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Combining Modelica and deal.II for Dynamic Simulation and Optimization of District Heating and Cooling Systems
Kecheng CHEN, Jiahui YANG, Kenichi SOGA, Peter NICO, Patrick DOBSON
[UC Berkeley, USA]
District heating and cooling (DHC) systems increasingly rely on borehole thermal energy storage (BTES) for sustainable operation. Accurate dynamic simulation tools are essential for predicting system performance, designing control strategies, and optimizing large-scale deployments. However, widely used reduced-order methods, such as G-functions, cannot capture important transient and nonlinear effects in coupled pipe-ground interactions, especially for complex borefield configurations. This work presents a framework that combines Modelica, a multi-physics, equation-based modeling language, with deal.II, a high-performance finite element library, to enable integrated, high-fidelity dynamic simulation of DHC systems. The framework leverages Modelica’s system-level modeling and control capabilities while embedding deal.II-based 3D subsurface simulations to resolve detailed heat transfer and groundwater flow phenomena. The coupling methodology, numerical solvers, and validation strategy are described in detail. Validation studies begin with a single-borehole case, evaluating coupling accuracy when exchanging different variables either heat flux to the ground or water temperature. A two-borehole case then examines accuracy under dynamic operating conditions, including time-varying heat injection and variable water flow rates. The framework is subsequently applied to borefields to verify coupling accuracy under multi-borehole conditions. Case studies illustrate how G-function approximations can underestimate thermal interactions in series-connected borefields and compare the 10-year performance of parallel- versus series-connected configurations. Extensions to phenomena beyond the reach of G-functions, such as inclined boreholes, are also discussed.
Topic: Modeling