> on rainy nights my food gets wet
Indeed. But overall this guy sounds like a good person to have in your apocalypse survival community.
Using a solar oven as a radiant refrigerator at night
21–30 of 94 posts
Re: Using a solar oven as a radiant refrigerator at night
#22This 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...
Re: Using a solar oven as a radiant refrigerator at night
#23Re: Using a solar oven as a radiant refrigerator at night
#24Re: Using a solar oven as a radiant refrigerator at night
#25If you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729
Re: Using a solar oven as a radiant refrigerator at night
#26I’m missing the basic premise here, how does pointing an insulated box at the sky at night cool whatever’s in the box?
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!)
it's easy to calculate how big the effect is with units(1)
You have: stefanboltzmann tempC(20)**4
You want: W/m**2
* 418.76592
/ 0.0023879689
You have: stefanboltzmann tempC(0)**4
You want: W/m**2
* 315.65782
/ 0.0031679874
tens or hundreds of watts of cooling is quite significant indeed when we're talking about making some ice or cooling some food
Re: Using a solar oven as a radiant refrigerator at night
#27I’m missing the basic premise here, how does pointing an insulated box at the sky at night cool whatever’s in the box?
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!)
There are some IR bands that are transparent between the ground and space so if you optimize your emissions in those bands (because you are not an idealized black body) and insulate yourself from conduction and convection heating, you can beat your local surroundings and cool yourself lower than ambient to a useful degree.
https://en.wikipedia.org/wiki/Infrared_window
There are materials and even paints that have emission spectrums designed for this.
For example: https://www.parc.com/technologies/self-cooling-paint/
Normally you would just be in the same thermal equilibrium with everything else having similar emission spectrums you'd give and receive similar amounts of radiative heating and cooling. Tweak your spectrum and you tip the balance in your favor.
Re: Using a solar oven as a radiant refrigerator at night
#28If you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729
Why 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.
Re: Using a solar oven as a radiant refrigerator at night
#29I’m missing the basic premise here, how does pointing an insulated box at the sky at night cool whatever’s in the box?
Great 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_co...
I also posted this as a separate post for visibility. It’s an amazing technique that more should be aware of.
Re: Using a solar oven as a radiant refrigerator at night
#30Earlier 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!)
If 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-in...
Wow unradiant heat, or more accurately radiant cooling I suppose. Fascinating