Calibration and validation of a thermal energy storage model: Influence on simulation results

In this paper a 1-D model of a thermal energy storage (TES) was experimentally validated and calibrated. The experimental tests showed an overall heat transfer coefficient for heat losses four times higher than the theoretical value. This was due to the thermal bridges associated with the hydraulic and sensor connections. Moreover, the lack of thermal insulation at the bottom of the TES causes an increase in dissipation through thermal bridges. The experimental data enabled the evaluation of effective TES heat capacity, which differed from the theoretical value instead based on net storage tank volume. By means of an optimization tool, a fictitious value of the TES volume was calculated. In order to model the natural convection heat transfer coefficient of the heat exchanger immersed in the water storage tank, a Nusselt-Rayleigh correlation was experimentally calibrated. The data derived from tests conducted in a test facility of Università degli Studi del Sannio (Italy) were then compared with a computer simulation based on a calibrated TES model by means of commercial software. The validation procedure showed a satisfactory agreement between experimentally measured temperature values and those predicted by the model. Finally, different dynamic simulations of solar thermal heating systems are carried out in order to highlight the influence of the TES model and its calibration and validation on annual energy performance.