Simplified dynamic modeling of single-tank thermal energy storage systems

The paper analyzes the behavior of the most common single-tank configurations of thermal storage capacities that involve transfer of mass (open systems) or/and heat (closed/hybrid systems), in presence or not of solid or phase-change filler materials. This is done using simplified dynamic models of different complexity: zero-dimensional, quasi-one-dimensional and one-dimensional. The aim is to show whether, and within which limits, simplified models can substitute more complex and time consuming two or three-dimensional ones. The comparison with experimental data showed that the onedimensional model is able to predict performance, thermal stratification and any other relevant aspect of the storage behavior with sufficient accuracy. Conversely, the other two approaches do not show this ability because they neglect or underestimate the heat transferred along the longitudinal direction of the storage capacity. One-dimensional simulations show that higher charging efficiency can be achieved using open systems (þ2.4% points compared to closed systems) and reducing the diameter of the filler material particles, if present. In closed systems the length of the cold heat exchanger can be reduced to half of the tank height with minimum decrease (about 0.6% after 1 h) of the temperature at which the thermal energy can be taken from the storage.