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Siemens Building Technologies
HVAC Products
26.2.2 Maximum limitation in heating mode
The limit value for maximum limitation in heating mode is generated from the following
variables:
• Function can be activated or deactivated for each heating circuit (selection on oper-
ating line 171)
• Upper constant value (setting on operating line 172)
• Lower constant value (setting on operating line 175)
• Slope (setting on operating line 173)
• Start of compensation (setting on operating line 174)
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
compensation (setting on operating line 174), the current limit value is the constant
value entered on operating line 175
• 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
= T
+ [ ( T
L
L constant min
However, the current limit value T
T
PR
90
80
70
T
L constant min
60
50
40
30
20
30
20
10
T
A
s
Slope (operating line 173)
T
Actual outside temperature
A
T
Upper constant value (operating line 172)
L constant
T
Lower constant value (operating line 175)
L constant
T
Start of compensation (operating line 174)
L start
T
Primary return temperature
PR
Limitation operates according to the selected characteristic:
• When the outside temperature falls, the return temperature will initially be limited to
the lower constant value
• If the outside temperature continues to fall, it will reach the selected starting point for
shifting compensation. From this point, the limit value will be raised as the outside
temperature falls. The slope of this section of the characteristic can be adjusted.
The setting range is 0...40; the effective value is 10 times smaller
• If the outside temperature falls further, the return temperature will be limited to the
upper constant value
26.2.3 Maximum limitation in d.h.w. mode
In contrast to maximum limitation in heating mode, maximum limitation of the primary
return temperature in d.h.w. mode uses a constant value. It is to be set on operating
line 176.
In order to reach the required anti-legionella temperature in the storage tank, a specific
maximum return temperature setpoint is used during the time the legionella function is
Basic documentation RVD240
26 Function block DRT and maximum limitation of the return temperature
– T
) × s × 0.1 ]
L start
A
cannot be higher than the upper limit value.
L
T
L constant max
s
T
L start
-10
0
CE1P2384en
27.05.2004
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