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 fair

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/ 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.