Chiller control system and method

Abstract

A method and system of dynamically controlling a water pump system that includes a water pump. The method includes determining a pressure differential at the water pump, determining a water flow rate based on the pressure differential, and determining a speed set point for the water pump. The method also includes sensing a water flow speed at the water pump, generating a pump speed control signal based on the speed set point and the water flow speed, and modulating a speed of the water pump based on the pump speed control signal.

1 . A method of dynamically controlling a water pump system including a water pump, the method comprising: 
 determining a pressure differential at the water pump;    determining a water flow rate based on the pressure differential;    determining a speed set point for the water pump;    sensing a water flow speed at the water pump;    generating a pump speed control signal based on the pump speed set point and the water flow speed; and    modulating a speed of the water pump based on the pump speed control signal.    
   
   
       2 . The method of  claim 1 , further comprising determining an efficiency of the pump based on the modulated speed.  
   
   
       3 . The method of  claim 1 , wherein determining a water flow rate comprises determining a pump power value based on a pump curve of the pump.  
   
   
       4 . The method of  claim 1 , wherein generating a pump speed control signal comprises converging the pump speed to within a predetermined range of the pump speed set point.  
   
   
       5 . The method of  claim 4 , wherein the pump has an associated design pump speed, and wherein the predetermined range is between about 0 percent and 15 percent of the design pump speed.  
   
   
       6 . The method of  claim 1 , wherein the water pump system further includes a chiller unit.  
   
   
       7 . A controller to dynamically control a water pump system including a variable speed water pump, a pump head sensor operable to sense a pressure differential at the water pump, and a water pump speed sensor operable to sense a water flow speed of the water pump, the controller comprising: 
 a flow rate module configured to determine a water flow rate based on the pressure differential;    a speed set point module configured to determine a speed set point for the water pump;    a speed control module configured to generate a pump speed control signal based on the speed set point and the water flow speed; and    a modulator configured to modulate the water pump based on the pump speed control signal.    
   
   
       8 . The controller of  claim 7 , further comprising a pump efficiency module configured to determine an efficiency of the pump based on the modulated speed.  
   
   
       9 . The controller of  claim 7 , further comprising a pump power module configured to determine a pump power value based on a pump curve of the pump.  
   
   
       10 . The controller of  claim 7 , wherein the speed control module is further configured to converge the pump speed to within a predetermined range of the pump speed set point.  
   
   
       11 . The controller of  claim 10 , wherein the pump has an associated design pump speed, and wherein the predetermined range is between about 0 percent and 15 percent of the design pump speed.  
   
   
       12 . The controller of  claim 7 , wherein the water pump system further includes a chiller unit.  
   
   
       13 . A chiller system comprising: 
 a chiller unit configured to chill a medium;    a pump coupled to the chiller unit and configured to return a medium to the chiller unit;    a variable frequency drive coupled to the pump and configured to run the pump at a selected speed; and    a controller coupled to the variable frequency drive, the controller configured to determine a flow rate generated by the pump, to determine a pump speed set point based on the flow rate, and to modulate, with the variable frequency drive, the pump speed such that the pump speed converges to within a predetermined range of the pump speed set point.    
   
   
       14 . The chiller system of  claim 13 , further comprising: 
 a supply conduit coupled to the chiller unit and configured to supply chilled medium from the chiller unit;    a temperature sensor coupled to the supply conduit and configured to sense a temperature of the chilled medium;    a return conduit coupled to the chiller unit and configured to return medium to the chiller unit; and    a second temperature sensor coupled to the return conduit and configured to sense a temperature of the returned medium.    
   
   
       15 . The chiller system of  claim 14 , wherein the controller is further configured to determine a pump power value based on a difference of temperatures sensed by the respective temperature sensors.  
   
   
       16 . The chiller system of  claim 13 , wherein the controller is further configured to determine an efficiency of the pump based on the modulated speed.  
   
   
       17 . The chiller system of  claim 13 , wherein the controller is further configured to determine a pump power value based on a pump curve of the pump.  
   
   
       18 . The chiller system of  claim 13 , wherein the pump has an associated design pump speed, and wherein the predetermined range is between about 0 percent and 15 percent of the design pump speed.