Viessmann VITOCAL 250-A - Page 95

95
2796.0 Enable external heat generator, room heating
The external heat generator can be enabled for heat-
ing mode.
If the heat pump cannot cover the heat demand from
the heating circuits, the external heat generator is star-
ted. If the boiler water temperature is sufficiently high,
the boiler water will be supplied to the heating circuits
via the mixer for external heat generators (downstream
of the buffer cylinder). This mixer regulates to the set
flow temperature of the system.
Other conditions for room heating with an external heat
generator:
■
The dual mode temperature is not reached.
Or
■
There is a special heat demand, e.g. frost protection
of a system component.
Value Meaning
0 External heat generator is blocked for room
heating.
1 External heat generator is enabled for room
heating.
2796.1 Enable external heat generator, DHW heating
The external heat generator can be enabled for DHW
heating.
If the heat pump cannot cover the heat demand from
the DHW cylinder, the circulation pump for DHW
reheating and the external heat generator will be acti-
vated.
Value Meaning
0 External heat generator is blocked for DHW
heating.
1 External heat generator is enabled for DHW
heating.
2853 Start delay, external heat generator
2853.0 Start threshold, external heat generator
To prevent the external heat generator starting immedi-
ately if the set flow temperature in the secondary cir-
cuit is not reached for a short time, the control unit
uses the output integral as start criteria. This output
integral is the integral from duration and extent of the
deviation of the set flow temperature to the actual
value. In Fig. 27, the output integral is the grey area
between the time line of the actual value and the hys-
teresis of the flow temperature secondary circuit.
A
D
C
B
t
Fig. 27
A
Secondary circuit set flow temperature
B
Secondary circuit flow temperature actual value
C
Hysteresis, flow temperature secondary circuit
D
Output integral
Parameter group for external heat generator
2796 Configuration of external heat generator
6218234
Parameter