Exploring opportunities for temperature reduction in existing district heating infrastructures

The integration of renewable energy sources into existing district heating systems is imperative for the decar- bonization of the global energy system. This transition is particularly challenging in existing systems that were originally supplied by fossil fuel plants and designed to operate with high supply temperatures. Reducing supply temperatures to facilitate the integration of low exergy heat may not be suitable for the existing infrastructure, due to both the heating devices or the thermal substations that may not support significant reductions or to the distribution infrastructure that can be unable to handle the required mass flow rate increases. To address these challenges, this paper focuses on the distribution infrastructure by introducing a physical-based approach to explore the current potential for supply temperature reduction of existing district heating infrastructures, taking into account the hydraulics of the system. Indeed, being able to identify the possible hydraulic bottlenecks arising in the network is essential to enable the transition of the networks and requires an accurate modelling of the fluid dynamic of the system. The methodology is fast and versatile, making it suitable for applications from small-scale to large-scale systems. An application to a real large-scale network is presented, proving the wide applicability of the methodology. Promising results in terms of temperature reduction are shown to be possible: the analyzed infrastructure is currently capable of shifting its operation from 120 ◦C to about 102 ◦C without considering invasive structural interventions on the network, and further reductions up to 90 ◦ C are conceivable by assuming some adjustments to the system configuration