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Notes on planning
Choosing the rated output
The boiler should be selected on the
basis of the required heat demand includ
ing domestic hot water heating.
With condensing boilers, the output can
be higher than that required on the basis
of the calculated heat demand of the
building.
The efficiency of condensing boilers re
mains stable over the full boiler load
range and remains virtually unchanged
even with twice the output required for
the heat demand concerned.
System design parameters
H The max. boiler water temperature is
limited to 75 °C.
To minimize distribution losses, we rec
ommend that the heating and domestic
hot water system are based on a maxi
mum flow temperature of 70 °C.
H In certain countries, a permit may be
required for the installation of a
condensing boiler.
H Due to the low return temperatures re
quired for condensing, where possible
no mixing devices should be incorpo
rated in the heating circuit. If mixers are
required, e.g. for multi-circuit systems
or underfloor heating systems, only
3-port mixers should be used.
Safety equipment
According to DIN 4751-2, and to comply
with the design approval conditions, the
boilers
H for hot water heating systems up to
100 °C flow temperature and
H for hot water heating systems up to
120 °C flow temperature
must be equipped with a type-tested
safety valve. According to TRD 721, this
must bear the designation letter
H "H" up to 3.0 bar max. operating
pressure and max. 2700 kW output,
H "D/G/H" for all other operations
conditions.
24
Underfloor heating systems
For underfloor heating systems we rec
ommend the use of impermeable plastic
pipes in order to prevent the diffusion of
oxygen through the walls of the pipes. If
non-impermeable plastic pipes are used
(DIN 4726) in underfloor heating systems,
we recommend system separation. For
this purpose, we supply separate heat ex
changers.
In the case of condensing boilers, too, un
derfloor heating systems and heating cir
cuits containing a very large volume of
water must be connected to the boiler via
a 3-port mixer; please refer to the Techni
cal Guide "Control of underfloor heating
systems" or consult the "Technical Guide
for Vitodens boilers".
A limit thermostat for limiting the maxi
mum temperature must be installed in
the flow of the underfloor heating circuit.
Please observe the requirements of DIN
18560-2.
Plastic pipe systems for radiators
We recommend the use of a limit thermo
stat for limiting the maximum tempera
ture also in the case of plastic pipe sys
tems for heating circuits with radiators.
Low water indicator
On boilers up to 350 kW, according to DIN
4751-2 there is no need for the low water
indicator otherwise required if it is ensured
that overheating due to low water cannot
occur.
Viessmann Vitodens 100 boilers are
equipped with a low water indicator (boil-
dry safety device). Tests have shown that,
in the event of low water due to a leak in
the heating system while the burner is in
operation, the burner is switched off with
out the need for additional equipment be
fore overheating of the boiler and the flue
system occurs.
Notice of completion
In some countries, within a specified
period after the initial commissioning of
the heating system, the operator must
notify his local authority accordingly.
(GB: Not applicable).
Condensate and condensate
neutralizing
Please refer to the "Technical Guide for
Vitodens boilers".
Additional requirements to be
observed where LPG-fired
boilers are installed in rooms
below ground level
According to TRF 1996-Vol. 2 - valid since
1st September 1997 - an external safety
solenoid valve is no longer required for
Vitodens 100 boilers installed below
ground level.
However, the external safety solenoid
valve has proved so effective in achieving
a high standard of safety that we shall
continue to recommend its installation in
conjunction with Vitodens 100 boilers in
stalled below ground level, for which the
adaptor (connection extension) must be
ordered at the same time.
Technical Guide
For further information on planning and
system parameters, please refer to the
"Technical Guide for Vitodens boilers".
Subject to technical modifications.
Viessmann Werke GmbH & Co
D-35107 Allendorf
Tel: (06452) 70-0
Fax: (06452) 70-2780
Internet: www.viessmann.de
Viessmann Limited
Hortonwood 32
Telford, Shropshire TF1 4EU
Tel.: (01952) 670261
Fax: (01952) 670103
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