Development of renewable and system-supportive heat supply concepts and infrastructures for existing districts

Abstract

The transformation of the energy system is a crucial task for achieving the climate goals. A major challenge is the transformation of the heat supply of the building sector. In that process, one of the most far-reaching and cost-intense infrastructure decisions made at the municipal and district level is about the implementation of a district heating system. This decision becomes increasingly complex in future sector-coupled energy systems. Therefore, this thesis aims to develop future-proof renewable and system-supportive heat supply concepts and district heating infrastructures for existing districts, as well as software tools and methods for achieving this purpose.

The methodical approach of this thesis is based on techno-economic optimization models for the different components of district energy systems, including the district heating network, the design of the heat supply site and the energy supply at the building level. The approach and the tools support planning and decision making at district level and aim to broaden the conventional planning perspective and methods towards a systemic approach that respects the local energy system as part of an integrated overall system. By the in-depth analysis of an existing district with a sparse to moderate heat density, where it is undecided if district heating is a future-proof infrastructure, the impact of the different scenarios on the design and feasibility of district heating compared to individual heat supply options is studied.

The results of the optimization of the heat supply site shows that heat pump capacities in combination with thermal storage are of great importance for a future carbon-neutral and system-supportive heat supply in all considered scenarios. A combined heat and power unit helps to reduce emissions in short term. However, only if the gas network has a high share of renewable energies, this technology will compete with electricity based heating via heat-pumps. The comparison of district heating and individual heat generation shows that district heating systems are economically feasible at lower heat densities if a carbon-neutral electricity and heat supply is the goal. The impact of the scenarios of the upstream gas network considering a low or a high share of renewable synthetic gas on the heat density threshold is low. In scenarios with a high availability of renewable gas, district heating is even favored in some scenarios, as the synthetic gas can be more efficiently used at an aggregated level in a district heating facility compared to the building level.