Numerical simulation of PCM-based storage units to be integrated into commercial hot water storage tanks

In future energy systems, storage will have a primary role, allowing smaller generation units. What is more for non-intermittent renewable energy sources such as solar and wind, storage is strictly necessary. The cost of electrical batteries is still very high, so one of the preferred storage technologies is the thermal one. In fact, thermal energy is used both as it is and as a source to be convert it into other forms. Thermal energy storage can increase the efficiency of industrial plants by exploiting waste heat and the efficiency co-generation plants by making the generation independent from the demand curve. Among thermal energy storage phase change materials(PCM) represent an opportunity thanks to their large latent heat that can reduce the size of storages. The main purpose of this thesis is the modelling of phase change material units macro-encapsulated in commercial hot water storage tanks. It starts with a literature review about the different phase change materials for latent heat storage applications and the numerical methods to model them. These methods are tested by launching different simulations of a study case on Comsol. The numerical results are compared to each others and to the experimental results in order to verify which of the methods better models the real case. The best one is then used to model the charge and discharge of a PCM unit in a climatic chamber. The results are then compared with the experimental ones to validate the model and a study on the effects of the different empirical parameters on the solution is done. In chapter 7 two different commercial hot water storage tanks are modelled on Matlab with the finite volumes method and are both validated with experimental results. The first tank has one immersed coil, while the second one has two coils for charge and discharge. These models can be coupled with the one of the PCM-unit to simulate the behaviour of the PCM macro-encapsulated into commercial hot water storage tanks. One of the prospective studies is, indeed, the validation of the model of the PCM-water tank storage system.