Comment by kees99 | Hacker News Reader

Comment by kees99 | Hacker News Reader

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> heat pumps themselves are much more efficient.

For electricity-to-heat conversion, heap pumps are indeed much more efficient relative to resistive heating, yes. About 4 times more efficient.

In absolute terms, though - that is still only 50% of "Carnot cycle" efficiency.

https://en.wikipedia.org/wiki/Coefficient_of_performance

Similarly, heat-to-electricity conversion is about 50% efficient in best case:

https://en.wikipedia.org/wiki/Thermal_efficiency

So, in your scenario (heat->electricity conversion, then transmission, then electricity->heat conversion), overall efficiency is going to be 50% * 50% = 25%, assuming no transmission losses and state-of-art conversion on both ends.

25% efficiency (a.k.a. 75% losses) is pretty generous budget to work with. I guess one can cover a small town or a city's district with heat pipes and come on top in terms of efficiency.

We've got lots of heating districts around the world to use as examples. They only make sense in really dense areas. The thermal losses and expense of maintaining them make them economically impractical for most areas other than a few core districts in urban centers... Unless you have an excess of energy that you can't sell on the grid.

Geothermal heat is also not that functional in cities, you'd need so many wells so close together that you'd most likely cool down the ground enough in winter so your efficiency tanks.

I don't understand, what am I missing? The heat pump increases efficiency by having COP 2-4 right? Assuming air to air and being in, say, Denmark.

Heat (above 100C, say, burning garbage) to electricity: 50% (theoretical best case)

Electricity to heat (around 40C): 200%-400%

Net win?

The surplus energy comes from air or ground temperatures..

Yes you cannot heat back to the temperature you started with but for underfloor heating 40C is plenty. And you can get COP 2 up to shower water of 60C as well.

Yes, this is exactly why I asked. You need to include the COP in the calculations.

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