Co-simulation methodology of a hybrid latent-heat thermal energy storage unit

Abstract

In a hybrid steam/latent heat storage concept as previously proposed, containers filled with phase change material (PCM) are installed at the shell surface of a Ruths steam storage (RSS) to increase storage capacity through retrofitting. The detailed knowledge of the thermophysical behavior of such a concept is crucial to exploit its full potential. For this purpose, a novel high-fidelity co-simulation model is developed in this work, implementing an efficient and accurate thermal coupling concept of a dynamic RSS model with detailed conduction/convection PCM cell models. It accounts for the significant influence of angular position and orientation of the PCM cells at the RSS shell surface as well as the filling level in the RSS. To reduce computational effort, the PCM cells are logically aggregated to PCM sectors with similar thermodynamic behavior using a new optimization method that minimizes the total error. Therefore, quantitative criteria to find an optimized PCM cell aggregation are formulated. The efficiency and accuracy of the proposed reduced-complexity co-simulation is demonstrated in typical operation modes of the hybrid storage. In the simulation study, the error can be reduced from 4.5% to 0.5% by using the newly developed optimal aggregation criteria. The computation time can be shortened up to 73%, whereby equally accurate results can be achieved compared to a model with high resolution. The developed co-simulation model serves as a foundation for design optimization, model reduction, dynamic state-of-charge estimation, and ultimately enables model-based control.