Here's a brochure from the heat pump manufacturer about the plant: https://www.friotherm.com/wp-content/uploads/2017/11/katri_vala_e012_uk.pdf https://www.friot

Here's a brochure from the heat pump manufacturer about the plant: https://www.friotherm.com/wp-content/uploads/2017/11/katri_vala_e012_uk.pdf https://www.friotherm.com/wp-content/uploads/2017/11/katri_v... In general, the evolution in district heating networks is towards lower temperatures, allowing better efficiencies with things like heat pumps. As you say, integrating heat pumps into existing district heating networks designed for combustion based heating is suboptimal, but redoing the network for lower temperature operation is incredibly expensive as well. Currently, in the case referenced above, during the winter the heat pumps are AFAIU the "first leg" when the cold water returns to the plants; the output of the heat pumps is then routed via the fossil fueled CHP plants for topping up (depending on how cold it is, it's heated up to IIRC ~120C) before it's sent out in the network again. The challenge is that due to climate change, the fossil fuel plants need to be replaced with something else (no, biofuels are not an environmentally sensible solution). What that something else is, is not entirely clear. Moar heat pumps + wind + heat storage? Or geothermal? Or nuclear?