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A comment on The whitest paint could eliminate the need for air conditioning.

Re:The whitest paint could eliminate the need for air condit... by wayfarer1291 on Saturday September 18, 2021 @01:40AM (#28573961)
Barium sulfate based coatings have been used for decades, maybe a century, as the 'whitest' reflecting standard for optical instruments. I hate to be that guy, but there's nothing that new here. Though Purdue and this prof sure are hyping the heck out of this, it's pretty funny for anyone in the optics world.. we buy it all the time for integrating spheres! This wasn't published in a high profile academic journal for a reason...

The actual challenge with any solar reflective paint is that it loses its solar reflectivity after multiple years of outdoor exposure. This can be seen at the third party Cool Roof Rating Council's website: https://coolroofs.org/directory

Outdoor white paints that start at 90+ % solar reflectance drop to the low 80s with time. Same thing will happen with this one, so the added benefit of the high reflectance will decrease quickly. Figuring out how to maintain this high reflectance in a paint exposed outdoor remains a very hard problem.

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Re:The whitest paint could eliminate the need for air condit... by gricardo99 on Saturday September 18, 2021 @01:50AM (#28574011)
I don’t know anything about this, but wouldn’t low 80s still be far better than standard roof material? I’m guessing your average roofing, like shingles, absorbs +90% of solar energy?
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Re:The whitest paint could eliminate the need for air condit... by Iv on Sunday September 19, 2021 @03:47AM (#28582492)
Yes but at that point you may simply use classic white paint I guess. Also one thing to consider is that going front 90% to 80% may not look like a big difference but that's still doubling the heat that comes in
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Re:The whitest paint could eliminate the need for air condit... by milleramp on Saturday September 18, 2021 @02:37AM (#28574213)
Yes you can make you own by adding barium sulfate to white paint, not as good as the expensive integrating sphere paint but pretty good for large white diffuse panels on a budget.

I watched as the rooftop out my window was painted white, it was extremely reflective. After a year, visibly the roof is dark gray. I wish I would have taken a daily picture and spectral measurement, maybe next time.

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