Parameter 148: Operating Mode Of The Cascade; Par 148 = 0; Par 148 = 1 - Riello Condexa PRO NA 75P Installation, Operation And Service Manual

171 defines the time (from the start of the request) from which
the setpoint modulation is started
176 defines the proportional term for setpoint modulation
177 defines the integrative term for setpoint modulation

6.4 Parameter 148: operating mode of the cascade

It is possible to adopt cascade management which can be modi-
fied according to different strategies. These different strategies can
be set using the parameter known as "Cascade mode" Par. 148.

6.4.1 Par 148 = 0

The start-up/shutdown of each boiler is based on the following
graph.
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 rela-
tion to the value of the setpoint sent by the Manging boiler to the
boilers.
Setp + Par 146
-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 options are defined on the basis of the temperature read (by
the Managing boiler) on the supply manifold of the primary sys-
tem.
− In the central option,Power balance, defined (by the vari-
able parameters) around a setpoint, no start-ups or shut-
downs of the Depending boilers are made.
The parameters which define this band are 77 and 78.
− In the options,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 options,Remove dependent Faster and Add depen-
dent 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 option 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 option, Clear demand, all the boilers are immedi-
ately stopped. This option is above the value defined by
parameter 146.
Clear Demand
(no time)
Remove Depending faster
Time = Par 143
-1 -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

6.4.2 Par 148 = 1

In this mode the system manages the cascade so that the mini-
mum number of boilers is on.
The first difference in relation to mode 0 refers to the logic with
which the modulation of the Depending boilers within the cas-
cade is managed.
In fact, while each boiler modulates with its own PID in mode 0,
no more than two Depending boilers modulate with the same cri-
teria in mode 1, while the remaining boilers operate at maximum
power. The diagram is represented in the following figure:
Managing
PID
Managing
PID PID
Managing
100% PID
Managing
100% 100%
Managing
100% 100%
Practically speaking, if more than two boilers are on, only two
boilers are controlled via PID, while the others receive a signal to
move to maximum power.
The second difference refers to the start-up/shutdown rules of the
individual modules.
In any case, the start-up and shutdown rules are managed ac-
cording to the indications shown in the previous graph. The dif-
ference is that it is also possible to have start-ups/shutdowns of
the Depending boilers in the "balancing" zone.
This additional start-up criteria (valid in the balancing band only)
ensures that a boiler is started-up when any one of the two boil-
ers controlled by a PID adjustment has reached a threshold power
(Par 82) once a specific wait time defined by Par 75 has elapsed.
Similarly (still within the balancing band), a boiler is shutdown if
both boilers controlled by a PID adjustment have reached a per-
centage of power which is below the minimum power threshold
(Par 83) once a specific wait time defined by Par 75 has elapsed.
97
SETTING PARAMETERS OF THE CASCADE SYSTEMS
PID
PID PID
100% PID PID