Dependency on external power supply to operate large-scale heat pumps to decarbonize Cogeneration-based District Heating Networks.

Abstract

The sector integration of large-scale heat pumps (LSHP) into existing district heating networks (DHN), most of which are operated by combined heat and power plants (CHP), is observed to grow rapidly over the past few years. Due to significant lower operational and initial costs, the predominant configuration in DHN is a CHP+LSHP combination, where the LSHP is operated by internal power supply, provided by the CHP-plant. In a dynamic simulation based on aggregated data over the course of one year, specific CO2-emissions are calculated according to the exergetic Carnot methodology, fulfilling the first and sec-ond law of thermodynamics. In order to determine and quantify the ecologic benefit of a generic sector integrated LSHP, the specific CO2-emissions of the heat of the most common CHP-plants are compared to a LSHP operated by internal (CHP+LSHP) and external power supply (electrical grid and volatile renew-able energy sources (RES)). The analysis shows, that a generic LSHP operated by internal power supply out of every examined CHP-plant, seasonally independent generates heat with higher specific CO2-emissions over the heat from the CHP-plant alone. In contrast, the heat provided by the LSHP operated with external electricity from RES, achieves 5 to 16-fold lower CO2-emissions showing, that with growing share of power from RES in the electric grid, regulation to ensure that external power supply is economically feasible will be mandatory in order to achieve ecologic beneficial operation of sector integrated LSHPs.