## 5 Discussion  
The comparative analysis of temperature distribution in the XY and ZY planes reveals a significant dependence of the thermal field on the geometry of the passive facade cavity. In the XY plane, the observed temperature difference between the configuration with the minimum cavity width (4 cm) and that with the maximum width (12 cm), amounting to 10.20% at the outer extremity, highlights the influence of the air channel dimension on the overall heat transfer. Larger cavity widths promote higher maximum temperatures in this region, suggesting an increased heat transfer capacity. In the ZY plane, the temperature profile exhibits the staged evolution characteristic of a thermal boundary layer. The initial linear decrease over the first 0.2 normalized units (Y+) indicates the dominance of conductive heat transfer within the viscous sublayer. The subsequent zone, ranging from 0.2 to 0.8 (Y+), marked by a stable thermal gradient, corresponds to a transitional or buffer region where convective effects become more pronounced, although without significant thermal stratification. The final linear increase toward the maximum value reflects the influence of thermal boundary conditions at the outer edge of the boundary layer.  
A comparative analysis of the velocity profiles, presented for the five distinct widths of the passive facade's channel, reveals a consistent parabolic velocity distribution. This classic hydrodynamic profile shape is a clear indication of the \"stack effect.\" According to this thermo-gravitational principle, warm, less-dense air rises within the cavity, generating a low-pressure zone at its base and a high-pressure zone at the top, thereby driving the upward airflow.  
The peak velocity values exhibit a directly proportional correlation with the channel width. Wider channels allow for the development of significantly higher maximum velocities. This observation suggests that channel width is a critical geometric parameter in determining the heat transfer rate through the passive facade, thereby directly affecting its thermal performance. A wider channel offers lower hydrodynamic resistance, facilitating an increased volumetric flow rate under the action of driving forces. Moreover, the analysis of the velocity gradient near the channel walls reveals a steeper slope for narrower channels. This pronounced gradient indicates higher intensity of viscous shear forces in that region, a consequence of stronger interaction between fluid layers in confined geometries. The increase in viscous shear affects the momentum transfer, which in turn impacts the heat transfer by reducing its effectiveness.  
The study brings a potentially innovative perspective by demonstrating that a larger cavity width (12 cm in this case) leads to significantly superior thermal efficiency, manifested by an outlet heat flux approximately 44 times greater compared to the 4 cm variant. This contradicts a possible initial intuition that a narrower cavity might be more efficient for convective heat transfer or that an optimal limit might exist at a smaller width. This finding offers new perspectives for the optimal design of passive facades.  
A correlation is identified between channel width, outlet temperature, mass flow rate, and heat flux. The increase in heat flux with channel width suggests a greater capacity of the facade to preheat incoming air during the cold season or to evacuate heat during the warm season. At the same time, the extremely low mass flow rates indicate a slow flow regime dominated by natural convection, characterized by relatively weak driving forces.