AERCO Control System (ACS) - Manual (Page 59)

MC2: 04/23/13 Page 59 of 144
GF-131
AERCO Control System (ACS)
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, New York 10913 • Phone: 800-526-0288
Installation, Operation, and Maintenance Manual
OMM-0081_0D
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.
3.11.3 DERIVATIVE GAIN
Derivative Gain is a function of time. It senses and responds to the rate of change of the
setpoint error. A slow rate of change will yield a small amount of derivative gain. Conversely, a
fast rate of change will yield a large derivative gain. Too high a derivative gain setting will
produce a large output for a short time. This can result in overshoot of the setpoint. Too low a
derivative gain setting will have the opposite effect, producing a small output for a longer period,
and may result in slow system response or the system undershooting the setpoint.
3.11.4 Decreasing Boiler Cycles
The five settings below - HI_DB_SETPT_EN, DEADBAND HIGH, DEADBAND LOW, SETPT
DOWN RATE, and DEMAND OFFSET - are meant to decrease boiler cycles. They each will be
defined and then their inter-operation will be explained.
3.11.5 HI_DB_SETPT_EN (High Deadband Setpoint Enable)
This value sets the percent level output at which the setpoint will be changed to its maximum
limit - Setpoint + DEADBAND HIGH. The effect will be that as we approach the shutdown limit,
we aim for the highest setpoint value allowed thereby delaying the shutdown of the boilers. If
we go back above this value after making the setpoint adjustment, the SETPT DOWN RATE will
define the rate at which to decrease the adjusted setpoint (Setpoint + DEADBAND HIGH) back
down to the normal setpoint. This value defaults to the BLR STOP LEVEL.
3.11.6 DEADBAND HIGH
This defines how many degrees above setpoint we can allow the temperature to drift without
changing the percent level output value. This is also the value that is added to the setpoint
when doing the HI_DB_SETPT_EN adjustment. The default is set to 3°.
3.11.7 DEADBAND LOW
This defines how many degrees below setpoint we can allow the temperature to drift without
changing the percent level output value. The default is set to 3°.
3.11.8 SETPT DOWN RATE (Setpoint Down (descending) Rate
If we go back above the HI_DB_SETPT_EN value, after first going below it and adjusting to
'Setpoint + DEADBAND HIGH', this defines the rate at which to decrease 'Setpoint +
DEADBAND HIGH' back down to Setpoint. The default is set to 100° per minute.
3.11.9 DEMAND OFFSET
This setting defines an offset to the Active Setpoint such that when the ACS shuts down the
whole boiler plant, it will not allow any boiler to fire again until both the Header Temperature <
Active Setpoint - DEMAND OFFSET, and the Percent Level Output >= the BLR START LEVEL.
During the time that the output is being kept at 0%, the ACS will flash the second line of its
default display. The default value here is 10°F.