Multiscale Modeling Methods for District Heating Systems: From Physics-Based Approaches to Data-Driven Integration

District heating systems are transitioning from conventional high-temperature systems to 4GDH/5GDHC systems, giving system modeling more pronounced multiscale characteristics in physical hierarchy, temporal dynamics, and model abstraction. To support planning, optimization, control, and fault diagnosis, this paper systematically reviews district heating system modeling methods based on 185 representative publications and relevant sources. The review is organized around four modeling objects: heat sources, distribution networks, end users, and core components. It summarizes steady-state, quasi-dynamic, and dynamic physics-based modeling methods, and classifies physics–data fusion modeling into Parameter Calibration-Based, Surrogate Module-Based, and Physics-Informed Approaches. In addition, the applicability of representative modeling software and simulation platforms is compared. The results show that no single method or platform can simultaneously satisfy planning, simulation, optimization, and real-time control requirements. Future research should focus on multiscale collaborative modeling, cross-platform co-simulation, adaptive-complexity fusion models, and dynamic end-user modeling.