Comparative Numerical Evaluation of PCM Composite Integration in the Attic Space: A Case Study

This case study numerically investigates PCM integration into attic constructions to mitigate summer overheating and improve indoor thermal stability. Attic spaces are vulnerable to overheating due to lightweight construction and intense solar radiation on the roof envelope. Simulations were performed in DesignBuilder using the EnergyPlus engine on a model validated against in situ measurements. Three variants of an organic paraffin PCM composite with aluminum encapsulation were defined: ceiling, sloping roof, and floor under the roof window, at thicknesses of 20 and 40 mm with a melting temperature of 28 °C (Rubitherm RT28HC) based on measured temperatures. Results demonstrated that the integration position is the dominant factor governing effectiveness. Floor integration yielded the most favorable results due to direct solar radiation exposure, reducing time exceeding 30 °C by 63% at 20 mm thickness. Increasing thickness to 40 mm brought substantial improvement for the floor variant (up to 4.85 °C reduction in maximum operative temperature), while ceiling and roof variants were marginal. These findings confirm that targeted floor-level PCM placement effectively reduces peak summer overheating, though mild overheating duration above 26 °C increases as thermal exposure is redistributed from extreme peaks to a milder band.