Bad Science

In the break area at work, they have a few crappy gossip magazines on the table (don’t know who brings them in, the one I’m referring to is called “That’s Life“). I don’t usually read them, but I was grabbing a drink and noticed the page had been left open at a ‘tips’ page.

One of the tips was something like this: “If you have freezer which isn’t full, fill empty milk cartons with water and put them in. These store the cold meaning your freezer won’t have to work so hard.” (Words to that effect, anyway). There was also a cheesy picture of a guy with a milk carton filled with water standing next to a freezer.

I had to do a couple of double-takes when I read that. Speaking as someone who doesn’t know much about physics (did an A-Level in it, but have forgotten most of it!)… surely that can’t be right! To start with, your freezer would have to cool down the cartons of water to form ice – this would take energy. Then, the freezer would have to maintain the temperature to keep them frozen (taking more energy).

But what I can’t get my head around is the fact that having what is essentially a great big block of ice in your freezer would actually help keep it cool. The question comes down to: does it take less energy to keep a block of ice cool, or a block of air?

I’m guessing that it takes less energy to keep air cool, because it’s more dense. But I could be wrong on that (my old physics teachers would probably be shaking their heads by now at my terrible forgetfulness). Thus, a completely empty freezer would do less work than a freezer loaded with ice.

Am I going mad?!

2 thoughts on “Bad Science

  1. This isn’t actually as crazy as it sounds – over christmas I found a duvet in my Grandparent’s freezer – by filling in empty space it mean’s there’s less air to keep cool and apparantly that’s harder…

    Still I can see a Duvet expanding a bit more then bottles of ice…

  2. Well, yes and no. Yes, if you fill the space with something then there is less air in the freezer so the freezer has to work less hard to keep things cold. On the other hand, freezers generally aren’t clever enough to know how much air is inside them – they work on a thermostat which measures how cold it currently is, regardless of how much stuff is in there.

    The energy required to freeze several bottles of water is significant, and not really worth the effort – the water will effectively suck out the cold that should be elsewhere, making the freezer work harder. Once it’s frozen it’s not too much of an issue; if there is no temperature difference between the air and the ice then there is no further energy required to keep it at that constant temperature.

    What warms a freezer up is opening the door and letting all that cold air out, and that’s the only reason you might stuff your freezer full of something. That way when you open the door the cold stays inside (because a bottle of ice or a duvet can’t escape as easily), and when you close the door again the freezer has less work to do to bring the temperature down again.

    So in that sense, water is not a good idea (because it doesn’t like changing temperature. However, empty bottles would do the job, as the air would get cold inside them but wouldn’t escape when you open the freezer door.

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