How a system operates at design conditions is not always a good indicator of its overall annual performance. This article emphasizes controls logic and design conditions and how they can be used to optimize chiller, cooling tower and condenser pump system performance throughout the year. A software model of hour-by-hour energy use for a typical office building in three cities demonstrates the effect of different cooling seasons and wet-bulb profiles. (Results are presented in energy use [kWh]. Actual dollar savings can be estimated by assuming a blended energy rate.)