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Comment by jitl | Hacker News Reader

I read a lot about district heating systems yesterday after seeing an article on NYC's steam system on HN (https://news.ycombinator.com/item?id=33388473). District heating systems allow you to capture waste heat at the power plant (called co-generation), and use that to heat & cool (via cooling compressors) many, many buildings at once. The wikipedia article about it is very informative as well: https://en.wikipedia.org/wiki/District_heating.

Usually district heating systems route heat into your building's pipes using a heat exchanger - so the network's fluid never actually intermingles with your building's fluid lines. These systems also use the same heat exchanger to return excess heat back to the network. District heating systems require a large initial investment, but over the long term are very efficient.

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The problem with district heat schemes in the UK (at least) is they are becoming mandatory for new large housing developments but are 100% unregulated every step of the way. The builders do the cheapest job possible because the efficiency targets they're supposed to hit are never measured or verified post install. And unlike the rest of domestic energy in the UK, pricing is totally unregulated. The residents can (and are) charged high rates because it's impossible for them to change supplier. Any potential savings are undone by these two things. The energy regulator has so far refused to do its job because they supposedly don't want to stifle growth in this new market.

It is a good idea but it's been sabotaged by greed.

It seems sabotaged by incompetence on the part of regulators. You can’t make something both 100% mandatory and unregulated and then go shocked-Pikachu when the monopoly grantee takes advantage.

Charitable of you to assume it is incompetence rather than malice :/

> You can’t make something both 100% mandatory and unregulated and then go shocked-Pikachu

The shocked-Pikachu face is the face they make when trying to figure out if anyone will notice the bribe they took to gift the contract to their buddy joe.

The mirror image of this is combined heat and power (CHP). That is, instead of burning fuel to heat the home, use the fuel to power a generator of some sort, and using the electricity to power the home. The waste heat (most of the energy from the fuel ends up as waste heat) is then captured to heat the home It's basically free electricity, if you were already heating the home by means of combustion anyway (e.g. oil, natural gas, propane).

I live in a post-Soviet country that has district heating systems, and rather quickly the demand for heat outstripped the demand for electricity, so in my city this is now mostly fulfilled by 'heat plants' burning gas. The price you pay per kWh of heat is quite a bit higher than you would pay for having a gas furnace or heat pump at home, so I'm not sure how efficient it is.

Also the heat plants are not that far from residential areas, so if they were to burn more polluting fuels (apparently when they were built, they burnt bunker fuel) it wouldn't really be any better than burning at the point of use.

If you have some kind of geothermal source (proper geothermal, not a ground source heat pump) it seems like it would make sense, but if not I think heat pumps at the point of use are a much better solution. In apartment blocks you could have a centralised system for the building, you don't need each unit to have its own system.

District heating here in The Netherlands is a great way to be screwed by a supplier. We have pretty good competition between suppliers for gas and electricity(). Households that get their heat from district heating can only say yes or no to one supplier. They will generally pay the maximum price regulation allows.

() This competition has led the way in greenifying electricity usage for Dutch households. Dutch electricity was mostly coal and gas generated, but there were energy suppliers that guaranteed green electricity. Green-minded people could use market mechanisms to increase carbon neutral electricity(*) usage. I've always liked that personal power in market mechanisms.

(*) Similar contracts exist for gas usage, but it's mostly based on "compensation", which at best isn't very good, and at worst completely useless.

It is worth pointing out that a more modern approach to district heating will use ground source heat pumps on-premise in people's homes, and will circulate fairly low grade heat (20C or less). Top-ups in system temperature can come from refrigerated warehouses inputting into the system, or solar photovoltaic-thermal setups that cool PV with circulating water, or just the ambient heat of the ground (10C most of the year far enough down).

See: https://www.cibsejournal.com/technical/take-it-down-low/

These networks are advantageous because the heat pumps using them can still produce enough heat even if the system temperature drops - they just do so less efficiently.

Why not feed that heat back in to the power plant to squeeze more electricity from it?

I'm no power-plant engineer, but vaguely remembering back to thermodynamics 101, in a perfect heat-engine efficiency is relative to the temperature delta.

You can't just turn heat to electricity, so below a certain threshold it's only good for warming spaces.

They exist but you're right that you can't just use the waste heat directly. You have to pump in some extra heat to make it worthwhile.

They are called co-generation power plants. The one I used to work at took the waste heat from gas turbines, added more heat with HRSGs (heat recovery steam generators) and fed it into a steam turbine. It adds a significant amount of efficiency.

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