AERCO Control System (ACS) - Manual (Page 54)

MC2: 04/23/13 Page 54 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
3.9.3 PARALLEL MODE
When PARALLEL MODE is selected, all boilers are simultaneously started by the ACS. The
BLR START LEVEL and BLR STOP LEVEL set in the Configuration Menu (see below) have no
effect when in this mode. Regardless of the number of Boilers in the plant, the turn-down ratio in
the Parallel Mode is fixed at 20:1 for KC1000 Series Boilers (except 11:1 for KC Low NOx). For
Benchmark Series Boilers, the turn-down ratio is fixed at 20:1 for BMK2.0, 2.0LN, and 1.5LN
Boilers. However, for BMK3.0LN Boilers the turn-down ratio is fixed at 15:1.
3.9.4 SEQUENTIAL
When SEQUENTIAL MODE is selected it provides a greater turn-down ratio than the
PARALLEL MODE. This is due to the fact that the turn-down ratio in the Sequential Mode is
equal to the number of Boilers multiplied by the 20 for KC1000 Series and Benchmark Series
units.
In Sequential Mode, each boiler is started one at a time based on the load and start/stop levels
programmed in the ACS. The ACS will start a single Modulex boiler when there is a load
demand or a Benchmark or KC1000 boiler when the boiler start level is reached. Once the first
boiler reaches twice the start level, a second boiler will be started and the load will be distributed
evenly between the two boilers.
For instance, if a start level of 25% is chosen, when the first boiler reaches 50% a second boiler
will start (after a 30 second delay), and the ACS will distribute the load 25% for each boiler. If
the firing rate of both boilers reach a combined value equal to 3 times the start level, a third
boiler is started by the ACS (after a 30 second delay), and the load will be distributed across all
three boilers. This sequence will continue based on load demand and the number of boilers
connected to the ACS.
3.9.5 SYS INTLK CONFIG
This option selects when the System Start Interlock takes effect. The available choices are
START ENABLED (default) and ALWAYS ENABLED. If START ENABLED is selected, the ACS
will wait 30 seconds after the System Start Relay is activated before looking for a closure across
the System Start Interlock selected. (See SYS START INTLK in the RELAY MENU). If no
closure is seen after 30 seconds, the ACS will stop the boilers and display a fault message and
activate the fault relay. ALWAYS ENABLED will cause a fault whenever the interlocks are
opened.
NOTE
The BLR START LEVEL and BLR STOP LEVEL must be
programmed in the ACS by the user. Refer to Appendix I for
additional information on START/STOP LEVELS.
3.9.6 BLR START LEVEL
The Boiler Start Level (BLR START LEVEL) sets the percentage level at which the Boilers
connected to the ACS will start. The allowable entry range is from 1% to 100% (default = 20%).
See important note below.
3.9.7 BLR STOP LEVEL
The Boiler Stop Level (BLR STOP LEVEL) menu option set the percentage level below which
the Boilers connected to the ACS will stop. The allowable entry range is from 1% to 40%
(default = 16%). See important note below.