The commercial building engineering design world requires analysis tools that can be learned quickly while still delivering accurate and actionable results. This typically means applying rigid, application specific tools with limited system analysis flexibility. In contrast, Modelica offers a multi-domain and flexible modeling environment for building mechanical systems, but its learning curve can be daunting for new users, especially in the commercial building space where engineers juggle multiple project deadlines with short design windows. This may leave engineers wondering where to start when embarking on their first modelica modeling project. This case study reviews the process and lessons learned from a mechanical engineer’s first modelica-based plant energy model. The journey starts with selection of a modelica platform and continues through the project deliverable that evaluates the energy use of a chilled water plant, covering modelica system development complete with system controls and equipment performance matching the constructed project.