Employing modular phase change filler structures to enhance comprehensive performance of pipe-embedded energy walls under intermittent injection mode

The pipe-embedded energy walls (PEWs) are recognized as promising low-carbon solutions capable of lowering high-grade energy consumption while maintaining comfortable conditions in buildings. To address issues of potential thermal barrier failure and performance degradation encountered by PEWs during intermittent heat injection operations, modular pipe-embedded energy walls are proposed by setting the latent thermal storage structure filled with phase change material (PCM) around the pipe, i.e., PCM-PEW. Subsequently, a transient thermal analysis model is established and verified to explore the technical effectiveness of the proposed structural optimization design and investigate the impacts of several structural design and thermal property variables on thermal modulation and energy performances of PCM-PEW under intermittent operation conditions. The result indicated that PCM-PEWs had a notable suppression effect on surface thermal fluctuations, and compared to C-PEW, the daily temperature fluctuations on the inner surface could be significantly reduced by up to 94.82 %. It is recommended to use PCM fillers that have a heat conductivity exceeding 0.8 W/m/°C to obtain additional energy performance improvements. Besides, PCM fillers with an average phase-transition temperature close to or slightly greater than the average value of indoor controlled point and injection temperature were beneficial for promoting fluctuation modulation effect and room-side heat load reduction effect. As the PCM filler's latent heat grew above 250 kJ/kg, the benefits of the PCM filler structure would reach the upper limit. Moreover, the PCM filler with a heat conductivity higher than that of the load-bearing layer was recommended to achieve further improvements by effectively improving the heat diffusion rate in the PCM filler region. Last but not least, the PCM filler structure was particularly suitable for application in load-bearing layers with lower thermal conductivities, otherwise, coordinate optimization with other thermophysical parameters of PCM filler should be considered to achieve synchronous improvement in energy performance and fluctuation modulation.