For many reasons, which will be briefly reviewed in this article, the air cooled packaged chiller is a very popular choice for HVAC designers in capacitiesup to and slightly above 1,900 kW (550 tons). Until recently, the only compressor types commonly available in air cooled packaged chillers across thatentire range were of the positive displacement type. By contrast, for nearly 100 years, the efficiency and other inherent advantages of centrifugal compressorshave made them a popular compressor choice in water cooled packaged chillers with capacities as low as 350 kW (100 tons). This article will brieflyexplore the history of centrifugal compressors when applied in air cooled chiller systems. It will also explain how recent market influences, advances incentrifugal compressor technology, and even new refrigerant choices have coincided to make centrifugal compressors a viable application option for today'sHVAC designer choosing to use air cooled packaged chillers.