This paper presents a Bond Graph (BG) modellingapproach to add and exploit on existing Modelica mod-els some information on the energy structure of thesystems. The developed models in the ThermosysProlibrary (Modelica-based) are already validated againstthe experimental data in previous works. A plate heatexchanger (PHE), which is equipment for nuclear powerplants, is considered as a case study in this paper.Simulation results of the BG model for the counterflowPHE are compared with simulation results of the testedModelica model. Comparisons show good agreementbetween both model results.