vanes 94 and output 92 controls the speed of a motor 96 that drives compressing element 74 varying the output capacity of a chiller by varying the speed of its compressor and or adjusting the position the compressor 39 s inlet guide vanes are well known to those skilled in the art thus control unit 82 is schematically illustrated to encompass a myriad of control circuits including but not limited to microcomputers programmable controllers integrated circuits discrete circuitry and various combinations thereof it should also be appreciated by those skilled in the art that the number and type of inputs and outputs might vary depending on the desired operating features of the specific chiller system being controlled in a preferred embodiment control 82 modulates the position of inlet guide vanes 94 to maintain a temperature at tube sensor 80 or 80 u2032 that is just marginally above 32 degrees fahrenheit this allows the average lcwt as sensed by sensor 78 to be safely maintained at 36 degrees or lower moreover sensor 80 or 80 u2032 being properly positioned allows the refrigerant temperature as sensed by refrigerant sensor 76 to be safely lowered below 29 degrees and perhaps down to 27 degrees or lower thus chiller 10 normally operates in response to feedback 88 from tube sensor 80 or 80 u2032 as opposed to feedback 86 from lcwt sensor 78 also if the temperature at the tube sensor 80 or 80 u2032 drops below 33 degrees or below some other predetermined limit control 82 shuts down the operation of chiller 10 to prevent feeding the chilled water in some embodiments feedback 86 from lcwt sensor.