Boiler Control Alternatives
16
VITOROND 200, VD2A
Single-Boiler System: Vitorond 200, VD2A with Therm-Control
Applications
Heating system with manifold installed close
to the boiler. The boiler water flow rate
must be able to be reduced.
Main components
Single boiler system with:
H
Vitorond 200, VD2A, 125 to 270.
H
Vitotronic 300, GW2 model or Vitotronic
100, GC1 model with Vitocontrol panel
and integral weather-compensated
Vitotronic 200-H, HK1S / HK3S model or
Vitotronic 100, GC1 model and external
weather-compensated control unit.
H
Therm-Control for operating boilers
without low temperature return package.
Function description
The Therm-Control will affect the heating
control unit(s) or the heating circuit pump(s),
if the factory-set temperatures are not
reached at the Therm-Control temperature
sensor. In the start-up phase (e.g. during
commissioning or after a night or weekend
shutdown), the boiler water flow rate must
be reduced by at least 50%.
The boiler is protected to an optimum level
when using the Vitotronic 300, GW2 model
or if the heating circuits are regulated via a
Vitotronic 200-H connected to the boiler
control unit. No additional on-site protective
measures are required.
When it is impossible to reduce the boiler
water flow rate, e.g. in older systems, we
recommend contacting Viessmann for other
possible piping layouts.
No minimum return water temperature
needs to be maintained. Shunt pumps and/or
boiler circuit pumps/costly mixing valves are
not required for elevating the return
temperature.
DHW heating
The DHW is heated up when the actual
temperature falls below the DHW
temperature selected for the tank
temperature sensor, subject to tank heating
being enabled by the time switch.
The boiler water temperature is raised to the
set DHW tempe20 K / 36ºF and the
tank primary pump is started, if the boiler
water temperature is 7 K / 12.6ºF above the
actual DHW temperature.
The heating circuit pumps M2 and M3 are
closed, subject to absolute priority being
enabled, if the heating circuits are regulated
via the Vitotronic. Subject to modulating
priority, the heating circuit pumps M2 and
M3 remain switched ON and the mixing
valves M2 and M3 are closed far enough for
the set boiler water temperature for tank
heating to be achieved.
Heating operation
Depending on the control unit used, the flow
temperature of heating circuits can be
operated in modulating mode, subject to the
outside temperature. The boiler water
temperature is regulated 8 K / 14.4ºF higher
than the set flow temperature.
Wiring Diagram: Single-Boiler System, Vitorond 200, VD2A with Therm-Control
The Therm-Control wiring in heating
systems with heating circuit control units, is
not connected to the boiler control unit via
the LON.
Required coding:
Change “4C” to “2” - use the plug-in
connector
sÖ
A1 to close the downstream
mixing valve. Change “0D” to “1” - the
Therm-Control acts on the mixing valve of
the downstream heating circuits (for
Vitotronic 200 and 300, delivered
condition).
Legend
A
Contactor relay, field supplied
sÖ
A1 Closing mixing valves (Vitotronic 100,
GC1)
A
Contactor relay, field supplied
B
Downstream heating circuit control
unit
Switching contact closed:
signal for close mixing valve(s)
C
Power connection 120 VAC 60 Hz
D
Junction box, field supplied
5
3
5
4
7
8
7
v
1
.2
Fig. 11
A
A
C
D
A
B
