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Using a solar oven as a radiant refrigerator at night

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Re: Using a solar oven as a radiant refrigerator at night

#41

Post by mateo1 »

satori99 wrote: post #20
mateo1 wrote: post #3

Earlier quoted context omitted.

I'm guessing he just froze water when the temperature dropped below zero at night, and everything else is nonsense.

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_...

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.

Re: Using a solar oven as a radiant refrigerator at night

#42

Post by ShakataGaNai »

simonblack wrote: post #34

Many years ago, I had an indoor swimming pool with solar heating. Some days in the middle of summer that water got too warm. So I'd run the water through the black plastic solar collectors at night-time to throw away that excess heat.

I installed a new pool solar (water) heating system a few years ago. It's got electronic controls for when to send the water up based on temperature etc. It has an integrated cooling mode, which does exactly what you described. Not useful for my location but I've learned in more warm climates it can be quiet a problem.

Re: Using a solar oven as a radiant refrigerator at night

#44

Post by satori99 »

mateo1 wrote: post #41
satori99 wrote: post #20

Earlier quoted context omitted.

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_...

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…

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/

Re: Using a solar oven as a radiant refrigerator at night

#45

Post by thfuran »

richardw wrote: post #33
bamboozled wrote: post #14

Earlier quoted context omitted.

Snow is a near perfect black body radiator

Therefore imagine the impact of reduced snow and ice due to global warming. It’s free cooling and we’re throwing it away.

The albedo is the part that's bad to lose. I don't think snow emits especially strongly in the frequencies relevant for this. A highly imperfect blackbody emitter could cool more effectively.

Re: Using a solar oven as a radiant refrigerator at night

#46

Post by alexpotato »

bamboozled wrote: post #14
JohnVideogames wrote: post #8

Earlier quoted context omitted.

A black body will emit radiation (and receive radiation) until it's in equilibrium with its surroundings. In theory, the black bit of box radiates heat into space, and receives some of the CMB until both are at ~3K. It's how we cool satellites and spacecraft. But the effect is quite small, and I'm suspicious of it (as the nearest surroundings are the hot planet, which transfer heat more effectively!)

Snow is a near perfect black body radiator

This was a key plot point in the 1990s video game: Midwinter

https://en.wikipedia.org/wiki/Midwinter_(video_game)

Re: Using a solar oven as a radiant refrigerator at night

#47

Post by madaxe_again »

dave333 wrote: post #22

This can also be used to heat and cool a building. Harold Hay experimented with a "Skytherm roof" back in the 1970s and built a house at Atascadero, CA. https://www.sciencedirect.com/science/article/abs/pii/S09601... Harold Hay LA Times article: https://www.latimes.com/archives/la-xpm-2007-nov-10-fi-harol...

This is how buildings heat and cool, mostly - every part of a structure that can see the sky allows radiative heating AND cooling. People forget about the second part.

And this is why we built our current house on a north facing slope, in a forest - against all common wisdom about siting.

Place stays cool in the summer, warm in the winter - the other side of the valley literally caught fire this summer, and gets intense cycles of cooling in the winter, as it gets only ~4h of sunlight and 20h of radiation - our more sheltered side gets 0h of sunlight, but the slope and tree cover drastically reduce radiative cooling at night - it’s insane how much the temperature varies as you walk around at night, and you can feel the katabatic winds flowing down the valley and side valleys.

Re: Using a solar oven as a radiant refrigerator at night

#48

Post by coffeebeqn »

madaxe_again wrote: post #47
dave333 wrote: post #22

This can also be used to heat and cool a building. Harold Hay experimented with a "Skytherm roof" back in the 1970s and built a house at Atascadero, CA. https://www.sciencedirect.com/science/article/abs/pii/S09601... Harold Hay LA Times article: https://www.latimes.com/archives/la-xpm-2007-nov-10-fi-harol...

This is how buildings heat and cool, mostly - every part of a structure that can see the sky allows radiative heating AND cooling . People forget about the second part. And this is why we built our current house on a north facing slope, in a forest - against all common wisdom about siting. Place stays cool in the summer, warm in the winter - the other side of the valley literally caught fire this summer, and gets int…

> katabatic winds

New word! So that’s what I experienced on a mountain side in Wyoming

Re: Using a solar oven as a radiant refrigerator at night

#49

Post by slimsag »

liamwire wrote: post #37
contemporary343 wrote: post #25

If you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729

Checking my understanding here: in a very simplified sense, is this saying that we’re taking energy, be it from ambient temperature during the evening or that plus solar radiation during the day, and essentially bottlenecking/‘forcing’ it to radiate in the spectrum that’s atmospherically transparent and can thus escape to space? Seems the use of insulating it in a vacuum would be to minimise heat loss until it’s cool…

You might like NightHawkInLight's videos on the topic[0] and Tech Ingredients[1] - they've been working on making paint using this technology with an at-home DIY process and experimenting with it.

[0] https://www.youtube.com/watch?v=KDRnEm-B3AI&t=285s

[1] https://www.youtube.com/watch?v=dNs_kNilSjk

Re: Using a solar oven as a radiant refrigerator at night

#50

Post by hifikuno »

tagawa wrote: post #18
hifikuno wrote: post #7

Earlier quoted context omitted.

I wonder how you prove/disprove this. I imagine if you had a control box with water exposed to the air that wasn't "radiating heat," then that should show if the solar freezer was indeed working or not.

He did try a basic control with his first version: “i got ice consistently over several nights, even though there was no frost on the ground, and pots of water sitting next to the box cooker did not freeze.”

Ah you're right! I totally missed that line. Cheers.
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