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Siemens Building Technologies
Basic Documentation RVL471
CE1P2524E
HVAC Products
14 Function block "District heat"
23.10.2002
14 Function block "District heat"
Together with function block "3-position actuator heating circuit", 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, if acts as a
•
flow temperature controller for weather-compensated control of space heating with a
district heat connection (plant type 3–x)
•
primary controller for demand-compensated control of a main flow (plant type 6–x)
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
.
14.1 Operating lines
Line
Function, parameter
Unit
Factory
setting
Range
112
Slope of maximum limitation of return temperature
0.7
0.0...40
113
Start of shifting limitation of maximum limitation of return
temperature
°C
10
−
50...+50
114
Integral action time of maximum limitation of return tem-
perature
min
30
0...60
115
Maximum limitation of return temperature differential
°C
--.-
--.- / 0,5...50
116
Minimum stroke limitation (Ymin function)
min
6
-- / 1...20
14.2 Limitations
14.2.1
Maximum limitation of the primary return temperature
The primary return temperature uses maximum limitation to
•
make certain that too hot water will not be fed back to the district heating network
•
minimize piping losses of the district heating utility
•
comply with the regulations of the utility
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 is lower than 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 ]
Purpose
Generation of the maxi-
mum limit value