Abstract:
A heating apparatus for generating a hot air flow comprises a single fan, a burner heating element and a resistance heating element. In this respect, 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.

Description:
[0001]    The invention relates to a heating apparatus for producing a flow of hot air, in particular for a camper. 
         [0002]    The invention additionally relates to a method of operating a heating apparatus for producing a flow of hot air, in particular for a camper. 
       BACKGROUND OF THE INVENTION 
       [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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 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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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 and 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. 
         [0010]    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. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0011]    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. 
         [0012]    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. 
         [0013]    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. 
         [0014]    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. 
         [0015]    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, 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. 
         [0016]    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. 
         [0017]    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. 
         [0018]    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. 
         [0019]    The combustion air flow can be set in dependence on the combustion quality at the burner. 
         [0020]    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. 
         [0021]    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. 
         [0022]    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. 
         [0023]    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. 
         [0024]    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. 
         [0025]    It is also possible that the control element is a guide element within the fan with which an internal backflow can be released. The volume flow can already be influenced within the fan in this manner. 
         [0026]    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. 
         [0027]    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:
       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.       
 
         [0031]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The invention will be explained in the following with reference to different embodiments that are shown in the enclosed drawings. In the drawings, 
           [0033]      FIG. 1  schematically shows a first embodiment of the heating apparatus in accordance with the invention; 
           [0034]      FIG. 2  schematically shows a second embodiment of the heating apparatus in accordance with the invention; 
           [0035]      FIG. 3  schematically shows a third embodiment of the heating apparatus in accordance with the invention; and 
           [0036]      FIG. 4  shows a partly sectioned representation of a fourth embodiment of the heating apparatus in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    A first embodiment of a heating apparatus  10  can be seen in  FIG. 1 . The heating apparatus  10  is configured to generate a hot air flow  12 . 
         [0038]    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 . 
         [0039]    The resistance heating element  18  can be an electric heating element, for example. 
         [0040]    The burner heating element  20  transmits heat energy that is produced by a burner  22  to the useful air flow  16 . 
         [0041]    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 . 
         [0042]    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 . 
         [0043]    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. 
         [0044]    Alternatively to the shown arrangement of the control element  32 , it can also be arranged upstream of the fan wheel  30 . 
         [0045]    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 . 
         [0046]    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 . 
         [0047]    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 . 
         [0048]    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. 
         [0049]    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. 
         [0050]    It can therefore be the case that the fan wheel  30  feeds too much air into the combustion air passage  24 . 
         [0051]    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 . 
         [0052]    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 . 
         [0053]    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 . 
         [0054]    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 . 
         [0055]    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 . 
         [0056]    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. 
         [0057]    A second embodiment of the heating apparatus  10  is shown in  FIG. 2 . Unlike the first embodiment of  FIG. 1 , the control element  32  in this embodiment is arranged in a backflow line  36  that connects the combustion air passage  24  to an inlet  38  of the fan  28  flow-wise. 
         [0058]    To prevent air from flowing from the inlet  38  via the backflow line  36  into the combustion air passage  24 , the control element  32  and comprise a check valve  40 . 
         [0059]    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 . 
         [0060]    The return air flow  42  is adjustable via the control element  32 . 
         [0061]    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. 
         [0062]    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. 
         [0063]    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. 
         [0064]    The fan wheel  30  may therefore feed too much air into the combustion air passage  24 . 
         [0065]    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 . 
         [0066]    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 . 
         [0067]    The combustion quality is again detected by the sensor  34  and the sensor value is used to set the control element  32 . 
         [0068]    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 heating element  20 , only a smaller combustion air flow  26  is required at the burner  22 . 
         [0069]    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. 
         [0070]    A third embodiment of the heating apparatus  10  is shown in  FIG. 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. 
         [0071]    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 . 
         [0072]    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 . 
         [0073]    The control element  32  is arranged analogously to the second embodiment (see  FIG. 2 ) in the backflow line  36  in this embodiment. 
         [0074]    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. 
         [0075]    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 . 
         [0076]    It is also conceivable in this embodiment to arrange the control element  32  outside the backflow line  36 . 
         [0077]    A fourth embodiment can be seen in  FIG. 4  that, analogously to the third embodiment shown in  FIG. 3 , comprises the useful air fan wheel  50  and the combustion air fan wheel  52 . 
         [0078]    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. 
         [0079]    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 . 
         [0080]    The function of the heating apparatus  10  in accordance with the fourth embodiment is analogous to the third embodiment in  FIG. 3 .