Multiple Boiler Control Sequencer - Burnham Apex APX399 Installation, Operating And Service Instructions

X. Operation
D. Multiple Boiler Control Sequencer (continued)
D.

Multiple Boiler Control Sequencer

1. "Plug & Play" Multiple Boiler Control Sequencer
When multiple boilers are installed, the Control's
Sequencer may be used to coordinate and optimize the
operation of up to eight (8) boilers. Boilers are connected
into a "network" by simply "plugging in" standard
ethernet cables into each boiler's "Boiler-To-Boiler
Communication" RJ45 connection.
2. Sequencer Master
A single Control is parameter selected to be the Sequencer
Master. The call for heat, outdoor and header sensors,
and common pumps are wired to the Sequencer Master
"enabled" Control.
3. Lead/Slave Sequencing & Equalized Run Time
One boiler is a "Lead" boiler and the remaining networked
boilers are "Slaves". When demand is increasing, the
Lead boiler is the first to start and the Slave boilers are
started in sequential order (1,2,3,...) until the demand
is satisfied. When demand is decreasing, the boilers are
stopped in reverse order with the Lead boiler stopped
last (...,3,2,1). To equalize the run time the sequencer
automatically rotates the Lead boiler after 24 hours of
run time.
4. Improved Availability
The following features help improve the heat availability:
a. Backup Header Sensor: In the event of a header sensor
failure the lead boiler's supply sensor is used by the
Sequence Master to control firing rate. This feature
allows continued coordinated sequencer control even
after a header sensor failure.
b. "Stand Alone" Operation Upon Sequence Master
Failure: If the Sequence Master Control is powered
down or disabled or if communication is lost
between boilers, individual boilers may be setup to
automatically resume control as a "stand alone" boiler.
c. Slave Boiler Rate Adjustment: Each slave boiler
continues to monitor supply, return and flue gas
temperatures and modifies the Sequence Master's
firing rate demand to help avoid individual boiler
faults, minimize boiler cycling and provide heat to
the building efficiently.
d. Slave Boiler Status Monitoring: The Sequence Master
monitors slave boiler lockout status and automatically
skip over disabled boilers when starting a new slave
boiler.
5. Customized Sequences
Normally, boilers are started and stopped in numerical
order. However, custom sequences may be established
to optimize the heat delivery. For example, in order to
minimize boiler cycling, a large boiler may be selected
to run first during winter months and then selected to
run last for the remainder of the year.
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6. Multiple Demands
The Sequence Master responds to Central Heat, DHW
and frost protection demands similar to the stand alone
boiler. For example, when selected and DHW priority
is active, the sequence master uses DHW setpoint, "Diff
Above", "Diff Below" and pump settings.
7. Shared or Isolated DHW Demand
When the Indirect Water Heater (IWH) parameter is set
to "Primary Piped" the Sequence Master sequences all
required boilers to satisfy the DHW setpoint (default 180
F). When "Boiler Piped" is selected only the individual
slave boiler, with the wired DHW demand and pump,
fires to satisfy the DHW setpoint.
8. DHW Two boiler Start
When the Indirect Water Heater (IWH) parameter is set to
"Primary Piped" and the DHW Two Boiler Start parameter
is set to "Enabled" two boilers are started without delay
in response to a DHW call for heat. This feature allows
rapid recovery of large IWH's and multiple IWH's.
9. Optimized Boiler Modulation
Boiler firing rate is managed to increase smoothly as
boilers are started. For example, when a second boiler is
started the initial firing rate is 100%/2 or 50%, when the
third boiler is started the firing rate starts at 200%/3 or
66%. After the initial start, the Sequence Master develops
a unison firing rate demand based on it's setpoint and
sensed header temperature.
10. Innovative Condensing Boiler Control
During low loads, the Sequence Master limits firing rates
to a 'Base Load Common Rate" to ensure peak operating
efficiency. Lower firing rates boost efficiency by helping
increase the amount of flue gas water vapor condensation.
The Control maintains a "Base Load Common Rate" until
the last lag boiler is started. At this point, the "Base Load
Common Rate" is released to allow boilers to modulated
as required to meet heat load.
11. Advanced Boiler Sequencing
After there is a Call For Heat input, both header water
temperature and boiler firing rate percent are used to start
and stop the networked boilers. The control starts and
stops boilers when the water temperature is outside the
user selected "Diff Above" and "Diff Below" settings.
Also, in order to minimize temperature deviations, the
control adjusts the number of boilers running based on
the firing rate. This combination allows the boilers to
anticipate slow load changes before they disrupt water
temperature yet still respond quickly to sudden load
changes. These special sequencer features help reduce
energy wasting system temperature swings and the
resulting unnecessary boiler cycling.
12. Stop All Boilers
All boilers are stopped without delay if the Call for Heat
input is removed or if the header temperature is higher
than 195°F (field adjustable).