CFD-Driven Passive Cooling and Renewable Retrofits for Nearly Net-Zero University Buildings in a Hot–Humid Climate

Achieving net-zero energy and zero-emission buildings is a critical pathway toward decarbonizing the built environment, particularly in cooling-dominated regions where operational energy demand remains exceptionally high. Existing university buildings in hot–humid climates face significant challenges due to intensive cooling requirements, limited passive cooling potential, and the economic burden associated with large-scale renewable energy deployment. This study develops and evaluates a climate-responsive retrofit framework that integrates sequential energy optimization, CFD-based passive-cooling analysis, and on-site renewable energy systems to transform an operational university building in Jeddah, Saudi Arabia, into a nearly net-zero energy building (NZEB). A high-fidelity DesignBuilder–EnergyPlus model was calibrated using three years of monthly measured electricity consumption data, achieving strong agreement with utility records (NMBE = 2.19%, CV(RMSE) = 7.93%). The proposed framework prioritizes demand-side load reduction through optimized HVAC operation, envelope enhancement, daylight-responsive lighting control, natural ventilation, and Passive Downdraught Evaporative Cooling (PDEC) before renewable energy integration. The baseline building exhibited an Energy Use Intensity (EUI) of 613 kWh/m2·year, with cooling accounting for approximately 70% of total electricity consumption. Sequential optimization reduced annual energy demand by 58%, while CFD-supported passive cooling strategies provided an additional 17% reduction in cooling energy and improved indoor airflow performance. Crucially, nearly 80% of total energy savings were realized prior to photovoltaic (PV) deployment. A 1586-kW rooftop photovoltaic system subsequently offset the residual annual demand, achieving a nearly net-zero annual energy balance. Over 25 years, the proposed retrofit pathway reduced life-cycle costs from 7.51 million SAR to 3.13 million SAR. The findings demonstrate that climate-responsive demand reduction is the primary enabler of NZEBs in hot–humid regions, substantially reducing renewable energy requirements and long-term economic costs while providing a scalable pathway to decarbonize existing campus infrastructure.