Effects of Outer Phase-Change Mortar Layer on Heat Transfer Characteristics of Walls Under Solar Radiation Conditions in Summer

The phase-change material (PCM) layer plays a critical role in governing the heat transfer characteristics of building walls. To evaluate this effect, two experimental test rooms with identical structural configurations were constructed and monitored under summer solar radiation conditions. One room incorporated an external phase-change mortar layer, whereas the other utilised a conventional, ordinary mortar layer wall to serve as a reference control. The heat transfer characteristics of the walls of both rooms were comprehensively evaluated under natural weather conditions. The experimental results indicate that, under the tested summer conditions, an external phase-change mortar layer with an appropriate phase-change temperature can improve the thermal regulation performance of the wall system. In particular, the wall incorporating PCM with a phase-change temperature of 32 °C effectively reduced the external surface temperature, with the maximum external surface temperature remaining below 44 °C. However, when the external surface temperature exceeds 44 °C, the PCM layer does not contribute to temperature reduction; instead, it may increase both the surface and overall wall temperatures due to ineffective phase change under mismatched thermal conditions. This study provides support for the engineering applications and parameter optimisation of phase-change thermal storage walls.