Model-based analysis of thermal energy storage for multiple temperature level heat supply

Thermal Energy Storages (TES) are widely used in many energy systems and improving their performance has become increasingly important. Various CFD models are currently available, both one-dimensional and multidimensional, with different level of accuracy, computational cost and capability to be generalised. This work is aimed at analising the relevant phases, i.e. charge, discharge and low inertial discharge, of a couple of hot water TES characterized by different inlet temperatures and flow rates, with three numerical approaches: 1D, 2D, and a reduced model. In particular, the latter approach provides a simple analytical function for the evaluation of the temperature profile inside the tanks. The numerical models are validated on experimental data obtained from a test bench with two hot water tanks, in which one tank is connected to a micro-CHP while the other is connected to a heat pump, and operated at different temperature levels. The results of the 2D and the reduced models are in good agreement with experiments showing a maximum error lower than 1.2 K during the discharge cycles; nevertheless, the reduced model has a much lower computational cost and the dimensionless nature of the implemented function allows generalising the validity of the results to storage tanks operating at different conditions.