Each boiler in a group needs a position number, defined by parameter SYS-01, starting with “1” and ascending without gaps.
In a heating system with multiple boilers, the boilers can be arranged into groups and will be controlled in sequence or parallel, according to the configuration set in the heating strategy.
A heat generator stage will switch on, if the strategy asks to on or off, when the heating control strategy requests increasing or decreasing number of stages via the communication signal “HtgGenDemandG1”.
When the modulating stage is released, it will take values between the minimum and maximum modulating signal. The control of the modulating output signal „ModStage“ will be according to the next figure.
Fig. 2. Boiler modulating stage
In a boiler sequence the operation of the modulating stages depend on the operation mode set in the strategy. In sequential mode only the last active boiler modulates. All the boiler with lower position number than the last will keep their modulating stages at 100%. In parallel mode all the active heat generators will modulate.
The parameters ST1-02 and ST1-03 define the minimum on and off times of “Stage1Cmd”. The parameter ST1-04 defines the “Stage1Cmd” the blocking time to switch on the modulating stage.
The parameter ST1-05 defines the Stage1Cmd the blocking time to switch off the previous heat generator stage.
The modulating stage does not have minimum on and off times but it will be ramped up with STM-08. When the modulating stage is in the value range of its minimum and maximum modulating signals +/- 5%, it does not allow to switch other boiler stages setting the blocking signal to the value 4. When it reaches its maximum value STM-07 - 5% it starts the blocking timer to start the next boiler (STM-04). If the modulating stage gets lower than STM-07 - 10% during the blocking time, the timer STM-04 will be reset.
When the modulating stage has a value STM-06 + 5% or lower, the blocking time STM-05 starts and locks “Stage1Cmd” to switch off. If the modulating stage gets higher than STM-06 +10% value during the blocking time, the timer STM-05 will be reset.
The figure shows the operation of the blocking signal for a staged heat generators:
Fig. 3. Blocking times for a staged heat generator
Table 8. Blocking signal values
Value DISP-01 |
Function |
0; 1 |
no blocking |
2 |
blocking increasing the number of stages |
3 |
blocking decreasing the number of stages |
4 |
blocking increasing and decreasing the number of stages |
When a boiler is in operation, the boiler specific minimum supply temperature, defined by parameter BST-04 is transmitted to the heating control strategy macro, to maintain the required boiler temperature limits within the whole heating system.
When a boiler is in operation, the boiler specific minimum return temperature, defined by input “RetTempSp” is transmitted to the heating control strategy macro, to maintain the return temperature only if minimum return temperature control was configured (SYS-02 = 1).
For details of grouping, sequencing and cyclic changeover of the heat generators, please refer to the documentation of the heating control strategy.
Table 9. Parameter List
Description |
Value Range |
Default Value |
Unit |
BST-04: minimum boiler supply temperature |
0...500 |
60 |
°C |
ST1-01: capacity stage 1 |
0...1E6 |
0 |
kW |
ST1-02: minimum on time stage 1 |
0...3600 |
240 |
sec |
ST1-03: minimum off time stage 1 |
0...3600. |
240 |
sec |
ST1-04: blocking time to switch on next stage or boiler |
0...3600 |
600 |
sec |
ST1-05: blocking time to switch off next stage or boiler |
0...3600 |
300 |
sec |
STM-01: capacity modulating stage |
0...1E6 |
0 |
kW |
STM-04: blocking time to switch on next stage or boiler |
0...3600 |
600 |
sec |
STM-05: blocking time to switch off next stage or boiler |
0...3600 |
300 |
sec |
STM-06: minimum output modulating stage |
0...100 |
0 |
% |
STM-07: maximum output modulating stage |
0...100 |
100 |
% |
STM-08: maximum raise per minute |
1...2000 |
25 |
% |