AERCO BMS II BOILER - Manual (Page 44)

OPERATION
3-12
3.10 TUNING MENU
The TUNING MENU options are used to select PID (Proportional Integral Derivative) control functions
incorporated in the BMS II. These functions govern temperature control and response of the ‘BMS II to
the boiler system. Since each system is different, these PID controls can tune the BMS II to the
characteristics of your specific installation. The factory defaults preset by AERCO work well for most
applications. In instances when there is a large error between the setpoint and the actual supply water
temperature, the BMS II may appear to require PID tuning. However, it is best to observe BMS II
operation over a period of time prior to making any PID changes. Contact AERCO, or an AERCO
representative, prior to making any PID setting changes.
The TUNING MENU options include Proportional Bandwidth, Integral Gain, Derivative Gain and Header
Temperature Deadband.
PROPORTIONAL BND
The Proportional Bandwidth (degrees) represents the immediate response to a setpoint error. This value
is the temperature deviation from setpoint for which a 100% output change is desired. This is a part of
the PID output calculation in the BMS II.
For instance, proportional band of 50°F is chosen. The header temperature setpoint is 180°F and the
actual incoming supply water temperature is 130°F. This is a 50°error and the following is true:
Temp. Error_____ X 100 = Firing Rate in %
Prop Bandwidth
Therefore:
50 X 100% = Firing Rate
50
1 X 100 = 100 % Firing Rate
With an error of 30° and a bandwidth of 50, the following would be true:
30/50 X 100 = .6 X 100 = 60% Firing Rate.
INTEGRAL GAIN
The Integral Gain (repeats/min) responds to the setpoint error over time. Integral references the
proportional band error signal and sums itself with respect to the period of time the error exists. Based on
the previous example, if the integral gain is 0.15 repeats/minute at a firing rate of 60% and a temperature
error exists for one minute, then the following is true:
(0.15 reps/min.) x (60% firing rate) = 9% actual firing rate
60% firing rate +9% firing rate = 69% firing rate
If the error continues and is present for another minute, another 9% correction factor will be added:
69% firing rate +9% firing rate =
78% firing rate
If, after a load change, the supply water temperature stabilizes at a temperature above or below the
setpoint, the integral gain should be increased. If, after a load change, the supply water temperature
overshoots and oscillates excessively, integral gain should be reduced.