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I'm well aware that the default answer to this textbook default question is "it doesn't work", but still, I believe it does.

To cool the insides of the fridge, the compressor must do work, and since the efficiency isn't 100% you are constantly warming the whole room to cool it's insides, the winning move here is simply turning the fridge off. However, let's suppose the fridge must stay on, wouldn't it be better to open the door?

In other words: Isn't opened fridge turned on better than closed fridge turned on for the whole room temperature?

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Let me see if I understand the question. Are you asking if a room is cooler with a running fridge that has a door closed vs a running fridge with a door open? – cspirou Aug 3 '13 at 17:57
Yes. In summary, this was my initial question. – ShizukaSM Aug 3 '13 at 21:16
up vote 8 down vote accepted

No, you are making the fridge do extra work, so more energy is coming in (through the plug) as the pump continues to run since it's not reaching it's cold point. A normal operating fridge does not manifest cold air; it just pumps all the heat out of the inside of the fridge.

The action of pumping the heat out also has heat as a byproduct (which is waste heat from the power coming through the plug as it does work with the pump). So you're really just generating more heat and moving heat around.

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Hmm, it seems that my doubt was because I didn't understand how fridges works, then. I didn't know the compressor could in fact monitor temperature changes and adjust it's work accordingly, that makes sense. Thanks. – ShizukaSM Aug 2 '13 at 23:14
@ShizukaSM if you vented the heat off the back of the fridge outside of the room, then it would cool the room. You need to isolate the heat from the fridge evaporator from the room in order to cool it down just like the little window AC units do. – user6972 Aug 3 '13 at 5:36
Opening the door will probably cool the room temporarily, as the cold air in the fridge flows into the room. But over time, the extra work done by the compressor will tend to heat the room. – Keith Thompson Aug 3 '13 at 18:43

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