PCM materials embedded in building envelopes: a comprehensive hygrothermal analysis

In this paper the results of a comprehensive study focused on the energy performance analysis of building envelopes integrating Phase Change Materials (PCMs) is presented. PCMs are capable to reduce building energy consumptions and to enhance the hygrothermal comfort of occupants in indoor building spaces by increasing the thermal energy storage capacity of the building envelopes. Nevertheless, their real benefits are highly subjected to the building usage and weather conditions. In addition, depending on the specific building use and envelope material, for the best system performance it is crucial the selection of the optimal PCM typology. This depends on some pivotal thermodynamic parameters, such as: phase change melting and peak temperatures, latent heat of fusion, thermal conductivity, solid and liquid phase properties, thickness and position within the building envelope construction layers. Although several studies have been published on this topic, specifically aimed to understand and to model the PCM dynamics and potentials, this study contributes to the state-of-the-art by further analysing the PCM effectiveness by a comprehensive dynamic simulation analysis. In particular, with the aim to find out suitable criteria to be easily adopted for the selection and the design of PCMs for building applications, a numerical analysis, carried out by means of dynamic simulations, is presented. For this purpose, a numerical model is embedded in a suitable computer code (written in MatLab and called DETECt 2.3) for complete building energy, economic and hygrothermal comfort investigations. The developed model was validated by comparing the obtained simulation results vs. experimental tests ones (achieved by suitable prototype tests). The whole building code allows to assess the performance of PCMs by embedding them in building enclosures (e.g. roofs and walls or transparent elements) for any building envelope configuration (e.g. by placing PCMs in different positions with respect to the construction layers). By means of such developed computer tool, several comfort indexes (e.g. PPD, PMV, etc.) can be also calculated. Finally, a suitable case study based on a set of buildings of different design and operating features, located in diverse climate zones is carried out. A comprehensive parametric study is performed in order to assess the effects of the above mentioned operating and design parameters on the system energy and economic performance and on the hygrothermal occupants comfort. Interesting design criteria for the development and adoption of building embedded PCMs are provided.