Did you say geothermal energy?
The principle of geothermal energy is to exploit the heat or cold naturally stored underground to preheat or cool water, which is then distributed through a network of underground pipes to the new district.
Depending on requirements, this water is then either distributed as is, or locally heated or mechanically cooled by a heat pump system. More environmentally friendly than traditional gas heating methods, this technique offers a number of advantages, including simplicity and reliability of operation, as well as and especially reduced and stable energy running costs. It also enables buildings to be passively cooled (geo-cooling), by capturing and removing excess heat from buildings through the heating network.