Comprehensive performances investigation of a modular hydronic thermal barrier system for low-energy buildings with filler cavity and filling material design

The hydronic thermal barrier is a promising energy-efficiency technique for opaque envelopes of low-energy buildings. A modular hydronic thermal barrier (MHTB) wall with filler cavities and thermal diffusive material is designed to solve the capacity mismatch in the process of heat injection and thermal diffusion. To quantify its dynamic thermal behaviors and the influence of several key variables, a parametric study regarding thermal barrier formation and performance enhancement is carried out. Results show that the inlet velocity range can be divided into high-influence and low-influence regions, and 0.2–0.3 m/s is recommended to achieve a good performance at relatively small flow rates. Besides, heat load at inner surface of MHTB walls in studied orientations and cities can be further reduced by 35.79% and 34.02–35.98% respectively, and primary energy consumption savings of 11.24% and 8.81–11.56% can be achieved under the assumed energy-supply scheme. Furthermore, increasing a:b-value of filler cavities in the range of 1:1–1:3 is effective to form a more continuous and stable thermal barrier zone, heat load at inner surface of MHTB walls can be reduced by 72.89–91.87% at a charging temperature of 22 °C compared with CW wall, and this effect is more obvious at larger pipe spacings or higher charging temperatures. Meanwhile, increasing filler's thermal conductivity in the range of 1-12λ0 also possesses positive effects in enhancing the thermal diffusion in the direction parallel to the wall surface, the maximum further reduction ratio in heat load at inner surface of 42.26% and a further primary energy consumption savings of 13.30% can be obtained at pipe spacing of 300 mm and charging temperature of 22 °C. The results verified the effectiveness of MHTB concepts and could provide useful references for further research and application of MHTB walls. •A novel MHTB wall with filler cavities and filling material design is proposed.•Effectiveness of MHTB in various flow rates, orientations and climates is verified.•The effects of cavity size and filler's thermal conductivity on MHTB are explored.•The heat load/injected heat can be further reduced/increased by up to 45.8%/24.1%.•The preliminary design and application strategies of MHTB walls are discussed.