Exhaust hood with electrostatic filter unit

Description

[0001] The invention relates to a cooker hood with at least one electrostatic filter unit.

[0002] US Patent 2008 / 170971 A1 describes an air purification device comprising an ionizer, a photocatalyst, a UV light source, and at least one porous electrostatic filter downstream of the ionizer. The air purification device may include a pre-filter, which may be an electrostatic filter or a mechanical filter.

[0003] US patent 2009 / 010801 A1 describes an air purifier comprising a housing and a catalytic reactor. An electrostatic precipitator may be positioned upstream of the catalytic reactor. Additionally, a pre-filter may be provided to remove large, visible particles.

[0004] CN 106 733 194 B describes an electrostatic device and a range hood. The device comprises an electrostatic collection module, an electrostatic needle module, and an electrostatic ionization module stacked in series.

[0005] CN 208 066 543 U describes an electrostatic steam cleaning system for kitchen utensils. The device comprises a hood and a first filter arranged in the direction of steam flow, a second filter, a UV lamp, an electrostatic ionization unit, an electrostatic adsorption unit, and a third filter.

[0006] CN 202 630 184 U describes a type of exhaust hood with a static smoke separator. The device comprises an oil fume separator containing an arrangement of three electrode plates stacked in the direction of smoke flow.

[0007] CN 208 161 831 U describes a plate electrode device for cleaning kitchen exhaust gases. The device comprises an ionization zone and an adsorption zone, wherein the negative electrode plate has a sheet structure and the positive electrode plate has a network structure. The negative and positive plates are located within the adsorption zone. The ionization zone is located at the beginning of the adsorption zone.

[0008] Air purification devices can include, for example, air purifiers for filtering room air, devices for filtering air drawn into passenger cabins in automobiles, or kitchen extractor hoods. These devices are designed to filter liquid and solid contaminants as well as odors from the polluted air or from cooking fumes and vapors. Mechanical filters are typically used for this purpose. Examples of mechanical filters include expanded metal filters, perforated metal filters, baffle filters (also known as eddy current filters), perimeter filters, and porous foam media. All of these filter media operate according to mechanical separation mechanisms such as diffusion, barrier, and, most importantly, inertial filtration.

[0009] In inertial separation processes, the particle, due to its inertia, cannot follow the flow of the gas (air) around the individual filter fibers, expanded metal layers, porous media, or similar materials and consequently collides with them. With regard to the dominant inertial effect, the probability of a particle striking an individual fiber of the filter medium (corresponding to the overall separation efficiency) increases with increasing particle velocity, increasing particle diameter, increasing filter packing density and thickness in the flow direction, and decreasing filter fiber diameter of the filter medium.

[0010] One disadvantage of these filter units is that a high flow velocity is particularly necessary to ensure satisfactory filter efficiency for particle diameters greater than 1 µm.

[0011] Furthermore, a cooker hood is known, for example, from DE 2146288 A, in which an electrostatic filter unit is used. In this cooker hood, the electrostatic filter unit consists of plate-shaped separation and counter electrodes as well as wire-shaped ionization electrodes. The plate-shaped separation and counter electrodes are connected to each other via electrically conductive bridges and are arranged such that the air entering the filter element first flows over the separation electrodes with the wire-shaped ionization elements located between them and then reaches the counter electrodes, which are positioned higher up. The separation electrodes are attached to the cooker hood housing via a partition. In addition, a high-voltage device is provided in the cooker hood housing near the intake opening, which is connected to the electrodes of the filter unit.

[0012] One disadvantage of this filter unit is that it takes up a lot of space and also poses a danger to the user.

[0013] The invention is therefore based on the objective of creating a solution by means of which sufficient filter efficiency can be reliably ensured with a simple design, while still guaranteeing safe use.

[0014] According to the invention, the problem is therefore solved by a cooker hood with the features of claim 1.

[0015] The electrostatic filter unit is also referred to as the filter unit or electrostatic filter in the following. The filter unit comprises an ionization unit and a separation unit. The ionization unit can also be called the ionization zone, and the separation unit the separation zone. To enable the electrostatic separation of particles in the air, these particles must first be electrostatically charged (ionized). The ionization unit performs this function. The separation unit is located downstream of the ionization unit in the direction of airflow. The ionization unit preferably comprises at least one ionization electrode and at least one counter electrode. The ionization electrode is subjected to a voltage, preferably high voltage.As contaminated air flows through the ionization unit, solid and liquid particles are electrostatically charged by means of corona discharge via the ionization electrode, which can also be called a spray electrode. The ionization electrode, which can be a wire ionization electrode, is preferably arranged between two plate-shaped counter electrodes in the ionization unit. This is necessary because the particles in their original state usually have no electrical charge or an insufficient charge for efficient electrostatic deposition. The aim of the ionization unit is to electrically charge each individual particle to its maximum electrical saturation charge.

[0016] The collection unit comprises at least two collecting electrodes. These at least two collecting electrodes are preferably arranged parallel to each other. The at least two collecting electrodes are subjected to a high electrical voltage, thereby generating an electric field between them. At least one collecting electrode is a negative collecting electrode and at least one is a positive collecting electrode. The magnitude of the electric field strength depends primarily on the electrical potential, i.e., the voltage in kV, the distance between the positive and negative collecting electrodes, and the geometric shape of the collecting electrodes.

[0017] The air exiting the ionization unit, containing the electrically charged particles, flows into the separation unit. Due to the electric field generated between the precipitation electrodes, the particles are deposited at the electrodes and thus filtered out of the air.

[0018] For the ionization and subsequent separation of airborne particles, a high electrical voltage of several thousand volts is required; both positive and negative high voltage can be used. A high-voltage transformer, also known as a high-voltage generator or high-voltage power supply, is used to generate this necessary high voltage. This transformer supplies the ionization and separation zones of the electrostatic filter cartridge with the required high voltage and electrical energy. The high-voltage transformer is preferably integrated into the electrostatic filter unit, which can also be called a filter module or filter cartridge.The electrostatic filter module / filter cassette is preferably located in the air intake area of ​​the extractor hood to protect the components downstream from cooking fumes / aerosols / dirt. However, such a filter device can optionally also be located in the air outlet area of ​​the extractor hood or along the airflow path between the inlet and outlet areas of the extractor hood.

[0019] According to the invention, the precipitation electrodes are air-permeable. The precipitation electrodes are made of an air-permeable material. In this case, the precipitation electrodes are also referred to as porous precipitation electrodes. The precipitation electrodes can all be made of the same air-permeable material. However, it is also within the scope of the invention that different precipitation electrodes are made of different materials. The advantage of using an air-permeable material for the precipitation electrodes is that, firstly, the manufacture of the electrostatic filter is simplified, since the required air permeability is provided by the material itself. Secondly, with an air-permeable material, the openings in the material are small, which ensures efficient particle separation due to the mechanical separation effect.According to a non-inventive embodiment, in which the collecting electrode consists of an airtight material with at least one air perforation, it is also possible that only some of the collecting electrodes, for example, only the positive or only the negative collecting electrodes, consist of such a material, while the other collecting electrodes consist of an air-permeable material. Furthermore, it is also possible that, for example, only the first collecting electrode, i.e., the one facing the ionization unit, consists of an airtight material with air perforations. The airtight material can, for example, be a sheet of metal. The air perforations can, for example, be holes punched into the sheet of metal or introduced in some other way. In particular, the airtight material with air perforations can be expanded metal.

[0020] The material of at least one collecting electrode can therefore be, for example, expanded metal, wire mesh, fiber material, nonwoven fabric, sintered plastic, or foam. This offers several advantages. Firstly, the airflow can not only flow along the collecting electrodes, as in the prior art, but can also flow through them. Due to the air permeability of the collecting electrodes, they can thus serve as a mechanical filter. Since the separation unit is located downstream of the ionization unit in the direction of airflow, the particles contained in the air enter the separation unit in an electrically charged state. Therefore, the separation of the particles at the collecting electrodes is achieved through both mechanical filtering effects and electrical charge, i.e., through the electrostatic filtering effect.

[0021] Classical mechanical filters have the characteristic that, due to the dominant inertial effect for particles with a diameter >1 µm, the filter efficiency increases with increasing flow velocity. In contrast, with purely electrostatic filters, the filter efficiency increases with decreasing flow velocity because the residence time of the particle in the ionization and separation zone increases. The present invention efficiently utilizes the advantages of both mechanical and electrostatic filter mechanisms.

[0022] Furthermore, the filter efficiency of conventional electrostatic filters is significantly dependent on the magnitude of the electrical ionization and separation voltage. If the electronic high-voltage component fails (voltage dropout) or is damaged due to short circuits, no filtering performance is achieved at all. In contrast, the present invention retains the mechanical filter mechanisms and filter effects. Therefore, a total failure of the overall filter performance does not occur.

[0023] Finally, due to the air permeability of the precipitation electrodes, particles can be retained, at least partially, in the pores or other air openings of the precipitation electrodes.

[0024] According to the invention, the electrostatic filter unit has at least one protective element for at least one of the elements of the ionization unit. For the purposes of the invention, a protective element is defined as an element or device that protects the user from direct or indirect contact with one of the elements of the ionization unit and / or protects the elements of the ionization unit from mechanical damage.

[0025] By providing at least one such protective element, the electrostatic filter unit can be operated with high voltage, thereby increasing filter efficiency and protecting both the user and the filter unit.

[0026] According to one embodiment, the protective element provides protection against the impact of forces. In this embodiment, the protective element can preferably be a planar element arranged upstream of the ionization unit in the direction of flow. The protective element is permeable to air.

[0027] Additionally or alternatively, the protective element can be a shielding element for electrical shielding. In particular, the ionization unit and the deposition unit can be shielded.

[0028] According to the invention, the protective element is a safety device that has at least one layer and is positioned upstream of the ionization unit in the direction of flow. By positioning the protective element upstream of the ionization unit in the direction of flow, both physical contact with the ionization unit by the user and electrical shielding of the ionization unit from the user can be ensured. The size of the safety device is preferably such that the side of the ionization unit facing the direction of flow is completely covered by the position of the safety device.

[0029] According to the invention, at least one layer of the intrusion protection device constitutes a pre-filter. A pre-filter is defined as a layer that serves to filter relatively large dirt and dust particles, in particular particles with a diameter of d hyd ≥ 1 µm. By designing the protective element as a pre-filter, the filter efficiency of the electrostatic filter unit can be increased, in addition to preventing user interference with the ionization unit and preferably providing electrical shielding for the ionization unit and the separation unit. The pre-filter can be made of expanded metal, perforated sheet metal, wire mesh, welded mesh, or woven wire mesh.

[0030] According to one embodiment, the intrusion protection device comprises, in addition to the pre-filter, at least one protective layer and a spacer element. The spacer element is arranged between the pre-filter and the protective layer. The protective layer is preferably the layer that is the first layer of the intrusion protection device in the direction of flow. The protective layer can be made of an electrically conductive material, in particular metal, or of an electrically insulating material, in particular plastic.

[0031] According to one embodiment, the protective element consists at least partially of an electrically conductive or antistatic element with a surface resistance R ≤ 10 Ω. Particularly preferably, at least the pre-filter consists of such a material. By using such a material, any voltage present in the pre-filter can at least be dissipated.

[0032] According to a further embodiment, at least one protective element constitutes at least part of a housing for the ionization unit. In particular, in this embodiment, the protective element preferably constitutes at least part of an insulating housing for the ionization unit. In this embodiment, the protective element is preferably made of an insulating material. By providing an insulating protective element, especially voltage-carrying elements of the ionization unit can be enclosed in such a way that they cannot be accessed by the user.

[0033] According to one embodiment, the filter unit includes a high-voltage transformer, which is integrated into one of the housing components. This prevents user access to the high-voltage transformer. Furthermore, integrating the high-voltage transformer into the filter unit simplifies the design of the air purification device, as it only requires low-voltage wiring and contact points.

[0034] According to a preferred embodiment, the filter unit has a protective element that represents a pre-filter, and the pre-filter is connected to the return of the secondary side of the high-voltage transformer.

[0035] According to one embodiment, the electrostatic filter unit has a filter frame and the filter frame is connected to the return of the secondary side of the high-voltage transformer.

[0036] According to the invention, the precipitation electrodes are arranged perpendicular to the airflow direction through the ionization unit. The airflow direction through the ionization unit is preferably parallel to the counter electrode(s) of the ionization unit. Thus, the precipitation electrodes are preferably arranged transversely and, in particular, perpendicularly to the counter electrode(s) of the ionization unit.

[0037] This orientation of the air-permeable precipitation electrodes allows the airflow entering the separation unit to pass completely through the electrodes. This further increases filter efficiency. Furthermore, this orientation of the precipitation electrodes minimizes the installation space required for the filter unit. In contrast to filter units where the precipitation electrodes are parallel to the airflow and preferably parallel to the counter electrode(s) of the ionization unit, the height or length of this embodiment of the filter unit according to the invention is reduced because the precipitation electrodes are oriented transversely in this direction.

[0038] According to one embodiment, the precipitation electrodes are positioned adjacent to one another. In conventional electrostatic filters with plate or tube separators in the separation unit, considerably more space is required for the electrostatic filter as a whole, and especially for the separation area. In the filter unit according to the invention, the precipitation electrodes are air-permeable. Preferably, the precipitation electrodes are air-permeable plates or layers. Thus, even when several precipitation electrodes are stacked on top of each other, the overall height of the stack of precipitation electrodes remains low. Furthermore, due to the small distance between the precipitation electrodes, the particles separated / filtered between the individual air-permeable electrodes can be retained between them by capillary action.Thus, the separation area according to the invention can store these particles in addition to storing them in the precipitation electrode itself.

[0039] According to the invention, the order of the precipitation electrodes in the separation unit can be freely selected. For example, it is possible to arrange a positive precipitation electrode on the side of the separation unit facing the ionization unit and where the air enters the unit, and then to arrange alternating negative and positive precipitation electrodes. Alternatively, a negative precipitation electrode can be arranged as the first precipitation electrode on the side facing the ionization unit, followed by alternating positive and negative precipitation electrodes.

[0040] According to another embodiment, it is also possible for at least two adjacent collecting electrodes to have the same polarity. Thus, for example, two or more negative collecting electrodes can be arranged between two positive collecting electrodes.

[0041] According to a preferred embodiment, at least one of the collecting electrodes has an insulating coating. The insulating coating can be applied to the collecting electrodes by powder coating, dip coating, or another coating process. Preferably, the respective collecting electrode is completely electrically insulated, with the insulating coating being omitted at the electrical contact point required for applying voltage to the collecting electrode. This prevents electrical short circuits and associated voltage dips between the individual alternating, energized collecting electrodes.

[0042] According to the invention, all collecting electrodes of the separation unit can be provided with an insulating coating. Preferably, however, only the positive collecting electrodes are electrically insulated. The particles are charged in the ionization unit. If a positively charged particle strikes a negative collecting electrode, it should be able to release its charge again, as otherwise the electric field between the layers would weaken over time. However, because the positive collecting electrodes have an insulating coating in the aforementioned embodiment, an electrical short circuit between the positive and negative collecting electrodes can be prevented even if they are close together or in contact with each other.

[0043] Advantages and features described for the electrostatic filter unit apply – where applicable – to the extractor hood and vice versa.

[0044] The air purification device can be, for example, an air purifier for filtering room air, a device for filtering air drawn into a passenger cabin in an automobile, or a kitchen extractor hood. The air purification device can have several electrostatic filter units. The at least one electrostatic filter unit is preferably arranged on the intake side of the air purification device. However, it is also within the scope of the invention to provide at least one additional or alternative electrostatic filter unit on the air outlet side of the air purification device.

[0045] According to the invention, the air purification device is a range hood.

[0046] According to one embodiment, the extractor hood has at least one contact point for contact with a high-voltage transformer of the filter unit.

[0047] The invention is described in more detail below with reference to the accompanying figures. These show: Figure 1: a schematic perspective view of an embodiment of an air purification device according to the invention; Figure 2: a schematic exploded view of an embodiment of an electrostatic filter unit according to the invention; Figure 3: a schematic exploded view of the intervention device of the electrostatic filter unit according to Figure 2 Figure 4: a schematic exploded view of the ionization unit of the electrostatic filter unit according to Figure 2 Figure 5: a schematic exploded view of the separation unit of the electrostatic filter unit according to Figure 2Figures 6a and 6b: schematic perspective views of embodiments of the precipitation electrodes of the electrostatic filter unit according to Figure 2 Figure 7: a schematic sectional view of an embodiment of the precipitation electrodes of the electrostatic filter unit according to the invention; Figures 8a and 8b: schematic sectional views of further embodiments of the precipitation electrodes of the electrostatic filter unit according to the invention; Figure 9: a schematic representation of the wiring of an embodiment of the electrostatic filter unit according to the invention; and Figure 10: a schematic diagram showing the filter efficiency of the electrostatic filter unit according to the invention compared to expanded metal filters.

[0048] In Figure 1Figure 1 shows an embodiment of an air purification device 1 according to the invention. In the embodiment shown, the air purification device 1 is a range hood. An intake opening is formed in the front of the air purification device 1, in which, in the embodiment shown, two electrostatic filter units 2 are arranged. However, it is also within the scope of the invention that only one or more than two electrostatic filter units 2 are arranged in the intake opening. An air outlet nozzle 3 for the air exiting the air purification device 1 is provided in the top of the device. In the embodiment shown, the intake opening and thus the electrostatic filter units 2 are located vertically. However, it is also within the scope of the invention that the intake opening and thus the electrostatic filter units 2 are located at any angle between the vertical and the horizontal.In the illustrated embodiment, the electrostatic filter units 2 have a cassette shape. The electrostatic filter units 2 are therefore also referred to as filter cassettes. In particular, the electrostatic filter units 2 each have a width and length that is greater than their depth. Depth here refers to the dimension in the main flow direction, which in the illustrated embodiment is horizontal. The main flow direction is indicated in the figures by a block arrow. The electrostatic filter units 2 completely cover the intake opening. Thus, all the air flowing towards the air purification device 1 is passed through the electrostatic filter units 2.During operation of the air purification device, the contaminated air flows through the large filter surfaces of the electrostatic filter units 2 and is freed from liquid and solid contaminants / particles, especially those with a hydraulic diameter D hyd ≥ 0.001 µm, by means of both electrostatic and mechanical filter mechanisms. When the electrostatic filter units 2 have reached their saturation point with contaminants, they can be removed from the air purification device and cleaned in a dishwasher or manually by hand using water and detergent.

[0049] In Figure 2Figure 1 shows a schematic exploded view of an embodiment of an electrostatic filter unit 2 according to the invention. In the embodiment shown, the electrostatic filter unit 2 consists of a filter frame 40, a safety guard 60, an ionization unit 100, and a separation unit 170. These individual functional assemblies of the electrostatic filter unit 2 each have a planar shape or define a surface. In the embodiment shown, the filter frame 40 consists of two parts. The Figure 2The lower part is referred to below as filter frame front 4, and the upper part of filter frame 40 is referred to as filter frame back 5. To manufacture or assemble the electrostatic filter unit 2, the intrusion protection device 60, the ionization unit 100, and the separation unit 170 can be placed in filter frame front 4 and then closed with filter frame back 5.

[0050] In Figure 3The embodiment of the intrusion protection device 60 is shown in an exploded view. The intrusion protection device 60 forms a protective element according to the present invention. In the embodiment shown, the intrusion protection device 60 consists of three individual parts. In particular, the intrusion protection device 60 consists of a protective layer 6, a spacer element 7, and a filter layer of the pre-filter 8, which is also referred to as the pre-filter in the following. The individual parts of the intrusion protection device 60 each have a planar or layered shape. The first layer, which forms the actual protective layer 6, protects the individual parts of the intrusion protection device 60 behind it and assemblies of the electrostatic filter unit 2 from improper external force. In addition, the protective layer 6 can contribute to the appearance of the entire filter cartridge as a design element.The protective layer 6 can be made of an electrically conductive material, in particular metal, or of an electrically insulating material, in particular plastic.

[0051] In addition to providing mechanical protection against impact, the intrusion protection device 60 can also serve as an electrical protective element. In particular, the pre-filter layer 8 acts as an electrical protective element. This pre-filter layer 8 serves two purposes: firstly, it acts as a pre-filter for relatively large dirt and dust particles, especially particles with a d hyd ≥ 1 µm; and secondly, it also provides electrical shielding. This shielding is achieved by the pre-filter layer 8 according to the principle of a Faraday cage. Specifically, the ionization unit 100 and the separation unit 170, which are located downstream of the pre-filter layer 8 in the direction of flow, are shielded by it.In particular, the filter layer of the pre-filter 8 ensures that the outer intake area, i.e., the area located upstream of the electrostatic filter unit 2 in the direction of flow, remains field-free due to the static and quasi-static electric fields of the ionization unit, and that the resulting electrical induction to the outside, especially outside the protective layer 6, is prevented. Unwanted static charges on the protective layer 6 are thereby prevented. The filter layer of the pre-filter 8 preferably consists of an air-permeable, electrically conductive or antistatic material. For example, the filter layer of the pre-filter can be made of electrically conductive plastic. However, the filter layer of the pre-filter 8 can also consist of expanded metal, perforated sheet metal, wire mesh, welded mesh, or woven wire mesh. The filter layer of the pre-filter 8 preferably has a surface resistance R ≤ 10 Ω.In the illustrated embodiment, the filter layer of the pre-filter 8 consists of only one layer. However, it is also within the scope of the invention for the filter layer of the pre-filter 8 to consist of more than one layer.

[0052] Between the filter layer of the pre-filter 8 and the protective layer 6, a further layer of the intrusion protection device 60 is provided. This is referred to as the intrusion protection spacer element 7 and serves to keep the filter layer of the pre-filter 8 and the protective layer 6 at a defined distance from each other.

[0053] In the Figure 4Figure 1 shows an exploded view of an embodiment of the ionization unit 100 of the electrostatic filter unit 2. In the embodiment shown, the ionization unit 100 comprises an inner frame 9, two insulating housing parts 10, 11, counter electrodes 15, and ionization elements 16, which can also be referred to as spray electrodes. Furthermore, spacers 12 are provided in the embodiment shown, which maintain a distance between the counter electrodes 15. The ionization unit 100 also includes a high-voltage transformer 14 and a high-voltage busbar 13.

[0054] The insulation housing parts 10 and 11 are inserted into the inner frame 9. Each insulation housing part 10 and 11 has a rectangular rod shape and is inserted into the inner frame 9 at opposite ends, particularly longitudinal ends. Each insulation housing part 10 and 11 has contact openings on one side into which the ionization elements 16 are inserted. The insulation housing parts 10 and 11 are inserted into the inner frame 9 such that the contact openings face each other. This allows the ionization elements 16, which can be wires, to be stretched between the insulation housing parts 10 and 11. The counter electrodes 15, which in the illustrated embodiment are formed by plates, are inserted into the inner frame 9 and preferably also into the insulation housing parts 10 and 11. In addition, the spacers 12 are attached, which keep the counter electrodes 15 spaced apart from each other along their entire length.The insulating housing parts, 10, 11, preferably consist of an electrically insulating material and preferably have a surface resistance R ≥ 10 Ω. The insulating housing parts 10, 11 preferably consist of ceramic or plastic.

[0055] In one of the insulation housing parts 10, 11, or in the illustrated embodiment, in insulation housing part 11, an additional installation space is provided. This installation space contains the high-voltage transformer 14, the high-voltage busbar 13, and various wiring elements and contacts (not shown) necessary for the electrical connection of the relevant components. The ionization elements 16 are then mounted between the insulation housing parts 10, 11, and in particular between the high-voltage busbar 13 of insulation housing part 11 and insulation housing part 10.

[0056] In Figure 5Figure 170 shows an embodiment of the separation unit 170 of the electrostatic filter unit 2. The separation unit 170 is composed of negative precipitation electrodes 17, spacer elements 18, and positive precipitation electrodes 19. The spacer elements 18 maintain the positive and negative precipitation electrodes 17 at a defined distance from each other. The positive precipitation electrodes 19 are preferably connected to a high voltage U > 1 kV DC (direct current). Preferably, the positive precipitation electrodes 19 are completely electrically insulated with an electrically insulating coating, except for the contact points 20, to prevent electrical arcing and short circuits. The positive precipitation electrodes 19 can be coated for insulation. Suitable coating methods include functional powder coating, fluidized bed sintering, sol-gel, dip coating, enameling, or painting.A conductive material, especially a metal, is preferably used as the base material or substrate for the positive collecting electrodes 19. Particularly preferably, the materials specified in the [document / section] can be used as the substrate for the positive collecting electrodes 19. Figures 6a and 6b The materials shown are used. In the embodiment according to Figure 6a The substrate is expanded metal and after Figure 6b a welded mesh.

[0057] As an alternative to metal for the substrate of the positive precipitation electrodes 19, electrically conductive or antistatic plastics with a surface resistance R <= 10 11< Ohm are also suitable.

[0058] The negative precipitation electrodes 17 are also made of an air-permeable medium. The negative precipitation electrodes 17 are also made of an electrically conductive material, for example metal, or of an antistatic material, for example plastic, with a surface resistance R ≤ 10 Ω.

[0059] For the negative precipitation electrodes 17, expanded metals, wire mesh, woven wire grids and plastic mesh can be used, for example.

[0060] In Figure 7 An alternative embodiment of the precipitation electrodes 17, 19 of the separation unit 170 is shown. In the Figure 7In the illustrated embodiment, the negative precipitation electrode 17 consists of a single component arranged in a serpentine or meandering pattern between the positive precipitation electrodes 19. This embodiment has the advantage that the individual negative precipitation electrodes 17 do not need to be electrically contacted separately via contacts or other means.

[0061] In Figures 8a and 8bFurther embodiments of the precipitation electrodes of the separation unit 170 are shown. In this embodiment, the precipitation electrodes 17, 19 each have a pleated or corrugated structure. This measure serves, on the one hand, to reduce the pressure loss Δp [Pa] when flowing through the filter medium (the separation unit 170) and, on the other hand, to increase the filter efficiency while otherwise maintaining the same boundary conditions. In particular, the area of ​​the precipitation electrodes 17, 19 can be increased while maintaining the same width and length of the filter frame 40.

[0062] In each embodiment of the collecting electrodes 17, 19, the electrode can consist of a single layer. Alternatively, the positive collecting electrode 19 can be composed of several layers n>=1. The same applies to the negative collecting electrode 17.

[0063] The number of positive precipitation electrodes 19 per filter module is >= 1. The number of negative precipitation electrodes 17 per filter module is also >= 1. To increase filter efficiency, spacer elements 18 can be used. Alternatively, these can be omitted, and the positive and negative precipitation electrodes 17, 19 can be stacked directly on top of each other. However, the spacer elements 18 result in an increase in filter efficiency.

[0064] Preferably the order of the positive and negative precipitation electrodes 17, 19 is as shown, for example, in Figure 5As shown, alternating. The first and last precipitation electrodes in the flow direction can each be either positive or negative. This means that the first layer or electrode can be positive or negative, and the last layer or electrode can also be positive or negative.

[0065] The electrical wiring of the electrostatic filter unit 2 is in Figure 9 schematically represented. The electrical power supply with extra-low voltage (<= 50V AC; <= 120 V DC) or low voltage (<= 1000V AC; <= 1500 V DC) is provided via contact points or connections of the low voltage 26 on the primary side of the high-voltage transformer 14.

[0066] Power is supplied via contact elements (not shown) between each individual electrostatic filter unit 2 and the extractor hood or air purification device 1. Ideally, the electrical contact is made between the contact surface of the filter frame (rear side 5) and the air purification device 1 in the area of ​​the intake opening. The contact surface of the filter frame (rear side 5) is the one shown in Figure 2 upward-facing surface of the filter frame rear side 5. Alternatively, the electrical contact interface can be located at any point on the outer surface of the filter frame elements 4 and 5.

[0067] On the secondary side, the high-voltage line 24 with U > 1kV DC is connected via the high-voltage busbar 13 (see below). Figure 4) connected to the ionization elements 16 and also to all positive precipitation electrodes 19. The return line 23 of the secondary side is connected to all counter electrodes 15 and to the negative precipitation electrode(s) 17. The filter frame front 4, the filter frame rear 5 and filter layer of the pre-filter 8 are also connected to the return line 23 and are at the same electrical potential.

[0068] In Figure 10 The diagram shows the filter efficiency of an expanded metal filter and an embodiment of the electrostatic filter unit 2 according to the invention for a mean flow velocity c < 1 m / s in the particle size range 0.3 ≤ d hyd ≤ 3 µm. As can be seen from the diagram, the electrostatic filter unit 2 according to the invention has a significantly better filter efficiency than the classic expanded metal filter of a cooker hood.

[0069] The present invention has a number of advantages.

[0070] The fully enclosed, electrically conductive or antistatic casing, preferably with a surface resistance R ≤ 10⁻¹¹ ohms, serves as electrical shielding and protects the user / consumer and their environment from electrical hazards. All components under high voltage are completely encapsulated by conductive or antistatic elements due to this design. Electrostatic charging of the outermost components directly accessible to the consumer, particularly the filter frame and safety guards, is prevented.

[0071] According to the invention, the filter unit has at least one protective element for at least one of the elements of the ionization unit, wherein at least one protective element is an anti-contact device. This allows electrostatic filter mechanisms to be used without posing a risk to the user. This results in significantly improved filter efficiency for liquid and solid particles with a hydraulic diameter d hyd < 100 µm compared to conventional cooker hood grease filters, especially at low flow velocities c < 2 m / s. The improved filter efficiency is particularly pronounced in the embodiment of the electrostatic filter unit that uses porous precipitation electrodes, thereby overriding the still-active mechanical separation mechanisms through diffusion, barrier, and inertia effects of the electrostatic filter mechanisms.Due to the significantly improved filter efficiency, especially at low flow velocities (c < 2 m / s), the downstream components of the extractor hood (fan, housing, odor filter) remain free of oil and dirt accumulation. Specifically for recirculating extractor hoods that have an odor filter (activated carbon or zeolite filter) downstream of the grease filter, the service life of this recirculation filter is extended because it is not contaminated with fine particles and therefore does not become clogged. Such an electrostatic filter cartridge, in contrast to a conventional extractor hood grease filter, exhibits a significantly lower pressure drop (Δp) while maintaining the same filter efficiency.

[0072] By providing a protective element according to the invention, which can be, for example, an insulating housing component, the high-voltage carrier can be implemented in the electrostatic filter unit without posing a danger to the user. Furthermore, since the electrostatic filter unit can be supplied with electrical energy from the air purification device via contacts, using low voltage (<= 50 V AC; <= 120 V DC) or low voltage (<= 1000 V AC; <= 1500 V DC), the electrical hazard to the user / consumer is further reduced.

[0073] Finally, the preferred use of air-permeable, "porous" precipitation electrodes instead of plate packs (plate packs correspond to the design of classic electrostatic precipitators for precipitation) reduces the complexity and cost of the overall system because fewer individual components are used. The use of an air-permeable (porous), insulating precipitation electrode creates a fine-meshed electrostatic field with a high electric field strength. This enables high precipitation efficiency in a very small installation space compared to the classic plate electrostatic precipitator based on the Penney principle. The present invention allows this high electric field strength to be utilized without endangering the user.

[0074] Furthermore, the use of air-permeable collecting electrodes provides a greater storage capacity compared to conventional electrostatic precipitators with plate separation, which, due to their design, have limited storage capacity. In conventional electrostatic precipitators with plate separation, filtered / collected particles are gathered on the surface of the airtight separator plate. With larger particle accumulations, the surface's holding capacity is exhausted, leading to the detachment of the filtered / collected particles. These are then carried away again, for example, by the airflow. The use of air-permeable / porous collecting electrodes creates storage structures, significantly reducing the detachment of already collected particles.

[0075] Finally, the preferably provided electrically insulating coating of the positive collecting electrodes allows the electrodes to be in direct contact without the electric field collapsing due to leakage currents and spark discharges between the positive and negative collecting electrodes. This results in improved leakage current resistance for the electrostatic filter unit. Reference symbol list

[0076] 1 Air purification device 2 Electrostatic filter unit 3 Air outlet nozzle of air purification device 40 Filter frame 4 Filter frame front 5 Filter frame back 60 Protective element 6 Protective layer 7 Spacer element, finger guard 8 Filter layer of pre-filter 9 Inner frame 10 Ionization unit 10 Insulation housing part 11 Insulation housing part incl. installation space 12 Spacer 13 High-voltage busbar 14 High-voltage transformer 15 Counter electrode 16 Ionization element / Spray electrode 170 Separation unit 17 Negative precipitation electrodes 18 Spacer element, separation unit 19 Positive precipitation electrode 20 Contact of the positive precipitation electrodes 23 Return path of the secondary side / Connection of the negative precipitation electrode 24 High-voltage connection / High-voltage line of the secondary side 26 Low-voltage connection Dhyd = hydraulic diameter

Claims

1. Extractor hood, which has at least one electrostatic filter unit, wherein the filter unit (2) comprises an ionisation unit (100) and a separation unit (170) with at least two collecting electrodes (17, 19), wherein the at least two collecting electrodes (17, 19) are air-permeable and the filter unit (2) has at least one protection element for at least one of the elements of the ionisation unit (100), at least one protection element (60) takes the form of an intervention protection device which has at least one layer and is connected upstream of the ionisation unit (100) in the direction of flow and at least one layer takes the form of a prefilter (8), characterised in that the at least two collecting electrodes (17, 19) consist of an air-permeable material and lie perpendicular to the direction of flow of the air through the ionisation unit (100).

2. Extractor hood according to claim 1, wherein the protection element (60) takes the form of a screening element and / or a protection element against the effect of force.

3. Extractor hood according to one of claims 1 or 2, wherein the intervention protection device has at least one protection layer (6) and a spacer element (7).

4. Extractor hood according to one of claims 1 to 3, characterised in that the protection element (60) consists at least partially of an electrically conductive or antistatic element having a surface resistance R <= 1011 Ohms.

5. Extractor hood according to one of claims 1 to 4, wherein at least one protection element (60) takes the form of at least part (10, 11) of a housing for the ionisation unit (100).

6. Extractor hood according to claim 5, wherein the filter unit (2) has a high-voltage transformer (14) and the high-voltage transformer (14) is integrated in one of the housing parts (10, 11).

7. Extractor hood according to claim 6, characterised in that the prefilter (8) is connected to the return of the secondary side of the high-voltage transformer (14).

8. Extractor hood according to claim 7, characterised in that the electrostatic filter unit (2) has a filter frame (40) and the filter frame (40) is connected to the return of the secondary side of the high-voltage transformer (14).

9. Extractor hood according to one of claims 1 to 8, wherein at least one of the collecting electrodes (17, 19), in particular the positive collecting electrodes (19), have an insulation coating.

10. Extractor hood according to one of claims 1 to 9, wherein the extractor hood has at least one contact point for the contact to a high-voltage transformer (14) of the filter unit (2).