Abstract
Abstract
Large scale heat pumps (LSHP) have seen a rapid proliferation in recent years, with projects and initiatives aimed at integrating electrically driven LSHP into existing district heating networks (DHN). The financial advantages have driven most LSHP installations to be powered by electricity generated by on-site cogeneration (CHP), given CHP’s dominant role in DHN. This LSHP + CHP combination poses the question, to what extent ecological improvements, measured as a reduction in specific CO2 emissions through LSHP operation can be achieved, contingent on the source of electricity and heat source employed. In this paper, the LSHP + CHP combination was generally analysed under usage of exergy analysis and a 2nd law derived method is presented. This method allows to evaluate the magnitude of CO2 reduction through LSHP operation across all common heat sources in 1st to 4th generation DHNs in conjunction with CHP. Results show, that in LSHP + CHP combination, heat from LSHP using either of the 2 heat sources ambient air or surfaced water, inevitably comes with higher specific CO2 emissions over the CHP heat. Only when using a sufficiently hot and emissions-free heat source, the LSHP heat from a LSHP + CHP combination can yield to an annual best case of half the CO2 emissions of the CHP. Importantly, the choice of power source has a far more significant impact, as LSHP powered by electricity from renewable energy sources achieve more than an eight-fold reduction in emissions compared to the LSHP + CHP combination. Therefore, power consumption with sufficiently low specific CO2 emissions out of external source is imperative to fully realize the ecological benefit of LSHP in DHN, underlining that the successful heat transition through LSHP relies heavily on the transformation of the electricity supply.
Graphical Abstract