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Building Technologies Boiler Sequence Controller RMK770 CE1P3132en
HVAC Products 6 Boiler sequence management 23.04.2009
100
200
300
400
100
200
300
30
400
240
180
95
105
120
160
1K 1K
1K
1K
1K
1K
1K
1K
1K
1K
60
K+
kW
70
50
150
250
350
60 60 60
60 60 60
47.547.5
80 80 80
90
90
95
3132D07
The diagram above shows an example with 4 modulating boilers that are sequentially
switched on and off.
The basic stage of the first boiler be 30% of the rated capacity.
As heat consumption increases, each boiler modulates up to 100 kW (100%) before the
next boiler is switched on. Hence, 4 boilers can modulate delivering a total output of
400 kW.
The downward sequence output limit is set to 60%.
To enable the fourth boiler to be switched off, all 4 boilers must have modulated below
240 kW (60% of 400 kW) for 20 minutes, that is, below 60 kW on average. After switch-
ing off, the operating point of the remaining 3 boilers is at 80 kW.
To enable the third boiler to be switched off, all 3 boilers must have modulated below
180 kW (60% of 300 kW) for the duration of the switch-off delay, that is, below 60 kW
on average. After switching off, the operating point of the remaining 2 boilers is at
90 kW.
To enable the second boiler to be switched off, both boilers must have modulated
below 95 kW for the duration of the switch-off delay, that is, below 47.5 kW on average.
If switching off took place at 60 kW as above, the second boiler would switch on again
after a short period of time due to insufficient heat supply. Hence, the operating point of
the remaining boiler after switching off is at 95 kW.
If the boilers cannot modulate at a sufficiently low level, the main flow temperature rises
until a boiler is switched off via the temperature-time integral.
Example
Switching boiler 4 off
Switching boiler 3 off
Switching boiler 2 off
Note
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