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Siemens Building Technologies
Basic Documentation RVD110, RVD130
CE1P2381E
HVAC Products
17 Function block D.h.w. actuator 2
27.05.2004
The use of a flow switch is recommended especially in smaller plants (single-family
houses, etc.).
Supervision of faults is not possible since both short-circuit and open-circuit are permit-
ted states.
Functions that are dependent on the flow switch are the adjustable load limit (subsec-
tion 17.4.7 Adjustable load limit) and child-proofing (subsection 17.4.8 Child-proofing).
17.4.4 Offsetting the heat losses
In general, the d.h.w. temperature is maintained at a constant level, irrespective of
d.h.w. consumption.
Also, when using a flow switch and a circulating pump, it is possible to configure
whether the control shall also be active when there is no d.h.w. consumption, in other
words, whether the heat losses resulting from radiation, circulation, etc., shall be com-
pensated for.
The configuration is to be made on operating line 54. If a flow switch is used, an open-
ing signal is temporarily supplied to the primary valve when d.h.w. consumption starts,
and a closing signal when d.h.w. consumption is ended.
To ensure overtemperature protection and a fast response, an immersion temperature
sensor QAE22... must be used with the configurations with no circulating pump since it
is immersed into the heat exchanger.
Mode of operation
23
81S
1
0
23
81S
1
1
Plant without flow switch
Plant with flow switch
Setting on
operating line 54
Flow switch
present
Circulating pump
present
Heat losses will be com-
pensated for
0
No
Either way
Yes, completely (100 %)
1 Yes
No
No
2
Yes
Yes
Yes, partly (80 %)
3
Yes
Yes
Yes, completely (100 %)
Efforts are made to maintain the d.h.w. setpoint and all heat losses will be completely
compensated for. If a circulating pump is used, it need not be configured.
When there is no d.h.w. consumption, the d.h.w. will not be heated, even if the circulat-
ing pump runs.
Since heat losses are not offset, the d.h.w. temperature will eventually drop to the am-
bient temperature.
A temporary drop of the d.h.w. flow temperature is tolerated. Heat losses will only be
partly offset. The flow temperature is allowed to fall by 20 %. Heating the d.h.w. to its
setpoint after the temperature drop has occurred always takes a minimum of 5 minutes.
For offsetting the heat losses with plant type no. 4, the circulating pump must be re-
leased. If it is not released, no control is provided, independent of the d.h.w. flow tem-
perature. With plant type no. 5, the heat losses will always be compensated for.
D.h.w. setpoint T
BWw
= 50 °C
Cold water temperature T
Nx
= 10 °C (fixed value):
Permitted setback
∆
T = 20 %
Minimum d.h.w. flow temperature T
BWV
= ?
T
BWV
= T
BWw
–
∆
T × (T
BWw
– T
Nx
) = 50 – 0.2 (50 – 10) =
42 °C
General
Caution
Explanations relating to
the settings
Setting 0
Setting 1
Setting 2
Example
