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There's a saying I've heard in so many places.. "It was so cold that we used to huddle next to our refrigerator to keep warm..." I had heard this phrase uttered some 30 or so years ago, and it's stuck with me ever since...

Which gets me thinking...

Imagine it's -40 degrees (Fahrenheit or Celsius, it's the same number for both scales). Your fridge is by comparison capable of blasting chilled air at +4 degrees Celsius (39.2 degrees Fahrenheit)... give the temperature difference between environment and the refrigerator, could an average human of body temperature of ~37 deg C potentially warm themselves by an open fridge blasting chilled air at +4 deg C in a surrounding environment of -40 deg C and keep "warm"?

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According to the second law of thermodynamics, sustained cooling below the ambient temperature requires work. The fridge's electric motor does this work to cool the air inside the fridge, in the same time it has to warm air outside the fridge - this is how one can "huddle next to a fridge" to keep warm (you can easily find the warm place of your fridge, usually at its rear), you do not keep warm with air cooled in the refrigerator.

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    $\begingroup$ Wouldn't a refrigerator in an environment of -40 deg C have to keep the air inside warm instead of cold? $\endgroup$ – wythagoras Aug 16 '15 at 13:53
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    $\begingroup$ @wythagoras: Refrigerators are designed to transfer heat from inside to outside. If the ambient temperature outside is lower than the thermostat temperature inside, the temperatures will equilibrate. Refrigerators are not designed to keep their contents warm. In order to do so, you would need a separate thermostat connected to a heating element inside. $\endgroup$ – Ernie Aug 16 '15 at 14:01
  • $\begingroup$ I've used an environmental test chamber that could be set to any temperature from about -70 F to +300 F. It had only one thermostat (Well, PID controller, actually), but you're right about the other part: It had a two-stage refrigeration system and a resistive heating element. $\endgroup$ – Solomon Slow Aug 16 '15 at 16:38
  • $\begingroup$ If it's colder outside the fridge than inside, the thermostat will turn the fridge off an no work will be done. There will be no warm spot. $\endgroup$ – Floris Aug 17 '15 at 19:08
  • $\begingroup$ @Floris: It depends on the design of the fridge. The design that you describe can create problems for the freezer at low ambient temperature (appliance-repair-it.com/garage-refrigerator.html ), so in some designs the fridge runs at low temperature (see the previous ref. and beko.co.uk/support/faqs/fridges/… ) $\endgroup$ – akhmeteli Aug 18 '15 at 0:14
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Refrigerators are not designed to warm up air. If the outside temp is -40 C and you open the door of a fridge set to 4C, the air in the open fridge will quickly cool to -40C and the fridge compressor will turn off. Refrigerators are designed to maintain a maximum temperature setting, not a minimum temperature setting.

Furthermore if you leave the fridge door shut, since the fridge is not perfectly insulated, the air inside will eventually cool below 4C and the fridge will turn off, the air inside will eventually reach equilibrium with the outside -40C temp.

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Suppose you would actually go sitting inside your refrigerator and close the door, so that you are in an environment of +4 degrees Celsius. If you are literally warming up, then you was colder than 4 degrees Celsius in which case you probably had died from hypothermia.

If you are wearing protective clothing, the clothing itself can be much colder than +4 degrees Celsius after being exposed to -40 degrees Celsius for a while. If you then go to the refrigerator, your clothing will warm up. However your body will keep cooling down if it wouldn't preventing itself from cooling down by producing heat. This is because it is warmer inside the clothing, where your body is, than outside, in the refrigerator, so heat will float out.

The speed of the heat going out is proportional to the difference between the heat inside and outside the clothing, at the refrigerator we have that the difference is $\Delta T = 37^\circ C - 4^\circ C = 33^\circ C$, but outside we have $\Delta T = 37^\circ C - -40^\circ C = 77^\circ C$, so you will cool down twice as slow inside the refrigerator.

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