Modeling the thermally adaptive performance of building exterior walls with linear temperature-dependent thermal conductivity

The concept of adapting to variable external thermal environments by varying the thermophysical properties of building envelopes has gained increased attention in recent years. This study aims to evaluate the thermally adaptive performance of exterior walls incorporating linear temperature-dependent thermal conductivity-based insulation (LTTI). A variant resistance–capacitance nodal model was developed and validated against Fluent simulations, demonstrating high accuracy and time efficiency. The study evaluates the thermally adaptive indices (i.e., the adaptive time lag, adaptive decrement factor, and thermally adaptive ratio) for LTTI-based walls with at different temperature-dependent slopes under the Beijing climate. The results show that the dynamic thermal indices follow a parabolic pattern, whereas the monthly adaptive indices exhibit a folded line pattern with the extreme value in July. The maximum value for the adaptive time lag and decrement factor reached 3.8 h and 0.003 at −1.0 mW·m⁻¹·K⁻², while minimum extreme value is observed at 1.0 mW·m⁻¹·K⁻² with −3.8 h and −0.003, respectively. Furthermore, the study determines the relationship between the heating, cooling, and overall thermally adaptive ratios and the seasonal month and the temperature-dependent slope. At a temperature-dependent slope of 1.0 mW·m⁻¹·K⁻², the heating, cooling, and overall thermally adaptive ratios were approximately 0.162, −0.045, and 0.160, respectively. These findings suggest that LTTIs with a positive slope adapt to the thermal environment in Beijing, while those with a negative slope exhibit the opposite, anti-adaptive performance. These results could provide insights into the development of energy-efficient and thermally adaptive building envelopes based on LTTI materials. © 2024 Elsevier Ltd