[gligorot]

Honestly first time I’m hearing that a city is heated like this…I mean it’s logical, but over here they heat water and then pump it out, which for some reason always felt very wasteful. This _feels_ better.

But what do they do to the steam once it gets to the top of a building? Is it just released into the atmosphere or the water is somehow cycled back down?

[greenyoda]

> But what do they do to the steam once it gets to the top of a building?

There are return lines that bring the hot water back to the plant. But the steam from the central system never gets to the top of a building. The heat from that steam gets transferred to the building's own closed system through a heat exchanger. The process is described here: https://en.wikipedia.org/wiki/District_heating#Heat_distribu...

A diagram can be found here: https://en.wikipedia.org/wiki/File:District_heating.gif

[reaperducer]

Honestly first time I’m hearing that a city is heated like this

Lots of American cities have district steam, and sometimes district cooling, too. Usually is limited to dense downtown areas.

Chicago and Houston come to mind. I think Seattle has steam.

[ars]

Hot water is more efficient - heating something to 500F just to then use it to heat air to 70, or a shower to 130 is thermostatically not favorable (the bigger the difference in temperature the less energy is transferred). It's better to heat water to 180 and pump that - the initial transfer of heat from the flame is much more efficient.

Releasing the steam would be a huge waste - but of energy, not of water. The water is quite minimal.

[userbinator]

Steam is more efficient specifically because it is very hot; you don't need as much of it to transfer the same amount of energy as water, nor does steam need pumped (which also takes energy).

[jabl]

The trend in district heating systems is towards lower temperatures. Lower temperatures means that more of the waste heat in the power plant can be extracted, lower heat losses in the piping, and also if using heat pumps then lower temperatures can give a big efficiency boost. But yes, the downside is higher massflow, but this is certainly an optimization problem that engineers have calculated the optimal point for, given the available technology.

Steam heating is an ingenious invention, but it was also made in a world where pumps, the electricity to run them, PID controllers and whatnot, were expensive. That's why you tend to find it in the oldest district heating grids around.

[ars]

But it's far less efficient to create the steam in the first place. And the lack of pumping is not free, the energy comes from the steam itself.

Sure for the end users point of view it might seem more efficient but as a net hot water is far far more efficient.

[Symbiote]

No -- for one example, Copenhagen has just finished replacing the old steam-based district heating system with one based on hot water.

[bombcar]

You can build a one-pipe system where the steam goes up and water goes down the same exact pipe. Takes some skill but it works and it is bog simple.

[doctor_eval]

apparently, FTA,

> Steam rises naturally, so it enabled buildings to get heated without using additional energy to get the heat to rise up.

But I’m not so sure about that…