[automatic control system of liquid chillers]

Abstract

An automatic control system of the invention comprises a plurality of liquid chillers, a principal controller, and a plurality of secondary controllers respectively connected to the liquid chillers and the principal controller. The automatic control system stores a British Thermal Unit (BTU) table that includes a predetermined high load limit parameter and a predetermined low load limit parameter varying according to the number of liquid chillers in operation. The principal controller compares an actual load of the currently operating liquid chillers with the high and/or low load limit parameter to determine an adequate number of liquid chillers that have to be operated. By evaluating the number of liquid chillers currently operating, the principal controller then determines whether liquid chillers have to be switched on or switched off through the secondary controllers.

1 . An automatic control system of liquid chillers, comprising: 
 a plurality of liquid chillers for producing chilled liquid; and    a principal controller, operating from data of a British Thermal Unit (BTU) table, wherein the principal controller compares an actual load of chilled liquid production with a load limit of the BTU table to determine an adequate number of liquid chillers to be operated, and after having compared a number of currently operating liquid chillers with the adequate number of liquid chillers to be operated, the principal controller accordingly outputs a command signal to command an on-switch, off-switch, or no-operation of the liquid chillers.    
     
     
         2 . The system of  claim 1 , further including a secondary controller that receives the command signal to either switch on or switch off at least one of the liquid chillers.  
     
     
         3 . The system of  claim 1 , wherein the principal controller comprises a plurality of control units that are alternately given a control right.  
     
     
         4 . The system of  claim 3 , wherein the control units are programmable logic circuits.  
     
     
         5 . The system of  claim 1 , wherein the BTU table includes a high load limit; if the actual load in chilled liquid production is higher than the high load limit, additional liquid chillers are switched on.  
     
     
         6 . The system of  claim 1 , wherein the BTU table includes a low load limit; if the actual load in chilled liquid production is lower than the low load limit, currently operating liquid chillers are switched off.  
     
     
         7 . The system of  claim 1 , wherein the BTU table further includes an on-switch delay time that allows a confirmation that the outputted command signal commanding an on-switch corresponds to a steady need of capacity increase and not due to erroneous noise signals.  
     
     
         8 . The system of  claim 1 , wherein the BTU table further includes an off-switch delay time that allows a confirmation that the outputted command signal commanding an off-switch corresponds to a steady capacity decrease and not due to erroneous noise signals.  
     
     
         9 . The system of  claim 1 , wherein an on-switch/off-switch time interval is automatically set.  
     
     
         10 . A control method of liquid chillers, comprising: 
 comparing an actual load of chilled liquid production with a predetermined high and low load limit of the liquid chillers to determine an adequate number of liquid chillers to be operated;    comparing the adequate number of liquid chillers to be operated with a number of currently operating liquid chillers;    if the adequate number of liquid chillers to be operated is greater than the number of currently operating liquid chillers, at least one additional liquid chiller is switched on;    if the adequate number of liquid chillers to be operated is less than the number of currently operating liquid chillers, at least one currently operating liquid chiller is switched off; and    if the adequate number of liquid chillers to be operated is equal to the number of currently operating liquid chillers, the currently operating liquid chillers are maintained.    
     
     
         11 . The method of  claim 10 , wherein if the adequate number of liquid chillers to be operated is greater than the number of currently operating liquid chillers, an additional liquid chiller is switched on after an on-switch delay time has elapsed, the on-switch delay time being used to confirm whether there is a steady need of capacity increase.  
     
     
         12 . The method of  claim 10 , wherein if the adequate number of liquid chillers to be operated is less than the number of currently operating liquid chillers, a currently operating liquid chiller is switched off after an off-switch delay time has elapsed, the off-switch delay time being used to confirm whether there is a steady capacity decrease.