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Cascade CH setpoint adaption
When the system temperature is not high enough the setpoint for all boilers will be adjusted.
The boiler setpoint will be increased when the system temperature drops below Cascade_Setpoint and decreased
when it rises above Cascade_Setpoint temperature.
Dependent Boiler
The CH mode for the cascade is defined by the setting of the managing boiler. CH mode settings on dependents
are ignored. In case a boiler is set as dependent (Address = 2-8/16) the setpoint is always provided by the
managing boiler.
The modulating power of the ALL boilers is PID controlled by the boiler itself by comparing the calculated setpoint
from the managing boiler and T_Supply. The managing boiler itself will be controlled in the cascade system as it
would as if it was a dependent boiler. Only the circulators and sensor inputs are used.
Boiler input Rates
A cascade system operates most effective and efficiently when all of the boilers in the system are the same size.
15.2.4
C
– D
ASCADE
OMESTIC
In the installer DHW menu of the managing boiler control the DHW_Mode must be set.
Available DHW modes in cascade are mode 1 or 2.
Dependent Boiler
In case a boiler is set as dependent (Address = 2-8/16) the DHW setpoint is always provided by the managing
boiler, the internal control of the setpoint functions are disabled.
Managing Boiler
If there is a request for a "Store Warm Hold" for the tank and no central heating request the managing boiler is
going to burn for the DHW tank. This (the heating of the DHW tank) is interrupted when there comes a central
heating request and the managing boiler and cascade are burning for the central heating system.
15.2.5
C
– DHW
ASCADE
The boiler cascade system has multiple options for priority and parallel DHW and heating.
The following levels of priority are configurable (and possible):
Priority level
Description
0)
Switch Priority
When both CH and DHW demand have to be served, the priority it is given to the DHW demand
for a given interval (indicated with parameter Minute_Switch_Priority).
As soon as the interval has expired the priority switches to CH demand.
The interval time will be reloaded and priority will switch again after the interval is over.
1)
CH
The priority is permanently given to CH Demand
2)
DHW
The priority is permanently given to DHW Demand
Table 15-2
Relevant variables
Specific Parameters
DHW Priority
Both, CH or DHW priority, Parallel
DHW Max Priority Timer
Interval time for switching the priority
Table 15-3
15.2.6
C
– S
ASCADE
TART
The managing boiler sends the calculated Cascade_Setpoint to the dependent boilers. The power of the boilers
is PID controlled based on the Calculated_Setpoint and T_Supply. Depending on the temperature difference
between T_System and Cascade_Setpoint (CH or DHW) the dependent boilers will start or stop using different
algorithms.
Quick Starting and Stopping Boilers
When there is a big difference between the T_System and the Cascade_Setpoint the call for a start or stop of the
next or last depending is done quicker.
H
W
S
OT
ATER
ETTINGS
PRIORITY
Level
(Default) Value
2: Installer
2
2: Installer
60 min.
/
STOP SEQUENCE
E93.1601EN032.C VGH installation manual
Range
0, 1, 2
1..60 min.
95
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