Thermal Mass–Ventilation Interaction in Naturally Ventilated School Classrooms: A Building Performance Simulation Study Evaluated Against Field Measurements in South East Nigeria

Field measurements undertaken in six paired primary school classrooms in Anambra State, Nigeria, previously demonstrated that interlocking compressed earth block (ICEB) classrooms maintained significantly lower occupied-hour temperatures than adjacent sandcrete block (SCB) classrooms. This study applies DesignBuilder/EnergyPlus simulation, evaluated against field measurements, to investigate the physical mechanisms underlying this observed thermal advantage and to explore seasonal performance beyond the period accessible through field monitoring. Simulation models were developed using literature-derived thermophysical properties and validated against field measurements collected at Awkuzu Primary School on 2 July 2024. Model accuracy was assessed using ASHRAE Guideline 14 metrics. The ICEB model achieved NMBE of −6.4% and CV(RMSE) of 6.8%, satisfying both recommended thresholds. The SCB model achieved CV(RMSE) of 15.6%, while NMBE of −14.0% marginally exceeded the recommended threshold because of conservative TMYx boundary conditions. Results indicate that the superior wet-season performance of ICEB classrooms is attributable to the interaction between high thermal mass (μ = 0.31; φ = 9.1 h) and continuous cross-ventilation. Parametric crossover simulations demonstrated that ventilation was the dominant cooling mechanism, while ICEB wall thermal mass provided an additional independent thermal benefit of approximately 0.31 °C. This material contribution is secondary in magnitude to the ventilation effect and is not presented as a standalone practical advantage. Dry-season simulations suggested a possible reversal of performance under near-calm harmattan conditions; however, the magnitude and direction of this effect remain uncertain because of EPW boundary-condition limitations. The findings suggest that classroom thermal performance depends on the interaction between envelope thermal mass and ventilation configuration rather than material properties alone and highlight the potential importance of controllable ventilation in naturally ventilated educational buildings in tropical climates.