I'm no physicist but I assume that you'd need to put a lot more energy into the system before the water starts boiling, so you wouldn't have to worry about it?

If the energy would just be lost otherwise, you might as well go all the way to 100℃?

That's at 1 atm, perhaps the water is a bit pressurized as well?

A bit further down there's this confusing quote though:

> District heat is stored in two rock caverns in Mustikkamaa. The temperature of the water in the caverns varies between 50 and 90 °C.