Note: Descriptions are shown in the official language in which they were submitted.
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Description
System for controlling the combustion air supply
Technical field of the invention
The invention relates to a system for controlling the combustion air supply in
a sol-
id fuel furnace with a primary air supply and a secondary air supply.
Prior art
In wood or coal-burning solid fuel furnaces the air required for combustion is
usu-
ally supplied by a primary air supply and a secondary air supply. In such a
case,
the primary air required for heating up and for the combustion of coal is
supplied to
the furnace's combustion chamber in the lower area, i.e. through the grate. On
the
other hand, during the combustion of wood the combustion air is supplied into
the
upper area of the combustion chamber only via the secondary air supply
following
the heating up phase in which the combustion air is supplied via the primary
air
supply and secondary air supply.
Usually, the primary air supply and secondary air supply are set manually. The
disadvantage of this control method, however, is that settings can only be
made by
trial and error and by making estimates. In addition, making settings in this
way is
very time-consuming as corrections have to be repeatedly made depending on the
state of combustion.
Optimum combustion cannot therefore be achieved. Very many different types of
systems for controlling the air supply have therefore since been developed to
op-
timize the combustion of solid fuels such as wood or coal.
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For example, a solid fuel furnace is known from DE 20 2010 003 329 U1 which
has a regulating device for the primary air supply and a regulating device for
the
secondary air supply, both of which can be activated by a linkage which is
coupled
to an adjusting device,
The disadvantage of this solution is that the regulating device, and therefore
the
solid fuel furnace as well, is costly and complicated to construct.
A chimney furnace is described in EP 2 221 534 A2 with a control device for
the
air supply. To set the volume of the primary air supply and secondary air
supply
the respective air ducts leading into the combustion chamber are closed to a
greater or lesser extent by means of a rotatable control disk in which
geometrically
different openings are arranged.
Apart from the fact that this embodiment too is very costly and complicated to
con-
struct, it has the further disadvantage that the volumes of air flowing
through it can
be set only in steps over the cross section created by the geometrically
different
openings in the control disc.
A further means of controlling the combustion air supply into the combustion
chamber of a furnace via the primary or secondary air supply is presented in
EP 2 096 356 A2. This solution requires only one control mechanism, comprising
a
temperature sensor and a flow regulator. However, the embodiment requires its
own valve mechanism for the primary air supply and its own valve mechanism for
the secondary air supply. In addition, the embodiment also has separate shut-
off
elements which must be activated independently of the control mechanism in or-
der to close the air supply that is not required.
Despite the inherent simplicity of its design made possible because only one
con-
trol mechanism is required, the embodiment is still very costly to construct.
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The principal reason why all these systems listed above for controlling the
air supply
are costly and complicated to manufacture is that they are combined with the
furnace.
An associated additional disadvantage of all the embodiments previously
referred to
is that they cannot be retrofitted.
Statement of the invention
The present invention addresses the problem of developing a system for
controlling
the combustion air supply to a solid fuel furnace with a primary air supply
and a
secondary air supply in which the supply of air to the primary or secondary
air supply
is to be controlled in an infinitely variable manner. Its structure and
manufacture are
to be as simple as possible and the system is to be capable of being
retrofitted in
furnaces with a primary and secondary air supply.
The problem is solved according to the invention in that there is provided a
system for
controlling a combustion air supply in a solid fuel furnace with an inlet for
the supply
of a combustion air, an insert which has an opening assigned to a primary air
supply
of the furnace and an opening assigned to a secondary air supply of the
furnace,
wherein cross sections of the openings are variable by means of a pivotally
mounted
motion link which can be actuated by means of a drive unit which can in turn
be
controlled by a control unit, wherein the insert which is of a pot-shaped
design and is
located in a housing arranged between the furnace and the air supply line has
on an
outer surface the openings for the primary and secondary air supply, wherein
both
openings are arranged in a tangential direction one behind the other and
wherein the
rotary angle of the motion link is restricted by one or a plurality of stops.
The problem is solved according to the invention in that there is provided a
system for
controlling a combustion air supply in a solid fuel furnace with an inlet for
the supply
of a combustion air, an insert which has an opening assigned to a primary air
supply
of the furnace and a secondary air supply of the furnace, wherein cross
section of the
opening is variable by means of a pivotally mounted motion link which can be
actuated by means of a drive unit which can in turn be controlled by a control
unit,
Date Recue/Date Received 2022-02-04
81794918
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wherein the insert which is of a pot-shaped design and is located in a housing
arranged between the furnace and the air supply line has on an outer surface
the
opening for the primary and secondary air supply, wherein the opening is
arranged in
a tangential direction and wherein the rotary angle of the motion link is
restricted by
one or a plurality of stops.
A solution has therefore been found which overcomes the disadvantages of the
prior
art referred to above. The use of a motion link provides a very simple
solution which
does not require additional mechanical adjusting devices such as valves, rods
and
the like.
The structure of the furnace is simplified and, at the same time, the need for
an
additional large installation space in the furnace is eliminated because it no
longer
has to accommodate complicated control components
Date Recue/Date Received 2022-02-04
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The openings located in the housing which are normally closed and which can
function as a bypass enable additional air to be supplied, if required, into
the pri-
mary air supply and/or secondary air supply, by bypassing the system for
control-
ling the combustion air supply. This ensures that there is always a minimum
chim-
ney draft to avoid the danger of the accumulation of dangerous gases.
Execution example
An exemplary embodiment of a system for controlling the combustion air supply
according to the invention is described in detail below by means of an
execution
example. The diagrams show the following details:
Fig. 1 a perspective view of the inlet side of a system according to the
invention
for controlling the combustion air supply,
Fig. 2 a perspective view of the outlet side of a system according to the
invention
for controlling the combustion air supply,
Fig. 3 a view of a system according to the invention for controlling the
combustion
air supply,
Fig. 4 a section A - A from Fig. 3 in the closed position of the system for
control-
ling the combustion air supply,
Fig. 5 a section B - B from Fig. 3 in the open position of the system for
controlling
the combustion air supply,
Fig. 6 a section A - A from Fig. 3 during the control of the combustion air
supply of
the primary air supply
Fig. 7 a section A - A from Fig. 3 during the control of the combustion air
supply of
the secondary air supply.
As can be seen in Figs. 1 and 3, the system according to the invention for
control-
ling the combustion air supply comprises a housing 1 fitted on the inlet side
with a
collar 2 which provides a means of accommodating a flexible air hose (not
illus-
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trated) for supplying the air required for combustion, if this is not to be
removed
from the installation space. A basket-shaped attachment 11 fastened in a fixed
position, for example by means of a bayonet lock 12, is located on the inlet
side of
the housing 1. A drive unit 13, described in detail below, is arranged in the
interior
of the attachment 11 (Fig. 5). The air required for combustion can flow
through slit
14 through the housing 1 in the direction indicated by a directional arrow.
On its outlet side the housing 1 has a flange 4 by means of which the system
for
controlling the combustion air supply can be connected to a furnace which is
also
not illustrated and which is suitable for the combustion of solid fuels such
as wood
and/or coal and which has for this purpose a divided inlet for the combustion
air
supply, in this execution example an inlet divided into a primary air supply
on one
side and a secondary air supply on the other side.
In the housing 1 there is a pot-shaped insert 5 which is opened to the inlet
side of
the housing 1 and, in addition, separates the inlet side from the outlet side
(Fig. 2).
In manufacturing this as a plastic component it has proved to be advantageous,
as
shown in this execution example, to construct housing 1 and insert 5 as a
single
piece. The inner wall of the housing 1 is connected to the outer wall of the
insert 5
by intermediate webs 6, thereby continuing in the housing 1 the division of
the
combustion air supply existing at the inlet of the furnace into a primary air
supply 7
on one side and a secondary air supply 8 on the other side. The inlet side of
the
housing 1 is fluidically connected to the primary air supply 7 on the outlet
side by
means of an opening 9 located in the circumferential area of the insert 5 and
is
fluidically connected to the secondary air supply 8 on the outlet side by
means of
an opening 10, also located in the circumferential area of the insert.
The base of the pot-shaped insert 5 has in its center a bore which has been de-
signed as a bearing 15 for an axle which serves as a fulcrum for a motion link
17
attached to it. As can be clearly seen from Figs. 4 and 5 the radius of the
motion
link 17 has been determined such that the exterior circumferential area of the
mo-
tion link 17 slides on the inner wall of the insert 5.
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At the same time the arc length of the circumferential area of the motion link
17 is
dimensioned such that the two openings 9 and 10 can be completely covered on
the one hand (Fig. 4), but also almost completely opened on the other hand
(Fig.
5). The pivoting range of the motion link 17 required for this operation is
defined by
a rib 18 located on the internal side of the motion link 17 and a stop 19
located on
the attachment 11.
The drive unit 13, which has already been referred to above and which is
attached
in the interior of the attachment 11, serves to bring the motion link 17 into
the re-
quired position. A rotary motion is generated in the drive unit and
transmitted to a
driver 20 which is arranged centrally to the axle 16 and which incorporates a
coun-
terpart 21 located on the axle 16 to enable the motion link 17 to be pivoted
into the
required position.
An electronic control unit 23, which in this execution example is attached by
means of a holder 22 to the housing 1, controls the drive unit 13 by means of
a
cable which has not been depicted for the sake of clarity, with control
effected on
the basis of data determined by sensors and processed in the electronic
control
unit 23. In this case the sensors comprise, for example, a door contact
switch, a
sensor for recording the temperature of the furnace body and a flue gas
tempera-
ture sensor.
In addition, in this execution example the system according to the invention
for
controlling the combustion air supply enables additional air to be supplied to
the
primary air supply and/or the secondary air supply by bypassing the controlled
air
supply. To that end the flange 4, as can be seen in Fig. 5, has a plurality of
closed
openings 24 in the area of the primary air supply 7 and the secondary air
supply 8
which must be opened in varying numbers and assignments dependent on the
design of the furnace to which the flange is connected. Where plastic is used
as a
material, this component can be conveniently manufactured, as described above,
in the form of a thin plastic layer with re-closable predetermined breaking
points. If
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necessary, the openings 24 can, for example, be re-closed by stoppers that are
not illustrated.
The system according to the invention for controlling the combustion air
supply
described in this execution example has the following mode of operation:
In Fig. 4 the system for controlling the combustion air supply is shown in the
closed position, i.e. in standby mode. The heating up phase begins as soon as
the
furnace is filled with the selected fuel, an operation signaled by the door
contact
switch. The motion link 17 is pivoted so far that both openings 9 and 10 are
opened by the electronic control unit 23 by means of the drive unit 13 as
shown in
Fig. 5.
The control phase begins on completion of the heating-up phase, usually
defined
as a minimum as the attainment of a specific flue gas temperature and furnace
body temperature.
If coal is used as a fuel, the combustion air supply of the primary air supply
7 is
controlled. The motion link 17 is pivoted so far that the opening cross
section of
the opening 9 for the primary air supply 7 is opened and the opening 10 for
the
secondary air supply 9 is closed (Fig. 6). This ensures that the opening 10
for the
secondary air supply 8 remains closed by the motion link 17, even when the
open-
ing cross section of the primary air supply 7 changes when the positions of
the
motion link 17 change during the control process.
By contrast, if wood is used as a fuel, the combustion air supply of the
secondary
air supply 8 is controlled. The motion link 17 is pivoted so far that the
opening
cross section of the opening 10 for the secondary air supply 8 is opened and
the
opening 9 for the primary air supply 7 is closed (Fig. 7). It goes without
saying that
the system ensures in this case too that the opening 9 for the primary air
supply 7
remains closed by the motion link 17 when the opening cross section of the sec-
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ondary air supply 8 changes because of the changing positions of the motion
link
17 during the control process.
On completion of the control phase the system for controlling the combustion
air
supply assumes the standby mode shown in Fig. 4. Both openings 9 and 10 are
closed by the motion link 17.
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List of reference numerals
1 Housing
2 Collar
3 Directional arrow
4 Flange
Insert
6 Intermediate web
7 Primary air supply
8 Secondary air supply
9 Opening (primary air)
Opening (secondary air)
11 Attachment
12 Bayonet lock
13 Drive unit
14 Slot
Bearing
16 Axle
17 Motion link
18 Rib
19 Stop
Driver
21 Counterpart
22 Holder
23 Control unit
24 Opening
