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Siemens Building Technologies Basic documentation RVD240 CE1P2384en
HVAC Products 15 Function block D.h.w. heating 27.05.2004
15.3 Control of the circulating pump
Depending on the type of plant, the function block can control a circulating pump, if pre-
sent. The pump is always optional. Exceptions are plant types 2–2, 3–1, x–8 and x–9,
where the pump is controlled externally.
The circulating pump prevents the d.h.w. piping system from cooling down.
For the release of the circulating pump, the following settings can be made on operat-
ing line 102:
Setting Release
0 The circulating pump is always released (24 hours a day)
1 The release takes place according to the heating circuit programs for both
heating circuits entered on operating lines 6 through 12. A "maximum
selection" is made; the pump is released as long as one of the 2 heating
circuits provides heating.
There is no forward shift
2 The release takes place according to the d.h.w. program entered on op-
erating lines 17 through 23.
On operating line 120, it is possible to select whether or not during d.h.w. heating the
control output shall be inactive:
Setting Release
0 OFF during d.h.w. heating
1 ON during d.h.w. heating
If the circulating pump is assigned to one or several heating programs, it immediately
starts running when the heating period begins. When, according to the d.h.w. assign-
ment, all heat consumers are in holiday mode, the circulating pump will be deactivated.
For more detailed information, refer to chapter 19 "Function block Assignment of
d.h.w.".
Speed control of the circulating pump is not possible.
15.4 Switching differential of d.h.w. control
D.h.w. heating is switched off when the d.h.w. temperature has reached its setpoint. It
is switched on again when the d.h.w. temperature has fallen below the setpoint by the
amount of the switching differential.
The switching differential is to be set on operating line 103. It only acts with the plant
types that use a storage tank.
15.5 Legionella function
The legionella function is described in chapter 17 “Function block Extra legionella func-
tions“.
15.6 Priority of d.h.w. heating
15.6.1 General
Depending on the amount of heat available, it may be practical to restrict the quantity of
heat delivered to the heating circuits during d.h.w. heating. That means that in this
case, d.h.w. heating is given priority over space heating. On operating line 106, the
controller offers 3 types of priority:
• Absolute priority
• Shifting priority
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