Accumulating solar and/or environmental heat in walls of apartment buildings or houses is a way to level-out daily temperature differences and significantly cut back on energy demands. A possible way to achieve this goal is by developing advanced composites that consist of porous cementitious materials with embedded phase change materials (PCMs) that have the potential to accumulate or liberate heat energy during a chemical phase change from liquid to solid, or vice versa. This paper aims to report the current state of art on numerical and theoretical approaches available in the scientific literature for modelling the thermal behavior and heat accumulation/liberation of PCMs employed in cement-based composites. The work focuses on reviewing numerical tools for modelling phase change problems while emphasizing the so-called Stefan problem, or particularly, on the numerical techniques available for solving it. In this research field, it is the fixed grid method that is the most commonly and practically applied approach. After this, a discussion on the modelling procedures available for schematizing cementitious composites with embedded PCMs is reported.

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Thermal-Energy Storage (TES) properties of organic phase change materials have been experimentally investigated and reported in this paper. Three paraffin-based Phase Change Materials (PCMs) and one bio-based PCM are considered with melting temperatures of 24 °C, 25 °C and 26 °C. Sensible heat storage capacities, melting characteristics and latent heat enthalpies of the studied PCMs are investigated through Differential Scanning Calorimetry (DSC) measurements. Two alternative methods, namely the classical dynamic DSC and a stepwise approach, are performed and compared with the aim to eliminate and/or overcome possible measurement errors. In particular, for DSC measurements this could be related to the size of the samples and its representativity, heating rate effects and low thermal conductivity of the PCMs, which may affect the results and possibly cause a loss of objectivity of the measurements. Based on results achieved from this study, clear information can be figured out on how to conduct and characterize paraffin and bio-based PCMs, and how to apply them in TES calculations for building applications and/or simulations. It is observed that both paraffinic and bio-based PCMs possess a comparable TES capacity within the selected phase transition temperature, being representative for the human thermal comfort zone. The phase change of bio-based PCMs occurred over a much narrower temperature range when compared to the wider windows characterizing the paraffin-based materials. Bio-based PCMs turned out to be very suitable for building applications and can be an environmentally friendly substitute for petroleum-based PCMs.