Chiller system with low capacity controller and method of operating same

Abstract

A method ( 126 ) and a low capacity controller ( 28 ) enable a chiller system ( 20 ) to operate below a minimum allowable capacity. The chiller system ( 20 ) includes a chiller ( 40 ) and a chiller fluid loop ( 30 ), having a supply line ( 36 ) for conveying a chiller fluid ( 34 ) from the chiller ( 40 ) and a return line ( 38 ) for returning the chiller fluid ( 34 ) to the chiller ( 40 ). A capacity demand for the chiller ( 40 ) is determined. When the capacity demand is less than a minimum allowable capacity of the chiller ( 40 ), the chiller fluid ( 34 ) is routed from the return line ( 38 ) to a heat exchanger ( 96 ) of the low capacity controller ( 28 ) where the chiller fluid ( 34 ) is warmed and returned to the return line ( 38 ). The warmed chiller fluid ( 34 ) establishes a false capacity demand, detectable at the chiller ( 40 ), that is at least the minimum allowable capacity.

1 . A method of operating a chiller system, said chiller system including a chiller and a fluid loop, said fluid loop including a supply line for conveying a fluid from said chiller and a return line for returning said fluid to said chiller, said method comprising: 
 determining a capacity demand for said chiller; and    when said capacity demand is less than a minimum allowable capacity of said chiller, warming said fluid in said return line to establish a false capacity demand, detectable at said chiller, that is at least said minimum allowable capacity.    
     
     
         2 . A method as claimed in  claim 1  wherein said determining operation comprises: 
 measuring a supply temperature of said fluid in said supply line;    measuring a return temperature of said fluid in said return line; and    ascertaining a difference between said return temperature and said supply temperature to determine said capacity demand.    
     
     
         3 . A method as claimed in  claim 2  wherein said determining operation further comprises calculating said capacity demand as a function of a flow rate of said fluid and said difference between said return temperature and said supply temperature.  
     
     
         4 . A method as claimed in  claim 1  wherein said chiller system further includes a heat exchanger in communication with said return line, said fluid is a first fluid, and said warming activity includes transferring heat from a second fluid in said heat exchanger to said first fluid.  
     
     
         5 . A method as claimed in  claim 4  wherein said second fluid is condenser fluid, and said method further comprises transporting said condenser fluid to said heat exchanger via a condenser fluid loop interposed between said chiller and a cooling tower of said chiller system.  
     
     
         6 . A method as claimed in  claim 1  wherein said fluid is a first fluid, and said method further comprises: 
 routing a portion of said first fluid in said return line through a secondary loop, said secondary loop being in heat exchanging relation with a second fluid; and    returning said portion of said first fluid back to said return line via said secondary loop.    
     
     
         7 . A method as claimed in  claim 6  wherein said returning activity comprises modulating a return of said portion of said first fluid to said return line.  
     
     
         8 . A method as claimed in  claim 6  wherein said secondary loop is coupled with said supply line, and said returning operation comprises: 
 conveying said portion of said first fluid into said supply line; and    routing said portion of said first fluid to said return line via a bypass valve of said chiller system interposed between said supply line and said return line.    
     
     
         9 . A method as claimed in  claim 6  wherein said secondary loop is coupled with said return line, and said returning operation comprises routing said portion of said first fluid from said secondary loop directly into said return line.  
     
     
         10 . A method as claimed in  claim 9  further comprising regulating a flow of said portion of said first fluid into said return line.  
     
     
         11 . A method as claimed in  claim 6  further comprising: 
 selectively operating said chiller system in a chiller bypass mode;    when in said chiller bypass mode, deactivating said chiller;    when in said chiller bypass mode, transporting said portion of said first fluid through said secondary loop to cool said portion of said first fluid; and    when in said chiller bypass mode, returning said portion of said first fluid from said secondary loop to said supply line.    
     
     
         12 . A method as claimed in  claim 1  wherein said warming activity comprises adjusting a volume of said fluid warmed in response to said capacity demand.  
     
     
         13 . A method as claimed in  claim 1  further comprising when said capacity demand is greater than said minimum allowable capacity, discontinuing said warming activity.  
     
     
         14 . A chiller system for providing a fluid to a heat exchange unit comprising: 
 a chiller;    a pump for forcing said fluid through said chiller;    a fluid loop having a supply line for conveying said fluid from said chiller to said heat exchange unit, and a return line for returning said fluid from said heat exchange unit to said chiller;    means for determining a capacity demand for said chiller; and    when said capacity demand is less than a minimum allowable capacity of said chiller, means for warming said fluid in said return line to establish a false capacity demand, detectable at said chiller, that is at least said minimum allowable capacity.    
     
     
         15 . A chiller system as claimed in  claim 14  wherein said determining means comprises: 
 a first temperature sensor for measuring a supply temperature of said fluid in said supply line;    a second temperature sensor for measuring a return temperature of said fluid in said return line;    means for determining a flow rate of said fluid in said fluid loop; and    means for calculating said capacity demand as a function of said flow rate and a difference between said return temperature and said supply temperature.    
     
     
         16 . A chiller system as claimed in  claim 14  wherein said warming means comprises: 
 a heat exchanger; and    a secondary loop in communication with said return line and in heat exchanging relation with said heat exchanger, a portion of said fluid in said return line being routed through said secondary loop to warm said fluid in said heat exchanger when said capacity demand is less than said minimum allowable capacity, and said portion of said fluid being returned to said return loop via said secondary loop when said fluid is warmed.    
     
     
         17 . A chiller system as claimed in  claim 16  wherein: 
 said chiller system further comprises a bypass valve interposed between said supply line and said return line; and    said secondary loop comprises: 
 a supply conduit for transporting said portion of said fluid from said return line toward said heat exchanger;  
 a return conduit coupled with said supply line for conveying said portion of said fluid from said heat exchanger; and  
 a modulating valve in fluid communication with said return conduit for modulating a return of said portion of said fluid to said return line, said portion of said fluid being returned to said return line via said bypass valve.  
   
     
     
         18 . A chiller system as claimed in  claim 16  wherein: 
 said secondary loop comprises: 
 a supply conduit for transporting said portion of said fluid from said return line toward said heat exchanger;  
 a return conduit coupled with said return line for returning said portion of said fluid from said heat exchanger to said return line;  
 a modulating valve in fluid communication with said return conduit for modulating a return of said portion of said fluid to said return line; and  
   said chiller system further comprises means for regulating a flow of said portion of said first fluid into said return line.    
     
     
         19 . A chiller system as claimed in  claim 18  wherein said regulating means is a pump interposed along said return conduit.  
     
     
         20 . A chiller system as claimed in  claim 18  wherein said regulating means is a three-way valve positioned at a junction of said return conduit with said return line.  
     
     
         21 . A chiller system as claimed in  claim 16  further comprising: 
 a cooling tower; and    a condenser fluid loop interposed between said chiller and said cooling tower, said second fluid loop being routed through said heat exchanger, and said condenser fluid loop conveying a second fluid through said heat exchanger when said capacity demand is less than said minimum allowable capacity such that heat from said second fluid is transferred to said portion of said fluid.    
     
     
         22 . A chiller system as claimed in  claim 21  further comprising: 
 means for selectively operating said system in a chiller bypass mode;    means for, in said chiller bypass mode, deactivating said chiller;    means for, in said chiller bypass mode, transporting said portion of said fluid through said secondary loop for enabling heat transfer in said heat exchanger between said condenser fluid loop and said secondary loop to cool said portion of said fluid; and    means for, in said chiller bypass mode mode, returning said portion of said fluid from said secondary loop to said supply line.    
     
     
         23 . A low capacity controller for a chiller system, said chiller system including a chiller and a first fluid loop, said first fluid loop including a supply line for conveying a chiller fluid from said chiller and a return line for returning said chiller fluid to said chiller, said chiller being operable above a minimum allowable capacity for said chiller, and said low capacity controller comprising: 
 a heater;    a secondary loop interposed between said first fluid loop and said heater;    means for enabling a transfer of said chiller fluid through said heater via said secondary loop when a capacity demand is less than said minimum allowable capacity, said chiller fluid being warmed at said heater; and    means for returning said chiller fluid from said heater to said return line via said secondary loop.    
     
     
         24 . A low capacity controller as claimed in  claim 23  wherein said chiller system further includes a cooling tower and a condenser fluid loop interposed between said chiller and said cooling tower, said condenser fluid loop carrying a condenser fluid, and said low capacity controller further comprises means for enabling a transfer of said condenser fluid through said heater via said condenser fluid loop when said capacity demand is less than said minimum allowable capacity for said chiller.  
     
     
         25 . A low capacity controller as claimed in  claim 23  wherein said returning means comprises a modulating valve for modulating a return of said chiller fluid to said return line.  
     
     
         26 . A low capacity controller as claimed in  claim 23  wherein said chiller system includes a bypass valve interposed between said supply line and said return line, and said secondary loop comprises: 
 a supply conduit for transporting said portion of said fluid from said return line toward said heat exchanger;    a return conduit coupled with said supply line for conveying said portion of said fluid from said heat exchanger, said portion of said fluid being returned to said return line via said bypass valve.    
     
     
         27 . A low capacity controller as claimed in  claim 23  wherein said returning means adjusts a volume of said chiller fluid returned to said return line in response to said capacity demand.