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Note
Siemens Building Technologies
HVAC Products
26
Function block DRT and maximum
limitation of the return temperature
26.1
Operating lines
Line Function, parameter
171
Maximum limitation of primary return temperature heating circuits
172
Upper constant value, maximum limitation of the primary return
temperature
173
Slope, maximum limitation of the primary return temperature
174
Start of compensation (point of inflection), maximum limitation of the
primary return temperature
175
Lower constant value, maximum limitation of the primary return
temperature
176
Maximum setpoint of the return temperature with d.h.w. heating
177
Maximum limitation of the secondary return temperature, reduction
to the primary limit value
178
Integral action time of the primary return temperature limitations
179
Limit value of the maximum limitation of the temperature differential
180 Max. setpoint of the return temperature during d.h.w. heating on
legionella setpoint
This function block contains all parameters of the district heat network. Since many
district heat utilities demand locking of the settings, they are arranged on the locking
function level.
The following function blocks also belong to the locking function level. It includes all
operating lines from 171 through 196. This level can only be accessed with a code.
Also refer to subsection 31.1.6 "Setting levels and access rights".
In addition, locking on the hardware side is possible (operating line 196).
26.2
Maximum limitation of the primary return
temperature
26.2.1 General
The primary return temperature uses maximum limitation to
• ensure that too hot water will not be fed back to the district heat network
• minimize the pumping power of the district heat utility
• comply with the regulations of the utility (connection requirements)
Maximum limitation of the return temperature measures the return temperature on the
primary side and throttles the primary two-port valve if the limit value is exceeded.
Maximum limitation acts separately on both heating circuits and on the d.h.w. circuit.
The limit values and basic settings made on operating lines 172 through 178 apply to
both heating circuits, but the control operates independently.
With the types of plant that use a common flow (2–x and 3–x), the valid limit value is
controlled by the demand for heat of the heating circuits and of the d.h.w. circuit. When
both the heating circuits and the d.h.w. circuit call for heat, the higher of the limit values
applies.
Maximum limitation of the primary return temperature has priority over minimum limita-
tion of the flow temperature in the heating circuit.
For primary temperatures exceeding 130 °C, a Pt 500 temperature sensor can be used.
Basic documentation RVD240
26 Function block DRT and maximum limitation of the return temperature
Unit
Factory
Range
setting
0
0 / 1
Vari-
°C
70
able...140
7
0...40
°C
10
–50...+50
°C
50
0...variable
°C
---
--- / 0...140
°C
---
--- / 0...50
min
30
0...60
--.- /
K
--.-
0.5...50.0
°C
---
--- / 0...140
91/126
CE1P2384en
27.05.2004
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