Siemens RVL471 - 13 Function Block Setpoint of Return Temperature Limitation; Operating Line; Description; Minimum Limitation of the Return Temperature

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Siemens Building Technologies Basic Documentation RVL471 CE1P2524E
HVAC Products 13 Function block "Setpoint of return temperature limitation" 23.10.2002
13 Function block "Setpoint of return
temperature limitation"
On the function block "Setpoint of return temperature limitation”, the setpoint of mini-
mum limitation of the return temperature or the constant value for shifting maximum
limitation of the return temperature can be adjusted.
13.1 Operating line
Line Function, parameter Unit
Factory
setting
Range
101 Setpoint of return temperature limitation – Constant value °C --- --- / 0...140
13.2 Description
On operating line 101, the setpoint of minimum limitation of the return temperature or
the constant value for shifting maximum limitation of the return temperature can be
adjusted.
When entering ---, the function is deactivated, which means that the return temperature
will not be limited.
For more detailed information about the function “Maximum limitation of the return tem-
perature”, refer to section “14 Function block "District heat"”.
If the settings of this function block have been locked (contact H3, or on operating line
198; refer to the respective sections), the display shows
when pressing buttons
and .
13.3 Minimum limitation of the return temperature
This function block ensures minimum limitation of the boiler return temperature where
possible or required. This applies to the following plant types:
• Plant type 1–x – space heating with mixing valve
• Plant type 4–x – precontrol with mixing valve
• Plant type 5–x – precontrol with boiler
Minimum limitation of the return temperature prevents boiler corrosion due to flue gas
condensation.
13.3.1 Acquisition of measured values
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return. With plant type 1–x, the return temperature can also be delivered via LPB. In
interconnected plants, only one return temperature sensor per segment may be used.
13.3.2 Mode of operation
If the return temperature falls below the set minimum limit value, the temperature differ-
ential between minimum limit value and actual value will be integrated. From this, a
critical locking signal will be generated and transmitted to the connected loads. This
causes the loads to reduce their setpoints, thus consuming less energy.
If the return temperature returns to a level above the minimum limit, the integral will be
reduced, resulting in a reduction of the critical locking signal. The connencted loads rise
their setpoint values.