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Siemens Building Technologies
Basic Documentation RVD230
CE1P2383en
HVAC Products
17 D.h.w. heating
27.05.2004
17.3.6 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 no excessive temperatures occur and the response of the control is fast, a
QAE21.93 immersion sensor must be used in the case of configurations with no flow
switch, since that sensor immerses into the heat exchanger.
23
83S
3
1
B32
238
3S
32
B32
Plant without flow switch
Plant with flow switch
Operating
line 55
Operating
line 54
Function Flow
switch
circulating
pump
0 No
≠
4
1, 2, 3
Full compensation of heat losses
No
Yes
4
0, 1
No compensation of heat losses
No
No
4
2
Partial compensation of heat los-
ses, maximum flow temperature
reduction by 20 % permitted
Yes Yes
4
3
Full compensation of heat losses
Yes
Yes
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
circulating pump runs. Since heat losses are not compensated for, the d.h.w. tempera-
ture will drop to the room temperature level eventually.
A temporary drop of the d.h.w. flow temperature is accepted. Heat losses are only
partially compensated for; the flow temperature may drop by a maximum of 20 %. Sub-
sequent heating up to the d.h.w. setpoint always takes a minimum of 5 minutes.
For the compensation of heat losses, the circulating pump must be released. If it is not
released,
no
control is provided independent of the d.h.w. flow temperature.
D.h.w. setpoint T
BWw
= 50 °C
Cold water temperature T
Nx
= 10 °C (fixed value):
Permissible reduction
∆
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
The aim is to maintain the d.h.w. setpoint and all heat losses will be fully compensated
for. A circulating pump is used.
General
Caution!
Mode of operation
Settings 0 and 1
Setting on operating
line 2
Example
Setting on operating
line 3
