Technical data

125
Function description – Vitocontrol-S, VD2/CT3/CM2
Cascade control (continued)
Control sequence
Stand-alone (Autonomous) type of control sequence
Parallel boiler arrangement
(coding 3b: 0 without supply
temperature sensor or
coding 3b: 1 with supply
temperature sensor)
With the stand-alone type of control in
a parallel hydraulic boiler arrangement,
the cascade control unit defaults the
set boiler water temperature for all
active boilers.
Every Vitotronic 100, GC1 individually
regulates the defaulted set
temperature.
Boilers arranged in series
(coding 3b: 2 without supply
temperature sensor or
coding 3b: 3 with supply
temperature sensor)
With the stand-alone type of control in
a hydraulic boiler arrangement series,
the cascade control unit pre-sets the
set boiler water temperature for all
active boilers.
Difference to parallel arrangement:
When the lead boiler (condensing boiler)
does not achieve the required boiler water
temperature, it will only act to control the
return temperature of all downstream
boilers.
In a boiler arrangement series, only the
net calorific strategy 2 (see page 127) is
useful. The conventional boiler is
started late and is also shut down late.
The control sequence is subject to the start-up and shutdown criteria set by the control strategy (coding address 3C):
Gross calorific strategy.
Net calorific strategy 1.
Net calorific strategy 2.
With supply temperature sensor:
The control deviation is calculated from
the set supply temperature and the
actual supply temperature to determine
the start-up and shutdown criteria.
Without supply temperature sensor:
The control deviation is calculated from
the set boiler water temperature and
estimated average actual boiler water
temperature of the active boiler to
determine start-up and shutdown
criteria. Only those boilers are taken
into consideration whose isolation
valve is not closed.
5351 340 v1.4