Q: Does opening a refrigerator cool down the room?

Physicist: Briefly yes, or no, not at all.  If you think of the room as including the inside of the refrigerator, then opening the door does nothing.  Otherwise, it does almost nothing.  But ultimately, if you leave the door open the only end result will be spoiled food.

Refrigerators, and the opening of same.

It seems like it makes sense to say that things like refrigerators and air conditioners “make cold”, but like every other machine ever created (or ever to be created) they ultimately just make heat.  A refrigerator “creates cold” in very much the same way that a drain “creates lack-of-water”; it moves heat from its inside to its outside.  Specifically, it pulls heat out of the freezer, and drops it into the coils on the back side. (It’s worth noting that about the worst possible place to put cooling coils is in a tiny gap next to a wall).

It’s a general thermodynamic fact (a law even!) that generating cold is impossible.  You can generate heat, and you can move it around by taking advantage of the fact that heat always tries to “even out” (this is the idea behind all “cooling devices”), but that’s pretty much it.  So just like any other machine, refrigerators generate heat.  When you first open the door you’ll get a burst of cold air, but that’s about it.  An open fridge is like a water pump in the middle of the ocean, pointlessly moving stuff around.  It’ll cool the room a little, but also heat it up a lot more.

A clever thing to do would be to put the heating coils outside of the room.  The room would get cooler, the outside would get warmer (slightly), and you’d have re-invented air-conditioning.

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10 Responses to Q: Does opening a refrigerator cool down the room?

  1. michael jacobs says:

    Can you explain why you can generate heat but not cold? Is there no possibility that in the future someone could invent the opposite of a microwave oven, a device in which you put a warm can of beer, push a button and it comes out cold?

  2. Will says:

    Because cold is just the absence of heat. The way you ‘produce’ cold is by pumping heat from A to B and not letting any more heat get into A: The same way you ‘produce’ a vacuum.

    Basically, cold is to heat as a vacuum is to matter. Cold is basically ‘nothing’ and you can’t create nothing.

  3. Andy says:

    @ michael jacobs
    In principle a fridge is such an “anti oven”, except we leave it on all the time, and you could probably use a really powerful fridge to achieve the quick cooling of beer. The problem is that when we extract heat energy from the food in the fridge it has to go somewhere else and ends up being dumped in the coils. Also because the fridge is not perfectly efficient, it also requires electrical energy to run, and that energy gets dumped as well. Therefore, while we use the fridge to cool down food, it heats up the room much more than it cools down the food.
    This is called the increase of entropy (more or less the randomness of the universe) over time. As heat is a particularly random form of energy (difficult to control and very inclined to disperse into the air) it ends up that most processes convert usable energy into heat.

  4. michael jacobs says:

    I understand that cold is the absence of heat energy, and is to heat as a vacuum is to matter. But we can create a vacuum in a chamber. And I can quickly drain the energy out of a battery by shorting it. And I’m not saying I want a machine that destroys the heat energy, just one that transfers it into some other receptacle object, or that converts it to another form, like light or radio waves, that could safely be sent into a room. My “invention” is an object approximately the size of a microwave oven that only has to be turned on as needed (unlike a refrigerator) and in a minute or so can turn a glass of water into ice by quickly draining its heat energy. As a green bonus, I would add a converter to the back end that would take the removed heat and convert it into something useful, like electricity or light. (I know some energy would be lost in the process, that it can’t be 100% efficient.) Is this science fiction or just something we don’t know how to do yet?

  5. Locutus says:

    You do realize that the second law of the thermodynamics has been violated, right?
    http://arxiv.org/pdf/1207.6872v1.pdf
    http://www.technologyreview.com/view/428670/entangled-particles-break-classical-law-of/
    So maybe, one day, we will be able to “create cold”. Of course, that might require the same technology to create universes, too.

  6. Will says:

    michael: What you want would be entirely possible if you had access to a small nuclear reactor to power the system. The reason we don’t have instant flash-freezing microwaves is not because it’s impossible but because the power requirement is obscene.

    There have been a few examples of people creating ‘super freezers’, one guy built himself a fully functional turbojet engine in his garage and then used it to power a beer cooler and even that took several minutes to cool to beer down.

  7. Stefan says:

    But then again, in supermarkets there are a lot of open freezers. And the air is noticeably colder in their vicinity. Why is that?

  8. The Physicist The Physicist says:

    @Stefan
    The radiators for those refrigerators dump their heat outside of the building. If you walk around the back, usually around the loading docks, you can often see/hear them.

  9. vignesh says:

    how is cold climate created in universe?where is the heat dumped??

  10. The Physicist The Physicist says:

    @vignesh
    Anywhere else. In the case of refrigerators the heat is dumped into the coils on the back.

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