Sporleder, MaximilianMaximilianSporlederRath, MichaelMichaelRathRagwitz, MarioMarioRagwitz2025-01-202025-01-202024https://publica.fraunhofer.de/handle/publica/48147710.52202/077185-0064Climate change forces district heating operators to reduce their CO2-emissions and decarbonize their district heating systems (DHSs). A solution for a decarbonized system might be the combination of central and decentral units. This combination offers the possibility to supply each consumer with their individual temperature. However, it raises the question of the optimal design between central and decentral units and how they perform against a central supply. Therefore, a mixed-integer linear programming (MILP) model was developed capable of designing and operating several supply systems inside the network at different locations - decentralized and centralized. In this study, the combined system is compared to a centralsupply. Every energy converter’s and storage’s design and operation are optimized based on an objective function, minimizing the total system cost consisting of the annuity of operational and capital expenditures (opex and capex). The model can select central options such as a buffer tank, photovoltaic (PV) field, combined heat and power (CHP) plant, biomass boiler, large-scale wastewater heat pump (WWHP), and a solar thermal field. The combined system additionally designs booster heat pumps - other decentral options are not viewed in this study. The optimization horizon is one year in 24 h timesteps. The MILP method and all necessary component models are implemented as an open-source Python package. The method was applied in a case study with a district heating network (DHN) supplying 22 buildings distributed into six classes. Every class has a demand and supply temperature curve. In this study, different temperature levels and electricity prices were investigated. The results show that the combined system of central and decentral units performs best at a maximum network temperature of 85 °C, installing booster heat pumps only at high-temperature buildings. The combined system can distribute the temperature’s lift, increasing the coefficient of performance (COP) for the central heat pump. Furthermore, the lowered network temperature decreases the investment for the WWHP because a second compressor stage is no longer needed. The best configurations supply heat between 14 ct/kWh and 16 ct/kWh.enconference paper