Shading–Ventilation Trade-Offs in Courtyard-Cluster Rural Buildings: A CFD–UTCI Assessment of Courtyards and Covered Semi-Open Spaces in Hot-Humid South China

Courtyard-cluster layouts are common in rural public buildings in hot-humid regions, but their open-space types remain poorly quantified. We assessed a completed elderly-care center in Shaoguan, South China, using steady-state RANS CFD (simpleFoam, standard k–ε, OpenFOAM 8), porous-media vegetation, Solar Cal-based mean radiant temperature (MRT), and pedestrian-level Universal Thermal Climate Index (UTCI). Published component-level validation was used to assess toolchain reliability. Simulations represented peak heat stress at noon on 24 July (air temperature 30.3 °C, relative humidity 69%, southwesterly wind 2.9 m/s). Relative to an unobstructed reference (MRT 60.1 °C; UTCI 40.0 °C), architectural open spaces reduced mean MRT by 21.2 °C (35%) and UTCI by 5.3 °C (13%). Covered, laterally open grey spaces were coolest (mean MRT 34.63 °C; UTCI 33.61 °C), whereas open courtyards were warmer (41.79 °C; 35.34 °C) but 18% better ventilated (0.87 versus 0.74 m/s) and served as ventilation nodes. With uniform air temperature and humidity, UTCI variation was strongly associated with MRT (R = 0.989) and weakly with wind speed (R = −0.182). These scenario-bounded results support a shade-first strategy in which courtyards supply ventilation to adjacent covered spaces.