AERCO BMK 1.5 LN July 2011 - Manual (Page 58)

CHAPTER 5: MODE OF OPERATION
Page 58 of 152 PR2: 05/09/12
Benchmark 1.5LN Low NOx Boiler
Operation and Maintenance Manual
OMM-0041_0D
GF-120
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913 • Ph: 800-526-0288
(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 B.M.S. (PWM) IN and/or RS485 COMM wiring connections. Shields should be
terminated only at the BMS and the boiler end must be left floating. Each unit’s wiring must
conform to the above.
BMS Setup and Startup 5.6.2
This mode of operation is factory preset and the AERCO BMS 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 BMS 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)
NOTE
Only BMS Model 168 can be utilized for the Combination Mode,
not the BMS II (Model 5R5-384).
A Combination Control System (CCS) is one that uses multiple boilers to cover both space-
heating and domestic hot water needs. An AERCO Boiler Management System (BMS) Model
168 and a Combination Control Panel (CCP) are necessary to configure this system. Typically,
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.
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 the
domestic hot water are capable of switching between constant setpoint and BMS modes of
operation. These boilers are the combination units and are referred to as the combo boilers. The
combo boilers heat water to a constant setpoint temperature. That water is then circulated
through a heat exchanger in a domestic hot water storage tank.
When the space-heating load is such that all the space-heating boilers are at the 100% valve
position, the BMS will then ask the Combination Control Panel for the domestic boilers to
become space-heating boilers. Provided the domestic hot water load is satisfied, the combo
(hot water) boilers will then become space-heating boilers. If the domestic hot water load is not
satisfied, the combo boiler(s) remain on the domestic hot water load. If the combo boilers
switch over to space heating, but there is a call for domestic hot water, the CCP switches the
combo units back to the domestic load.
When the combo units are satisfying the domestic load they are in constant setpoint mode of
operation. When the combo units switch over to space heating, their mode of operation changes
to the BMS mode. For more information concerning the operation of the Combination Control
Panel see the AERCO CCP-1 literature.
Combination Control System Field Wiring 5.7.1
Wiring for this system is between the BMS Model 168 panel, the CCP and the B.M.S. (PWM) IN
terminals in the I/O Box. Wire the units using a shielded twisted pair of 18 to 22 AWG wire.
When wiring multiple units, each unit’s wiring must conform to the above. For a complete CCP
system-wiring diagram see the AERCO CCP-1 literature.