Imagine that this steel container is instead the water pipe that enters your house. (Unless you collect rainwater or make water from hydrogen and oxygen, you probably have one.) If it gets too cold, the water can freeze and literally burst your pipe. That is bad. Now for some questions and answers.
Why doesn’t this happen more often in the south?
Water pipes in homes are almost always underground – and that’s a good thing. While air temperatures can vary drastically from summer to winter, the soil temperature is much more constant. In the southern states, this soil temperature is not likely to drop below freezing, so the water in the pipes will also be above freezing (and remain liquid).
But there are some exceptions. In some places with warm climates, not all parts of a water supply system will be underground and pass through aerial areas. (Heck, I have water pipes in my attic and I live in a warmer location). Although there is a small temperature difference between cold water (say 1 degree Celsius) and warm ice (0 C), there is a huge energy difference. It takes quite a bit of energy to change water from the solid phase to a liquid. We call this the latent heat of fusion. For water, this has a value of 344 joules per gram. That might be hard to understand, so what about an example?
Suppose you have a liter of ice (with a mass of about 1,000 grams). If you wanted to take this ice at 0 C and turn it into 1 C water, it would take 344,000 joules of energy (plus a little bit more energy to raise the temperature of water). How much energy is that? Let’s say you have a smartphone with a 3,000 mAh (milliamp hour) battery. This is equivalent to 41,000 joules. So it might have enough energy to run your phone for a whole day, but you need eight or nine of these phones to melt all that ice.
It’s actually a good thing. It means you can use melting ice to cool your drinks – and you don’t actually need that much ice. That also means that you have to extract quite a bit of thermal energy from your pipes to make them freeze. A cold night is probably not enough to burst your pipes.
Does it help to run a faucet?
Yes. Okay, imagine you’re in a hookah. (Yes, you’re super small now.) If the water is standing still, you may be trapped in a part of the pipe exposed to cold air. You could even freeze, and then you would have to break the tube. But now suppose it is running water caused by a tap dripping a little. You are still a tiny person in a pipe, but now you are also on the move. You go through the section of the cold pipe and you get cold – but you don’t freeze. Instead, you just move on to other areas of the house.
Oh, but more water is coming out of the underground mains into that cold part of the pipe. Would it freeze? It’s not that likely. Remember that the water pipe is at ground temperature, which is almost certainly not below freezing. So the incoming water is not super cold and hopefully it will not freeze.
What about insulation?
Insulation helps. If you wrap some foam insulation around exposed pipes, it will do the same as your cooler or insulated drinking cup. The insulation reduces the rate at which energy is transferred from the hot to the cold thing through a thermal interaction. When you put a cold drink on the table, energy is transferred into the drink, causing it to rise in temperature. By contrast, placing the drink in a cool box increases the insulation and reduces the rate of energy transfer, so that the drink takes longer to heat up.