Parametric Evaluation of a PCM-Integrated Exterior Wall Across Turkish Climate Zones Using Building Energy Simulation and Machine Learning

This study evaluates the energy and operational carbon performance of phase change material (PCM) integrated into one external wall of a reference office building across 19 Turkish cities representing six TS 825 climate zones. A full-factorial parametric analysis was conducted using DesignBuilder by varying five nominal melting temperatures (21–29 °C), three PCM thicknesses (5, 10, and 20 mm), and four façade orientations. The lowest-energy tested PCM configuration reduced annual total site energy consumption in all investigated cities, with savings ranging from 0.38% in Kayseri to 2.86% in Samsun and average savings of 1.89%. The corresponding CO2 reductions ranged from 0.26% to 1.84%, with an average reduction of 1.25%. Among the investigated thicknesses, a 20 mm PCM layer produced the lowest annual total site energy consumption in all 19 cities. Melting temperatures of 21 °C and 23 °C generally provided the greatest energy savings, while the best-performing façade orientation varied with climate. A machine-learning surrogate model was also developed for rapid PCM screening by comparing Ridge regression, Random Forest, and Gradient Boosting models. Random five-fold cross-validation produced high predictive accuracy. Leave-one-city-out validation showed limited accuracy for absolute annual energy prediction in cities excluded from model training but stronger performance for energy- and CO2-saving percentages. The model is therefore suitable for preliminary screening and ranking PCM configurations, while detailed simulations remain necessary for final design validation.