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Cooling Paint: How to Make Surfaces Stay Cool in the Sun
(www.youtube.com)
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this post was submitted on 29 Nov 2023
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Has anyone here ever owned a white building?
They’re very hard to keep clean, especially in urban environments, which soak up most of the power used for cooling and where this product would be most beneficial.
How easy is this stuff to clean? Is it easily damaged by pressure washing? What kind of cleaners are needed for this to function reliably? Are those cleaners safe for the environment?
You are absolutely right to be skeptical. There are a great many downsides to this technology. Getting it grimy, pointing it out of the sky, cloud cover, etc. will nullify any cooling effect. And yes, the DIY preparation shown would be completely destroyed by a powerwasher, or even a moderate storm. That said, I read recently of a university of maryland research team made an improved coating, allowing the nanospheres to withstand significantly increased weathering while still remaining effective.
If I understand it right, it's not a laser shooting heat into space. It doesn't require a clear sky to function. It's just moving the heat effectively away from itself by bypassing the atmospheric insulation, wherever that might be. And that goes for pointing it as well, except you wouldn't really want it under direct sun for best heat transfer
Radiant heat transfer in the real world often appears quite odd in its behaviour despite being seemingly simple. I learned quite a bit about it when I decided to implement radiant ceilings in my home.
Yes, the panel radiates the same amount regardless of where it's pointing. However, other rays are incident on it from other surfaces that deliver heat back to the surface. Thus the point of a selective emitter that emits more than it absorbs. Likewise solar thermal panels are optimally made from selective absorbers, but IRL flat black paints are so much cheaper that it's not worth it.
So thermal comfort often is a result of radiant balance. Your 20° clothing radiates to the walls - the 20° walls radiate to you - there is no net loss of heat, and you are warm.
Step out under the dry, cloudless prairie sky at night, you radiate into the infinite blackness of space. Nothing radiates back. You cool off rapidly. It's not so much that the heat needs to be dumped into space, but that space offers no heat in return.
Seriously it's pretty neat to point my thermal scanner at the night sky and see it read -INF. The night sky is an effectively unlimited radiant sink.
My white building is currently covered by spiders and crud. Luckily it'll soon be cleaned spotless by the first blizzard of the season, which would also polish off this paint.
However this is really just some science YouTubers replicating an experiment, far from a commercial product. It's just for interest. I like Tech Ingredients, they try to do fairly rigorous work on the border of pure and applied science.
It's like thst new type of batteries that is revolutionary, but never turns into a product
You're right: it's probably not practical to paint a building with the stuff. Nighthawkinlight briefly comments on this. I believe the idea is to use it on passive radiator panels to sink heat from a pumped coolant fluid. That way you can strategically place panels (e.g. on the roof) and control them, just like solar heating panels.