ation on the outdoor temperature sensors.
An active delayed outdoor temperature adaptation is signalized in the operating level by a
blinking outdoor temperature in the display. When you keep key pressed down, the Calcu-
lated outdoor temperature is shown in the display.
If the function Time-controlled summer time operation (FB 3 = ON) is activated, the calculated
outdoor temperature is not indicated in the display.
4.8 Limitation of the return flow temperature
For an economical operation of a district heating system, it is required that as much heat as
possible be extracted from the heat transfer medium (water) circulating through the system. The
difference in temperature between the flow and return flow in the network is used to indicate
how much energy is being consumed: a large difference in temperature indicates a high level of
energy efficiency and a small difference indicates a low level of energy efficiency. One return
flow temperature sensor is sufficient to evaluate the difference in temperature when the flow
temperature in the network is predetermined.
The function is as follows: the return flow temperature can either be limited depending on the
outdoor temperature (variable) or by a fixed value. If the return flow temperature measured at
the return flow sensor RüF1 exceeds the limit value calculated from the set return flow charac-
teristic or the fixed limitation value by the value x, the respective calculated or fixed set point
(flow temperature of heating, charging temperature) is reduced by the value x, multiplied by re-
turn flow temperature limitation factor. As a result, the primary flow rate is reduced with the ef-
fect that the return flow temperature drops. Both the measured value of the Return flow tem-
perature and the set point (flow temperature of heating, charging temperature) blink in the dis-
play when a limitation case occurs. The function is already activated by the function block set-
ting FB 20 = ON.
In system code numbers 2 and 3 (drinking water heating implemented in the secondary circuit),
the controller switches during the heating up of drinking water over to the parameter Return
flow limitation temperature during drinking water heating from the return flow temperature
limitation value (calculated from the return flow temperature limitation characteristic). This en-
sures that the return flow limitation temperature in the heating circuit can be held low in the sea-
sonal interim period.
In system code number 4, a separate return flow temperature limitation in the drinking water
circuit is additionally possible, provided FB 21 = ON.
System code number 5 allows you to include the return flow temperature of the drinking water
circuit. For this purpose, the return flow temperature sensor must be mounted in a return flow
pipe used in both circuits, and the function block FB 21 must be activated (ON). When FB 21 is
activated (ON), the parameter Return flow limitation temperature during drinking water heat-
ing (the temperature is adjustable at the controller) is activated. When drinking water is being
heated, the highest value from both return flow temperature limitation values (heating circuit
and drinking water circuit) is used for the limitation control. When a limitation occurs, both the
set point in the heating circuit and the set point in the drinking water circuit are reduced. If the
priority for drinking water through set-back operation is additionally activated (FB 8 = ON, set-
ting "Ab"), the reduced heating circuit set point is also further reduced when a limitation occurs!
In system code number 6, a return flow temperature limitation is only possible in the heating cir-
cuit.
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