Thought Problem

Suppose it’s winter, and you’ve just come back from the packie* with a six-pack of warm beer.

If your goal is minimizing your household’s overall energy consumption, is it better to throw the beer straight into the fridge, or put it out on the porch until it’s cold, then put it in the fridge?

( * I’m from Massachusetts originally.)

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6 Responses to “Thought Problem”

  1. Pop Says:

    I say on the porch. But if you are asking there must be more to it. By the way, if you try to fail and you succeed, did you succeed or fail?

  2. Mom Says:

    Assuming it is < 32 degrees outside and knowing that the freezing point of alcohol is less than that of water (and way less than the temp in your fridge), do this:
    Put the beer on the porch.
    JUST before the beer freezes and (hopefully) just when you need to get milk or yogurt or something from the fridge and would therefore be opening it anyway, move the beer to the fridge.
    Coordinate so that you do not make a special door-opening just for the beer.

  3. brandonthomson Says:

    Likely spoilers ahead: don’t read if you wanna solve it yourself!

    If energy consumption is the only concern, then intuitively I expect the porch will be better if the house is unheated. Letting the beer cool to outdoor temperature will reduce the amount of energy consumed by the refrigerator, which seems to be the only relevant energy consumer in this case.

    If the house is being heated (or we care about its internal temperature), then it becomes a much harder question. Extra energy will likely be consumed pumping the heat from the warm beer in the fridge out of the fridge and into the house. The extra heat in the house is a benefit because it will reduce the amount of heat we need to generate through other means. But, the refrigerator’s heat pump may also be less efficient than whatever process we would have otherwise used to generate the heat for the house. For example if we are using wood to heat this hypothetical house, we may conclude that direct wood heat is more efficient or more environmentally friendly than the refrigerator’s heat pump (which consumes electricity generated from burning coal or whatever the case may be) in the specific conditions of this hypothetical house. And if the efficiency of the fridge heat pump is less than that of the alternative heat source, then this makes the porch look like the better option.

    However there is another factor to consider: if you leave the beer on the porch, then the front door would probably have to be opened twice: once to enter the house, and once again later to bring it inside. It is expected that more heat will escape if you open the door twice than if you only open the door once, and that loss works in favor of “put the beer directly into the fridge” being the better option.

    There are other factors involved too, but those seem like the biggest ones.

    Fun question =) Hope I got it right =o

    • coldhousejournal Says:

      Yep, I agree with Brandon. The fridge, as a heat-mover, will suck heat out of the beer and deposit it in the house. To do this it will use only a fraction of the energy that would be required to produce the same heat de novo. (I hadn’t considered the extra-door-opening aspect, but that adds to the argument. As does the fact that, around here, a good fraction of our electricity supply comes from renewable energy.)

      The question remains, how much energy does the fridge mechanism consume, to move one unit of heat energy from beer to house? It is hard to know. Household fridges are not rated in this way. In scanning the web, it seems the answer might be anywhere from 0.1X to 0.8X input to get 1X output. (Here is a great post by a guy who went to great lengths in an attempt to get an empirical measurement of his fridge: http://physics.ucsd.edu/do-the-math/2012/06/heat-pumps-work-miracles/)

      Musing leads to another thought problem: Assume: the fridge needs 0.3 kWh of electricity to move 1kWh of heat, electricity costs 13¢ / kWh, the fridge stays at 36ºF, and jugs of bottled water come at 70º from the store. At what price per gallon for water is this a more efficient means of heating that burning wood?

      [Addendum: freezing water in a freezer, then chucking it outside, would probably be even more cost-effective…]

  4. coldhousejournal Says:

    So, based on that last thought, I ran a few numbers… to see if it would be practical to heat the house by getting a big ice maker and freezing quantities of tap water all winter. Answer: no. To get the equivalent heat of our one-ish cord of firewood, we would need to be freezing on average 3 gallons of water an hour throughout the heating season. (Put another way, a cord of firewood can melt about 14,000 gallons of ice.) Perhaps most interestingly, the retail cost of 14,000 gallons of tap water here is roughly the same as a cord of kiln-dried firewood…

  5. Patrick Ledwith Says:

    I have three post-its full of numbers from a few days ago sitting on my desk right now, but gave up on the question because there were too many variables. I’m glad some other folks gave it a shot, and also glad to see we’re sharing similar thoughts and theories.

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