrees for a few hours daily is the norm, I am always looking for ways to cool the casa. Thanks for the information, I need to research to see if it would help here in Mexico.
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  2. Having grown up in New York City, and then getting to know a man from a then-rural suburb and experiencing both environments for about four years before I left the City for good, I experienced, and remember, the “heat island” effect. Happy to see this type of work continuing despite the pandemic.
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  3. that is cool!! I recall reading that many places around the world have started painting or having roads/sidewalks coated with paints like this to keep things cooler..
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