I'm not a thermodynamics expert, but I think you probably need some density of heat sinks so it only really works in cities.
I wonder if in the summer, it could work in reverse? I speculate there are two options for summer operation: (a) a centralized AC plant sends cold fluid into the pipes, or (b) a decentralized AC heats hot fluid.
With option (a) I suppose it's not very backward compatible with a heat-only system, if you have a bunch of customers who built their factory expecting "this pipe will always be hot" they might have a bad time if you make it cold half the year. With option (b) it's more backward compatible but I think customers might not like it. I'm pretty sure AC gets less efficient based on temperature gradient so pumping AC into a heat transportation pipe would be more expensive for customers (electricity, wear-and tear on AC, takes longer to get to the commanded temperature when you reduce the set-point). So you'd have an incentive to unhook your AC from the system and just send heat into the air instead.
Some apartments dig a deep hole into the ground, and pump the heat up during the winter, pump the heat down during the summer.
The main disadvantages are that they require enormous amounts of co-ordination socially and you pretty much have to run the 24/7 (and then store heat which is wasteful). You also need a heat source (normally a large body of water) nearby.
Having high density housing with proper social co-ordination involved is not a bad thing. That it has to be run 24/7 means it can be more efficient that something that turns on/off all the time. Also, large thermal storage is much cheaper than many small ones and allows to better leverage changing electricity supply from renewables.
I like the idea of social co-ordination, but these days it is incredibly hard to actually do. :(
Latest generation district heating systems distribute the heat pumps around the system for greater efficiency.
Big units might be the simple option for upgrading older systems from fossil fuels but they can probably do better with a little planning.
Without these it's impossible to understand the environmental viability of these projects when compared to fossil fuels.
So are these a significant improvement or just PR pieces for the suppliers? Give us the figures!
accurate reporting , as ever , from the BBC
