73/118
Siemens Building Technologies
Basic Documentation RVL471
CE1P2524E
HVAC Products
19 Function block "D.h.w. storage tank"
23.10.2002
With plant types 4–x, 5–x, and 6–x, setting 1 on operating line 125 makes no sense,
since there is no own heating circuit. In that case, changeover to the electric immer-
sion heater would take place at midnight at the latest, after 48 hours of operation.
19.3 D.h.w. temperature and d.h.w. switching dif-
ferential
The kind of d.h.w. storage tank temperature acquisition must be entered on operating
line 126. It can be measured with one or 2 sensors, or with one or 2 thermostats.
If temperature sensors are used, the switch-on / off temperature for charging is deter-
mined as follows:
T
BWx
25
24
D
0
2
ON
OFF
SD
BW
T
OFF
= T
BWw
T
ON
ON
D.h.w. charging ON
OFF
D.h.w charging OFF
SDBW Switching differential of d.h.w. charging
T
ON
Switch-on temperature
T
OFF
Switch-off temperature
TBWw D.h.w temperature setpoint
TBWx
D.h.w. temperature
If the d.h.w. storage tank is equipped with thermostats, the switch-on / off temperature
is determined by the thermostats.
Determination of the switch-on temperature (start of d.h.w. charging):
Operating line 126 Measurement
Switching criterion
0
1 sensor
T
BWx1
< (T
BWw
– SD
BW
)
1
2 sensors
T
BWx1
< (T
BWw
– SD
BW
) and T
BWx2
< (T
BWw
– SD
BW
)
2
1 thermostat
Thermostat contact B31 closed
3
2 thermostats
Both thermostat contacts B31 and B32 closed
Determination of the switch-off temperature (end of d.h.w. charging):
Operating line 126 Measurement
Switching criterion
0
1 sensor
T
BWx1
> T
BWw
1
2 sensors
T
BWx1
> T
BWw
and T
BWx2
> T
BWw
2
1 thermostat
Thermostat contact B31 open
3
2 thermostats
Both thermostat contacts B31 and B32 open
SDBW
D.h.w. switching differential
(operating line 128)
TBWw
Setpoint of d.h.w. temperature (operating line 26 or 28)
T
BWx1
Measured value d.h.w. storage tank sensor (B31)
T
BWx2
Measured value d.h.w. storage tank sensor (B32)
From the 2 tables above, it is obvious that when using 2 sensors, it is irrelevant which
of the 2 sensors is fitted at the top and which at the bottom of the d.h.w. storage tank.
.