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So imagine that this steel container is instead the water pipe that enters your house. (Unless you harvest rainwater or make water out of hydrogen and oxygen, you probably have one.) If it’s too cold, the water can freeze and literally burst your pipe. It’s bad. Now for some questions and answers.
Why isn’t this happening more often in the South?
Residential water lines are almost always underground – and that’s a good thing. Although air temperatures can vary widely from summer to summer, the temperature of the ground is much more constant. In the southern states, this ground temperature is not likely to drop below freezing, so the water in the pipes will also be above the freezing point (and remain liquid).
But there are exceptions. In some places with hot climates, not all parts of a water pipe system will be underground and will not pass through aerial regions. (Heck, I have water pipes in my attic and I live in a warmer place). Although there is a small difference in temperature between cold water (say 1 degree Celsius) and hot ice (0 C), there is a huge difference in energy. It takes a lot of energy to change water from its solid phase to a liquid. We call this the latent heat of fusion. For water, this has a value of 344 joules per gram. It can be hard to figure out, so how about an example?
Suppose you have a liter of ice (with a mass of about 1000 grams). If you want to take that ice at 0 C and turn it into water at 1 C, it would take 344,000 joules of energy (plus a little more energy to raise the temperature of the water). How much energy is that? Well, let’s say you have a smartphone with a 3000mAh (milliampere-hours) battery. This equates to 41,000 joules. So it might have enough power to run your phone for an entire day, but you’d need eight or nine of those phones to melt all that ice.
This is actually a good thing. This means that you can use melting ice to chill your drinks and you don’t really need a lot of ice. It also means that you have to remove some heat energy from your pipes to make them freeze. A cold night is probably not enough to burst your pipes.
Is it worth leaving a faucet on?
Yes. OK, imagine you are inside a water pipe. (Yes, you are very small now.) If the water is stationary, you might be stuck in a part of the hose that is exposed to cold air. You might actually freeze, then you have to break the pipe. But now suppose it is running water, caused by a slightly dripping faucet. You are still a tiny person inside a pipe, but now you are moving as well. You go through the section of the cold pipe and you are cold, but you are not freezing. Instead, you just move on to other parts of the house.
Oh, but more water from the main underground line goes into this cold part of the pipe. Would it freeze? It is not as likely. Remember that the water pipe is at ground temperature, which is almost certainly not below zero. So the incoming water is not very cold and hopefully it will not freeze.
What about the insulation?
Insulation helps. If you wrap foam insulation around exposed pipes, it does the same thing as your cooler or thermal mug. Insulation decreases the rate at which energy is transferred from the hot thing to the cold thing by thermal interaction. If you put a cold drink on a table, energy is transferred into the drink to heat it up. Putting the drink in a cooler, on the other hand, increases insulation and decreases the rate of energy transfer, so the drink takes longer to heat up.
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