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Benchmark 2500DF-3000DF Installation, Operation & Maintenance Manual
5.6 AERCO CONTROL SYSTEM (ACS)
The ACS mode of operation is used in conjunction with an AERCO Control System. The ACS mode is
used when it is desired to operate multiple units in the most efficient manner possible. For this mode of
operation, an ACS Header Sensor must be installed between 2 and 10 feet downstream of the LAST
boiler in the boiler plant's supply water header. The ACS can control up to 40 boilers; Up to 32 via
Modbus (RS485) network communication. For ACS programming, operation and Header Sensor
installation details, see ACS Operations Guide, GF-131. For operation via an RS485 Modbus network,
refer to Modbus Communication Manual GF-114.
To enable the ACS Mode, the following menu settings must be made in the Configuration Menu:
Menu Option
Boiler Mode
Remote Signal
Refer to section 3.3 for instructions on changing menu options.
5.6.1 ACS External Field Wiring
Wiring connections for RS485 Modbus control are made between the 485 A- and 485 B+ terminals on the
ACS (boilers 9 through 40) and the RS485 COMM terminals in the I/O Box on the front of the boilers.
Wire the units using shielded twisted pair wire between 18 and 22 AWG. Observe the proper polarity for
the ACS RS485 COMM wiring connections. Shields should be terminated only at the ACS and the boiler
end must be left floating. Each unit's wiring must conform to the above.
5.6.2 ACS Setup and Startup
This mode of operation is factory preset and the ACS controls the firing rate (air/fuel valve % open
position). There are no setup instructions for each individual unit.
To operate the unit in manual mode, press the AUTO/MAN switch. The REMOTE LED will go off and the
MANUAL LED will light
To change back to the ACS mode, simply press the AUTO/MAN switch. The REMOTE LED will again
light and the MANUAL LED will go off.
5.7 COMBINATION CONTROL SYSTEM (CCS)
Only ACS can be utilized for the Combination Control System.
A Combination Control System (CCS) is one that uses multiple boilers to cover both space-heating and
domestic hot water needs. The theory behind this type of system is that the maximum space-heating load
and the maximum domestic hot water load do not occur simultaneously. Therefore, boilers used for
domestic hot water are capable of switching between constant setpoint and ACS control.
For a typical CCS, an adequate number of boilers are installed to cover the space-heating load on the
design-day. However, one or more units are used for the domestic hot water load as well. These boilers
are the combination units and are referred to as the combo boilers. The combo boilers heat water to a
OMM-0099_0A
GF-145
CHAPTER 5 – MODE OF OPERATION
NOTE
ACS can utilize only RS485 signaling to the Boiler.
Setting
Direct Drive
Network (RS485)
NOTE
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913
Ph.: 800-526-0288
Page 73 of 234
PR1: 05/21/2014
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