How Air Conditioning Works


If you’re feeling the summer heat, you might
be tempted to switch on the machine that makes all the problems go away: your air conditioner. And the source of that sweet relief? Well, of course it’s chemistry. Air conditioners pull off the seemingly magical
feat of making the air inside a home, car, or shopping mall deliciously chilly. Air conditioning — and refrigeration, which
is the same thing just in a slightly smaller box — rely on the laws of physical chemistry. And p-chem tells us that as a liquid evaporates
into a gas, it absorbs heat. The molecules in a liquid are held together
by weak intermolecular interactions. Not quite chemical bonds, just enough passing
attraction to keep them from flying apart. Some of the molecules absorb enough heat energy
— in other words, they get moving fast enough — to overcome these intermolecular attractions,
ESCAAAAPE and take gaseous form. That’s the reason you feel chilly getting
out of the shower, and why we sweat to stay cool. The water has to absorb heat to evaporate. And it carries that heat away from you. An air conditioner’s basic job, then, is
to use a fluid called a refrigerant that constantly changes from a liquid to a gas and back to
a liquid again to move heat from one place (your sweaty bedroom) to another (outside,
where it’s already hot and miserable anyway, so who cares.) Here’s a admittedly very schematic-ified
version of how most a/c units work. The liquid refrigerant flows through a series
of coils exposed to the air in your home. The refrigerant has a low boiling point, so
the heat from the interior air is enough to make it turn into a gas. Which means there’s now more heat in the
refrigerant, and less in the air. A fan blows that colder air into your room. Or straight into your face, we’re not judging. So now your A/C has to do two things: dump
the heat absorbed by the refrigerant outside, and two, it has to condense the refrigerant
back into a liquid so it can be used again. And to do those things it uses a compressor
to ramp up the pressure on the gaseous refrigerant — so much that it can condense into a liquid
again, even though it’s at the warmer outside temperature. As it condenses, the refrigerant loses heat
to the air around it, which another fan blows outside, where it’s already all sticky anyway. Which is a neat trick, boiling something at
a low temperature and then condensing it at a high one. Nothing in thermodynamics is free, and the
compressor needs energy to do the work of compressing the refrigerant. Which may explain your power bills in July. After the refrigerant condenses, the air conditioner
backs off the pressure with an expansion valve, so that the refrigerant can boil at the lower
temperature again. Which it does, in a loop, over and over until
your home reaches the temperature you set the thermostat to, or your housemates complain
and switch it off. While the refrigerant could be practically
any substance, there are some chemicals that do the job better than others, and these refrigerants
have a checkered history. A refrigerant needs to have a pretty low boiling
point, and one that can be adjusted to where you want it by changing the pressure on it. It should also be pretty good at conducting
heat, be able to absorb a lot of heat as it boils. AND THEN it needs to be cheap, widely available,
and as non-flammable and non-toxic as possible. That kinda narrows your choices of chemical. Scientists thought they’d found the perfect
refrigerant with Freon, the trade name of a group of chemicals called chlorofluorocarbons. But CFCs are actual murder to the ozone layer. They’ve been largely replaced with hydrofluorocarbons,
or HFCs. HFCs don’t damage the ozone layer, which
is good! But they have a different problem…they’re
greenhouse gases. So the search is on to phase out HFCs too. Some alternatives? Simple hydrocarbons like these have been approved
in the USA. Hydrofluoroolefins like this one are less
rough on the climate than HFCs, but also more expensive. The most surprising potential replacement
is CO2. CO2 totally works as a refrigerant, and even
though it is the literal poster child for greenhouse gases, it’s also way less potent
than HFCs. Whatever we use in the future, it doesn’t
seem likely that we’ll give up on AC altogether. Not in a scorching summer like this one. Pass the popsicles, wouldja? Thanks for watching, and if you want to help
us keep making great videos like this one, remember to subscribe, turn on notifications,
share this video, and brag at your next cocktail party that you know all about the machine
that’s keeping everyone from sweating their eyes out. We’re…pretty sure y’all go to cocktail
parties. We’ll see you next week.

59 thoughts on “How Air Conditioning Works

  1. If the refrigerant used is maintained in the loop, why would it matter which one you use? Other than leaks or malfunctions, of course.

  2. I was under the impression the a fan blowing through heat fins/radiator block helped to dissipate the heat given off by the refrigerant condensing, but that wasn't mentioned. Is that not correct?

  3. If CO2 is used as a refrigerant, then lots of CO2 will be taken out of the atmosphere! That means we will trap a greenhouse gas and keep it from hanging around in the atmosphere. Then infrared energy (heat) will dissipate better during the night side of Earth, and the temperatures will come back down, say, increasing our polar ice, saving polar bears and seals, maybe make the Sahara and Ethiopia livable, lush areas again, and maybe even helping our US deserts recede some, creating a little more lush land, and bringing more rain into those areas.

    Seas could return to the salinity of before, strengthening the underwater streams that make more Northern places more livable like UK and Ireland. (They get the warm gulf stream from the Gulf of Mexico that directly makes these isles livable.)

    Salinity drives the ocean streams, circulating warm and cold waters like a body is regulated by its bloodstream.

  4. And whatever you do, if you run your AC, don't open your windows! They undermine each other!
    I mean, your AC is still going to work. It's still going to cool you down, but it's going to cool you down a lot better if your windows are closed.

  5. Dr Sanjay Basu, author of The Body Economic: How Austerity Kills, suggests that climate collapse will lead to an increase in suicide.

    Think you could work on explaining the neurochemstry that would drive that?

    Or, here’s a good one, what kind of toxic sludge will NY Gondolas be paddling through in the next decade?

  6. I'm a certified HVAC tech. I found your explanation pretty comprehensive. Although the coloring on the diagram you used was a bit misleading.

  7. Also I would consider it physics as well. It's more thermodynamics than anything else. I highly doubt us adopting CO2 for a few reasons, CO2 requires much higher operating pressures due to it being a supercritical liquid, basically CO2 only likes being in 1 of 2 states gas or a solid, unless its compressed to mind numbing pressures. With practical and conventional methods and materials it's not totally achievable. Then again I've went from seeing the rocket shuttle landing on a runway to seeing them land on the launchpad they started at. So who knows. Just my 2 cents for whatever they're worth

  8. See and learn about one of the wonders of this world
    It really is wonderful
    subscribe to The channel motivates us to continue
    Your opinions interest us
    https://www.youtube.com/watch?v=FX6GrPVCnpI

  9. https://youtu.be/1MiQCBIx1mM here. 2 times slower, 3 times shorter and plain and simple explanation. Thanks though. I understand it's free content. Just trying to give some feedback 🙂

  10. The great irony with AC is that you're actually making more heat.
    One more reason to hate laws of thermodynamics.

  11. Hello, on my channel you can find a video on air conditioning and its consequences ! This video is in french bthey are subtitles in English! Enjoy 😉

  12. I guess I'm a polar bear, then. Hot summers lately have been horrible. I don't think I'd survive without air conditioning… it was much easier to bear twenty years ago, when we didn't get this extreme heat.

  13. Your explanation is too fast my friend. Please consider next time your poor non native english speakers 💔😂 .. thanks for the video

  14. My house has no AC . It can get like 35°C or 95°F in the summer inside my house but the basement is nice and cool 80°F or 26°C

  15. Had ac problems today. My dad talked me through it and I fixed it. So had to look up how Ac worked out of curiosity. Been crawling around in attic working. I’ll admit, drank some beer too. Either I’m drunk, or this explanation isn’t great.

  16. i have 2 tons indoor unit and 1.5 tons outdoor unit all being Samsung with same digital inverter technology and refrigerant(R410a). They also have same model numbers with the exception of the size number(AR24JVFSAWKX/N and AR18JVFSAWKX). Can i use them together?

  17. Great explanation of thermodynamics! Some people will never be happy with explanations, no matter how basic they are, probably because they can't grasp the concepts no matter how they're explained. Not everyone can be a brain surgeon, no matter how much they want to be.

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