Boiler Control Instruction & Operation Manual
Page
12
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68
Product Features
Multiple Boiler Control Sequencer (continued)
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During low loads, the Sequence Master limits firing rates to a
“Base Load Rate” to ensure modulating
condensing boiler 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 Rate” until the last
lag boiler is started. At this point, the
“Base Load Common Rate” is released to allow boilers to
modulate as required to meet heat load.
185
Setpoint
180
5
175
1
2
Base Load
Rate Default
40% Range
(25
– 100%)
100
40
0
2
3
4
4
5
3
2
Fast
1
Load
0
Change
Slow
Load
Change
Start
Lead Boiler
Start
1
st
Lag
Start
2
nd
Lag
Stop
2
nd
Lag
Stop
1
st
Lag
Stop
Lead Boiler
Figure 9: Boiler Start and Stop Peer-To-Peer Network Sequence Diagram
(3 boiler system shown, typical for up to 8 boilers)
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
“Difference Above” and “Difference
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.
1
-
Lead Boiler Start
Water temperature is below the setpoint by more than
the
“On Point” differential.
2
-
Temperature Based Lag Boiler Start
Water temperature is below the setpoint by more than
the
“Difference Below” parameter for longer than the
adjustable time delay
(“Boiler Start Delay” parameter).
3
-
Modulation % Based Lag Boiler Start
The boiler modulation rate has been at the maximum
firing rate for longer than twenty minutes.
4
-
Lag Boiler Stop
The boiler modulation rate has been at minimum fire for
longer than twenty minutes. Additionally, lag boilers are
stopped when water temperature is above the setpoint
by more than the
“Difference Above” parameter for
longer than the
“Boiler Stop Delay” parameter.
5
-
Lead Boiler Stop
The last boiler remains on line until the water
temperature is above the setpoint more than the
“Difference Above” for longer than the time delay.
