New article on optimal decarbonization strategies for existing districts

Integrated energy system planning at the district level can contribute towards the sustainable transformation of the building sector by unlocking solutions beyond individual buildings. This is particularly true for existing districts, whose older buildings have a low energy performance and for which measures to reduce the energy demand and ensure a low-emission energy supply must be implemented. In the urban context, district heating networks (DHN) with carbon capture and storage (CCS) hold promise for emissions reduction. However, investment decisions must consider individual buildings as well as district solutions, as building-level demand-side interventions can affect energy demand patterns and densities.

Download This study presents a comprehensive methodology for determining optimal decarbonization strategies for existing districts while considering building-level energy supply and retrofitting investment decisions and the expansion of existing DHN. We do so by extending the MANGOret (Multi-stAge eNerGy Optimization - retrofitting) optimization framework for the long-term investment planning of building-level multi-energy systems and envelope retrofits. In addition, the study presents an approach for modeling CCS as an emission-reduction technology for the waste incinerator supplying the marginal expansion of the district heating network.

We applied this model to two case study neighborhoods in Chur, Switzerland, examining different neighborhood typologies and their impact on the expansion decision of the district heating network.

Key findings:

1. Retrofitting constitutes the largest share of total system costs, primarily borne by building owners. Lower-cost emission reductions are attainable through energy supply system changes, favoring technologies like air source heat pumps.

2. Expanding existing district heating networks is the economically optimal solution in densely developed districts with high heating demand. It also becomes the CO2-optimal choice with a low-emission district heating source, such as a waste incinerator with CCS. In contrast, decentralized heating systems benefit residential areas with lower heating demands.

3. Long-term planning is crucial, with retrofitting interventions often delayed to minimize total costs. The model offers insights into the timing and adoption of energy system technologies.