States that over the past 10 years, several manufacturers have introduced chillers with rotary screw compressors and have moved away from older reciprocating technology. Claims that rotary screw compressor technology offers many benefits over reciprocating types, including higher reliability and improved performance. Describes the two rotary screw compressor designs, the twin and the single. Describes their installation, trouble shooting practice and maintenance. Concludes that advanced machining capability coupled with innovative design opportunities will allow continuous design improvements resulting in more energy efficient machines in the future.