Energy-Saving Potential of Embedded Pipe Roof with Phase Change Material: Experimental, Numerical Analysis, and Optimization

• Integrated roof system enables active solar heating and passive insulation. • It provides 6-hour insulation, then cuts heat flux loss by 57.48% for over 5 hours. • A resistance-capacitance model accurately predicts dynamic thermal behavior. • Multi-objective optimization cuts energy demand by 38.6%, cost by 88.4%. • System demonstrates economic viability with 885-day payback. Traditional building facades are limited by their fixed thermal resistance, severely constraining their adaptability to dynamic environmental conditions and reducing energy saving potential. To address this limitation, this study proposes an innovative thermally-activated roof system with cascaded phase change material (PCM), which integrates active and passive building technologies within a unified structural configuration. The primary novelty lies in integrating this system with a solar collector and a heat storage module to create a ‘dynamic thermal barrier’ for load reduction. By utilizing the PCM as a latent heat storage medium, the system captures surplus energy and significantly extends operational duration. The system’s dynamic thermal performance was first evaluated through a scaled experimental model, which validated a newly developed high-fidelity resistance-capacitance (RC) model, demonstrating its applicability under dual-loop piping conditions. Subsequently, a comprehensive multi-objective optimization framework was established, coupling Morris sensitivity analysis with the NSGA-III algorithm to minimize thermal discomfort, energy demand, and PCM costs while maximizing heat exchange, thereby enabling a quantitative design strategy for similar structural configurations. Experimental and numerical results robustly justify the proposed system’s advantages. The cascaded PCM substantially enhances the roof’s thermal inertia, achieving a state of zero heat loss for six hours post-heating. This is followed by a sustained five-hour phase of effective heat retention, reducing heat flux loss by 57.48% compared to pre-operation baselines. The optimized roof configuration achieves a 38.60% reduction in daily energy consumption, a 233.47% increase in heat exchange capacity, and an 88.43% decrease in PCM usage, alongside improved indoor thermal comfort.