A convenient solution to increase energy density of conventional water thermal storage is with the use of encapsulated phase change materials that can be installed in the existing water tank through a flange. That kind of solution brings quick and pragmatic solution of energy density improvement but it leads to more complicated operation of thermal storage from state-of-charge point of view. The simulations can help in better understanding of thermal storage operating conditions. That is why the focus of present research is on simulations under different initial conditions with numerical model that was validated with measurement results. The investigation took place on water thermal storage tank with encapsulated phase change materials (PCM) that represented 30% of the thermal storage volume. The measurements of a 100 l water tank with 190 spherical capsules filled with PCM (hydrate salt mixture) were performed. The numerical model for latent thermal storages was used in TRNSYS environment and was adjusted according to the boundary and initial conditions of the experimental system and measurement conditions. The results of simulations were compared with the measurements in order to perform the validation of the numerical model. After successful validation, the simulations of different initial water temperatures to the thermal storage system were made in order to analyse its heat charge and discharge process.

This work was supported by the Slovenian Research Agency through the research program P2-0223 and by the EU Research and Innovation programme Horizon 2020 under grant agreement No. 768921 – HEART (Holistic energy and Architectural Retrofit Toolkit). The authors would like to thank the European Commission and Slovenian Research Agency for enabling the funding. Additionally, special tanks goes to authors of Trnsys model, dr. Andreas Heinz and dr. Hermann Schranzhofer from TU Graz for sending us the model Type 840.