Instantaneous Heating Water Heater - Viessmann VITOTRONIC 200 Service Instructions Manual

Booster heaters
(cont.)
Stop criteria
■
The heat pump control unit switches the external
heat generator off if both of the following conditions
are met:
– "Min. runtime external heat source 7B06" has
expired.
The system flow temperature is above the set
–
value for the duration of "Run-on time external
heat source 7B07".
DHW reheating
See chapter "DHW reheating with booster heaters" on
page 42.
Safety functions
To protect the heat pump against excessive flow and
return temperatures, the heat pump control unit does
not contain any safety functions for the external heat
generator.
For this reason, the following high limit safety cut-outs
(respective switching threshold 70 °C) must be used.
■ Central heating:
Provide 2 high limit safety cut-outs in the following
positions:
Flow secondary circuit, upstream of the instantane-
–
ous heating water heater (if installed)
– Secondary circuit return (between heat pump and
buffer cylinder)
Both high limit safety cut-outs must be connected
electrically so that, in each case, the external heat
generator and the secondary pump are switched off.
Note
– The secondary pump does not start if the return
temperature in the secondary circuit exceeds
67 °C.
– The compressor does not start, if at the end of
"Start delay compressor 5008" the return tem-
perature in the secondary circuit lies above the
max. flow temperature in the secondary circuit
minus 7 K.

Instantaneous heating water heater

An electric instantaneous heating water heater can be
integrated in the secondary circuit flow as an auxiliary
heat source.
Depending on the heat pump type, the instantaneous
heating water heater is either factory-fitted or available
as an accessory.
Subject to heat demand, 2 output stages (e.g. 3 and
6 kW) of the instantaneous heating water heater can
be controlled separately. When there is a high heat
demand, the heat pump control unit can activate both
stages simultaneously, e.g. 3 kW + 6 kW = 9 kW, (
output stage 3).
DHW reheating:
■
Provide 1 high limit safety cut-out in the following
position:
– Return secondary circuit (between heat pump and
DHW cylinder)
Connect the high limit safety cut-out electrically so
that either the circulation pump for cylinder reheating
is switched off or the 3-way diverter valve "Heating/
DHW" is set to "Heating".
Frost protection
If the boiler water temperature falls below 5 °C, the
heat pump control unit switches on the external heat
generator for the duration "Min. runtime external
heat source 7B06".
The output stage can be limited permanently with
"Max. output instantaneous heating water heater
7907". In order to be able to cover a possible high
heat demand every time the heat pump is switched on,
this limit will not be effective immediately after the heat
pump starts.
To limit the total power consumption, the heat pump
control unit switches off the instantaneous heating
water heater for a few seconds directly before the
compressor starts. Each stage is subsequently started
≙
individually one after the other at intervals of 10 s.
The instantaneous heating water heater can be called
for to support both central heating and DHW heating.
There are individual criteria options for each mode.
Function description
39