Air conditioner without heat output - Is it possible?

[jaumzaum]

Hello everybody! I was wondering today if physically, it'd be possible for the world to develop an air conditioner without an outdoor heat unit? I know this seems to violate the second law of thermodynamics, but the known version of the second law thermodynamics only consider this is impossible for devices that converts heat to work.

What about other types of energy? For example, if the heat I take out from a room in the infrared spectral range could be transformed by some process in energy in another spectral range, that my body does not perceive as "hot", or if this energy could be transformed to chemical or electrical energy, even charging a battery. Is that possible?

I know the process need to always increase the universe entropy, and decreasing the temperature of my room will always decrease the entropy, such that I would need another process that increases it. But can't humans develop some other process that deal with all the heat that should be generated and transform it in another energy type with a higher entropy? Specially if we could store it?

Thank you very much!

 

[Drakkith]

Sure, you could run the heat through a heat engine and convert some of it to useful work, but that vastly complicates the AC unit and probably isn't economical given the relatively low temperature difference between the hot exhaust and ambient temperature.

 

[Chestermiller]

Sure, you could run the heat through a heat engine and convert some of it to useful work, but that vastly complicates the AC unit and probably isn't economical given the relatively low temperature difference between the hot exhaust and ambient temperature.

The heat engine, to operate in a cycle, would have to discharge heat at a lower temperature, which is just the opposite of what the AC does.

 

[DrStupid]

But can't humans develop some other process that deal with all the heat that should be generated and transform it in another energy type with a higher entropy? Specially if we could store it?

Such as melting a solid?

 

[jaumzaum]

Such as melting a solid?

Melting a solid is a perfect example of what I was saying. But can that idea be viable for reducing the temperature of my bedroom 10 Celsius degrees is some decent time?

I am asking this because we need a tube to connect any air conditioner to the outside, and sometimes we cannot make any hole in the wall of the appartment. That tube annoys me a lot, making an air conditioning a not practical device So are there any other *viable* proceses? We know that after some time the solid would solidify again, and send heat to my room. If we have enough solid though, we could make this process continue for quite sometime, and when we are not using it, we wait for it to solidify in the outside or we could buy more solid (expensive option). Also, the solid has a very specific meling temperature. Would this air conditioner work in different temperature ranges? Could we make a dynamic mixture to change the melting temperature depending on the temperature that my room is? Is it fast enough to extract heat from a solid? Isn't there other possibilities? I really want to know why we didn't create something like this yet, why is that so difficult, expensive or inefficient?

 

[Vanadium 50]

Option A: get an air conditioner, and use the heat exhaust to melt some solid. We'll call it "ice".
Option B: just bring the ice in the room

Which is more efficient?

 

[hmmm27]

There are a variety of commercially available waxes, formulated for a phase change at various "room temperatures" which - within that range - is better than water's latent heat.

Of course, you still have to dump the heat, eventually.

(Sorry, I haven't done any real investigation, into pricing or efficiency, yet... sort of hoping somebody else will)

 

[Drakkith]

The heat engine, to operate in a cycle, would have to discharge heat at a lower temperature, which is just the opposite of what the AC does.

Of course, but there is nothing stopping you from using the small temperature difference between the exhaust and the ambient air to run a heat engine. It just won't be very powerful or efficient given the very small temperature difference.

 

[gmax137]

We'll call it "ice".

 

[Vanadium 50]

Ice, ice, baby!

 

[rcgldr]

https://en.wikipedia.org/wiki/Thermoelectric_cooling

 

[sophiecentaur]

sometimes we cannot make any hole in the wall of the appartment.

A landlord wouldn't spot two small microbore pipes going through holes but the heat exchanger, hanging on the wall outside would be noticeable.

I realize this is really a theoretical thread but there are practical solutions that involve large diameter pipes going in and out of a window, carrying air as a heat transport medium.

I just remembered that Peltier cooling is possible - but you will always need a heat exchanger outside, somewhere.

 

[russ_watters]

https://en.wikipedia.org/wiki/Thermoelectric_cooling

Those have heat rejection, so I don't see the relevance/point.

 

[sophiecentaur]

Those have heat rejection, so I don't see the relevance/point.

Yes, perhaps, but the other systems all involve 'carrying the heat' in the form of buckets of ice or equivalent - which is just an even more difficult alternative.

 

[JT Smith]

A landlord wouldn't spot two small microbore pipes going through holes but the heat exchanger, hanging on the wall outside would be noticeable.

I like the image of microbore pipes in a rental unit. Maybe they wouldn't be noticed and maybe you could cover up any evidence before you moved out. A bit of a risk.

But assuming that's viable, why not bring the outside inside? A well insulated box indoors could be "outside" if connected to the real outside by those tiny pipes.

That's not what the OP wants though. Unfortunately it's not possible.

 

[sophiecentaur]

A well insulated box indoors could be "outside" if connected to the real outside by those tiny pipes.

In principle but not in practice, the rate at which air could carry significant heat through those pipes would be very limited. The box need to be well insulated because it would get very hot. It would need to be right next to the wall. But the temperature for the expelled air would need to be very high, which would severely limit the coefficient of performance of the refrigerator. Also, the hole though the wall would need to be large - to allow for suitable insulation to protect the wall fabric.

I think the whole scheme fails in principle and in practice.

 

[Vitina]

Sure, you could run the heat through a heat engine and convert some of it to useful work, but that vastly complicates the AC unit and probably isn't economical given the relatively low temperature difference between the hot exhaust and ambient temperature.

Systems like this do exist in industry, where the heat generated is used in other possesses, or heat is stored with water, lithium bromide, or ammonia. Also in staged systems to fractionally improve efficiency or extend temperature differential. The downside is high cost, increased maintenence, and increased system complexity with additional failure points.

 

[sophiecentaur]

That tube annoys me a lot, making an air conditioning a not practical device

You could be really antisocial and use a heat pump to dump heat to the wall between you and the neighbour. If the heat exchanger that you put against the wall has a big enough area then you could work with a lowish temperature and your neighbour might not notice.

There are many practical measures that can be taken, in many situations, if you have to do without actual AC. Reflective blinds on the windows and an insulating layer on external walls (particularly where there's incident sunlight). From comments I read on PF about keeping homes cool, I notice that passive methods are often ignored. Closed windows are often much more effective than open windows. Swamp coolers work fine when the ambient humidity is low (hopeless in places like UK).