DIY radiative cooling paint from YouTuber NightHawkInLight - https://www.youtube.com/watch?v=N3bJnKmeNJY&list=PL1a2HkcVbm...

It has pretty impressive performance.

Tech Ingredients did one or two vids as well - https://www.youtube.com/watch?v=dNs_kNilSjk

Was thinking of whipping up a batch for my rv.

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kumarvvr a day ago | parent | next [-]

This concept is used all over India to cool down homes that are on the top floors.

https://www.amazon.in/EXCEL-CoolCoat%C2%AE-Reflective-Coatin...

Basically, have a highly reflective white coat on your roof, to reduce temperatures by about 3 Degrees Celsius.

Almost all homes in Urban India are made from concrete and bricks, which can hold a lot of heat.

I myself have been in houses that use this to cover only some rooms of the house (mainly the bedroom), and the temperature difference is definitely noticeable. It also makes the room livable in the extreme hot summers in India.

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kragen 15 hours ago | parent [-]

This is the opposite. It says, "Refelects [sic] 90% of solar infrared rays," because of its "High IR reflective Pigments [sic]," so its emissivity in the infrared is 0.1, but the IR-selective paints we're talking about here are optimized for high infrared emissivity, which means they absorb a lot of infrared.

Maybe there's some wiggle room here because solar infrared is mostly near IR and MWIR, and the place where we want high emissivity (absorptivity) is longwave IR, but to the extent that the advertisement makes any claims about infrared emissivity, it claims very low infrared emissivity, not high.

A paint with low emissivity across the spectrum will slow down the temperature rise when the sun is up, but also slow down the temperature drop when the sun is down. This can still make rooms livable, but it isn't the same as what you get with regular whitewash, where the temperature of the roof is actually lower than the temperature of the air around it.

	▲	jcims 10 hours ago \| parent [-]
		It kind of blew my mind when I first learned about this whole phenomenon (mostly from the YouTube series I posted). Not all white paints are equal and it’s kind of interesting to think that something that looks mostly identical to our eyes has very different (passive) properties in the infrared. I think one of the things in the paints that Ben adds is a set of microspheres that reject incident incoming infrared beyond a certain angle but allow it to pass through when radiated. Something like that.

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kragen 15 hours ago | parent | prev [-]

IIRC, the papers they're working from mention that lime works very nearly as well as the baryta they're using. Guess what people have been painting their houses white with for several thousand years?

	▲	marcosdumay 9 hours ago \| parent [-]
		Not with the optimal mixture for maximum-packing of limestone nanospheres. That effect is almost not perceptible in normal milled limestone.