Assessment of Floor-Level Impact on Natural Ventilation and Indoor Thermal Environment in Hot–Humid Climates: A Case Study of a Mid-Rise Educational Building

The rapid urbanization of developing cities has intensified the challenge of maintaining thermal comfort in buildings, particularly in hot–humid climates. This study investigates the impact of floor level on airflow patterns and indoor temperatures in multi-purpose mid-rise buildings in Onitsha, Nigeria, where increasing urban density and frequent power outages necessitate effective passive cooling strategies. Through a mixed-method approach combining empirical measurements, computational fluid dynamics (CFD) simulations, and thermal performance analysis, the research examined variations in ventilation rates and temperature distributions across different floor levels of a six-story educational building over an annual cycle, focusing on the hottest (27 February), coldest (28 December), most windy (3 April), and least windy (17 September) days. Results revealed distinct floor-level ventilation patterns: upper floors (fourth–fifth) achieved 39–40 air changes per hour (ACH) during hot periods while maintaining temperatures of 30–35 degrees Celsius (°C); middle floors (second–third) showed moderate ventilation (15–22 ACH) but experienced heat accumulation (35–42 °C); and lower floors reached 20 ACH during windy conditions. Temperature stratification varied from 15 °C between floors across the entire building during peak conditions to 7 °C during windy periods. Stack-driven ventilation in upper floors contributed to temperature reductions of up to 3 °C, while wind-driven ventilation promoted uniform temperature distribution across all levels. These findings informed floor-specific design recommendations: hybrid ventilation systems with automated controls, strategic architectural features including a minimum floor level area of 15% for the central atrium, and comprehensive monitoring systems with six temperature sensors per floor. This study provides evidence-based strategies for optimizing thermal comfort in tropical urban environments, particularly valuable for designing energy-efficient buildings in rapidly developing cities with hot-humid climates.