Cleanroom energy benchmarking data shows that there is a variety of chiller plant designs and operating efficiency for cleanroom facilities. Chiller plants usually serve cleanroom facility and adjacent spaces simultaneously and use significant energy and water. The efficiency level of the overall chiller plant is influenced by the efficiency of individual components and subsystems in the plant. Major components include chillers, water pumps, and cooling tower or condenser fans. Figure 1 and Figure 2 show chiller energy end-use in typical semiconductor cleanroom facilities. In both cases, the portion of chiller energy usage was significant. It is, therefore, important to design, select, operate, and control chillers to achieve high efficiency and to lower life-cycle costs for cleanrooms and their adjacent spaces.