Siemens RVL471 - Temperature and D.h.w. Switching Differential

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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
2524D02
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.
.