Mono-Energetic Operation; Dual Mode Operation; Supplement For Dhw Heating - Viessmann VITOCAL 300-G Technical Manual

Design information

Mono-energetic operation

In heating mode, the heat pump system is supplemented by an instan-
taneous heating water heater (on site). The control unit switches the
instantaneous heating water heater on, subject to the outside temper-
ature (dual mode temperature) and heat load.
Note
That part of the electric power drawn by the instantaneous heating
water heater will generally not be charged at special tariffs.
Sizing of typical system configurations:
■ The heat pump heating output must be designed for approx. 70 to
85 % of the maximum required heat load of the building in accord-
ance with DIN EN 12831.
■ The heat pump covers approx. 95 % of the annual heat load.
■ Blocking periods must not to be taken into consideration.
Note
Compared to mono-mode operation, the heat pump will run for longer
due to its smaller size. To compensate for this, increase the size of the
heat source for brine/water heat pumps.
For a geothermal probe system, an annual extraction rate of
∙ p.a. should not be exceeded.
100 kWh/m
Instantaneous heating water heater (on site)
An electric instantaneous heating water heater can be integrated in the
heating water flow as an auxiliary heat source. The instantaneous
heating water heater is connected and protected via a separate power
supply connection.

Dual mode operation

External heat source
The heat pump control unit enables the heat pump to operate in dual
mode with an external heat source, e.g. oil boiler.
The external heat source is hydraulically connected to let the heat
pump also be used as a return temperature raising facility for the boiler.
System separation is provided either with a low loss header or heating
water buffer cylinder.
For optimum heat pump operation, the external heat source must be
integrated via a mixer into the heating water flow. A quick reaction is
achieved by directly controlling this mixer via the heat pump control
unit.
If the outside temperature (long-term average) is below the dual mode
temperature, the heat pump control unit starts the external heat
source. In case of direct heat demand from the consumers (e.g. for
frost protection or if the heat pump is faulty), the external heat source
is also started above the dual mode temperature.

Supplement for DHW heating

For general house building, a max. DHW consumption of approx.
50 litre per person per day at approx. 45 ºC is assumed.
■ This represents an additional heat load of approx. 0.25 kW per per-
son given a heat-up time of 8 h.
■ This supplement will only be taken into consideration if the sum total
of the additional heat load is greater than 20 % of the heat load cal-
culated in accordance with DIN EN 12831.
Low demand
*2
Standard demand
*1 With a DHW cylinder heat-up time of 8 h.
Select a higher supplement if the actual DHW demand exceeds the stated values.
*2
VITOCAL 300-G
(cont.)
DHW demand at a DHW temper-
ature of 45 °C
in l/d per person
15 to 30
30 to 60
The heat pump control unit regulates this function. The instantaneous
heating water heater can be enabled separately for central heating and
DHW heating.
If enabled the respective parameter, the heat pump control unit starts
stages 1, 2 or 3 of the instantaneous heating water heater, subject to
the prevailing heat demand. As soon as the maximum flow tempera-
ture in the secondary circuit is reached, the heat pump control unit
switches the instantaneous heating water heater off.
Parameter "Stage at power-OFF" restricts the output stage of the
instantaneous heating water heater for the duration of the power-OFF
period.
To limit the total power consumption, the heat pump control unit stops
the instantaneous heating water heater for a few seconds directly
before the compressor starts. Each stage is subsequently started indi-
vidually one after the other in intervals of 10 s.
If the instantaneous heating water heater is on and the differential
between flow and return temperatures in the secondary circuit does
not rise by at least 1 K within 24 h, the heat pump control unit displays
a fault message.
In addition, the external heat source can be enabled for DHW heat-
ing.
Note
The heat pump control unit does not contain any safety function for
the external heat source. To prevent excessive temperatures in the
heat pump flow and return in case of a fault, high limit safety cut-outs
must be provided to stop the external heat source (switching threshold
70 °C).
Specific available heat
in Wh/d per person
600 to 1200
1200 to 2400
Recommended heat load sup-
*1
plement for DHW heating
in kW/person
0.08 to 0.15
0.15 to 0.30
VIESMANN
35
3