Why is frost bad for a freezer? I thought snow/frost is an insulator, so doesn't it keep freezers cold longer? Why do people say it's bad?
Dave - The problem is, because it’s a good insulator.
The way a freezer works, you have a load of pipes at the back, you compress a gas in the pump, that makes it hot and loses the heat out of the back of the fridge or freezer. It then pipes this condensed, compressed room temperature gas into the freezer, it then expands, evaporates, gets cold, and so the coldest bits of the fridge are where this expanded gas is flowing through.
The problem is that wants to get the heat from the fridge, but if you've got a great big layer of ice, that's going to insulate the cooling part of the fridge from the contents of your fridge, so the fridge is going to be warmer, which means that the actual fridge-freezer is going to work harder to keep cold, which means it gets even colder, it means you get more ice that will build up so it’ll go horribly wrong until the fridge just conks out.
Chris - And you have a big bill.
Richard asked the Naked Scientists:
I think this idea comes from the misconception that the coldest point in a freezer is inside the freezer box. It isn't.
I have always rationalised the fact that the full freezer is more efficient by noting the cold air that rushes out when you open the door; the cold loaves and tubs of ice cream stay in the freezer whilst you replace the cold air with warm air from your room. the less cold air to re-cool every time you open the door the less power needed.
You have a few issues.