The technical solutions we envision to integrate low-grade RES in DH facilities have heat pumps as the enabling technology. Heat pumps can upgrade low temperature (and therefore low-grade) heat sources to higher temperature levels or to produce cold. Compression heat pumps use electricity to upgrade a low-temperature heat source, using a mechanical compressor working on a refrigerant.

Electric heat pumps in a district energy system play a crucial role since they allow to increase the temperature from a low to high level (e.g., temperature lift) and they couple the electricity and heating/cooling sectors. In a system dominated by RES, heat pumps allow coupling thermal and electricity sectors. Namely, if all the electric energy used by the heat pump compressor is generated through RES, the energy supply to the heat pump can be considered clean. Furthermore, the heat pump allows to upgrade low temperature (e.g., from RES sources such solar thermal or waste heat such as data centers) to high temperature energy sources for the integration in high temperature district heating network (or in the newest DHC generation) by supporting the global energy efficiency of the system.