Dynamic thermal performance and energy-saving potential analysis of a modular pipe-embedded building envelope integrated with thermal diffusive materials

In the context of racing to carbon neutrality, the pipe-embedded building system makes the opaque envelopes gradually regarded as the multi-functional element, which also provides an opportunity for thermal insulation solutions to transform from high to zero-carbon attributes. Based on the re-examination of the heat transfer process of conventional pipe-embedded radiant (CPR) walls, the modular pipe-embedded radiant (MPR) wall integrated with thermal diffusive materials is proposed to enhance the heat transfer capacity of CPR walls in the direction parallel to the wall surface, thereby forming a more stable and continuous invisible thermal barrier layer inside the opaque envelopes. A comprehensive thermal and energy-saving analysis study regarding the influence mechanism of several key factors of MPR walls, e.g., the inclination angle of the filler cavity (theta-value), geometry size of the filler cavity (a:b-value) and thermal conductivity of the filler (lambda f-value), is conducted based on a validated numerical model. Results show that the dynamic thermal behaviors of MPR walls can be significantly improved due to that the radial thermal resistance in the filler cavity of MPR walls can be reduced by 50%, while the maximum extra exterior surface heat loss caused by the optimization measures is only 2.1%. Besides, a better technical effect can be achieved by setting the major axis of the filler cavity towards the room side, where the interior surface heat load/total injected heat first decreases/increases and then increases/decreases with the increase of the theta-value. In particular, the MPR wall with theta L = 60 degrees can obtain the best performance when other conditions remain the same. Moreover, the performance indicators of MPR walls can be further improved with the increase of the cavity size (a:b-value), while showing a trend of rapid improvement in the lambda f-value range of 2-5 lambda C and slow improvement increase in the lambda f-value range of 5-12 lambda C. In addition, the improvement effect brought by optimizing the theta-value is more obvious as the a:b-value or lambda f-value increases.