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Siemens Building Technologies
HVAC Products
In the case of direct d.h.w. heating without circulating pump, the adjusted value is inac-
tive (no dwelling time).
17.1.5 Operation of circulating pump
The circulating pump can be forced to run during the period of time the legionella func-
tion is active. This ensures that hot water also circulates through the plant's hot water
distribution system. Entry (0 or 1) is made on operating line 128.
If the storage tank temperature exceeds the legionella setpoit minus 1 K, the circulating
pump will be forced to run.
If the storage tank temperature falls below the legionella setpoint by more than
SD + 2 K (switching differential plus 2 K), the circulating pump will no longer be acti-
vated.
17.1.6 Maximum limitation of the return temperature
Refer to section 26.2.3 "Maximum limitation in d.h.w. mode".
17.2 Mode of operation
Conditions for activation of the legionella function:
• The storage tank temperature is acquired with 1 or 2 sensors (legionella function
cannot be provided when using thermostats)
• The legionella function has been parameterized (operating line 104)
• D.h.w. heating is switched on (button
• The holiday function is not active
If the criteria "Set day" and "Time" are met, the legionella function will be released. Re-
lease of the legionella function causes the d.h.w. temperature setpoint to be raised to
the level of the legionella setpoint and to forced charging. If d.h.w. heating is switched
off or the holiday function is active, the legionella function will be released. On comple-
tion of the overriding function, d.h.w. charging to the legionella setpoint will be triggered
since the legionella function continues to be released.
The behavior of the legionella function as a function of the d.h.w. temperature is as
follows:
T
BWx
T
BWw
T
- SD
BWw
BW
T
- SD
- 2 K
BWw
BW
ON
1
OFF
ON
2
OFF
ON
3
OFF
4
①
Circulating pump
②
Forced charging
③
Release of the legionella function
④
Start conditions for the legionella function met
⑤
Start dwelling time
⑥
Reset dwelling time
Basic documentation RVD240
17 Function block Extra legionella functions
is lit)
5
6
7
⑦
Start dwelling time
⑧
Dwelling time has elapsed
T
D.h.w. temperature
BWx
T
D.h.w. temperature setpoint
BWw
SD
Switching differential of d.h.w. heating
BW
t
Time
8
t
CE1P2384en
27.05.2004
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