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?
Sad but thanks for letting me know. Makes sense that there is some reason for it dissipating as heat most of the time.
But there are actually studies done to find out if energy can be harvested from the temp differential in acs https://www.sciencedirect.com/science/article/pii/S2352484722019023
So I suppose there might be some use to it.
There is a lot of bogus “science” out there, and this is part of it.
You need a temperature differential to harvest electric energy. You also need a differential to get heat energy to flow (usually from inside your apartment to outside). If you have that differential, you do not need an AC, you just open the window. If you do not have a differential (or if it points the wrong way, i.e. outside is hotter than inside), you need an AC + energy to create that differential, that lets thermal energy flow from your room to outside. There’s no “free leftover differential” in this, the differential it creates is literally to transport heat energy = why you have turned on the AC. Every bit you use of this differential for harvesting energy, you could turn down the AC a notch and have it save more energy than you could possibly harvest.
This idea is as mute as mounting a wind turbine to your electric car to “harvest” the headwind from driving
I understand. Thanks for explaining.
What still eludes me is if I have 35c outside and want 25c inside, those 10c times cubic meters go outside in the form of 50 or 60c hot air. And I think thats why people like me think it is possible to get those 15-25c difference back in the form of electricity (or at least not spend them so that the excess heat is not pumped outside).
Those 15-25c difference exist to drive the heat energy from the radiator into the air. If one would want to not waste as much energy for this, the actual solution would be to use a bigger radiator that can dissipate the same heat energy per h while being lower temperature. That would need way less additional material and be way more efficient than building another harvesting machine.