Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est Numerical simulation and validation of commercial hot water tanks integrated with phase change material-based storage units Manfredi Neri a , Eliodoro Chiavazzo a , Luigi Mongibello ⁎ ,b a Department of Energy DENERG, Polytechnic University of Turin, Italy b ENEA Research Center of Portici, Italy ARTICLE INFO Keywords: Thermal storage PCM Numerical models Latent heat Numerical simulation Enthalpy porosity method Experimental validation ABSTRACT Thermal energy storage (TES) allows to extensively exploit solar thermal technologies by efectively handling the mismatch between energy production and demand thus possibly causing a downsizing of generation units. Among thermal energy storage technologies, those based on phase change materials (PCM) are particularly interesting because relatively large latent heat values may guarantee more compact systems (as compared to sensible TES). In this work, we report a numerical and experimental investigation on a hybrid latent-sensible heat storage characterized by a commercial hot water tank integrated with macro-encapsulated phase change materials. Those hybrid systems are interesting as they can possibly increase the overall thermal capacity of a sensible water tank. Despite all this, we demonstrate that increasing the efective storage capacity is a non trivial task with standard conditions and materials. To this end, three diferent numerical models have been developed and experimentally validated. The frst model is based on the enthalpy porosity method and simulates the charge and discharge of a PCM storage unit in a climatic chamber. The second model is a one-dimensional description of the water storage tank without PCM. Finally, the third model is obtained by coupling the previous two and simulates the whole PCM-water thermal storage. This fnal model was validated through an experimental test, which consisted in inserting 94 modules of PCM in the water tank and observing the resulting thermal behaviour for three days, applying the load curve of a detached house of 200m 2 . The model proved to be very accurate, with determination coefcients between 92.10% and 99.80% for the considered physical quantities (tempera- tures and thermal powers). As a main contribution of this work, we proved that the hybrid thermal storage system did not exploit the full latent heat potential of the PCM, since only 40% of it actually changes its phase, due to is thermal transport properties that negatively afect heat transfer. 1. Introduction The awareness on the importance of renewable energy sources to- wards the reduction of greenhouse gas emissions today is gaining an increasing popularity. However, especially solar and wind power are highly variable and have an unpredictable behaviour. As a con- sequence, they need to be coupled with storage technologies. In addi- tion to more traditional uses, energy storage systems may be also adopted for implementing smart energy management strategies. In fact, relying on efective storage technologies, customers may decide to purchase (at lower price) and store energy during of-peak periods for later use, when the price would be higher [1]. Moreover, a properly designed storage system may help in reducing the plant generation power with a corresponding downsizing and installation cost reduction. Among all types of energy storage technologies (electro-chemical, mechanical, thermal, etc...), thermal energy storage (TES) is attracting a large interest as it is a relatively mature and easily scalable tech- nology. Sensible TES is very common in residential applications like heating, cooling, air conditioning and domestic hot water. Large tanks containing molten salts at high temperatures are often installed in concentrated solar power plants, being one of the keys of the success of this technology [2]. Direct thermal energy storage systems can be di- vided into sensible heat thermal energy storage (SHTES) and latent heat thermal energy storage (LHTES). In addition to direct TES, indirect TES are manly based on reversible physi-chemical reactions, such as water sorption in microporous sorbents [3–5]. Indirect TES are beyond the scope of this work. Sensible heat storage is based on the variation of energy due to a temperature diference in the storage material, which usually is either liquid or solid. Packed beds of rocks are widely used for sensible thermal storage in solar air heaters, due to their low-cost and https://doi.org/10.1016/j.est.2020.101938 Received 6 July 2020; Received in revised form 14 September 2020; Accepted 25 September 2020 ⁎ Corresponding author. E-mail address: luigi.mongibello@enea.it (L. Mongibello). Journal of Energy Storage 32 (2020) 101938 2352-152X/ © 2020 Elsevier Ltd. All rights reserved. T