John_S wrote: ↑Tue Aug 24, 2021 4:23 pm There are several other large sources of low grade heat which are sizeable enough to potentially power district heat systems.
One such source is mine water generation from disused coal mines. When the mines were abandoned dewatering ceased and the ground water level in the mines rose, often eventually discharging into springs or water courses. These sources can be several degrees warmer than other sources and could be amplified with a heat pump.
My daughter studied one such outlet from an abandoned coal for her dissertation for her Hydrogeology MSC. She had to use data from the coal board as covid prevented field work. The coal board had hourly flow rates, temperatures etc going back at least a decade. As the mine filled up, warmer water rose to the surface discharge point, raising its temperature. It certainly had enough energy potential to power district heating.
Needless to say, there would be a lot of work to turn potential into a real project.
Round my way they are frequently building housing estates on top of disused coal mines. The mines are all flooded and the water temperature is reported to be 14℃ so great for a GSHP application. However the houses are built as cheap as possible and with little-to-no imagination. The insulation requirements of the latest building regs are impressive (although I don't think the properties are tested for air tightness). However I don't believe the volume housebuilders who throw up these housing estates are at all interested in anything that isn't uniform to every site they build. So I haven't heard of this warm groundwater being taken advantage of.