Note: Descriptions are shown in the official language in which they were submitted.
Heating apparatus and method of operating a heating apparatus
The invention relates to a heating apparatus for producing a flow of hot air,
in
particular for a camper.
The invention additionally relates to a method of operating a heating
apparatus for producing a flow of hot air, in particular for a camper.
Heating apparatus for producing flows of hot air for campers are known in the
prior art. Campers are understood in this context as mobile homes, trailers,
tents,
portable cabins, etc. Heating apparatus for producing flows of hot air are
furthermore generally used in motor vehicles to heat their passenger
compartments. The heating apparatus are mostly designed as so-called
independent vehicle heaters in this application case, i.e. the heating
apparatus
can be used independently of the operation of the propulsion engine of the
vehicle.
Heating apparatuses for producing a flow of hot air can heat an air flow to be
heated, for example, via a burner operated by diesel, gasoline or gas and/or
via
an electrical energy source.
So-called combination heating apparatuses are in this respect in particular
known that comprise a burner and a resistance heating element, e.g. an
electric
heating element. Such heating apparatuses have three general modes of
operation. First, they can be used in pure burner operation in which only the
burner is used as the heat source. Alternatively, only the electric heating
element
is used as the heat source in pure electric operation. Furthermore, both the
burner and the electric heating element are used as the heat source in so-
called
mixed operation. An operating state of the vehicle or of the camper and/or a
degree of filling of the associated energy store, e.g. a battery, a diesel
tank,
gasoline tank or gas tank, may be the decisive factor for the selection of the
energy source and thus of the operating state.
If such a heating apparatus is used in mixed operation, a combustion air flow
that in particular supplies the oxygen required for the combustion to the
burner
has to be provided, on the one hand, and an air flow of air to be heated, also
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called a useful air flow, has to be provided, on the other hand. The useful
air flow
becomes the hot air flow by heating. As a rule, fans are used for the
provision of
the air flows that comprise one or more fan wheels and one or more fan wheel
drives.
In mixed operation, different heating powers should be provided in
dependence on requirements in the form of hot air flows that differ with
respect to
the hot air temperature and/or with respect to the air volume flow. Heating
apparatuses are known from the prior art for this purpose in which a fan
provides
the combustion air flow and a fan driven independently thereof generates the
useful air flow. Two fans are consequently necessary that have drives that are
independent of one another. Such heating apparatus can always provide the
required combustion air flows and useful air flows, but require a
comparatively
large construction space and are complex in their structures.
Against this background, heating apparatuses are also known from the prior
art in which a fan is provided having one fan wheel to produce the combustion
air
flow and having one fan wheel to produce the useful air flow. The two fan
wheels
are fastened to a common drive shaft here so that only a single drive is
required.
Construction space can thereby be saved. However, the two fan wheels can then
not be operated independently of one another. This means that the combustion
air flow and the useful air flow are coupled to one another.
It can consequently occur during mixed operation that either too large a
combustion air flow or too small a combustion air flow is supplied to the
burner.
This can have the result that no optimum ratio of fuel an combustion air can
be
set at the burner. As a consequence, the burner will emit an increased
quantity of
pollutants. If much too large a combustion air flow is supplied to the burner,
combustion may also no longer be possible.
It is therefore the object of the present invention to provide a heating
apparatus for producing a hot air flow in which a suitable combustion air flow
can
always be provided to the burner in mixed operation. At the same time, the
heating apparatus should take up as little construction space as possible and
should be of a simple design.
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The object is achieved by a heating apparatus of the initially named kind
having a single fan, a burner heating element, and a resistance heating
element,
wherein an air passage that conducts air to be heated and a combustion air
passage that leads to a burner adjoin the fan downstream, wherein a combustion
air flow in the combustion air passage can be controlled by a control element
associated with the combustion air passage. A burner heating element is
understood in this context as a heating element that receives the required
heat
energy from a burner. The resistance heating element is preferably an electric
heating element. The combustion air flow is furthermore to be understood as
that
air flow that is required for the combustion taking place in the burner. The
air to
be heated, that is also called the useful air flow, is heated by the burner
heating
element and by the resistance heating element and then represents the hot air
flow. The control element is adjustable continuously or in steps, with the
steps
being able to correspond to settings of a heating program of the heating
apparatus. The combustion air flow can be set via the control element such
that a
clean combustion, i.e. a low-pollutant and efficient combustion, i.e. one that
uses
the energy content of the fuel as completely as possible, takes place at the
burner. The useful air flow can be set independently thereof. Since only a
single
fan is present that can e.g. be electrically operated only a small
construction
space is required.
In an embodiment, the control element is arranged in the combustion air
passage. Exactly that combustion air flow can thus be supplied to the burner
that
is required for clean and efficient combustion.
The setting of the combustion air flow by the control element preferably takes
place by a complete or partial closing of the combustion air passage.
A further embodiment provides that a backflow line connects the combustion
air passage and an inlet of the fan flow-wise. The combustion air flow that is
provided at the burner is consequently set in that a controllable excess
portion
thereof is conducted back to the inlet of the fan. Only the required
combustion air
flow therefore also arrives at the burner.
The control element can be arranged in the backflow line or also in the
combustion air passage. An adjustment spread of the combustion air flow can be
determined by the dimensioning of the control element and of the backflow
line,
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in particular of the cross-section of the backflow line. The arrangement of
the
control element in the backflow line additionally makes it possible to arrange
the
control element flexibly with respect to the other components of the heating
apparatus so that it is possible to react to possible restrictions of the
construction
space.
In a design alternative, the setting of the combustion air flow by the control
element takes place by a complete or partial channeling away of the combustion
air flow to an inlet of the fan.
The control element advantageously allows a flow of from the combustion air
passage to the inlet and blocks a flow from the inlet to the combustion air
passage. The control element is therefore configured as a check valve.
In a design variant, the heating apparatus comprises a sensor for detecting
the combustion quality at the burner, with the sensor being coupled to the
control
element. This sensor can detect a parameter by means of which a conclusion
can indirectly be drawn on the quality of the combustion, for example a
temperature, a pressure or an ionization signal. The sensor can alternatively
also
detect a parameter with which the quality of the combustion can be directly
determined. The sensor can, for example, detect the oxygen content or other
properties of the air in the combustion air flow. Alternatively, the sensor
can be
designed as a so-called airflow sensor or as a lambda probe, i.e. the sensor
compares the residual oxygen content after the combustion with the oxygen
content of the environmental air. The control element is set on the basis of
the
sensor values such that the combustion air flow required at the burner is
provided
as exactly as possible. A particularly clean and efficient combustion is thus
achieved.
The combustion air flow can be set in dependence on the combustion quality
at the burner.
The fan can comprise a single fan wheel that feeds the air passage and the
combustion air passage. The fan wheel therefore generates the air flow to be
heated, also called the useful air flow, and the combustion air flow. A very
compact construction of the heating apparatus is thus possible. The design of
the
heating apparatus is thus furthermore very simple.
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Alternatively, the fan can comprise a useful air fan wheel that feeds the air
passage and a combustion air fan wheel that feeds the combustion air passage.
The useful air fan wheel therefore only generates the air flow that becomes
the
hot air flow by heating. The combustion air fan wheel only generates the
combustion air flow. Two fan wheels are therefore present that taken on their
own
are each smaller in comparison with the embodiment with only one fan wheel.
In a preferred embodiment, the combustion air flow is provided by a
combustion air fan wheel and the useful air flow is provided by a useful air
fan
wheel.
In this respect, the useful air fan wheel and the combustion air fan wheel are
preferably rotatably supported, with a rotational movement of the useful air
fan
wheel being coupled with a rotational movement of the combustion air fan
wheel.
The fan wheels can in this respect be designed in different sizes and
configurations. The coupling preferably takes place via a transmission.
Alternatively, the fan wheels can be arranged on the same shaft. Due to the
coupling of the fan wheels, only one fan wheel drive is required so that only
a
small construction space is taken up.
Provision is made in accordance with a preferred embodiment that the control
element is a valve flap or a throttle plate. The available flow cross-section
and
thus also the volume throughput can be set in the desired manner with little
effort
in this manner.
It is also possible that the control element is a guide element within the fan
with which an internal backf low can be released. The volume flow can already
be
influenced within the fan in this manner.
It is a further object of the present invention to provide a method with which
a
heating apparatus for producing a hot air flow can be operated in mixed
operation
such that the burner is always supplied with a suitable air flow.
The object is achieved by a method of operating a heating apparatus for
producing a hot air flow, wherein the heating apparatus comprises a single fan
and wherein an air passage that conducts air to be heated and a combustion air
passage that leads to a burner adjoin the fan downstream. The method
comprises the following steps:
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a) providing a combustion air flow produced by the fan in the combustion
air passage;
b) providing a useful air flow produced by the fan in the air passage, with
the useful air flow becoming the hot air flow by heating; and
c) setting the combustion air flow by a control element.
The combustion air flow can thus always be set such that it exactly
corresponds to the air flow required at the burner. The combustion air flow
can in
particular be set independently of the useful air flow.
The invention will be explained in the following ,with reference to different
embodiments that are shown in the enclosed drawings. In the drawings,
- Figure 1 schematically shows a first embodiment of the heating apparatus
in accordance with the invention;
- Figure 2 schematically shows a second embodiment of the heating
apparatus in accordance with the invention;
- Figure 3 schematically shows a third embodiment of the heating apparatus
in accordance with the invention; and
- Figure 4 shows a partly sectioned representation of a fourth embodiment
of
the heating apparatus in accordance with the invention.
A first embodiment of a heating apparatus 10 can be seen in Figure 1. The
heating apparatus 10 is configured to generate a hot air flow 12.
For this purpose, the heating apparatus 10 comprises an air passage 14 into
which a useful air flow 16 is introduced. The latter is heated by a resistance
heating element 18 and by a burner heating element 20 so that the useful air
flow
16 becomes the hot air flow 12.
The resistance heating element 18 can be an electric heating element, for
example.
The burner heating element 20 transmits heat energy that is produced by a
burner 22 to the useful air flow 16.
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So that combustion can take place at the burner 22, a combustion air flow 26
is supplied to the latter via a combustion air passage 24.
In the embodiment shown, both the useful air flow 16 and the combustion air
flow 26 are generated by a single fan 28 having a single fan wheel 30. The two
air flows are nevertheless conducted separately, as is symbolized by the
continuous dividing wall 31.
The combustion air flow 26 can be set by a control element 32. In the
embodiment shown, the control element 32 is arranged in the combustion air
passage 24 and can block it completely or partially. The control element 32 is
designed as a valve element or as a throttle plate here. An actuator 33 is
provided for the adjustment.
Alternatively to the shown arrangement of the control element 32, it can also
be arranged upstream of the fan wheel 30.
A sensor 34 that can detect the combustion quality at the burner 22 is
additionally provided at the burner 22. The sensor 34 is coupled to the
control
element 32.
The function of the heating apparatus 10 will be described in the following
with reference to so-called mixed operation in which the useful air flow 16 is
heated both via the resistance heating element 18 and via the burner heating
element 20 and thus becomes the hot air flow 12.
Let a total heating power of 4 kW be required in a first application case of
which 2 kW are provided by the resistance heating element and 2 kW are
provided by the burner heating element 20.
The fan wheel 30 is now set so that it provides both the useful air flow 16
that
corresponds to a total heating power of 4 kW and at least the combustion air
flow
26 that is required for a burner power of 2 kW.
However, a ratio of the useful air flow 16 to the combustion air flow 26 is
predefined by the construction design of the air passage 14 and of the
combustion air passage 24. The ratio of the line cross-sectional areas of the
air
passage 14 and of the combustion air passage 24 can be the decisive criterion
for this.
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It can therefore be the case that the fan wheel 30 feeds too much air into the
combustion air passage 24.
This is, however, prevented by the control element 32 that is set such that
exactly that quantity of air corresponding to the burner power of 2 kW is
supplied
to the burner 22 via the combustion air flow 26.
During operation, the sensor 34 detects the combustion quality at the burner
22 and has the effect via the coupling with the control element 32 that the
combustion air flow 26 supplied to the burner 22 is readjusted in the case of
an
insufficient combustion quality. This takes place by a readjustment of the
control
element 32.
Let 4 kW total power again be required in a second application case. In this
case, however, 3 kW of the total heating power should be supplied via the
resistance heating element 18 and 1 kW of the total heating power should be
supplied via the burner heating element 20.
In comparison with the first application case, it now becomes clear that a
smaller combustion air flow is required despite an unchanging total heating
power
of 4 kW that is associated with an unchanging useful air flow 16.
The control element 32 is therefore set such that the combustion air flow 26
corresponds to a burner power of 1 kW. The position of the control element 32
can again be readjusted by a detection of the combustion quality with the aid
of
the sensor 34.
The sensor does not necessarily have to be arranged downstream of the
burner. It can also be arranged upstream of the burner depending on the
parameters that it detects.
A second embodiment of the heating apparatus 10 is shown in Figure 2.
Unlike the first embodiment of Figure 1, the control element 32 in this
embodiment is arranged in a backf low line 36 that connects the combustion air
passage 24 to an inlet 38 of the fan 28 flow-wise.
To prevent air from flowing from the inlet 38 via the backf low line 36 into
the
combustion air passage 24, the control element 32 an comprise a check valve
40.
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The air flow fed into the combustion air passage 24 by the fan wheel 30 is
thus divided into the combustion air flow 26 provided at the burner 22 and a
return air flow 42.
The return air flow 42 is adjustable via the control element 32.
Provision can alternatively also be made that the control element 32, that is
here likewise designed as a valve element or as a throttle plate, is arranged
in
the combustion air passage 24 and controls the volume flow by the stagnation
pressure produced there.
If now a total heating power of 4 kW is again required, of which a respective
2 kW should be provided by the resistance heating element 18 and by the burner
heating element 20, the fan wheel 30 is set such that it provides the useful
air
flow corresponding to 4 kW total heating power and at least the combustion air
flow 26 corresponding to 1 kW burner power.
As described in the first embodiment, the ratio of the air flow fed into the
combustion air passage 24 and of the air flow fed into the air passage 14 is
fixed
construction-wise.
The fan wheel 30 may therefore feed too much air into the combustion air
passage 24.
The excess air quantity in the combustion air passage 24 can therefore be
conducted back to the inlet 38 of the fan 28 via the backflow line 36 as a
return
air flow 42. In this respect, the amount of the return air flow 42 is set by
the
control element 32.
The air flow conveyed by the fan wheel 30 into the combustion air passage 24
less the return air flow 42 conducted back via the backflow line 36 therefore
arrives at the burner 22.
The combustion quality is again detected by the sensor 34 and the sensor
value is used to set the control element 32.
In the event that a total heating power of 4 kW is to be implemented in that
3 kW are provided via the resistance heating element 18 and 1 kW via the
burner
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heating element 20, only a smaller combustion air flow 26 is required at the
burner 22.
The combustion air flow 26 is then set by conducting back of a
correspondingly larger return air flow 42 through the backflow line 36. The
control
element 32 is adjusted accordingly for this purpose.
A third embodiment of the heating apparatus 10 is shown in Figure 3. Unlike
the first and second embodiments, the fan in this embodiment comprises a
useful
air fan wheel 50 and a combustion air fan wheel 52, that is a total of two fan
wheels.
In this respect, the useful air fan wheel 50 generates the useful air flow 16
and the combustion air fan wheel 52 generates the combustion air flow 26.
In the embodiment shown, the useful air fan wheel 50 and the combustion air
fan wheel 52 are rotatably supported. The rotational movement of the two fan
wheels is coupled in that they are arranged on a common shaft 54.
The control element 32 is arranged analogously to the second embodiment
(see Figure 2) in the backflow line 36 in this embodiment.
Alternatively, analogously to the first embodiment, the control element 32 can
also be directly arranged in the combustion air passage 24. Such a variant is
not
shown.
The function of the heating apparatus in accordance with the third
embodiment is as in the second embodiment. However, here the ratio of the air
flows fed into the air passage 14 and into the combustion air passage 24 is
fixed
by the design of the useful air fan wheel 50 and of the combustion air fan
wheel
52.
It is also conceivable in this embodiment to arrange the control element 32
outside the backflow line 36.
A fourth embodiment can be seen in Figure 4 that, analogously to the third
embodiment shown in Figure 3, comprises the useful air fan wheel 50 and the
combustion air fan wheel 52.
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The rotational movements of the useful air fan wheel 50 and of the
combustion air fan wheel are coupled here via a transmission 56 so that only
one
drive 58 is required for both fan wheels.
The amount of the return air flow 42 is again set via the control element 32
so
that a suitable combustion air flow 26 is always available at the burner 22.
The function of the heating apparatus 10 in accordance =with the fourth
embodiment is analogous to the third embodiment in Fig. 3.
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