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Product Features
Boiler Sequence (Continued)
Multiple Boilers
Setpoint
SYSTEM
TEMPERATURE
185
180
175
1
2
5
High Fire Limit
(Parameter 37)
BOILER
FIRING RATE
100
50
2
3
4
4 5
0
PLANT LOAD
(# BOILERS REQURED)
3
2
1
0
Start
Lead Boiler
Fast
Load
Change
Start
1 st Lag
Slow
Load
Change
Start
2 nd Lag
Stop
2 nd Lag
Stop
1 st Lag
Stop
Lead Boiler
1
2
3
4
Boiler Start and Stop Peer-To-Peer Network Sequence Diagram
(3 boiler system shown, typical for up to 8 boilers)
- Lead Boiler Start
Water temperature is below the setpoint by more than the “On Point” differential.
- Temperature Based Lag Boiler Start
Water temperature is below the setpoint by more than the “On Point” differential for longer than the adjustable
time delay (“Boiler On Delay” parameter).
- Modulation % Based Lag Boiler Start
The boiler modulation rate has been above the adjustable limit (“LL Start Trigger” parameter) for longer than the
time delay.
- Lag Boiler Stop
The boiler modulation rate has been below the adjustable limit (“LL Stop Trigger” parameter) for longer than the
time delay. Additionally, lag boilers are stopped when water temperature is above the setpoint by more than the
“Off Point” differential for longer than the “Boiler Off Delay” parameter).
5
- Lead Boiler Stop
The last boiler remains on line until the water temperature is above the “Off Point” setpoint for longer than the
time delay.
Notes
- The “Boiler Address” parameter assignment determines the boiler sequencing order.
- The Lead Boiler automatically rotates (when “Rotate” parameter is enabled) based on field adjusted time
(“Rotate After” parameter, default is 168 hours). When rotating, the lead boiler will move to the end of the lag
order and the 1 st lag boiler will become the lead. The rest of the boilers will then move up in the lag order
accordingly.
- Lead Boiler is the first boiler to turn on and the last boiler to turn off, (First On, Last Off, FOLO).
- Lag Boilers are turned on in order and turned off in reverse order, (First On, Last Off, FOLO).
- Tripped boilers are replaced without waiting for the Boiler On Delay timer. If a tripped boiler becomes available it
is returned to service.
TSBC Instruction Manual Page 8 of 48