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Humans have been using this technique (radiating heat into the cold of space) to freeze water in hot places, for a very long time.

https://www.realclearscience.com/blog/2018/07/09/how_people_...

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That's an interesting article. I'm aware of this sort of radiative cooling, but usually convection and conduction, along with evaporative cooling will be much, much more important than radiative cooling. I'd like to see some kind of report or article showing the cooling potential in W/m^2. I remember someone made a metamaterial optimized for emitting heat in the wavelength of the atmospheric window, but the value was quite low.

You might be thinking of the work led by Professor Shanhui Fan @ Stanford some years back;

https://news.stanford.edu/2017/09/04/sending-excess-heat-sky...

This is being commercialized, but I don't know how successful it has been to date.

https://www.skycoolsystems.com/

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