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Benefit
Description
Setting
Effect
Example
Pump overrun of
boiler pump
284/348
Siemens Building Technologies
HVAC Products
5.8
Pump overrun time
• Boiler:protection against overtemperature
• Use of residual heat in the boiler
Overrun of the primary, bypass, boiler, heating circuit and d.h.w. charging pump en-
sures that residual heat will be carried away from the boiler circuit. This makes certain
that overtemperature in the boiler will not occur, thus preventing the safety limit ther-
mostat from responding.
Setting range
0...20
All pumps that - at the time of burner shutdown - were operating, continue to run for the
period of time set here. The behavior is the same as with burner shut-down when, with
the burner deactivated, the demand for heat from the boiler becomes invalid. At the
same time, the previous flow temperature setpoint remains valid, allowing the mixing
valves of the controllers connected to LPB to stay open.
HK
BR
ON
OFF
Q
ON
OFF
Y
TVNw
TVRw
HK
Operating mode
BR
Burner
Q
Pumps
Y
Extenal mixing valve (via LPB)
TVNw
Nominal flow temperature setpoint
TVRw
Reduced flow temperature setpoint
Boiler pump overrun may get interrupted.
This is the case when the boiler temperature falls by 5 K below the actual value of the
flow temperature. Boiler pump overrun will be resumed, however, when the boiler tem-
perature lies only 2 K below the flow temperature. During the interruption, the time set
above continues to elapse.
Only plants with a pressureless header (ZuFu 12) and a common flow temperature
sensor (B10) allow the boiler pump overrun time to be interrupted.
Basic Documentation RVP540 / RVP550
Description of the EXP settings
Unit
min
tPN
Nominal operation
Reduced operation
tPN
Pump overrun time
Factory setting
5
t
t
t
t
CE1P2488en
18.10.2002
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