Viessmann Vitotronic 100 GC1 Installation And Service Instructions Manual page 108

Function description – Vitotronic 300-K, MW1S
Cascade control
(cont.)
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.
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.
108
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 series hydraulic boiler arrangement,
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 series boiler arrangement, only the
net calorific strategy 2 (see page 110)
is useful. The conventional boiler is
started late and is also shut down late.
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.