AERCO BMS 168 - Manual (Page 39)

As the load drops off, the firing rates
decrease. When all boilers reach the stop
level, the first boiler turned on will be shut
off by the BMS and its load will be evenly
distributed to the remaining firing boilers.
This off-sequencing continues until only one
boiler is left firing. The last boiler will turn off
when its stop level is reached.
4.4.5.2 Parallel Mode
When operating in Parallel Mode, the
boilers are simultaneously started by the
BMS. The start and stop levels have no
effect when in Parallel Mode. The turn-down
ratio in Parallel Mode is fixed at 14:1 for KC
1000 Series boilers and 15:1 for Benchmark
boilers, regardless of the number of boilers
in the plant.
4.4.5.3 Combination Mode
Combination mode is used only when the
boiler plant will be used to satisfy both
space heating and domestic hot water
needs. This configuration, known as a
Combination System, is used in conjunction
with an AERCO Combination Control Panel
(CCP). This system uses BMS-mode boilers
dedicated to space heating and
Combination boilers that are primarily used
to satisfy the domestic hot water need. The
domestic combination boilers are also
available for the space heating load when
the domestic hot water load is satisfied. This
is accomplished using a motorized valve
and storage tank equipped with a heat
exchanger. For additional information on the
Combination System, see AERCO’s CCP-1
literature.
4.4.5.4 Designating the Number of
Combination Boilers
A maximum of 4 combination boilers can be
connected to the BMS. However, when
using the Combination Mode, it is necessary
to tell the BMS how many combination
boilers there are. This is accomplished as
follows:
IMPORTANT
When connecting combination boilers
to the BMS, it is important that you start
at the BLR 8 terminals on Terminal
Strip JP2 and work towards BLR 5.
1. With the COMBINATION MODE
selected, press the BLR OP MODE key.
The display will read: COMBINATION
MODE X OF CCP BOILERS, (where X
is the number of combination boilers).
2. Enter the number of combination boilers
connected to the BMS using the ▲ and
▼ arrow keys.
4.4.6 HDR SET MODE
This key has two functions. First, it is used
to select the Indoor/Outdoor Reset,
Constant Setpoint, or Remote Setpoint
boiler mode operation. Second, it is used to
select the type of indoor temperature sensor
used with the BMS, if one is installed. The
type of sensor can be either resistive
(thermistor) or a constant voltage signal with
current varying from 4 to 20 mA.
Pressing the HDR SET MODE key once
selects the Header Set Mode function. If the
desired mode is not displayed, toggle the
display to the desired mode (IN/OUTDOOR
RESET, REMOTE SET TEMP or
CONSTANT SETTEMP) using the ▲ or ▼
arrow key.
Pressing the HDR SET MODE key a
second time toggles the display to indicate
the type of indoor temperature sensor which
will be used with the BMS (THERMISTOR
or 4-20 mA). If necessary, toggle the display
to the desired sensor type using the ▲ or ▼
arrow key.
If the REMOTE SET TEMP mode is
selected and the Indoor Temperature
Sensor feature is used, the Sensor input
type must be THERMISTOR (resistive)
since the BMS has only one 4-to-20 mA
input.
4.4.7 INTGL RATE GAIN, TEMP
BANDWIDTH and DERIV GAIN Keys
These three keys provide PID (Proportional
Integral Derivative) control functions which
govern temperature control and response of
the BMS to the boiler system. Since each
system is different, these PID controls can
tune the BMS to the characteristics of your
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