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?
I like the way you’re thinking. There’s more than one way to cool something. Air conditioners use the power of compression of certain materials to move heat from one side to the other. But there’s other ways to transfer heat. Just like a computer you could use water cooling. You have a reservoir of water, you can cycle that through areas that are hot to cool down the area. Using your water reservoir as a massive heat sink.
You can harness the wind to help evaporate of cooling be more efficient.
Environmentally friendly air conditioning design is a very interesting subject.
Thank you! It’s interesting indeed.
Currently, the most efficient way of cooling I know of in computers are vapor chambers, so instead of a copper block, you have a chamber (also made from copper) with 1/3 or so filled with water and the lowest point is the hottest part. The water boils, evaporates and settles in the porous walls of the chamber, dissipating the heat and flowing back to the bottom. Those then go into giant fins and are transferred to air. The Nvidia a100 does this in an interesting way. They built one giant vaporchamber system into it, transferring all the heat to the top. I presume its a lot more efficient than water but I lack the specific knowledge to judge the precise efficiency.
In any case, I assume there will be more efficient ways to transfer heat in the future. What eludes me is why we always have heat output and are unable to just transfer heat to electricity or at least movement. I think I‘m missing a key information.
Heat by itself is chaotic. It is the brownian motion of molecules vibrating. If you’re in a hot room, using that vibration to get something useful done can be difficult. Try to think of a way to get those randomly vibrating molecules to do some form of physical work.
When we talk about heat gradients we mean there’s one side that’s hot I.e. moving a lot, one side that’s cold, not moving at all. One of the laws of thermodynamics is things tend to stabilize, so the hot side and the cold side are going to mix they’re going to want to move into each other and find an equilibrium. You can use that preference for movement to do mechanical work, like turning a paddle.
This is all broad strokes. You’re trying to get organized energy, out of a chaotic system. Classically when humans use heat to generate workable energy they use the heat to make steam from water, and then they use the water to do mechanical motion.
None of these systems are 100% efficient. There’s always going to be waste heat. Energy you can’t capture. And that’s the problem. It’s the waste energy that’s making air conditioners most inefficient.
Yes, thanks. That makes a lot of sense.