Welcome again to everybody! Make yourself at house. In the time-honoured tradition of our group, here is our weekly discussion thread.
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Cooling more efficiently is definitely something we need to work on as well. I always imagine a symmetric system which can heat and cool using basically the same infrastructure, but I'm not sure how realistic that is.
District heating has been done, AFAIK, in small cities with smaller apartment blocks, big cities with apartment high rises, and suburbs and villages with primarily one or two family homes. It can also be used for industrial processes. I'm sure there are plenty of issues, such as energy losses during transport of heat from the source to the consumers, but nothing we can't and haven't overcome.
At its simplest, district heating just a central water heater for an area, where the hot water is then pumped into houses to heat water for local heating and hot water needs. It can also be combined with heat pumps on the consumption side to improve efficiency and reduce the need for a high temperature difference.
If it's hot water, you can get water solar panels/rigs, too. Probably not too helpful in some places but many places get enough hours of sunlight to start the hot water going. On top of insulating the pipes, most of the heat lost on the way to the rooms might be gained by being able to start the heating at however many degrees higher than it would be if you pulled it straight out the ground. Also good for jacuzzis in the summer, when you'll be getting 60°C+ water out the panels and nothing to heat except water for pots. It's a luxury but only because water's so expensive to heat and we're aiming for luxury, aren't we?