It's thermodynamics - ACs require more energy to move heat than you could ever extract from that heat, otherwise you'd have a perpetual motion machine (which is impossible lol).
this post was submitted on 17 Jul 2025
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It's not taking away any energy. It's just moving the heat from one place to another. And moving stuff takes more energy.
Aha, so this initial pocess requires energy. But then once the heat is accumulated somwhere we can harvest it there and run the proces of that energy (minus the effficency loss)
The point is that the heat isn't accumulated, it is dispersed. To the outside environment generally.
Harvesting excess heat from AC might be possible, but only on an industrial scale. The temperature difference is so small it's hard to make it do useful work.
In general, heat is a "high entropy" energy (high disorder), it is hard to convert heat energy to useful work. When doing any kind of work (converting energy from one form to another) there are heat losses.
Really interesting to think of it this way. High disorder/entropy = hard to put it to work.
Yes, but it's not really practical.
There is a limit to the heat gradient an AC can overcome. For example my AC can't go below 16°C . Similarly they won't work when you're trying to move the air to somewhere that is already very hot (so you won't be able to boil water by moving heat with a normal AC).
Also you're usually running an AC when it's already hot. So there really is no need to bother with recovering the heat moved by the AC. If you need warm air there is a bunch of it outside already! And probably also sun, so just use a solar panel.
Heat pumps (which are basically just air conditioners running in reverse) do "create" energy.
By that I mean that they provide much more heating energy than the electricity they consume, because what they do is move heat that's already there outside (but diffuse) and concentrate it in your house.
Air conditioners cannot create energy (that is literally impossible) but they do move energy out of your home. So some models are now able to move that energy underground in the summer, where the heat doesn't dissipate much at all, then re-use it in the winter as a heat pump to heat your home, making them both more eco-friendly and cheaper to run !
Heat pumps no more "create" energy as air conditioners do, as they're the exact same thing.
They simply move heat. No more, no less.
That you see moving heat to inside a container as "creating" hear doesn't make it so - it's just moving energy (as heat) from one container to another, same as AC, because it is an AC unit with a reversing valve (as you mentioned).
Saying they "create more heating energy than they consume" is accurate only if you compare it to using electric to heat using resistive heating on a per-watt basis. This is always the part people leave out when they say it's "500% more efficient".
Labels on electric space heaters saying 100% efficient have the same issue. While technically true in that all the electricity is turned to heat, it's a meaningless statement.
Resistive heating has never been a good idea, ask anyone who's had a home with resistive where heat is actually required on a regular basis. It's pretty easy to beat resistive.
I have nothing against heat pumps, it's a solid tech that's been with us as AC for 120 years, and specifically as heat pump for about 60 years. My only dislike is they depend on forced air which I personally find less comfortable than radiant.
Utility power plants don't "create" energy (because laws of conservation of matter and energy), but the terminology of utility power "production" is not controversial
Oh great, we can't call it 'power production' anymore. Now we have to call it 'power accumulation'. What next? You want everyone to swap the electron negative and positive symbols? Are you electron-negative you want that?
Radiant heat is great, and heat pumps absolutely can and should be used to supply the heat. Radiant cooling, while technically possible, has a lot of downfalls, forced air is your best bet there. The same heat pump can be used for both though, just need a valve to switch between different supply loops.
There is no means of generating energy from thermals that makes the conversion of surplus heat worth the effort, all gains would be lost to inefficiency. (5–20%). Although you have a solid hunch that air conditioning can move more energy than it consumes, on some accounts.
Short answer: Thermodynamics dictates that the energy you use moving this heat will always be less than the useful work you can get from it, and that's before you get into all the inefficiencies that exist in a real process.
Slightly longer answer: According to the second law of thermodynamics, you can never create any kind of machine (or group of machines) such that you can move heat from a cold spot to a hot spot without doing work. Now if you could use your air conditioner to generate energy in the way you describe, you would be able to use that energy to run the air conditioner, generating energy ad infinitum without ever inputting work from outside the system. This contradicts the second law of thermodynamics, so you can't do it; the power you get from your air conditioner contraption will always ve less than the power it requires to run.
AC's use electrical energy to take some heat energy, and move it outside. You can kinda reverse the process in certain types of heat pumps to generate power, but it's not even close to worth it, the efficiency is horrible.
You need a temperature gradient to capture heat energy, basically a cold thing and a hot thing, you harvest the energy as it moves from hot to cold. You've cooled your house down, and want to use the waste heat to create power, you'll either have to find a very cold place somewhere nearby (unlikely to be cold outside if you're using AC) or you can use the fact that your house is cold. So now you've both lost energy and heated up your house, because that lost energy has been added to the heat you originally tried to remove.
The simplified but always true rule of thumb is that whenever you use energy to create something from which you can harvest energy, you'll never be able to harvest more than what you spent. In reality you'll pretty much always lose energy trying to do this, I'm not aware of anything that's 100% efficient in both directions (or even one honestly).
if we take away the energy from the Air we have concentrated some heat elswhere which we should be able to harvest?
Yeah, we kind of can. If you place a mug of cold coffee on the the exterior coils of an air conditioner, the coffee will get warmed up a bit.
So i could make a small small steam engine there and run the compressor (at least partially) of the AC from that rotation?
One of the later more modern uses of a heat pump is a heat pump water heater where it takes the Heat out of the air and pumps it into the water.
I installed one and it dropped my power *bill by almost $30 a month even though I went from a 55-gallon hot water heater to an 80-gallon water heater.
I think the issue is finding a use for that heat energy that makes sense. Generating electricity with it doesn't make a lot of sense, but heating water so that you spend less energy heating water does.
That’s great in the summer when you want to be cooling the air inside your house, but not so great in the winter when you want you want to be heating it. I’m hoping some water heater manufacturer figures this out someday and builds a unit capable of switching air sources for the heat, such that the cold output air could be circulated directly into the living space or ducted in a loop to the outside (or attic).
It has the option to go to traditional electric heating if meed be, And if I really wanted to, I could rig up a system where it would vent the colder air outside, and it apparently can work down to nearly 30 degrees farenheight so I could just use outside air exclusively for it if I really wanted to 9-10 months out of the year.
Yes, but the addition of the steam engine would create a load on the air conditioner which would be greater than the power the steam engine could provide.
There's not really enough heat generated typically to be worth going through the losses of turning it back into electricity.
More advanced AC systems leverage full heat pumps to move heat around from places with more than wanted to places with less. Which is pretty effective at conserving energy in bigger buildings
I'm not 100% this example actually exists, but I would not at all be surprised if there are office buildings out there that use excess heat from their AC to heat hot water for the building
There is at least one device that uses the heat that is pumped out of your house as an energy source. A "heat pump water heater" extracts heat energy from your home and put it into your water.
A heat pump is most efficient when the temperature of the exhausted heat is only slightly above ambient. The higher the exhaust temperature, the more energy you needlessly added to the refrigerant.
For the heat pump water heater, "ambient" is the desired temperature of the hot water, not the outside air. It would be more efficient for the water heater to draw air from the hot outdoors, but by operating indoors, it also reduces the load on the air conditioning.
Look up heat pumps.