Abstract This paper presents a combined experimental and numerical procedure, developed to test the thermophysical behaviour of a real scale PCM wallboard, aiming at providing reliable data for the validation of building energy performance simulation tools. Data obtained from two experimental tests, conducted on real building elements integrating PCM undergoing complete and incomplete phase change, are considered for assessing the impact of thermal properties and hysteresis. A comprehensive comparative numerical analysis, performed by means of an in-house developed simulation tool, called DETECt, is carried out to investigate the reliability of several modelling and simulation approaches available in literature. Monitored data are used to compare the reliability of several modelling and simulation approaches (three different specific heat curves and four modelling approaches for hysteresis) to find out the appropriate temperature dependent heat capacity curves which realistically describe the PCM performance. Results The use of cp – temperature curves characterized through thermophysical analysis (e.g. DSC) under conditions much different than those that the PCM can undergo during the operation of a building can lead to significant discrepancies in performances with the actual data. Moreover, in case of incomplete phase transitions, the lower the accuracy of the cp – temperature curves, the higher the influence of the hysteresis modelling approach on the reliability of simulation results; a better agreement between monitored data and simulation results is observed when hysteresis is modelled by considering the transition between heating and cooling (and vice versa), by switching from the melting to the solidification curves according to the liquid and solid mass fraction. The study shows that the more refined modelling of the phase change allows results to be consistent with the thermo-physics phenomena of composite PCM under real conditions and achieve more reliable results.