External Heat Generator - Viessmann VITOTRONIC 200 Service Instructions Manual

Function description
Booster heaters
(cont.)

External heat generator

The heat pump control unit enables dual mode opera-
tion of the heat pump with an external heat source,
e.g. oil boiler.
The external heat generator is hydraulically connected
in such a way that the heat pump can also be used as
a return temperature raising facility for the boiler. Sys-
tem separation is provided with either a low loss
header or a buffer cylinder.
For optimum heat pump operation, the external heat
generator must be integrated into the system flow
downstream from the buffer cylinder via a mixer. The
heat pump control unit controls this mixer directly.
The external heat generator is switched via a floating
contact (terminals 222.3/222.4 on the expansion PCB).
Central heating
Enabling required
Parameter
"Enable external heat source
7B00"
"Enable external heat gen. for cen-
tral heating 7B0C"
Dual mode operation
■
The heat pump control unit enables operation of the
external heat generator for central heating if the
adjusted outside temperature ("Interval for long
term average outside temperature 7002") is below
the "Dual mode temperature external heat source
7B02".
Above the dual mode temperature, the external heat
generator only starts under the following conditions:
– The heat pump fails to start due to a fault.
or
There is a special heat demand, e.g. frost protec-
tion.
Dual mode operation
■
Possible operating modes for the external heat gen-
erator ("Dual mode heat pump operation 7B0E"):
– Dual mode parallel:
External heat generator and heat pump are
switched on simultaneously.
– Dual mode alternative:
Compressor stops when the external heat genera-
tor is switched on.
In most cases, dual mode parallel operation is more
efficient than dual mode alternative operation. With
low outside temperatures it may be more advanta-
geous, subject to heat pump type, to only permit dual
mode alternative operation ("Shutdown limit, heat
pump dual mode 7B0F").
38
Dual mode operation with ice store
■
If an ice store is available as a primary source, the
external heat generator can also be enabled subject
to the temperature in the ice store. For this, the dual
mode temperature must be captured via the temper-
ature sensor in the ice store ("Temperature sensor
for dual mode operation 7038" set to "1").
Start criteria
■
The system flow temperature is crucial for the start-
ing of the external heat generator. In order to prevent
brief undershooting of the set value resulting in the
immediate start of the external heat generator, the
output integral is used as start criterion (integral
resulting from the duration and amount of the devia-
tion between the set and actual flow temperature:
"Start threshold external heat source 7B03").
In the following cases, the start of the external heat
generator will be prevented for the duration of "Start
delay external heat source 7B04":
Setting
After a change in the "Time program heating" from
–
"1"
one operating state with low set temperature to a
higher set temperature, e.g. from "Reduced" to
"1"
"Standard"
– After changeover between central heating and
DHW heating
■ Regulating the system flow temperature
The mixer for linking in the external heat generator
remains closed until the boiler water temperature of
the external heat generator has reached "Min. flow
temperature mixer external heat source ON
7B05". This prevents cold heating water from the
external heat generator reaching the heating circuits.
After opening, the mixer regulates towards the set
flow temperature of the system.
Mixer for external heat generator
■
If the boiler water temperature of the external heat
generator falls below the "Min. flow temperature
mixer external heat source ON 7B05" when a
demand is present, "Enable min. temp. mainte-
nance for ext. HS 7B10" can be used to adjust the
following characteristics for the mixer:
The mixer remains in control mode until the
–
demand for the external heat generator is no lon-
ger present.
– Mixer closes. The mixer only opens again when
"Min. flow temperature mixer external heat
source ON 7B05" is reached.
To compensate for heat losses at the mixer, "Max.
excess flow temp external heat source 7B0B" can
be used to raise the flow temperature of the external
heat generator compared to the required set flow
temperature of the system.
In the event of a fault
■
If "Min. flow temperature mixer external heat
source ON 7B05" has not been reached 2 h after
starting the external heat generator, the heat pump
control unit issues the fault message "E1 External
heat source".