Theory of time constant correlation of a porous bed thermal energy storage tank - Experimental and numerical proof of concept

Analytical modeling of energy systems is used to estimate the potential of the system, but several simplifications used lead to progressive deviations from the actual potential. Thermal Energy Storage tanks are most often treated as black boxes, by limiting their characteristics to their energy efficiency and basic capacity only. This paper introduces the theory of a time constant that correlates the basic parameters of a porous bed heat storage tank and allows the charge level of the tank to be determined during the charging stage. The correlation for the time constant has a coefficient that has been fully validated both experimentally and numerically for a wide range of parameters. Coefficient values for different precision test runs have been indicated, and the prediction deviation using the time constant does not exceed a value of 5 % relative to the actual results. The proposed methodology for the analytical model of the tank accurately represents the cyclic operation of the heat storage tank. It has also been shown that the cyclic operation of the heat storage tank fixes the charge level in the range of 0.16–0.79. The methodology presented can be used to modelling and designing energy systems with heat storage. •The time constant parameter of the Thermal Energy Storage tank has been proposed.•The time constant was dependent on the parameters of the rock deposit and the fluid.•The methodology has been validated experimentally and numerically.•The methodology for determining the charge level over time was proposed.