Large-Scale District Heating Network Optimization

This study optimizes the structure and size of a district heating network. The optimization task is formulated as a mixed-integer problem on a graph of possible pipe locations. Both structure (where to build pipes) and size (pipe capacities) are decision variables in a mathematical description of the optimization problem. The validity of its results are then tested on a case study in Munich, using a published district heating extension plan as reference. The district heating model employs an idealized graph of the street network to represent potential sites for pipes. This street graph is derived from publicly available data, which is also the main source for estimating the heat demand of buildings. Heat demand of individual buildings is aggregated along streets; heat supply, in turn, is possible at pre-defined source locations. The structural optimization relies on a concave investment cost function which represents the diameter-independent part of pipeline investment costs. The case study results finally show a good correspondence between the overall structure of the optimized network and the real expansion plan of a district heating network.