Siemens Building Technologies
Basic Documentation RVL470
CE1P2522E / 30.03.2000
Landis & Staefa Division
Function block "District heat"
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12. Function block "District heat"
Together with function block "Three-position controller", this function block provides flow
temperature control in plants with an indirect (heat exchanger) or direct district heat
connection.
Depending on the type of plant, it acts as a
•
flow temperature controller for weather-compensated control of a space heating sys-
tem with a district heat connection (plant type 3)
•
primary controller for demand-compensated control of a main flow (plant type 6)
If the settings of this function have been locked (contact H3 or on operating line 198;
refer to the respective sections), the display shows
when pressing buttons
and
.
12.1. Operating lines
Line
Function, parameter
Unit
Factory
setting
Range
112
Maximum limitation of return temperature, slope
0.7
0.0...40
113
Maximum limitation of return temperature, start of
shifting limitation
°C
10
−
50...+50
114
Maximum limitation of return temperature Integral
action time
min
30
0...60
115
Maximum limitation of return temperature differential
°C
--.-
--.- / 0,5...50
116
Minimum stroke limitation (Y
min
function)
min
6
-- / 1...20
12.2. Limitations
12.2.1. Secondary flow temperature
Refer to section "9.2.1. Limitations of the flow temperature".
12.2.2. Maximum limitation of primary return temperature
12.2.2.1. Purpose
The primary return temperature uses maximum limitation to
•
make certain that too hot water will not be fed back to the district heat utility
•
minimize performance losses of the utility
•
comply with the utility’s regulations
12.2.2.2. Generation of maximum limit value
The maximum limit value is generated from the following variables:
•
Constant value (setting on operating line 101)
•
Slope (setting on operating line 112)
•
Start of compensation (setting on operating line 113)
The current limit value can be determined as follows:
•
If the outside temperature is higher than or equal to the value set for the start of com-
pensation (setting on operating line 113), the current limit value is the constant value
entered on operating line 101
•
If the outside temperature lies below the value set for the start of compensation, the
current limit value is calculated according to the following formula:
T
L
[°C] = T
L constant
+ [ ( T
L start
– T
A
)
*
s ]
