Enhancing thermal storage and release performance of pipe-embedded walls through spiral heat injection structure

The hydronic thermal barrier technology redefines opaque envelopes by enabling active thermal modulation via efficient exploitation of low-grade thermal energy. The spiral-tube-embedded hydronic thermal barrier walls (SHTBs) coupled with intermittent charging strategies are introduced to address the low charging efficiency and insufficient thermal barrier perfection of linear-tube-embedded walls (LHTBs). Comprehensive parametric analyses are performed with a numerical model validated against LHTB experimental data and subsequently extended to SHTB simulations to clarify key design factors governing performance. Benefiting from expanded spatial charging coverage, continuously operated SHTB achieves thermal barrier perfection degrees (TBPD) of 0.81–0.95, 35.00%–58.33% higher than LHTB, within the tested water temperature range. In addition, harmonizing daily charging duration and pulse frequency enables core indicators to reach over 90% of the continuous benchmark. Even with a 75% reduction in daily charging duration (6 h), intermittently operated SHTB still outperforms continuously operated LHTB in TBPD. Parametric sensitivity reveals diminishing returns beyond 10 turns per meter, and an optimal balance between tube usage and thermal output is achievable at moderate spiral densities and diameters. Finally, SHTBs effectively offset performance degradation induced by reduced external insulation, and a 40% insulation reduction only drops TBPD by less than 5% under the studied conditions.