Siemens LMS14 User Manual page 215

Additional parameters
Building Technologies Division
Boiler setpoint
With modulation based on the boiler temperature setpoint, the speed of the boiler pump
is reduced to such a degree that the sensor B2 will reach the required boiler
temperature setpoint.
Reaching the boiler temperature setpoint is primarily the task of the boiler controller.
Also, reaching this setpoint is dependent on the amount of water supplied by the boiler
pump.
The required boiler temperature setpoint can be attained more quickly if the amount of
water supplied by the boiler pump is reduced. But if the amount of water supplied is
reduced excessively, the boiler controller modulates the burner's output down. In that
case, the burner's capacity would only be partly used.
The speed of the boiler pump is calculated such that it can be lowered to the
parameterized minimum only when the burner's full capacity is reached.
When the burner operates at low output (relative output below 66%), the setpoint for
speed control is reduced by the parameterized difference (Pump setpoint reduction
(2329)). If the relative burner output exceeds 66%, the setpoint for speed control is
increased to such an extent that at 100% relative output, the setpoint for calculating the
speed corresponds to the setpoint for boiler temperature control.
This prevents the boiler from reaching the setpoint at a reduced output while the pump
continues to operate at reduced speed.
Speed control is ensured by a PID controller, using the controller coefficients for the
boiler pump (Speed Xp (2324), Speed Tn (2325), and Speed Tv (2326)).
For control of the pump speed with an active DHW heating request (in instantaneous
water heater operation also), the parameterized speed limits for charging pump Q3
apply. With all the other heat requests (heating circuit, consumer circuit, zone
extension), the speed limits parameterized for the boiler pump apply.
Setpoints
Setpoint
Boiler control
Setpoint
Speed control
0%
Figure 40: Speed control – boiler setpoint
Line no. Operating line
2324 Speed Xp
2325 Speed Tn
2326 Speed Tv
2329 Pump setpoint reduction
User Manual LMS14...
6 The settings in detail
2329
7471d71e/0811
66%
Burner output
100%
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CC1U7471en
07.05.2014