Siemens Building Technologies
Basic Documentation RVL470
CE1P2522E / 30.03.2000
Landis & Staefa Division
Function block "Setpoint of return temperature limitation"
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11. 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.
11.1. Operating line
Line
Function, parameter
Unit
Factory
setting
Range
101
Minimum limitation of return temperature
°C
---
--- / 0...140
11.2. Description
On operating line 101, the setpoint resp. the constant value are adjusted on operating
line 101. When entering ---, the function is deactivated, which means that the return
temperature will not be limited.
For more detailed information about these functions, refer to section “12. 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
.
11.3. 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 no. 1, "Space heating with mixing valve"
•
Plant type no. 4, "Precontrol with mixing valve"
•
Plant type no. 5, "Precontrol with boiler"
Minimum limitation of the boiler return temperature prevents boiler corrosion resulting
from flue gas condensation.
11.3.1. Acquisition of the measured values
A temperature sensor with a sensing element LG-Ni 1000
Ω
at 0 °C is required in the
return. With plant type no. 1, the return temperature can also be delivered via LPB. In
interconnected plants, only one return temperature sensor per segment may be used.
11.3.2. 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 criti-
cal 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 return temperature limit,
the integral will be reduced, resulting in a reduction of the critical locking signal, and
connected loads raise their setpoints again.
When the integral reaches the value of zero, the minimum return temperature limitation
will be deactivated, in which case the critical locking signal is zero.
If minimum limitation of the return temperature is active, the display shows .
Minimum limitation of the return temperature can be deactivated.
Section provides 13.4.7. “Gain of locking signal” information on who the critical locking
signal is sent to and how the loads respond to it.
The minimum limit value is to be set on operating line 101. Setting --- = inactive.
