The Series R(tm) air cooled liquid chiller, model RTAC, is available in capacities from 140 to 500 tons. One feature is the Helirotor(tm) direct drive, low-speed rotary screw compressor. The unit is designed to meet or exceed ASHRAE 90.1 for energy efficiency and operates with HFC-134a in ambient temperatures from 0 degrees to 125 degrees F.