Experimental characterisation, field validation, and numerical thermal analysis of a gypsum–PCM composite for lightweight building envelopes in a hot-arid climate

A gypsum–phase change material (PCM) composite incorporating paraffin wax and sodium sulfate decahydrate was developed and characterized for exterior application to lightweight building envelopes in hot-arid climates. The composite exhibited a melting peak temperature of 34.93 °C, thermal conductivity of 0.181 W/m·K, density of 1.019 g/cm³, and compressive strength of 4.8 MPa. DSC-derived heating and cooling specific-heat functions were incorporated into a one-dimensional transient heat-conduction model. For field evaluation, a 20 cm × 20 cm × 2 cm gypsum–PCM specimen was installed locally on the exterior South wall of a sandwich-panel (SP) test cabin. From 14 May to 6 June 2026, the measured outer gypsum–PCM and interior SP surface temperatures were imposed as time-dependent Dirichlet–Dirichlet boundary conditions, while the gypsum–paraffin/sandwich-panel interface temperature was predicted and independently compared with measurements. The model achieved an RMSE of 3.32 °C and R 2 of 0.708, indicating moderate agreement. The model was subsequently applied using measured wall-specific surface temperatures from a separate 43-day August–September 2025 period. The 20-mm gypsum–PCM configuration reduced cumulative positive inward conductive heat gain by 21.18%, compared with 20.75% for an equal-thickness constant- C p gypsum layer and 20.00% for an equal-thickness RT42 PCM layer. The close performance of these configurations indicates that, under the investigated hot-summer conditions, the thermophysical properties of the added layer dominated the conductive heat-gain reduction, with a smaller additional contribution from the temperature-dependent phase-change behavior. The results demonstrate the value of localized field model evaluation followed by controlled numerical assessment and highlight the need for broader seasonal evaluation to distinguish sensible and phase-change thermal-storage contributions.