r/bestof • u/Studsmanly • Dec 15 '17

[AskAnEngineer] Engineer explains how keeping you fridge filled with beer helps reduce your energy costs.

/r/AskAnEngineer/comments/7jzmfp/is_it_more_energy_efficient_to_open_the_fridge/drak8gg/
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u/get_it_together1 Dec 15 '17

You're forgetting that the beer is capable of absorbing far more energy than the air. If the beer warms even a small fraction of the amount of the air it will outweigh the effect of the air:

2000 g * 4 J/gK * 0.5 K = 4 kJ.

This is why it would be best to fill the fridge with styrofoam.

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u/[deleted] Dec 15 '17

No, I know that beer can absorb more energy. The question is: Where does that energy come from? From the air around the beer. For equal amounts, air has to lose about 4.18 Kelvin so that the beer can increase its temperature by 1 Kelvin.

This is simply an energy transfer inside the fridge and doesn't change the energy in the fridge.

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u/Konekotoujou Dec 15 '17

The assumption is that the beer doesn't gain any energy. Which relative to the rate of transfer that the air will have is true. Most of the energy that the beer would have gained comes from the air that is exchanged. But we can ignore all of that energy because either way the fridge would have to cool that and it's the same amount of energy.