Numerical Assessment of the Thermal and Ventilation Performance of an Earth–Air Heat Exchanger Coupled with a Solar Chimney for Passive Conditioning of Dwellings in a Warm–Humid Climate

Passive cooling strategies are essential to curbing the growing air-conditioning demand of dwellings in warm–humid regions. This work presents a Computational Fluid Dynamics (CFD) study, carried out with the open-source code OpenFOAM, of a passive system that couples an earth–air heat exchanger (EAHE) with a solar chimney (SC) serving a room-representative cavity, i.e., the coupled EAHE–SC device is analyzed together with the room it conditions. The methodology was built progressively: (i) a transient conduction sub-model (laplacianFoam) characterized the thermal inertia of the soil around the buried duct; (ii) a parametric study of eight coupling geometries identified the best relative position of the EAHE and the SC; (iii) three configurations—the complete system, the EAHE + cavity system, and the bare cavity—were solved under identical numerical conditions with the buoyancy-driven solvers of OpenFOAM and the k–ε turbulence model with the Boussinesq approximation; and (iv) the complete system was evaluated for a representative hot and a representative cold design day through a section-based post-processing of the ventilation and thermal-energy indicators. Over the four-day period simulated, the soil behaved as a stable thermal reservoir with no depletion. At the design condition, the complete system reached a mean cavity temperature of 33.2 °C, 8.32 air changes per hour (ACH) and 67.0 W of thermal power removed from the cavity, against 34.4 °C, 2.01 ACH and 4.56 W for the bare cavity; coupling the chimney raised ventilation by 94.8% and 313.9% relative to the EAHE-only and bare-cavity cases, respectively. The design-day comparison showed a marked climate-dependent response: on the hot day the EAHE dominated (air cooled by 5.75 °C, 2.51 ACH), whereas on the cold day the exchanger remained nearly neutral (+0.19 °C) and ventilation dropped to 0.69 ACH, lowering the cavity temperature to 24.1 °C. The results indicate a complementary, mutually reinforcing behavior—the coupled system removes more heat and renews more air than either device does on its own—for the design conditions analyzed.