64
20.2.11
S
UBSTITUTE
C
OMMON
F
LOW
T
EMPERATURE
(3538)
If a common flow sensor B10 is not connected, the cascade flow temperature is calculated depending on the setting of
parameter "Substitute common flow temp." There are 4 options available:
1.
None - No backup temperature is used for the cascade flow temperature. If a cascade is installed, the order
the cascade operates is calculated solely based on the output balance.
2.
Highest Source Value - The currently highest generator temperature determines the common flow
temperature.
i)
When a heat request to the cascade is made, the generators considered are only those that
currently deliver heat to it.
ii)
When there is no request for heat, all existing generators are considered.
3.
Internal source value -
The cascade master’s own generator determines the common flow temperature. If
this generator is not available or if its temperature sensor is faulty, the common flow temperature is not
valid.
4.
Mean Source Value - The temperature values of the generators currently released are averaged.
i)
The parameterized rated output of the individual generators is considered when averaging the
common flow temperature. Generators with great capacity have a greater impact on common flow
temperature averaging than generators with small capacity.
ii)
If no request to the cascade is made, a common flow temperature backup value is not calculated.
20.2.12
A
UTO
S
OURCE
S
EQUENCE
C
HANGE
O
VER
(3540)
Function "Auto source sequence changeover" can be used to balance capacity utilization of the generators in a
heating cascade. This is accomplished by defining the order of switching lead and lag generators.
i)
The generators are switched in the order of the LPB device addresses.
ii)
According to the number of hours run.
On completion of the number of hours set, the order of generators within the cascade changes. When
changing over, the generator with the next higher device address assumes the function of the lead
generator, and the previous lead generator is moved to the end of the generators (or generator group).
20.2.13
A
UTO
S
OURCE
S
EQUENCE
E
XCLUSION
(3541)
Setting the generator sequence exclusion is only used in connection with the activated generator sequence (line
3540). With generator exclusion, the first and/or last generator can be exempted from automatic changeover. There
are 4 options available:
1.
None - The order of switching on the generators changes when the number of hours set is reached (line
3540).
2.
First - The first generator in the addressing scheme always remains the lead generator. With the other
generators, the order of switching on changes when the set number of hours are reached (line 3540).
3.
Last - The last generator in the addressing scheme always remains the last. The other generators change
when the set number of hours are reached (line 3540).
4.
First and last - The first generator in the addressing scheme always remains the lead generator. The last
generator in the addressing scheme always remains the last. The generators in between change when the
set number of hours are reached (line 3540).
20.2.14
L
EADING
S
OURCE
(3544)
Setting of the "Leading source" is only used in connection with the fixed order of generator sequence (line 3540).
The generator defined as the lead generator is always the first to be switched on and the last to be switched off. The
other generators are switched in the order of their device addresses.
20.2.15
T
EMPERATURE
D
IFFERENTIAL
M
IN
(3590)
–
O
NLY IF A
C
OMMON
R
ETURN
S
ENSOR IS
F
ITTED
This function prevents excessive cascade return temperatures and improves the cascade’s switch-off behaviour.
If the temperature differential of flow and return sensor (B10 and B70) becomes smaller than the set minimum
temperature differential (line 3550), one of the generators is switched off as early as possible, independent of the
selected lead strategy.
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