What is the difference between chilled water variable flow system and fixed flow system ?

VARIABLE FLOW IS USED FOR VARIABLE LOAD , WHILE FIXED FLOW USED FOR STEADY LOAD. 

In Chilled Water variable flow system's , Chilled Water is supplied according to the load. Flow is varied by varying the speed of motor. For this Variable Frequency Drives(VFD) are used.

In fixed flow systems, Chilled water is supplied regularly irrespective of the load, hence a lot of energy will go wasted