A numerical analysis is performed for the three-dimensional, turbulent flow of air in a thyristor valve hall located at the Dorsey Converter Station, owned and operated by Manitoba Hydro. The goal of this analysis was to determine the configurations that result in increased air-side cooling effectiveness in the valve hall. The governing equations are solved using the Computational Fluid Dynamics (CFD) code CFX-5. This computer code uses a finite volume method of solution and is based on a finite element approach for representing the geometry. The effects of inlet and outlet opening geometry, inlet air mass flow rate, and inlet air angle on the thermal performance for the air-side cooling of the thyristor valve hall geometry are examined.