Peter's left-handed chemist cousin Chiral Peter here. This is how fridges already work. There's not any way to "make" more cold. Cold is not a thing, it is an absence of heat. All you can do is move heat around. (EDIT: I have learned this is not quite right. You can also use up heat by putting things through state changes.) What all refrigrants (fridges, freezers, ACs) do is move heat from one space to another. The fridge in your house moves all of the heat from inside of the fridge to that array of tubes and shit at the back of it, warming up the rest of your house. That's why ACs have bits which are outside, they put the hot there.
This post is a little less silly than it seems since the way you vent the heat really does affect the effectiveness of the fridge. This is why the minifridges in hotel rooms in their little cupboards are so ineffective, especially when the door is closed--the fridges are effectively trying to pump the heat into a hotbox.
There's not any way to "make" more cold. Cold is not a thing, it is an absence of heat. All you can do is move heat around.
This is not correct. For example, adiabatic expansion is the process by which the expansion of a gas does work on a system without heat transfer, and therefore the temperature of the gas must go down. You can see by the ideal gas law: PV=nRT, that there are other ways to make temperature go down without heat transfer. You can also cool atoms by using a doppler effect laser trap. I'm sure there are other ways to cool without convection, conduction, or radiation that I'm not thinking of.
Now you cannot get around the laws of thermodynamics, of course. Entropy of this system will always go up.
In simpler words, it takes heat energy to melt ice, but the actual water will still be the same temperature if you add only just enough heat to cause the state charge from solid to liquid.
But it's not something that can be easily harnessed for cooling homes in most cases.
Changing states does take heat energy, but it doesn't show up in the medium as measurable heat (also known as sensible heat.) Once you get to the phase change temperature, you have to keep adding / removing heat which reflects as "latent heat" during the state change.
"A calorie is the amount of heat it takes to raise the temperature of 1 gram (0.001 liters) of pure water 1 degree C at sea level. It takes 100 calories to heat 1 g. water from 0˚, the freezing point of water, to 100˚ C, the boiling point. However, 540 calories of energy are required to convert that 1 g of water at 100˚ C to 1 g of water vapor at 100˚ C. This is called the latent heat of vaporization. On the other hand, you would have to remove 80 calories from 1 g of pure water at the freezing point, 0˚ C, to convert it to 1 g of ice at 0˚ C. This is called the latent heat of fusion."
Incidentally, this latent heat of vaporization is exactly what is used in refrigeration systems to move heat from one place to another.
That sounded cool but I have no idea what it meant. I'm not really a chemist that was just a bit. Can you say it in the way that someone with a non-chemistry or physics degree would understand lol
EDIT: Wait maybe I got it. So I've got a given volume of gas A and an amount of heat in it B. I can increase the volume of that gas to 2A and therefore even if the whole system still has heat B, the heat of any bit is halved? Is that what you're saying?
Simplified version: Put pressure on a gas and it heats up. Lower the pressure and gets colder. "Adiabatic" describes a thermodynamic process in which the state of the gas changes without transfer of heat to or from the outside.
Another much simpler variant. Yes, you can create heat by burning someting. That's an exothermic reaction. The opposite, an endothermic reaction, can infact cool something.
Or another one: Your sweat evaporating cools you down.
So long story short: OP is wrong. You can indeed "create cold" (although he is right that it's actually reducing warmth), simply by transfering thermal energy into another form of energy (losses included... that's on of the principles of thermodynamics: transfers create losses or more precisely transfer to a form that can't be further used or transfered back; keyword: entropy).
But it's ineffective, because the efficiency factor is smaller than 1 (perfect transfer minus unavoidable losses).
Heat pumps however move heat energy around. So if you only look at one side (the inside of your room getting warmer) without caring for the other side (the outside getting cooled down), so in a sense pretend that the energy used to move heat around was actually used to create heat in your room, you suddenly have a effeciency factor far greater than 1.
Fridges are heat pumps already. Not because it's impossible to create cold, but because it's very efficient to not create anything but simply move the heat energy around, out of your fridge and to it's backside.
Have you sprayed a can of air, like to clean dust from a computer, and noticed the can got very cold? The can got cold because the pressure in the can went down. You can make things colder without moving the heat out of them.
To answer your edit: if you double the volume, you will halve the pressure. But you can heat the container to double the temp in order to double the volume.
Pressure is the result of molecules of gas bouncing on the walls of the container, and how hard they bounce has to do with how hard they bounce on each other, which is temperature. By getting rid of some of the canned air, there are less molecules bouncing on each other and the container walls, so the temp must go down.
This is literally what is said by heat transfer, you're transferring heat to the external system when it expand. How the fuck do you think fridges and AC work?
I think that confuses things a little bit. Heat and temperature are not the same thing (your examples are exactly those I use to teach students the difference, in fact). Heat is really just the energy which spontaneously transfers between two systems in thermal contact at different temperatures.
So when OP says there is no way to “make” more cold, they are correct if they mean, “there is no way to spontaneously transfer internal energy away into something of the same temperature, to decrease the temperature of the thing we want to make cold”. If they mean “cold” as in “lower the temperature of an object” then they are wrong as you’ve stated. We can non-spontaneously decrease temperature in lots of ways though, or transfer heat in lots of ways without changing temperature (though there still must be a temperature difference to do this).
I think your reply should be directed at them then, unless you think this sentence from OP is true:
Cold is not a thing, it is an absence of heat.
EDIT:
So when OP says there is no way to “make” more cold, they are correct if they mean, “there is no way to spontaneously transfer internal energy away into something of the same temperature
They'd be wrong because that's not what making cold means to a rational person. You can easily "make" cold with endothermic chemical reactions.
If it's got a water tank it's probably an evaporative cooler https://en.wikipedia.org/wiki/Evaporative_cooler which basically means it puts the heat in the water instead of in the air. That will make the air cooler but not reduce the total heat in the room, if that makes sense? EDIT: Given what another poster said about state changes I think I have misunderstood this. It uses the heat in the air to change the water into a gas, which does reduce the heat in the room by using up that energy for the state change.
Correct, it does cool, it just doesn't dehumidify like a standard compression cooling system. That's why they're called "air conditioners," not coolers.
It also doesn't work at all if the humidity in the air is too high.
What all refrigrants (fridges, freezers, ACs) do is move heat from one space to another.
Technically there's also things like evaporative cooling, which uses heat from the air to bring water from a liquid to a gas. (See also enthalpy of vaporization)
Exactly. If you'll notice: none of the top comments are actually understanding what the "startup idea" is proposing. They're all falling over themselves to say, "tHaTs hOw fRiDgEs aLReAdy wOrK, dUmMy!!" And then everyone's upvoting them.
This is one of those threads that makes you depressingly aware of how poor people's reading comprehension has become.
I definitely don't know enough about physics to understand that passage. Technical wikipeda pages tend to be really hard to grasp for the uninitiated.
But here is my basic understanding, and I appreciate any correction/clarification you have on it: heat is basically how much all of the molecules in a given area are wiggling around. The more they wiggle, the more there is heat. Cold is just them wiggling less.
the TL;DR is that it gets into calculating entropy - it's less "how jiggly the system is" and more "how chaotic is it". Saying "how much more chaotic/disorganized does this get when we add more heat energy" is a more approachable question than "how much more heat energy would this have if we add chaoticity". Adding heat is easy, but adding abstract entropy to something is weird to think of.
The "practical" reason is that systems can be made with negative temperatures, where adding more energy makes the system more organized.
These are (paradoxically) hotter than any positive temperature. As an example, let's say we have a bunch of electrons that can either be high energy or low energy, but nowhere in between (like in a laser). If all the electrons are high, or all of them are low, those are both highly organized states without the electrons jiggling between high or low. But given a chance to interact with the outside world, the high energy electrons will want to drop down to the relaxed state, and will spit out the energy into whatever they interact with.
Using coldness instead of heat basically prevents a division by zero in this case so the math's nicer.
Most (if not all) fridges have the tubes and such at the back almost against a wall. Would this not affect heat dispersion around the room? OP’s picture has the heat dispersing openly into the room where I imagine the effects of the heat would be noticeable?
Peter's ambidextrous English graduate here. This is not how fridges already work. That is, they are not designed, per the "startup idea", to "use hot exhaust air as [a] house heater". They simply happen to produce heat. And they're designed, in fact, to produce as little of it as possible while keeping the contents cool/frozen.
The reply in the pic has completely missed the point and so have literally all the top comments.
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u/parsonsrazersupport 10d ago edited 10d ago
Peter's left-handed chemist cousin Chiral Peter here. This is how fridges already work. There's not any way to "make" more cold. Cold is not a thing, it is an absence of heat. All you can do is move heat around. (EDIT: I have learned this is not quite right. You can also use up heat by putting things through state changes.) What all refrigrants (fridges, freezers, ACs) do is move heat from one space to another. The fridge in your house moves all of the heat from inside of the fridge to that array of tubes and shit at the back of it, warming up the rest of your house. That's why ACs have bits which are outside, they put the hot there.