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?
Energy is only “available” when there is a region of higher energy density and a region of lower energy density, that you can extract work from by allowing that energy to flow from the former to the latter until they are equalized, at which point no further energy can be extracted from that system.
In the case of air conditioning, you can make heat flow “uphill”, so to speak, by applying additional energy from outside of the inside air / outside air system, usually in the form of electricity generated at a power plant. In the very large picture, though, it’s all just moving energy around from other regions of higher and lower densities, a losing usable energy with each transfer. That’s what entropy means.
Veritasium did a really good video on this idea a couple months ago, if you’re interested: https://youtu.be/DxL2HoqLbyA?si=bru50t1VYEKXKmKX