Viessmann Vitocrossal 300 CA3 2.5 Installation And Service Instructions Manual page 129

Vitocrossal 300 CA3 Series 2.5 to 6.0 Installation/Service
Heating Circuit Control
DHW temperature
Priority control
H With priority control: (coding address "a2:2" in the
"Heating circuit..." group):
The set supply temperature will be adjusted to 32°F
(0°C) during tank heating. The mixing valve closes
and the heating circuit pump is switched off.
H Without priority control:
The heating circuit control unit continues to operate
with the same set value.
H With modulating priority control in conjunction with
heating circuits with mixing valve:
The heating circuit pump remains switched on.
During tank heating the set supply temperature
of the heating circuit will be reduced until the set
boiler water temperature has been reached.
The set supply temperature is determined from the
following coding:
– Outdoor temperature
– Differential between the set and the actual boiler
water temperature
– Heating curve slope and shift
– Set coding "a2" in the "Heating circuit..." group
Heating circuit pump logic – Economy circuits
The heating circuit pump is switched OFF [set supply
temperature set to 32°F (0°C)] if one of the following
criteria is met:
H The outdoor temperature selected in coding "a5"
in the "Heating circuit..." group exceeds the set value.
H The adjusted outdoor temperature exceeds the value
set in coding"a6" in the "Heating circuit..." group.
H The mixing valve has been attempting to close for more
than 12 min. (mixing valve economy function, coding
"a7" in the "Heating circuit..." group).
H The pump idle time selected in coding "a9"
in the "Heating circuit ..." group is reached.
Requirements:
– There is no risk of frost.
– Coding "b0" in the "Heating circuit..." group
must be set to 0.
Note: If, during the pump idle time, the system
is switched to heating mode or the set room
temperature is increased, the heating circuit
pump is switched ON,even if the time has
not yet elapsed.
H The actual room temperature exceeds the value
set in coding "b5" in the "Heating circuit ..." group.
(continued)
System dynamics
The mixing valve control characteristics can be influenced
at coding "c4" in the "Heating circuit..." group.
Central control
Coding "7a" in the "General" group enables you
to program central control to one heating circuit.
The operating and holiday program then applies to
all additional heating circuits of the system.
For these heating circuits, when the operating and
holiday program is enabled,"Central control" is displayed.
Any holiday programs that may have been set will be
deleted.
Party and economy modes cannot be enabled on all
control units.
Frost protection
The supply temperature is held in accordance with the
heating curve for the reduced set room temperature,
but at least at 50°F (10°C).
A variable frost limit can be set in line with coding
address "a3" in the "Heating circuit..." group.
Function Description
129