Viessmann Vitocrossal 300 Service Instructions For Contractors page 37

Further details regarding the individual steps
System version 2
One heating circuit without mixer,
one heating circuit with mixer and
DHW heating (optional solar DHW
heating)
Applications
Heating system with different heat sour-
ces and methods of DHW heating
■ One heating circuit without mixer
■ One heating circuit with 3-way mixer
Main components
■ Gas condensing boilers 26 to 60 kW
■ Heating circuit distribution
■ DHW cylinder (dual mode)
■ Solar thermal system
Function description
The heating circuits eP/rP and the DHW
cylinder qP/qR are regulated by the
boiler heating circuit controller 1. The
heating circuits and DHW cylinder are
each supplied by a separate circulation
pump eQ/rE and qE.
Heating mode
The boiler heating circuit controller reg-
ulates the boiler water temperature in
weather-compensated mode (= flow
temperature of the heating circuit without
mixer) and the temperature level of the
heating circuit with mixer via an exten-
sion kit for one heating circuit with
mixer.
Commissioning, inspection, maintenance
DHW heating without a solar thermal
system
If the temperature falls below the set
DHW temperature selected at control
unit 2, the burner of boiler 1 starts
and circulation pump qE of DHW cylin-
der qP or qR runs.
Within the periods selected at control
unit 2, DHW is heated with or without
priority.
In the case of absolute priority, heating
circuit pump rE of the heating circuit with
mixer is switched off and mixer rR is
closed. With modulating priority, the
heating circuit pump rE of the heating
circuit with mixer remains on, and mixer
rR is closed far enough for the set boiler
water temperature for cylinder heating to
be reached. In this case, DHW cylinder
qP or qR and heating circuit with mixer
rP are heated simultaneously.
DHW heating by the solar thermal
system
Solar circuit pump wE starts and DHW
cylinder qR is heated up, if the tempera-
ture differential between collector tem-
perature sensor wQ and cylinder temper-
ature sensor qT exceeds the start tem-
perature differential.
Pump wE is stopped according to the fol-
lowing criteria:
■ The actual temperature drops below
the stop temperature differential
■ Exceeding the electronic temperature
limit (up to 90 °C) set in the solar con-
trol module (type SM1) wZ
■ The temperature selected at high limit
safety cut-out qZ (if installed) is
reached
(cont.)
37