So imagine that this steel container is instead the water pipe that goes into your home. (Unless you’re collecting rainwater or making water from hydrogen and oxygen, you probably have one.) If it gets too cold, the water can freeze and literally burst your pipe. This is bad. Now for some questions and answers.
Why doesn’t that happen more often in the south?
Water pipes in residential areas are almost always underground – and that’s a good thing. Although air temperatures can vary dramatically from summer to winter, the soil temperature is much more constant. In the southern states, this soil temperature is not very likely to drop below freezing. Therefore, the water in the pipes is also above freezing (and remains liquid).
There are a few exceptions, however. In some places with warm climates, not all parts of a water pipe system are underground and run through regions of the air. (Heck, I have plumbing in my attic and I live in a warmer place). Although there is a small temperature difference between cold water (say 1 degree Celsius) and warm ice (0 ° C), there is a big difference in energy. It takes quite a bit of energy to convert water from its solid phase to a liquid. We call this the latent heat of fusion. For water this is 344 joules per gram, which may be difficult to understand. So how about an example?
Let’s say you have a liter of ice (about 1,000 grams in mass). If you want to take this ice at 0 ° C and turn it into water at 1 ° C, it takes 344,000 joules of energy (plus a little bit more energy to raise the water temperature). How much energy is that? Let’s say you have a smartphone with a 3,000 mAh (mAh) battery. This corresponds to 41,000 joules. So it might have enough power to keep your phone running for a full day, but it would take you eight or nine of these phones to melt all the ice.
It’s actually a good thing. That means you can use melting ice to cool your drinks – and you actually don’t need that much ice. This also means that you have to extract some heat energy from your pipes in order for them to freeze. One cold night probably won’t be enough to blow your pipes.
Does running a faucet help?
Yes. OK, imagine you’re in a water pipe. (Yes, you are very small now.) If the water is stationary, you may be stuck in a part of the pipe that is exposed to cold air. You could actually freeze, and then you’d have to break the pipe. Suppose it is running water caused by a faucet that drips slightly. You’re still a tiny person in a pipe, but now you’re moving too. You go through the section of cold pipe and go cold – but you don’t freeze. Instead, just move to other parts of the house.
Oh, but more water from the underground main line is coming 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 isn’t very cold and hopefully it won’t freeze.
What about insulation?
Isolation helps. Wrapping foam insulation around exposed pipes will work the same as it would with your cooler or insulated beverage mug. Insulation reduces the rate at which energy is transferred from the hot thing to the cold thing through a thermal interaction. When you put a cold drink on a table, energy is transferred into the drink to raise the temperature. Conversely, placing the drink in a cooler will increase the insulation and decrease the rate of energy transfer, so the drink will take longer to warm up.