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SYSTEM MANAGEMENT
5.12 Parameter 148: operating mode of the
cascade
It is possible to adopt cascade management which can be mod-
ified according to different strategies. These different strategies
can be set using the parameter known as "Cascade mode" Par.
148.
The start-up/shutdown law of each module is based on the fol-
lowing graph.
In the central band (Power Balance) no start-ups and/or shut-
downs of the Depending units are envisaged.
The shut-off values of the lines with the y axis are the sum or
the difference of the values of the corresponding parameter in
relation to the value of the setpoint sent by the Manging module
to the modules.
Setp + Par 146
-1
-1
-1
-1
-1
-1
-1
-1
Setp + Par 145
-1
-1
Setp + Par 78
Setpoint
Setp - Par 77
-1
-1
Setp - Par 144
+1
+1
+1
+1
+1
+1
+1
+1
Six bands are defined on the basis of the temperature read (by
the Managing module) on the delivery manifold of the primary
system.
− In the central band Power balance, which is defined
(again by variable parameters) around the setpoint.
− In the band Remove dependent and Add dependent,
the start-ups and shutdowns are carried out with "long"
time intervals which can differ between start-up and
shutdown.
The parameters which define this band are 77, 78, 144,
145. The time interval is defined by parameters 75 and
76.
− In the band Remove dependent Faster and Add depend-
ent Faster, start-ups and shutdowns are carried out with
a "short" time interval which, even in this case, can differ
between start-up and shutdown. The shutdown band is
between the values of parameters 146 and 145, while the
start-up band is below the value defined by parameter
144. The time range is defined by parameters 142 and 143.
− In the band Clear demand, all the thermal modules are
immediately stopped. This band is above the value de-
fined by parameter 146.
Clear Demand
(no time)
Remove Depending faster
Time = Par 143
-1
-1
-1
-1
-1
-1
-1
-1
Remove depending
-1
-1
Time = Par 76
Power Balance
Add Depending
-1
-1
Time = Par 75
Add Depending faster
+1
+1
+1
+1
+1
+1
+1
+1
Time = Par 142
5.12.1
Par 148 = 1
Not applicable
5.12.2
Par 148 = 2
In this mode the system manages the cascade so that the max-
imum number of modules is on.
This mode is similar to mode 0 apart from the start-up and
shutdown rules.
In this case the rules based on the information illustrated by the
previous graph are still valid, with the following differences (in
any case, always applicable to the "balancing" band only):
To add an additional depending module, the managing module
evaluates whether the sum of the power (calculated on the ba-
sis of the fan speed) of all the active thermal modules is greater
than the product between the number of the active depend-
ing modules increased by one and the minimum power value
(Par 152) increased by a hysteresis value (defined by Par 153). [Σ(
P1,P2,...Pn) > (n+1) * (Par 152) + (Par 153)].
To shutdown a depending access, the managing module eval-
uates whether the sum of the power (calculated on the basis of
the fan speed) of all the active thermal modules is less than the
product between the number of the active depending modules
and the minimum power value (Par 152). [Σ( P1,P2,...Pn) < (n) *
(Par 152)].
5.12.3
Par 148 = 3
In this mode the system manages the cascade so that the min-
imum number of modules is on.
This mode is similar to mode 0 apart from the start-up and
shutdown rules.
In this case the rules based on the information illustrated by the
previous graph are still valid, with the following differences (in
any case, always applicable to the "balancing" band only):
To start up an additional depending unit, the managing unit
evaluates whether the total power (calculated based on the fan
speed) of all the active thermal units is greater than the product
between the number of the active depending units increased
by one and the minimum power value (Par 82). [Σ( P1,P2,...Pn)
>(n+1) * (Par 82)].
To shut down a depending unit that has been started up, the
managing unit evaluates whether the total power (calculated
based on the fan speed) of all the active thermal units is less
than the product between the number of the active depending
units and the maximum power value (Par 83). [Σ( P1,P2,...Pn) <
(n) * (Par 83)].
9
We must consider that the percentage of power varies from
a minimum of 1% to a maximum of 100% and therefore,
the parameter values 152 and 153 are not to be taken as the
percentage of absolute power but relate to the units which
are active.
132
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