Experimental Verification and Building-Level Simulation of a PCM-Enhanced Multifunctional Building Envelope for Renewable Heat Integration

Increasing the share of renewable energies is a key challenge in residential heating systems, particularly when available solar heat cannot be effectively stored or used. This study examines a façade-integrated Multifunctional Building Part (MBP) incorporating a phase change material (PCM), with a hydronic circuit designed for active thermal charging and renewable heat integration. The PCM-enhanced MBP enables direct charging of latent thermal storage through a hydronic circuit and provides an active envelope-based approach for storing renewable heat and supporting space heating. The PCM behaviour was experimentally verified at the component level using the SmallHouse IV demonstrator, and the resulting model was subsequently integrated into the International Energy Agency Solar Heating and Cooling (IEA SHC) Task 32 single-family reference building for seasonal numerical simulations under selected climatic conditions. The building-level assessment considers the conventional reference building, the hydronically activated MBP without PCM, and the PCM-enhanced MBP, thereby distinguishing the overall effect of the MBP from the additional contribution of latent thermal storage. The results demonstrate a progressive improvement in renewable heat utilization and electrical energy performance from the reference building to the hydronically activated MBP and, under favorable climatic conditions, to the PCM-enhanced configuration. In Stuttgart, the MBP reduced electrical energy demand from 1719.7 to 1255.6 kWh, with a further reduction to 962.0 kWh after PCM integration. Correspondingly, solar thermal utilization increased from 1194 kWh for the reference building to 2756 kWh with the MBP and 3999 kWh with PCM. Across Stuttgart, Madrid, and Kabul, the additional PCM integration reduced electrical energy demand by 23–69% and increased solar thermal utilization by 22–45% relative to the MBP without PCM. In contrast, under the investigated Moscow climate, PCM integration increased electrical energy demand by 9.6% and reduced solar thermal utilization by 6.9%, indicating a deterioration in simulated system performance. Overall, the results indicate that the performance of PCM-based thermal storage within the building envelope is highly dependent on the interaction between heating demand, renewable heat availability, and the opportunities for latent heat charging and discharging. The study highlights the potential of component-verified PCM-enhanced and numerically investigated hydronically activated building components for climate-adaptive renewable heat utilization in residential building.