Energy Savings >> Proportional Integral Derivative (PID) Controllers and Outdoor Reset

We are equally amazed at how many heating plants that have variable firing rate burners are simply operating as on-off units. The overshoots in the process on an on/off control translates into energy inefficiency as can be seen in a simple graph below when compared to a proportional control.

Significant savings in energy can be obtained by varying the firing rate relative to the load requirements. PID controllers are used to measure the temperature, pressure, level or flow of a process (the measurement is referred to as "process variable"). Then PID controllers try and correct the difference between the measurement and the desired setpoint. "Proportional" refers to the action taken in an attempt to achieve setpoint and can be used alone as a Proportional Controller.

Further reduction in overshoots and subsequent energy savings can be seen in a PI controller and still further in a PID controller.

PID control can be used effectively in outdoor reset where the controller will change the setpoint based on changes in outdoor temperature. This can be done in both steam and hydronic systems. Other boiler-room processes can also benefit from the installation/upgrade of PID controllers. Savings of 7% to 10% can be achieved by upgrading combustion control equipment with PID controllers, especially when integrated with a linkageless burner control.