A framework for flexibility assessment of district heating and cooling systems

District heating and cooling (DHC) systems represent significant flexibility resources for electricity grids, yet systematic assessment and comparison of their flexibility potential are hindered by the absence of a consistent quantitative framework. This study introduces a comprehensive key performance indicator framework that integrates demand-side flexibility metrics with storage dynamics and system performance indicators to enable systematic evaluation and benchmarking of DHC flexibility provision. Applying the framework to a Norwegian case study across diverse scenarios demonstrates its ability to reveal heating-dominated flexibility patterns and assess the robustness of indicators under varying policy and climate conditions. The framework shifts the evaluation paradigm from traditional thermal output metrics to systematic flexibility assessment, enabling decision-makers to quantify not only whether DHC systems provide flexibility, but how much, under what constraints, and at what cost. This establishes a methodological foundation for comparing different configurations and developing flexibility-oriented approaches in DHC planning.