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Comment by mulmen | Hacker News Reader

The University of Idaho uses district heat. The pipes run under the sidewalks so the waste heat keeps the sidewalks clear in winter.

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By German standards that's still poor insulation. In winter in Leipzig the district heating pipes have snow sitting on them.

Sometimes this is intentional to keep paths clear. Idaho is much colder than Leipzig in winter.

When the sidewalks are melted, it becomes waste heat. The rest of the year, it is waste heat. No matter how cold it is, if you accidentally leak heat it is wasteful - even if the side effect is something you may otherwise want.

Idaho summers are very hot. The district heat only runs part time. It is all waste heat from the power plant. There’s ample hydroelectric and wind power in the region as well. I’m not sure if the plant does demand shifting over the course of seasons but it could only run in winter because it runs on biomass and employs students. Many campus facilities are essentially jobs programs for students. The mission is experiential learning. I got a B.S. in business that included welding.

That sounds pretty cool

It was actually a great experience. It’s a land grant university that does a lot of really good research and has solid mechanical engineering, business, law, and architecture schools. I worked several on-campus jobs like janitor and IT support. They set me up with good internships over summers and decent mentors. I wouldn’t be where I am in life without the University of Idaho.

You want to do that with the cooler water that is coming back to the power plant after the heat is delivered to the customer. Thus you use lower value heat to melt the streets. Assuming you do combined heat & power, as a bonus you get a small benefit on the power cycle as you get colder water into the pwrturbine cooling.

The sidewalks are actually the tops of tunnels that carry power and steam in both directions.

The historic averages don't look very different:

https://www.timeanddate.com/weather/germany/leipzig/climate

https://www.timeanddate.com/weather/usa/moscow/climate

though Moscow gets rather more snow

Great. How much energy do you spend clearing paths?

Probably less than you lose in energy from heating the paths all year round.

As I explained they aren’t heated year round.

It's a fun set of optimisations: to get the path-clearing effect do you run the pipes on less optimal routes (greater capital costs), or do you using varying grades of insulation (less effective under paths to get the clearing effect, more effective on the short-cuts between paths), and so on. I hope Idaho uses these scenarios in their maths lessons, in place of the hoary "the phone company needs to put a line across a property that includes a river where it costs three times as much per metre..." that I teethed with.

Well the shortest distance between two points is a straight line. Pipe and sidewalk routing have similar objectives and constraints.

Not all sidewalks are heated. It’s more like they paved the top of the service vaults.

I don’t recall this problem specifically but the university employs a lot of students and alums.

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