Chiller control apparatus

Abstract

A chiller control apparatus increases or decreases chillers in order to efficiently operate an entire chiller system. When the number of chillers increases, an insufficient load value calculation unit calculates an insufficient amount of a load for a required load. Then, using a COP obtained according to an operating environment of the chiller, a chiller-to-be-operated selection unit selects, from among stopped chillers, a chiller having the highest COP when operated with an insufficient amount of a load, as the chiller to be subjected to stage increase. Further, when the number of chillers decreases, an operation pattern extraction unit extracts operation patterns that are combinations of chillers to be operated according to the required load. Then, a chiller-to-be-stopped selection unit obtains a COP of the entire chiller system for each operation pattern, using the COP obtained according to the operating environment of the chiller, and selects a chiller subjected to stage decrease based on the operation pattern corresponding to the highest COP.

1 . A chiller control apparatus for controlling a plurality of chillers and supplying cold or heat, the chiller control apparatus comprising:
 a chiller selection unit configured to select the chiller to be operated from among the plurality of chillers according to a required load; and   an operation command unit configured to output an operation signal corresponding to the required load, to the chiller selected by the chiller selection unit,   wherein the chiller selection unit comprises:   a number-of-chillers change determination unit configured to determine based on the required load whether to change the number of currently selected chillers; and   a chiller determination unit configured to determine a chiller whose operation state is to be changed, based on a relationship between a load of each chiller and an efficiency index value acquired in advance and on the required load when the number of chillers is changed based on a result of determination by the number-of-chillers change determination unit.   
     
     
         2 . The chiller control apparatus according to  claim 1 , wherein the chiller determination unit comprises:
 an insufficient load value calculation unit configured to obtain an insufficient load value for each currently operating chiller by subtracting the required load from an optimal-load-range high value sum that is a sum of optimal-load-range high values, each of the optimal-load-range high values being set for each chiller as a threshold value of a load at a high load side that is an allowed efficiency range, in a case that the number-of-chillers change determination unit determines to increase the number of chillers; and   a chiller-to-be-operated selection unit configured to obtain, for each of chillers that are currently stopped, an efficiency index value when the chiller is operated with the insufficient load value, based on the insufficient load value obtained by the insufficient load value calculation unit and the relationship between the load and the efficiency index value, and select a chiller indicating the highest efficiency index value as a chiller to be operated.   
     
     
         3 . The chiller control apparatus according to  claim 1 , wherein the chiller determination unit comprises:
 a stage increase operation pattern extraction unit configured to obtain all chiller operation patterns of combinations of chillers selected from currently stopped chillers and currently operating chillers, in a case that the number-of-chillers change determination unit determines to change the number of chillers; and   a chiller-to-be-operated selection unit configured to obtain efficiency index values for all the chiller operation patterns obtained by the stage increase operation pattern extraction unit and select a chiller corresponding to the chiller operation pattern making the efficiency index value highest, as a chiller to be operated.   
     
     
         4 . The chiller control apparatus according to  claim 2 , wherein, in a case that there are a plurality of selectable chillers, the chiller-to-be-operated selection unit is configured to acquire an operation time of the corresponding chiller and selects a chiller having the shortest operation time. 
     
     
         5 . The chiller control apparatus according to  claim 1 , wherein the chiller determination unit comprises:
 a stage decrease operation pattern extraction unit configured to obtain all chiller operation patterns of combinations of chillers whose operation is kept by stopping one chiller of the currently operating chillers in a case that the number-of-chillers change determination unit determines to decrease the number of chillers; and   a chiller-to-be-stopped selection unit configured to obtain an entire efficiency index value for all the chiller operation patterns obtained by the stage decrease operation pattern extraction unit, and select a chiller corresponding to the chiller operation pattern making the efficiency index value highest, as a chiller to be stopped.   
     
     
         6 . The chiller control apparatus according to  claim 1 , wherein the chiller determination unit comprises:
 an excess load value calculation unit configured to obtain an excess load value for each currently operating chiller by subtracting from the required load, an optimal-load-range low value sum obtained by summing optimal-load-range low values, each of the optimal-load-range low values being set for each chiller as a threshold value of a load at a low load side that is an allowed efficiency range, in a case that the number-of-chillers change determination unit determines to decrease the number of chillers; and   a chiller-to-be-stopped selection unit configured to obtain, for each of currently operating chillers, an efficiency index value when the chiller is operated with the excess load value, based on the excess load value obtained by the excess load value calculation unit and the relationship between the load and the efficiency index value, and select a chiller indicating the lowest efficiency index value as a chiller to be stopped.   
     
     
         7 . The chiller control apparatus according to  claim 5 , wherein in a case that there are a plurality of selectable chillers, the chiller-to-be-stopped selection unit is configured to acquire an operation time of the corresponding chiller and select a chiller having the longest operation time.