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Flow Switch; Compensation Of Heat Losses Through Control - Siemens RVD240 Basic Documentation

District heating and domestic hot water controller.
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General
Caution
Mode of operation
Settings 0 and 1
Siemens Building Technologies
HVAC Products

16.3.5 Flow switch

If desired, a flow switch can be fitted in the heat exchanger's cold water return. For this
purpose, the RVD240 provides digital input H5, which is to be configured on operating
line 55.
The flow switch improves the performance of the heat exchanger's control. It indicates
to the control system when a demand for heat can be expected. When there is no flow,
it is possible to ensure that the d.h.w. delivered will not be too hot.
The use of a flow switch is especially recommended in the case of smaller plants (sin-
gle-family houses, etc.).
Fault status supervision is not possible since short-circuits and open-circuits are permit-
ted statuses.
Functions that are dependent on the flow switch are the adjustable load limit and the
child-proofing facility (refer to subsection 18.7.3).

16.3.6 Compensation of heat losses through control

Generally, heat losses due to d.h.w. consumption are always compensated for through
control.
In addition, when using a flow switch and a circulating pump, it is possible to configure
whether the control shall also be active outside periods of d.h.w. consumption, that is,
whether heat losses due to radiation, circulation, etc., shall be compensated for.
The configuration is to be made on operating line 54.
If a flow switch is used, the primary valve will temporarily be controlled by an opening
signal at the beginning of d.h.w. consumption, and by a closing signal at the end of
d.h.w. consumption.
To ensure that no excessive temperatures occur and the response of the control is fast,
an immersion sensor must be used in the case of configurations with no flow switch,
since that sensor immerses into the heat exchanger (e.g. type QAE21.93).
B32
Plant without flow switch
Operating
Operating
line 55
line 54
0
≠4
1, 2, 3
4
0, 1
4
2
4
3
Explanations relating to the settings on operating line 54:
There is no d.h.w. heating when no d.h.w. is consumed. This is true also when the cir-
culating pump runs. Since heat losses are not compensated for, the d.h.w. temperature
will drop to the room temperature level eventually.
Basic documentation RVD240
16 D.h.w. heating
Plant with flow switch
Function
Full compensation of heat losses
No compensation of heat losses
Partial compensation of heat
losses, maximum flow temperature
reduction by 20 % permitted
Full compensation of heat losses
B32
Flow switch circulating
pump
No
No
Yes
No
No
Yes
Yes
Yes
Yes
67/126
CE1P2384en
27.05.2004

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