In 2010, looking for a way to improve plant performance, HGA sat down to write an equation to describe the total energy use of a chiller plant. The plant at hand consisted of three different chillers, only one of which used a variable-speed drive. Thirty pages later, HGA had a clearer understanding of the degrees of freedom available to impact energy use, the interactions between components, and a realization that the performance ultimately came down to how engineers respond to two independent parameters: 1) system load; and 2) Outdoor air wet bulb temperature (Toawb). For any given load and Toawb, there is a most efficient set of operating parameters that result in the lowest energy use for the entire the plant. This is the Best Efficiency Point (BEP).