The district heating grid simulation is a long-term, sustainable method to optimize existing supply grids on the one hand and to plan new route sections and district heating grids on the other hand. Current and future problems, issues and associated decisions such as the decarbonization of supply grids and the energy transition itself are constantly creating new framework conditions for a future-oriented energy supply. Against this background, the engineers of EA Systems Dresden GmbH have developed the District Heating Grid Simulation Library. Thanks to their know-how and this powerful tool, all conceivable scenarios, problems and challenges in terms of the energy transition, both in the context of an inventory optimization, as well as in the new planning and route expansion, can be simulated long-term-sustainably, solved model-based and mastered.