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Building Technologies
7.8.2 Cold start thermal shock protection – multistage operation
The difference between multistage and modulating control is that with multistage
control, the output steps are defined by the number of burner stages. With modulating
control, any output value in % can be entered.
With multistage control, a maximum of 3 output stages are available:
1. Stage 1
2. Stage 1 and stage 2
3. Stage 1, stage 2, and stage 3
Use of the output stages 2 and 3 can be locked. In that case, the boiler is heated with
stage 1 only.
Parameter
Release Stages (release / no release)
When stages 2 and 3 are locked, the system may maintain low-fire operation until the
cold start function is ended, if the output delivered by stage 1 is not sufficient to reach
the switch-off threshold for thermal shock protection.
Setpoint
Spacing of temperature lines
corresponds to the setpoint steps
Stage 1
Burner off,
Setpoint step not
actual value
reached, but max. time
below thresh-
exceeded.
old ON.
Therefore, start of 2nd
Burner will be
stage
switched on
with stage 1
Figure 62: Cold start thermal shock protection – multistage operation
Basic Documentation LMV5...
7 Boiler controller / load controller
Actual value
Threshold OFF
Stages 1, 2 und 3
Stages 1 und 2
Setpoint step is reached
Actual value reached.
before max. time has elapsed.
Threshold OFF
Start of 3rd stage.
Change to multistage
Max. output will be delivered.
control
Manipulated
variable
Threshold ON
⇑
7550d05e/0704
CC1P7550en
22.05.2018
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