Thermal storages are part of highly integrated energy systems. The development of accurate and reduced models is critical for efficient simulations on a system-level and the analysis of the storage design, control, and integration. We present the experimental analysis and numerical modeling of a lab-scale shell and tube latent heat thermal energy storage (LHTES) unit with a (latent) storage capacity of about 10–15 kWh. The phase change material (PCM) is a high density polyethylene (HD-PE) with phase change temperatures between 120 and 135 °C. An efficient 2D numeric storage model is derived which accounts for design and material parameters of PCM, storage, and heat transfer fluid (HTF). Different probability distribution functions are used to model the PCM apparent specific heat capacity. From these functions the state of charge (SOC) can be predicted, which indicates the extent to which a LHTES is charged relative to storeable latent heat. Model predictions are fitted to experimental data from thermophysical measurements and from LHTES operation with partial and full charging/discharging. The storage model agrees well with experimental results. However, thermosphysical material analysis and storage operation indicated that the temperature range of phase transition is noticeable affected by storage loading operating condition, i.e., heating and cooling rates, which is not considered in the model. With this simplification it turns out that the model is limited by the quality of prediction of internal storage PCM temperatures.

Technical-grade and mixed solid/liquid phase change materials (PCM) typically melt and solidify over a temperature range, sometimes exhibiting thermal hysteresis. Three phenomenological phase transition models are presented which are directly parametrized using data from complete melting and solidification experiments. They predict hysteresis phenomena and are used to calculate effective PCM properties. Two models have already been implemented in commercial building simulation and/or multiphysics software, but not the third novel model. Applications are presented for two commercial PCM: a paraffin, and a salt water mixture with additives. Numerical implementation aspects are discussed, and significant differences in the predicted absorbed and released heat are highlighted when simulating consecutive incomplete phase transitions. The models are linked with energy balance equations to predict recorded PCM temperatures of a thermal energy storage. The cross-validation with data from 26 partial load conditions clearly indicate a superior predictive performance of the novel hysteresis model.

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