Example Layout 2 - Viessmann Vitocrossal 300 Service Manual

Service

Example Layout 2

System version 2
One heating circuit without mixing valve, one heating
circuit with mixing valve and DHW heating (optional solar
DHW heating)
Applications
Heating system with different heat sources and methods
of DHW heating
One heating circuit without mixing valve

One heating circuit with 3-way mixing valve

Main components
Gas condensing boilers 26 to 57 kW

Heating circuit distribution

DHW tank (dual mode)

Solar thermal system

Function description
The heating circuits eP/rP and the DHW tank qP/qR
are regulated by the boiler heating circuit controller 1.
The heating circuits and DHW tank are each supplied
by a separate circulation pump eQ/rE and qE.
Heating mode
The boiler heating circuit controller regulates the boiler
water temperature in weather-compensated mode
(= supply temperature of the heating circuit without
mixing valve) and the temperature level of the heating
circuit with mixing valve via an extension kit for one
heating circuit with mixing valve.
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 tank qP or qR runs.
Within the time program 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 mixing valve is switched off
and mixing valve rR is closed. With modulating priority,
the heating circuit pump rE of the heating circuit with
mixing valve remains on, and mixing valve rR is closed
far enough for the set boiler water temperature for tank
heating to be reached.
In this case, DHW tank qP or qR and heating circuit with
mixing valve rP are heated simultaneously.
32
Vitocrossal 300 CU3A 26 to 57 Service
DHW heating by the solar thermal system
Solar circuit pump wE starts and DHW tank qR is heated
up, if the temperature differential between collector
temperature sensor wQ and tank temperature
sensor qT exceeds the start temperature differential.
Pump wE is stopped according to the following criteria:
The actual temperature drops below the stop

temperature differential
Exceeding the electronic temperature limit [up to 194°F

(90°C)] set in the solar control module (type SM1) wZ
The temperature selected at high limit safety cut-out

qZ (if installed) is reached
Demands for the auxiliary function are met by circulation
pump wR.
Suppression of reheating of the DHW tank by the boiler
in conjunction with solar control module (type SM1)
Reheating suppression takes place in two stages.
Reheating DHW tank qR by boiler 1 is suppressed
as soon as DHW tank qR is heated by collectors wP. For
this, the set tank temperature for reheating is reduced by
boiler 1. Suppression remains active for a certain time
after solar circuit pump wE has been
switched off.
In the case of uninterrupted heating by collectors wP
(> 2 h) boiler 1 will only reheat, if the set tank
temperature (coding address "67") selected at boiler
circuit control unit 2 is not achieved.
In control unit 2, coding address "67" defaults a third
set DHW temperature [setting range 50 to 203°F
(10 to 95°C)].
This value must be below the first set DHW temperature.
DHW tank qR will only be heated by boiler 1 when
this set value is no longer achieved by the solar thermal
system.
Function/system
components
Operation with LPG
System with only one
heating circuit with mixing
valve (without unregulated
heating circuit)
Code
Adjust Delivered condition
82:1 82:0
00:4 00:6
00:3 00:5