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I recently had a discussion about ACs and how they heat up cities.

Then I found an article about theoretical increase of efficiency of acs by using the heat pulled from a room to run a thermoelectric device and getting some of the energy back that was used in the ac.

I‘ve had this downstream thought many times already: since hot air is basically just energy stored. Could we theoretically pull (all?) the energy from the air (depending on desired temp) to cool it and casually fuel our society’s energy needs?

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[-] McLovin@beehaw.org 19 points 1 year ago* (last edited 1 year ago)

You can’t output more energy than the one available in a system.

The real solution to cool off cities is trees and less pavement :)

[-] Haui@discuss.tchncs.de 1 points 1 year ago

I agree. It's thermodynamics, right?

The reason I'm asking is that 100 m³ of 60 C air would have a specific amount of energy (watts?) in them, right? And from there to absolute zero (0K) would be "available energy" in my perception. Or is "available" something else?

Thanks for elaborating. :)

[-] McLovin@beehaw.org 1 points 1 year ago* (last edited 1 year ago)

You would need an enormous amount of energy to achieve 0 K (-273 °C). See the system here is the atmosphere so you can think about the average outside temperature as the “state of least energy”. So you actually need to use a lot of energy to achieve that because you are going way further (although in the other direction- negative temps). Our system is earth, so 0K ain’t easy chief - check quantum computing (we need almost 0 K to work and those are huuuuge resource intensive machines). If you were in between the emptiness of galaxies, then that would be indeed the “normal default” which entropy would “go towards “. Basically, “our” entropy has a different temperature goal, because we are the system that is fed and bound to the sun. I can’t explain better because I also have limited knowledge, just the basics, sorry. Also the “” is to explain better, do not quote those as scientific.

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this post was submitted on 11 Sep 2023
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