Viessmann VITOLIGNO 300-C Installation And Service Instructions Manual page 24

Boiler Connections
Vitoligno 300-C Installation/Service
System Layout 3
Applications
DHW heating and central heating backup by the solar thermal
system; DHW and central heating by the pellet boiler.
Heating the heating water buffer tank
The boiler is started when a heat demand is issued to heat
the heating circuits. If the temperature at top boiler start
sensor 5 falls below the set value determined by the
control unit of solid fuel boiler 2, solid fuel boiler 1
starts up. Boiler circuit pump qZ delivers the heating
water to the heating water buffer tank. Any heat not
absorbed by heating circuits rP/tP is stored in the heating
water buffer tank. Heating of the heating water buffer
tank is stopped as soon as bottom buffer tank temperature
sensor 6 exceeds the set value determined by the solid
fuel boiler control unit.
Low temperature protection package
Solid fuel boiler 1 requires a minimum return temperature.
When boiler circuit pump qZ is running, the valve of return
low temperature protection package qU opens the route
from the central heating return to boiler 1 in line with the
increasing return temperature and closes the route from the
boiler supply to the boiler return (bypass).
Heating by heating water buffer tank
The heat required to heat heating circuits rP/tP is taken
from heating water buffer tank qP via heating circuit
pumps rQ/tQ. The respective supply temperatures are
controlled to their set value in weather-compensated
mode via 3-way mixing valves rE/tE.
Heating circuit control with mixing valves
The set supply temperature of every heating circuit is
determined by the following parameters: outdoor
temperature, set room temperature, operating mode and
heating curve. The supply temperature of mixing valve
circuits rP/tP is controlled by incremental opening and
closing of mixing valves rE/tE.
DHW heating by solid fuel boiler
The boiler is started when a heat demand is issued for DHW
heating. If the temperature at top buffer tank temperature
sensor 4 falls below the set value determined by the
control unit of solid fuel boiler 2, solid fuel boiler 1
starts up. Boiler circuit pump qZ delivers the heating water
to the heating water buffer tank. Heating of the heating
water buffer tank is stopped as soon as bottom buffer tank
temperature sensor 6 reaches the shutdown temperature.
Heating of the heating water buffer tank with solar energy
If the temperature differential between collector temperature
sensor wT and return temperature sensor wZ (bottom buffer
tank temperature sensor) exceeds the set start temperature
differential, speed-controlled solar circuit pump wE is started
and the heating water buffer tank is heated up. If the
temperature differentials reach their shutdown thresholds,
the solar circuit pump is switched off accordingly. When the
set temperature selected at the solar control unit is reached
at bottom reference temperature sensor wZ, solar heating of
the heating water buffer tank is stopped.
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