12 ms·
Using a solar oven as a radiant refrigerator at night
- jack_riminton 3y agoI’m missing the basic premise here, how does pointing an insulated box at the sky at night cool whatever’s in the box?
- mateo1 3y agoI'm guessing he just froze water when the temperature dropped below zero at night, and everything else is nonsense.
- hifikuno 3y agoI 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.
- toast0 3y agoYou could build a few test configurations. One as stated, insulated fridge, open on top. One, insulared fridge, open on top, under an open air shelter, no walls, just a roof, where the roof is a significant distance away from the top of the fridge, so airflow is not impacted, but there's no view or the sky. Possibly variations on this with the roof being ir transparent or not. Another test configuration could have the fridge closed, but with forced air ventilation.
- tagawa 3y agoHe 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.”
- hifikuno 3y agoAh you're right! I totally missed that line. Cheers.
- deleted 3y ago[deleted]
- satori99 3y agoHumans 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_created_ice_in_the_desert_2000_years_ago.html https://www.realclearscience.com/blog/2018/07/09/how_people_...
- mateo1 3y agoThat'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.
- satori99 3y agoYou 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/ 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/ https://www.skycoolsystems.com/
- punnerud 3y agoAlmost all surfaces radiates heat. You can heat and cool using radiation. It’s the same way satellites is cooled, when you can’t cool with convection (interact with other atoms). Black absorb more radiation, but it also radiates more
- vladms 3y agoI guess that not having other warm objects pointing at the water, will not warm the water (example: a wall radiates infrared so it heats the water if the wall has "sight" over the water). Insulating the walls of the container with the water servers the same purpose - not have the water get heat from the surroundings.
- JohnVideogames 3y agoA 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!)
- bamboozled 3y agoSnow is a near perfect black body radiator
- richardw 3y agoTherefore imagine the impact of reduced snow and ice due to global warming. It’s free cooling and we’re throwing it away.
- thfuran 3y agoThe 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.
- alexpotato 3y agoThis was a key plot point in the 1990s video game: Midwinter https://en.wikipedia.org/wiki/Midwinter_(video_game) https://en.wikipedia.org/wiki/Midwinter_(video_game)
- Scoundreller 3y agoIf you grow crops, your crops can freeze when it's a clear sky at night with stagnant air even though the air temperature only goes close to freezing. In some agri areas, you'll see "wind machines" to blow the warmer air around the crops to keep them from radiating their heat and frosting. https://www.ontario.ca/page/wind-machines-minimizing-cold-injury-horticultural-crops https://www.ontario.ca/page/wind-machines-minimizing-cold-in...
- deleted 3y ago[deleted]
- aaron695 3y ago[dead]
- richardw 3y agoGreat question! “PDRC surfaces are designed to be high in solar reflectance (to minimize heat gain) and strong in longwave infrared (LWIR) thermal radiation heat transfer through the atmosphere's infrared window (8–13 µm) to cool temperatures even during the daytime.” https://en.m.wikipedia.org/wiki/Passive_daytime_radiative_cooling https://en.m.wikipedia.org/wiki/Passive_daytime_radiative_co... I also posted this as a separate post for visibility. It’s an amazing technique that more should be aware of.
- toss1 3y agoCool. Might be able to do even better with self-cooling paint [0,1] during the day to reject heat and Vantablack [2] at night to radiate it? (although I wonder how Vantablack would do at radiating with its microstructured surface) [0] https://www.parc.com/technologies/self-cooling-paint/ https://www.parc.com/technologies/self-cooling-paint/ [1] https://www.purdue.edu/newsroom/releases/2021/Q2/the-whitest-paint-is-here-and-its-the-coolest.-literally..html https://www.purdue.edu/newsroom/releases/2021/Q2/the-whitest... [2] https://www.abc.net.au/news/science/2017-01-13/vantablack-where-is-it-being-used/8175042 https://www.abc.net.au/news/science/2017-01-13/vantablack-wh...
- alpaca128 3y agoThat self-cooling paint works at night as well. It's not just white paint that reflects light, it also radiates heat pretty well. The YT channel NigthHawkInLight developed a variation that can be produced with (more or less) household ingredients and it cools to 3-4 degrees below ambient temperature if I remember correctly.
- nothercastle 3y agoIt’s good for a couple degrees I think you can get water to freeze at 36 on a clear night for example
- huytersd 3y agoAs in when it’s 36 outside?
- klyrs 3y agoUnits, dammit!
- kurthr 3y agoIf it's either 36C or 36K at night, you've made a bad decision on where to live.
- deleted 3y ago[deleted]
- vitiral 3y agoDon't forget Rankine, although you are making equally bad decisions as Kelvin there
- kurthr 3y agoTIL about the Rømer and Réaumur temperature scales which are why Rankine is not just °R but °Ra. I guess everyone was doing it back then! https://en.wikipedia.org/wiki/R%C3%B8mer_scale https://en.wikipedia.org/wiki/R%C3%B8mer_scale
- bigiain 3y agoI agree, but it's simple to guess from context here.
- huytersd 3y ago
- btbuildem 3y ago> on rainy nights my food gets wet Indeed. But overall this guy sounds like a good person to have in your apocalypse survival community.
- dave333 3y agoThis 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/S0960148199000798 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-haroldhay10-story.html https://www.latimes.com/archives/la-xpm-2007-nov-10-fi-harol...
- madaxe_again 3y agoThis 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.
- coffeebeqn 3y ago> katabatic winds New word! So that’s what I experienced on a mountain side in Wyoming
- voisin 3y ago> And this is why we built our current house on a north facing slope, in a forest - against all common wisdom about siting. Can you comment or give more detail about the level of tree coverage required to have a noticeable effect of radiative cooling?
- madaxe_again 3y agoEnough that the ground is mostly shaded on a summer’s day. Dappled shade, I suppose. You’re basically thinking about what percentage of the sky a given point on the ground can see, and a surprisingly small amount of cover goes a long way.
- contemporary343 3y agoIf you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729 https://www.nature.com/articles/ncomms13729
- londons_explore 3y agoWhy isn't this replacing aircon over the whole world? Unless that IR-transparent window is made of gold dust, it has to work out cheaper than the energy cost of running an air conditioner.
- kragen 3y agomy air conditioner is rejecting 3000 watts to the outdoors right now, even though my bedroom is the same temperature as the nighttime outdoors. doing that with radiative cooling would require 8 square meters of emitter area at 400 watts per square meter and a clear, low-humidity sky (not necessarily night, but in the daytime, you additionally have to keep the sun off the panels). my air conditioner's condenser is significantly less than 1 square meter as seen from the sky and also works when it's cloudy or humid outside basically forced-air convection heat transfer is a motherfucking miracle, and vapor-compression refrigeration even more so
- semi-extrinsic 3y agoIf my napkin math is right, solar panels give around 2x higher electricity production per square meter than these devices give cooling power. Then that goes into a COP of ~3 for your aircon, and the solar panels have have a factor of 6x better cooling performance per area covered. Then factor in that electricity can be used for lots of other useful things than cooling, and that solar power variation during the day is perfectly matched with cooling demand, it's a no brainer.
- simonblack 3y agoMany 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.
- ShakataGaNai 3y agoI 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.
- s0rce 3y agoBetter than this https://www.youtube.com/watch?v=lcnr6YiT-g8 https://www.youtube.com/watch?v=lcnr6YiT-g8
- grecy 3y agoHuh, we had an outdoor pool with no heating other than just being outside in the sun, and it would regularly get too warm. We would only swim after about 11pm. We also thought it was too cold to swim if the air temp was below 35C (95F). Australia.
- aaron695 3y ago[dead]
- 20after4 3y agoSort of related: the YouTube channel "Tech Ingredients" do some cool things with radiant cooling: https://www.youtube.com/watch?v=dNs_kNilSjk https://www.youtube.com/watch?v=dNs_kNilSjk
- kulor 3y agoOne phenomenon I've found peculiar on frosty mornings is that the grass directly under my (apple) trees doesn't freeze, leaving a noticeable silhouette on the lawn. I've assumed it was due to the cool, heavy air falling and the tree acting as a shield but this article makes me think there are more complex factors at play.
- pard68 3y agoWith the exception of two vacations to California, I have lived my entire life in high humidity locations. This sounds like magic, I understand the science and all, but that it can actually work is wild. It might work for me in the winter, when we regularly get drier weather and spend a most nights flirting with freezing.
- nik282000 3y agoHey, this reminds me of Bill Beaty's Human IR Sense: http://amasci.com/weird/humanIR.html http://amasci.com/weird/humanIR.html