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Siemens Building Technologies
Basic documentation RVD240
CE1P2384en
HVAC Products
26 Function block DRT and maximum limitation of the return temperature
27.05.2004
active. If that setpoint is set inactive (operating line 180 =
- - -
), there will be no maximum
limitation of the return temperature during the time the legionella function is active.
When both the heating and the d.h.w. circuit call for heat
and
maximum limitation of the
return temperature acts on both circuits, the higher of the two limit values applies.
If, with plant type 1–3, maximum limitation of the return temperature is deactivated (en-
try ---), the d.h.w. temperature will be controlled according to the return temperature
acquired with sensor B71 because there is no sensor in the d.h.w. flow. The controlled
setpoint is the sum of the current d.h.w. setpoint plus the charging boost (operating
line 116).
The current d.h.w. setpoint is generated internally and can be visualized as follows:
Select operating line 26 and press
.
26.3 Maximum limitation of the secondary return
temperature
The secondary return temperature of both the heating and the d.h.w. circuit can be
limited at a maximum, depending on the type of plant. The limit value is to be entered
on operating line 177 as a reduction to the current limit value of the maximum limitation
of the primary return temperature.
This function can become active only when the respective maximum limitation of the
primary return temperature (heating circuits or d.h.w.) is switched on. Maximum limita-
tion of the primary return temperature can be deactivated on operating line 171 for the
heating circuit return (separately for each heating circuit), and on operating line 176 for
the d.h.w. return.
With plant type no. 2–2, the parameters are selected as follows:
Operating line 171 = 1
Maximum limitation of return temperature heating circuit
2 ON
Operating line 172 = 70 °C Upper constant value
Operating line 173 = 7
Slope
Operating line 174 = 10 °C Start of compensation at an outside temperature of
10 °C
Operating line 175 = 50 °C Lower constant value
Operating line 176 = 55 °C Maximum limitation of the return temperature in the
d.h.w. circuit
Operating line 177 = 5 °C
Reduction on the secondary side
When the outside temperature changes, the maximum limitations will change also:
Heating circuit 1
D.h.w. circuit
Outside tem-
perature
Primary side
Secondary side
Primary side Secondary side
15 °C
50 °C (operating
line 175)
45 °C (operating
line 175...177)
–5 °C*
60.5 °C**
55.5 °C
–20 °C
70 °C (operating
line 172)
65 °C (operating
line 172...177)
55 °C (oper-
ating line
176)
50 °C (operating
line 176...177)
* With shifting compensation
** Equation according to subsection 26.2.2 “Maximum limitation in heating mode
Example
