Emergency Diesel Generators (EDGs) are vital to nuclear power plant safety. This paper addresses a persistent operational challenge where an EDG unit experienced recurrent high-temperature alarms in its cooling circuits, a problem that eluded conventional diagnostic methods. To identify the root cause, a high-fidelity 3D Computational Fluid Dynamics (CFD) model was developed. This model integrated the heat exchanger's detailed geometry within the complex layout of the entire EDG room, enabling a holistic analysis of the coupled fluid flow and thermal environment. The analysis identified aerodynamic short-circuiting as the primary driver of the thermal issue. Simulations revealed that unsealed installation gaps around the air-cooled heat exchanger created a significant recirculation path for hot exhaust air. This phenomenon was quantified to elevate the cooler's inlet air temperature by 5°C, consequently reducing the system's heat rejection capacity by approximately 11%. This crucial finding shifted the diagnostic focus from individual component degradation to the critical system-level interaction between the machinery and its architectural enclosure. The efficacy of this simulation-driven approach was decisively validated when subsequent on-site retrofits, specifically sealing the identified gaps, completely resolved the long-standing overheating problem. This successful intervention confirmed the predictive accuracy of the CFD model and demonstrated its value as a powerful tool for diagnosing complex thermo-fluid system issues.

Building Aerodynamics,CFD,Emergency Diesel Generator,Hot Air Recirculation,Industrial Ventilation