Adaptive Thermal Comfort Assessment in Mixed-Mode Office Buildings Under Current and Future Sub-Saharan Tropical Hot and Dry Climate Scenarios

Mixed-mode offices in sub-Saharan hot semi-arid climates face growing thermal stress, yet long-term evidence remains scarce. This study addresses this gap via a stress-test framework (RCP8.5) applied to a compressed earth bricks office in Ouagadougou, Burkina Faso. A calibrated DesignBuilder/EnergyPlus model evaluated four strategies—free-running (FR), natural ventilation (NV), mixed-mode (MM), and fully air-conditioned (AC)—under current (2023) and future horizons (2030, 2060, 2090). Thermal comfort was assessed using ASHRAE-55 adaptive (80%) for FR, NV, and MM, and PMV-PPD for AC. Results show that outdoor temperatures rise by +0.73 °C (2030), +2.6 °C (2060), and +4.71 °C (2090). Passive-only strategies maintain zero energy but show severely growing discomfort. Under AC27, energy demand reaches 282.6 kWh/m2·year by 2090. MM27 reduces discomfort from 9.8% (2023) to 28.1% (2090) while consuming about half the energy of full AC (124.7 kWh/m2·year by 2090), corresponding to an AC/MM energy ratio of 1.9 to 2.3 times. The share of occupied hours with windows open falls below 50% already in 2023, and below 30% between 2030 and 2060—a transition toward cooling-dominated behaviour not previously quantified for the Sudano-Sahelian zone. These findings support mixed-mode as a climate-contingent strategy for sub-Saharan offices, though validation across multiple zones and typologies is needed.