Tailoring heat transfer path with non-uniform PCM distribution for optimized thermal performance in building envelope walls

The integration of phase change materials (PCM) into building envelopes can mitigate the impact of external temperature fluctuations on the indoor thermal environment, thereby lowering building operational energy consumption. While leveraging latent heat storage, the isotropic thermal conductivity of uniformly distributed PCM walls leads to bidirectional heat transfer (both indoors and outdoors), thereby increasing heating and cooling loads in winter and summer, respectively. In this work, a non-uniform dual-layer PCM wall with locally enhanced thermal storage density is proposed to optimize the internal heat transfer pathways of building envelopes during both winter and summer seasons, thereby reducing the daily cumulative heating and cooling loads. The results indicate that, compared to a conventional dual-PCM wall, the proposed design increases the temperature difference between the inner surface of the PCM-controlled zone and that of a standard concrete wall by 14.3% in winter and 15.4% in summer. It also delays the peak inner surface temperature by 4.7 h in winter and 4.2 h in summer, demonstrating a shift in building envelope performance from passive insulation toward active thermal regulation. Furthermore, the proposed wall achieves improvements of 127.91% in heating load reduction and 143.87% in cooling load reduction relative to the conventional dual-PCM wall.