How to deal with thermal expansion in a city wide heating system?
As part of the program to combat pollution in and around Beijing, my adopted city of Zhuozhou (population, over half million, about 90 minutes Southwest of central Beijing, inhabited for at least 5,000 years) is installing a hot water heating system. In the last 3 weeks, they have torn up every major street in town, and they are in the process of installing pipes.
There are two pipes because the water will be conserved; according to my father in law, the hot water will flow through one pipe, they enter nearby buildings, flow through the radiators in the building, then return back to the central heating facility.
Of course, everyone is happy as this will stop a lot of coal burning, and vastly improve the air quality. Nobody seems too bothered that every street in town has been dug up at once. While traffic is horrendous, it seems like they want centralized heat.
What I have seen thus far is that they put the pipes close to each other, then weld them together.
I think when the heat is running, the length and size of these pipes will change drastically. How do you make sure the street above the pipes won't buckle? When the pipes get longer, how to prevent them from leaking? Won't the welds break? Also, are they a special type of pipe?