Optimal phase-change temperatures for PCM-integrated building walls: Effect of orientation and positioning on thermal performance in China’s hot summer and cold winter zone

The phase-change temperature is crucial for the application of phase-change materials (PCMs) in buildings, and its performance is affected by the wall orientation and PCM layer positioning. To assess the impact of these factors on the thermal performance of PCM-integrated walls in the hot-summer/cold-winter zone (HSCW) of China, two types of phase-change walls were developed with PCM layers positioned externally and internally. Numerical simulations were conducted to determine the optimal phase-change temperatures for walls with different orientations and to analyze their heat transfer characteristics and cooling energy consumption. The results showed that the optimal phase-change temperature ranges of the outer and inner phase-change walls across the four cardinal orientations (east, south, west, north) were 34–36 °C, 32–34 °C, 34–36 °C, 32–34 °C, and 28–30 °C, 27–29 °C, 28–30 °C, and 27–29 °C, respectively. At their respective optimal phase-change temperatures, the thermal insulation performance of inner phase-change walls exceeded that of outer ones. Compared with conventional walls, inner phase-change walls reduced the maximum inner surface temperature by 1.06 °C, extended the temperature delay time by 3.5 h, and improved the attenuation factor by 390.18%. Buildings with inner phase-change walls reduced the cooling energy consumption by 2.96%, whereas those with outer phase-change walls reduced it by 2.08%. Neither type of PCM wall exerted a significant effect on building heating energy consumption. This study systematically defines orientation-specific optimal phase-change temperatures for both PCM wall configurations, enabling precise design of PCM-integrated walls for China’s HSCW zone.