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Siemens Building Technologies
Basic Documentation RVL471
CE1P2524E
HVAC Products
12 Function block "Boiler"
23.10.2002
t
2
5
22
D
1
3e
Boiler controller, stage 1
Forced signal
Overrun time
of boiler pump
Pump
Off
Y
t
Time
Y
Control signal boiler pump
All loads (heating and d.h.w. circuits) and heat converters that abruptly reduce their
demand for heat watch the data bus during the set pump overrun time to see if a forced
signal is being sent by the boiler.
•
If no forced signal is received, the consumers and heat converters only allow pump
overrun to take place (refer to section “25.4.4 Pump overrun“)
•
If, in this time window, a forced signal is received, the loads continue to draw heat from
the boiler in the following manner:
−
Plant types with heating circuits using a mixing valve maintain the previous set-
point
−
Plant types with pump heating circuits allow the pumps to continue running
D.h.w. plant type 4 (instantaneous d.h.w. heating via heat exchanger) does not respond
to forced signals since it can draw heat from the boiler only if there is demand for d.h.w.
If the boiler sets the forced signal to zero, the loads and heat exchanges that have
responded to the forced signal respond as follows:
•
They close their mixing valves
•
Their pumps run for the set pump overrun time and then stop
D.h.w. discharging protection has priority over protection against boiler overtempera-
tures.
12.5 Operating mode of pump M1
The operating mode during protective boiler start-up of pump M1 must be selected on
operating line 99:
•
Circulating pump with no deactivation (setting 0):
The circulating pump runs when one of the consumers calls for heat and when burner
stage 1 is switched on, that is, also during protective boiler startup.
•
Circulating pump with deactivation (setting 1):
The circulating pump runs when one of the consumers calls for heat. It is deactivated
during protective boiler startup.
