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X. Operation
D. Multiple Boiler Control Sequencer (continued)
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.
6. Multiple Demands
The Sequence Master responds to Central Heat,
Auxiliary 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 (82.2°C). 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. Modulating Condensing Boiler Control
During low loads, the Sequence Master limits firing
rates to a ‘Base Load Common Rate” to ensure peak
modulating condensing boiler 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 (90.6°C) (field adjustable).
Summary of Contents for Alpine ALP080B
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