Systems and methods for reducing energy consumption of a chilled water distribution system

Abstract

A chilled water distribution system includes a chilled water loop in fluid communication with a plurality of buildings and also in fluid communication with a plurality of chiller stations. A monitoring and control system communicates with one of the chiller stations, hereinafter referred to as a. “controlled” chiller station because it is configured with one or more variable frequency drives that are controlled by the monitoring and control system to modulate the speed of at least one chiller station component such as, but not limited to, a pump or a fan. By way of this modulation process, a differential pressure of the chilled water loop may be maintained in a “sweet spot” so as to optimize chiller station output while minimizing chiller station energy consumption.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A distributed process chilled water system comprising:
 a supply line having a supply line pressure sensor;   a return line having a return line pressure sensor, the supply line pressure sensor and the return line pressure sensor cooperating to provide a differential pressure between the supply line and the return line;   a plurality of buildings, each building having a building automation system controller, each building in fluid communication with the return and supply lines, the controllers communicatively networked together;   a plurality of chiller stations comprising at least one base chiller station, each chiller station in fluid communication with the return and supply lines, the chiller stations communicatively networked together, at least one of the chiller stations in communication with at least one of the buildings; and   an operating system operable to process machine-readable instructions, the opera system in communication with at least the e base chiller station, the operating system configured to receive a signal indicative of the differential pressure, the operating system further configured, based on the differential pressure, to determine whether to modulate a pump speed of the base chiller station, bring another chiller online or take another chiller offline to maintain the differential pressure within a desired range.   
     
     
         2 . The system of  claim 1 , wherein the base chiller station includes at least one chilled water pump coupled to a variable frequency drive. 
     
     
         3 . The system of  claim 1 , wherein the operating system modulates the pump speed of the base chiller station by communicating instructions to the variable speed drive. 
     
     
         4 . The system of  claim 1 , wherein the base chiller station includes at least one chiller operable to supply and receive water from at least one cooling tower. 
     
     
         5 . The system of  claim 1 , wherein the operating system includes one or more relational control algorithms for determining whether to modulate the pump speed of the base chiller station. 
     
     
         6 . The system of  claim 1 , wherein the operating system determines to bring another chiller online when an actual differential pressure exceeds a maximum set point pressure. 
     
     
         7 . The system of  claim 1 , wherein the operating system determines to take another chiller offline when an actual differential pressure falls below a minimum set point pressure. 
     
     
         8 . A method for controlling a chilled water distribution system, the method comprising:
 determining a real-time differential pressure at a selected location within a chilled water loop of the distribution system;   monitoring a real-time pump speed of a base chiller station that includes a variable frequency drive coupled to a chilled water pump;   determining an energy load for a plurality of buildings served by the chilled water loop;   modulating the pump speed of the base chiller station to approximately stay within a desired range of pre-determined set point differential pressures of the chilled water loop; and   determining whether to change the capacity of distribution system by bringing a chiller of another chiller station either online or offline.   
     
     
         9 . The method of  claim 8 , further comprising calculating a desired pump speed for at least one other chiller station based on the real-time differential pressure, real-time pump speed and energy load for the plurality of buildings. 
     
     
         10 . The method of  claim 8 , wherein modulating the pump speed of the base chiller station coincides with bringing a chiller of another chiller station either online or offline. 
     
     
         11 . The method of  claim 8 , wherein modulating the pump speed of the base chiller station include providing instructions to a variable speed drive coupled to the chilled water pump. 
     
     
         12 . The method of  claim 8 , wherein modulating the pump speed of the base chiller station to approximately stay within the desired range includes maintaining an output capacity of the base chiller station within a sweet spot range.