Thermal performances and invisible thermal barrier formation mechanism of arc-shaped metal-fin-enhanced thermally activated building envelopes with directional heat charging feature

Thermally activated building envelopes (TABEs) are multifunctional component that combines structural and energy properties. Based on re-examining the heat charging processes, an arc-shaped metal-fin-enhanced TABE (Arc-finTABE) with directional heat charging features is proposed to optimize the thermal barrier formation process. A comprehensive parameterized analysis is conducted based on a validated mathematical model to explore the influence of 5 fin-structure design parameters and the static insulation thickness. Results verified that the directional charging strengthening fins can improve transient thermal performances of Arc-finATBE and enlarge horizontal and vertical sizes of the thermal energy accumulation area surrounding the pipeline, while the maximum growth in extra heat loss is less than 3.17%. From the perspective of promoting heat injection into expected areas, the straight main fin configurations with the angle of main fins of 30°, shank length ratio of 0.4 and no leftward mounted fins are preferred in load-reduction mode, while the angle of main fins of 150°, shank length ratio of 0.8 and multiple fin designs, especially with one of the main fins horizontally toward the indoor side, are more favorable in auxiliary-heating mode. Besides, it is recommended to add one arc-shaped branch fin to each main fin to achieve a balance between performance improvement and material usage. Moreover, branch fins with larger arc angles are preferred in auxiliary-heating mode, while smaller arc angles are conducive to injecting heat into the wall along main fins in load-reduction mode and preventing the heat near the inner surface from being extracted. Under the direct influence of the strengthened invisible thermal barrier, Arc-finTABEs can reduce the amount of static insulation layer by 20%–80% while achieving equivalent thermal performances as conventional high-performance walls.