Optimal design of district heating networks with distributed thermal energy storages – method and case study

District heating systems have a great potential for supporting the energy transition towards a renewable energy system, and could also be an option in less dense populated urban districts and rural communities with a medium heat density. In these cases, distributed thermal energy storages at each building could improve the overall system performance by enabling a leaner sizing of the piping systems due to peak-shaving and reducing the heat losses of the distribution grid. But how can distributed storages be included in the design of the district heating network itself? And what are the benefits with respect to the district heating piping system? This paper answers these questions and presents a novel open source optimisation framework for designing the piping network of a district heating system that is based on a mixed-integer linear programming model with a high spatial resolution. Due to its modular structure, it allows the extensibility by additional energy storage and converter units. Additionally, a novel method to consider the simultaneity of demand is introduced. Within the QUARREE100 project, the tool is demonstrated on a real world case of an existing district with 129 houses in the provincial town Heide in Northern Germany by analysing the impact of distributed thermal storages on the piping system. In the scenario with an average volume of 1 m³ heat storages, the thermal losses of the district heating network can be reduced by 10.2 % and the total costs by 13.4 %.