Thermal and hydraulic performance of a campus district heating network under different building refurbishment strategies and clustering approaches

To meet the climate targets, natural gas-based heat supply must be replaced by renewable energy sources in many district heating systems around Europe, requiring the transition of the district heating system to fourth-generation district heating. A key step in this transition is the refurbishment of buildings that currently demand high supply temperatures. Based on the example of a research campus in Germany, this study investigates how building refurbishment and building clustering influence the thermo-hydraulic performance of district heating systems, focusing separately on demand reduction and temperature reduction. In the first part, heat demand is progressively reduced in defined consumer groups to quantify the impact on system operation. In the second part, refurbished buildings are organized into clusters supplied at different temperature levels between 35 °C and 65 °C. In addition, a new key performance indicator is proposed to estimate heat loss reductions resulting from lower supply temperatures, enabling quick assessments without additional simulations. The results show that the order in which buildings are refurbished does not have a substantial effect on the district heating system's performance. Although pump energy savings of up to 35 % can be achieved, they account for only a small share of the system's total energy demand. Clustering refurbished buildings and supplying them with lower temperature levels can reduce system's heat losses up to 23 % for this case study. Additionally, clustering facilitates the gradual integration of renewable energy sources, providing a viable pathway for the decarbonization of district heating systems.