Experimentally validated numerical model of adaptive envelopes with macroencapsulated PCMs under real conditions, including the effects of the capsule and indoor temperature variation

Incorporating macroencapsulated phase change materials (PCMs) in building envelopes is a strategy to reduce building energy consumption. However, most numerical models ignore the effects of encapsulation (capsule mass and thermal resistance), do not distinguish between solidification and melting dynamics, and assume constant indoor temperatures. This work presents an experimentally validated numerical model of envelopes based on Spanish standards that incorporate macroencapsulated PCM. Two envelope types with different thermal mass were simulated. The model includes the capsule effects and accounts for the distinct behavior of melting and solidification, as well as phase change interruption. Simulations were performed for typical winter and summer days in Gijón (Northwestern coastal city in Spain). A sensitivity analysis was conducted to evaluate the impact of PCM position, phase change temperature, and indoor temperature. The outputs included typical indicators of thermal inertia and three new parameters: thermal oscillation, phase change efficiency, and active time of the PCM. These new indices facilitate interpretating PCM dynamics and designing energy-efficient envelopes under realistic operating conditions. Results showed that lower thermal oscillation occurred when the PCM was active longer and its temperature remained near the peak phase change point. The relationship between PCM position, indoor temperature, and phase change temperature is critical. In this case study, the optimal case placed the PCM near the interior, with a peak temperature 0.5 °C above the winter indoor setpoint. Under these conditions, thermal oscillation dropped by 59.82%. An adaptive envelope with an adequate PCM shows better thermal performance than a thicker higher-mass traditional envelope.