Study on the Thermal Performance and Parameter Optimization of Aerogel–Phase-Change Mortar Composite Walls

Aiming to address the universal challenge that conventional phase-change material (PCM) walls for cold-climate rural buildings have low overall thermal resistance, causing rapid nocturnal heat loss and poor latent-heat utilization, this work develops composite specimens combining aerogel insulation coating and microencapsulated-PCM mortar for rural residences in Northern China. Experimental measurements and COMSOL Multiphysics®6.3 (COMSOL)-calibrated numerical simulations are adopted to investigate the coupled heat-transfer mechanism and multi-dimensional trade-offs among thermal regulation performance, mechanical properties and PCM cyclic-utilization efficiency. The results reveal that rising PCM dosage reduces the density and thermal conductivity of mortar; the specimen with a 30% PCM sand-replacement ratio plus 5 mm aerogel coating reaches a thermal conductivity of 0.116 W/(m·K). Owing to synergistic effects, aerogel mitigates external thermal disturbances to optimize PCM melting–solidification cycles while PCM buffers indoor temperature swings, delivering improved temperature-attenuation performance. Parametric analysis demonstrates that 30% PCM replacement and 23.0 °C phase-change temperature form a multi-objective equilibrium balancing thermal regulation, mechanical durability and PCM utilization, instead of a thermal-only optimum. Since these parameters are obtained under Dalian meteorological conditions and cannot be generalized, the proposed material–climate matching principle offers analytical references for low-carbon retrofitting of rural building envelopes in other high-latitude cold regions.