The design of Mechanical, Electrical, and Plumbing (MEP) systems for buildings stands as a crucial element in contemporary building design, where the optimization of MEP systems performance presents challenges, particularly in the context of complex facilities. Computational Fluid Dynamics (CFD) has appeared as an important tool to address these challenges. In this article, we delve deep into the application of CFD, employing technical language through real-world case studies. Each case study explains how CFD effectively resolves complex MEP design challenges, providing invaluable insights for MEP engineers and designers.