n through compressor discharge lines 17a n to the condenser wherein the gaseous refrigerant is condensed by relatively cool condensing water flowing through tubing 18 in the condenser 14 the condensed liquid refrigerant from the condenser 14 passes through the poppet valve 16 in refrigerant line 19 which forms a liquid seal to keep condenser vapor from entering the evaporator and to maintain the pressure difference between the condenser and the evaporator the liquid refrigerant in the evaporator 15a n is evaporated to cool a heat transfer fluid such as water or glycol flowing through tubing 13a n in the evaporator 15a n this chilled heat transfer fluid is used to cool a building or space or to cool a process or other such purposes the gaseous refrigerant from the evaporator 15a n flows through the compressor suction lines 11a n back to the compressors 12a n under the control of compressor inlet guide vanes 22a n the gaseous refrigerant entering the compressor 12a n through the guide vanes 22a n is compressed by the compressor 12a n through the compressor discharge line 17a n to complete the refrigeration cycle this refrigeration cycle is continuously repeated during normal operation of the refrigeration system 10 each compressor has an electrical motor 24a n and inlet guide vanes 22a n which are opened and closed by guide vane actuator 23a n controlled by the operating control system 20 the operating control system 20 may include a chiller system manager 26 a local control board 27a n for each chiller and a building supervisor 30 for monitoring and controlling various functions and systems in the building the local control board 27a n receives a signal from temperature sensor 25a n by way of electrical line 29a n corresponding.