Numerical coupling of Modelica and CFD for building energy supply systems

This paper presents an integrated method for the simulation of mixed 1D / 3D system models in the domain of building energy supply systems. The feasibility of this approach is demonstrated by the use case of a solar thermal system: the sub-model of a hot water storage is modeled as a detailed threedimensional CFD model, but the rest of the system model (solar collector, hydraulics, heat exchanger, controller etc.) is modeled as a simplified component-based DAE model. For this purpose, the hot water storage model is simulated with ANSYS CFD. This detailed sub-model is embedded in the solar thermal system model, which consists of component models of the Modelica library FluidFlow and is simulated with Dymola. The numerical coupling and integration of both sub-models is realized by the use of the co-simulation environment TISC. With a comparison of a pure Modelica system model and a mixed 1D / 3D system model of the same solar thermal system, advantages and disadvantages of both simulation approaches are worked out.