CARTRIDGE TYPE ELECTROSTATIC AIR FILTER

Abstract: An electrostatic air filter of the charged media type includes a disposable filter cartridge (23) to which a high voltage power supply (8) is removably attached. The filter can be easily retrofitted into an air duct of an existing air handling system, and includes a safety grounding element which discharges residual charge on the screens of the filter when the power supply is removed. A plurality of the filters, which can be powered by a single power supply, can be connected side by side in tandem to increase the filter area.

Description: The present invention relates to an electronic air filter of the charged media type in which the air filter includes two outside screens supported by two outside frames, two disposable filter pads disposed between the outside screens and an inside screen disposed between the filter pads, a high voltage power supply which supplies high voltage to the inside screen by means of a high voltage probe, the ground side of the high voltage supply being connected to the outside screens in order to create an electrostatic field which polarizes the fibres of the disposable filter pad. The high voltage power supply is supplied with voltage by a two conductor electrical cord and a plug connector which is adapted to be slidably received in a socket in the high voltage power supply. Such an electronic air filter is known from US-A-3 438 180. This filter is rather complex and includes a filter cell that accommodates two disposable fibrous filter pads, which filter cell has an ionizing section and an electrostatic charging section which is not disposable. The EP-A-0 229 857 and US-A-4 549 887 describe air filters in which disposable fibrous filter pads are supported in a hinged frame structure which permits replacement of soiled filter pads after removal of the filter pads from the rest of the assembly. Such known electrostatic air filters are cleaned by opening the filter and removing and replacing the individual filter pads. In cleaning these filters, some of the collected dust inevitably falls off of the pads, becomes airborne, and thus causes pollution. Another problem is that these known air filters also require a power supply which necessitates a special structural arrangement for the filter, and thus make it difficult to retrofit such a filter into an existing air handling system. It is therefore an object of the present invention to provide an electronic air filter in which the dust collecting media is in the form of a disposable cartridge, and in which the power supply is removably attached directly to the cartridge so that it can be easily retrofitted into an existing air handling system and the invention is characterised over EP-A-0 229 858 and US-A-4 549 887. According to the present invention, there is provided an electronic air filter of the charged media type which includes a pair of outside screens and an inside screen; a pair of filter pads, of non-conducting dielectric fibrous material, disposed between the outside screens and the inside screen; a high voltage power supply which supplies high voltage to the inside screen by means of a high voltage probe, the ground side of the high voltage supply being connected to the outside screens in order to create a electrostatic field which polarizes the fibres of the filter pads, the power supply being supplied with voltage by an electrical cord and a plug connector which is arranged to be slidably received in a socket in the high voltage power supply, characterised in that at least the filter pads and inside screen form an air filter cartridge of unitary construction including opposed sides, and an electrically conducting cartridge frame having a front and a back, whereby the frame, the opposed sides, the inside screen, and the filter pads provide a self-contained disposable unit. The air filter cartridge may be adapted for the mechanical attachment of a power supply for supplying voltage to the inside screen so that the power supply is mechanically attached in a supported manner directly and solely to the cartridge frame. The disposable filter cartridge in accordance with the invention preferably further includes an automatic grounding switch which discharges the high voltage on the filter cartridge when a high voltage power supply is disconnected from the cartridge. Thus a disposable air filter cartridge is provided which, although it operates at several thousand volts, can nonetheless be safely installed and removed from an air handling system. The filter can also be connected in tandem with other similar filters, and powered by a single high voltage power supply. This enables the cross sectional area of the filter to be increased as desired to accommodate various air duct sizes. The foregoing and additional objects and features of the invention will become apparent from the following detailed description thereof, taken in conjunction with the accompanying drawings, in which: Fig. 1 shows a first cartridge type filter of the invention with a high voltage power supply attached to the cartridge and a low voltage power supply connected to the high voltage power supply by a detachable cord; Fig. 2 is a cross-sectional view of the cartridge of Fig. 1 showing the two outside screens and the single inside screen; FIG. 3 shows an exploded view of the filter, the high voltage power supply having a high voltage probe and the low voltage supply being connected to it; FIGS. 4a and 4b are partial cross-sectional views showing the action of a grounding switch when the high voltage probe is inserted in an aperture on the cartridge; FIG. 5 shown an alternate arrangement wherein the high voltage power supply is provided with screens; FIG. 6 is an outside view of the alternate type cartridge filter of FIG. 5; FIG. 7 is a cross-sectional view of the cartridge shown in FIG. 6; FIG. 8 is a view of two filters connected in tandem showing the high voltage probes and a single high voltage power supply; FIG. 9 shows the elongated design of the high voltage power supply; and, FIG. 10 illustrates a frame and an electrode for receiving an air filter cartridge in yet another alternative embodiment of the invention. Turning now to a more detailed description of the invention, there is illustrated in FIGS. 1 and 2, an outside rectangular frame 1 which is made of a material such as an electrically conducting cardboard, plastic, or metal. A pair of electrically conducting outside screens, 2 and 3, are mechanically and electrically connected together with frame 1, with screen 2 being attached to the back side of frame 1, and screen 3 being attached to the front side of frame 1. Together, they form a disposable filter cartridge 23. An inside conducting screen 4 is disposed within cartridge 23, and is held in position by a mass of dielectric fibrous material 5, which can be made of a material such as plastic or glass that is easily polarized by an electrostatic field. If desired, screens 2-4 and material 5 can be pleated to increase the filter surface area, and decrease air resistance. A high voltage power supply 8, which includes a long and slender metal box 8a that houses the high voltage supply electronics (see also FIG. 3), is removably attached to filter cartridge 23 by means of a pair of spring metal retainer clips 6 and 7 on box 8a, that include retaining pins 6a and 7a, respectively, for engaging a pair of corresponding apertures 1a (one shown) in frame 1. Retainer clips 6 and 7 serve also to electrically connect frame 1, and screens 2 and 3, to power supply box 8a. A low voltage power supply 11, which can be plugged into a household electrical socket by prongs 12, is removably connected to power supply 8 by means of a two conductor electrical cord 9, and a plug and socket connector 10 on box 8a. A high voltage probe 13 extends from box 8a for engagement with inside screen 4 of cartridge 23 (see FIGs. 2, 4a, and 4b), and is electrically connected to the electronics of high voltage power supply 8. As illustrated in FIGs. 4a and 4b, probe 13 consists of a conductor 14 and an insulating sleeve 15 which covers conductor 14 so that only its tip is exposed. Filter cartridge 23 is provided with an opening 16 in outside frame 1 where probe 13 can be inserted to contact, and supply high voltage to, inside conducting screen 4. A flat metal spring element 17, which is affixed by an insulator 18 to the inside of frame 1, is electrically connected to inside screen 4 by a wire extension 19. Spring element 17 is arranged so that when probe 13 is inserted into opening 16 when power supply 8 is attached to cartridge 23, spring 17 makes contact with the tip of probe 13, and at the same time is lifted off of frame 1. In the operation of the filter, high voltage power supply 8 is attached to cartridge 23 by retainer clips 6 and 7. Low voltage power supply 11 is plugged into an electrical outlet, and cord 9 is plugged into high voltage power supply 8 via connector 10. Thus low voltage (6-28 volts) is supplied to the high voltage power supply. High voltage (4-10KV) from the high voltage power supply is provided to inside screen 4 via probe 13, spring element 17 and wire extension 19. The high voltage applied to inside screen 4 sets up on electrostatic field between inside screen 4 and outside screens 2 and 3. (Note that the outside screens are connected to the ground side of the high voltage power supply via frame 1 and retainer clips 6 and 7). The electrostatic field polarizes the fibers of fibrous material 5 which is located between the screens. The polarized fibers, which exhibit positive and negative charges on their surfaces, attract any dust particles which pass through the filter by electrostatic attraction. In this way the efficiency of the filter is enhanced. To replace the cartridge after it has been saturated with dust, low voltage power supply is disconnected from the high voltage power supply by disconnecting connector 10. Then the high voltage power supply 8 is detached from the cartridge by spreading retainer clips 6 and 7 apart. When the high voltage power supply is detached from the cartridge and probe 13 is pulled out of opening 16 (FIG. 4a), spring element 17 connects inside screen 4 to frame 1 (ground) and discharges the charge on screen 4 via wire 19. From the foregoing, it can be seen that cartridge 23 can be easily retrofitted into an existing air handling system in place of a conventional cartridge air filter. Since power supply 8 attaches directly to filter cartridge 23, and is contained in long slender box 8a, no modifications need to be made to the duct work of the air handling system to accommodate the filter unit. An alternate version of the cartridge filter system is illustrated in FIG. 5, and comprises a pair of outside screens, 20 and 21 supported by a frame 22. Frame 22 is permanently attached to high voltage power supply box 8a. The arrangement is such that there is space between screens 20 and 21 for a cartridge 23 (FIG. 6) which is similar to the one described before, but without outside screens 2 and 3. Instead of screens 2 and 3, cartridge 23 in FIG. 6 has two perforated retainer sides 24 and 25 made of metal, cardboard, plastic etc. The rest of the cartridge is made exactly the same as the cartridge shown in FIG. 1, i.e., it has outside frame 1, inside screen 4, opening 16, spring 17, wire 19, and insulator 18. Operation of the alternative arrangement is similar to the operation of the first arrangement. Cartridge 23 is placed between screens 20 and 21 and held in place by retainer clips 6 and 7. At the same time, high voltage probe 13 (not shown in FIG. 5) passes through opening 16 and supplies high voltage to inside screen 4 via spring 17 and wire 19. An electrostatic field is set up between inside screen 4 and outside screens 20 and 21, which polarizes the fibrous material, and thus attracts any dust particles which pass through the cartridge. In filtering systems, sometimes many small filters are used in tandem to cover a larger area in a duct. Using the cartridge type approach, it is possible to drive several filter cartridges in tandem using only one high voltage power supply. FIG. 8 shows such an arrangement. Power supply 8 provides high voltage to inside screen 4 of cartridge (a) via probe 13, spring 17 and wire 19. Inside screen 4 is connected to the next filter (b) by a high voltage probe 26. Probe 26 is similar to probe 13 in that it features a conductor inside an insulating sleeve. The sleeve is supported on outside frame 1 by a flange. Probe 26 supplies high voltage to screen 4 of cartridge (b) via spring 17, and wire 29 of cartridge (b). Cartridge (b) is identical to cartridge (a) and is also provided with a probe 26, which can supply high voltage to a third identical cartridge (not shown). Both cartridges (a) and (b) are provided with upper retainer clips 6 and lower retainer clips 7. By means of clips 6 and 7 these cartridges are attached to each other firmly so that probes 26 and 13 maintain good electrical contact with springs 17. Filters of the charged media type are usually made thin (about 1 inch thick). Because of this, the high voltage power supply 8 has to be made long and slender so that, when it is attached to the cartridge, a thin filter is formed. To achieve this, the high voltage power supply electronics (see FIG. 9) are made of three parts A, B, and C. A is an electronic oscillator which drives a transformer B. Transformer B provides about one tenth of the high voltage supply's output. Part C is a voltage multiplier which boosts the transformer's output to the final high voltage. By using this design, the voltage in the supply is gradually built up to the high voltage required to drive the filter without having any close parts at a high potential difference. Therefore, this design can be build on a narrow and long printed circuit board which can be contained in long and slender box 8a. Yet another alternative embodiment for use with filter cartridge 23 is illustrated in FIG. 10. Specifically, there is shown a frame 30 comprised of three U shaped channel type frame members 31, 32 and 33, and a fourth open frame member 34. Frame 30 can be installed into an air duct of an air handling system so that cartridge 23 (of either FIG. 1 or FIG. 6) can be slid into frame 30 via open member 34. Attached to the inside surface of frame member 32, is a voltage probe 35, which is designed in much the same manner as probe 13 shown in FIGs. 2, 3, 4a, and 4b. Probe 35 is positioned so that when cartridge 23 is slid into frame 30, probe 35 will penetrate opening 16 and contact spring 17 for supplying high voltage to center screen 4 as before. A high voltage cable 36 electricaly connects probe 35 to a high voltage power supply (not shown). Although the invention has been described in terms of preferred embodiments, it will be understood that numerous variations and modifications could be made without departing from the spirit and scope of the invention as set forth in the following claims.

Claims: An electronic air filter of the charged media type which includes a pair of outside screens (2,3; 20,21) and an inside screen (4); a pair of filter pads (5), of non-conducting dielectric fibrous material, disposed between the outside screens and the inside screen; a high voltage power supply (8) which supplies high voltage to the inside screen (4) by means of a high voltage probe (13), the ground side of the high voltage supply (8) being connected to the outside screens (2,3; 20,21) in order to create a electrostatic field which polarizes the fibres of the filter pads (5), the power supply being supplied with voltage by an electrical cord (9) and a plug connector (10) which is arranged to be slidably received in a socket in the high voltage power supply (8), characterised in that at least the filter pads (5) and inside screen (4) form an air filter cartridge (23) of unitary construction including opposed sides (2,3;24,25), and an electrically conducting cartridge frame (1) having a front and a back, whereby the frame (1), the opposed sides (2,3;24,25), the inside screen (4), and the filter pads (5) provide a self-contained disposable unit. An air filter according to claim 1, in which the air filter cartridge (23) is adapted for the mechanical attachment of the power supply (8) so that the power supply is mechanically attached in a supported manner directly and solely to the cartridge frame (1). An air filter according to claim 1 or claim 2, in which the outside screens (2,3) are contained in the unitary cartridge (23). An air filter according to claim 1, in which the air filter cartridge (23) includes first and second perforated retainer sides (24,25) which are in respective mechanical connection with the frame (1) and permit the substantially free passage of air through the air filter cartridge (23); and a power supply (8) for the air filter cartridge (23) further includes a frame (22) which is permanently affixed thereto and includes first and second spaced apart parallel outside screens (20,21) for slidably receiving the air filter cartridge (23), said first and second outside screens (20,21) being of substantially the same size and dimension as the perforated retainer sides (24,25) of the air filter cartridge (23). An air filter according to any of claims 1 to 4, in which the inside conducting screen (4) is retained in position within the cartridge (1) solely and directly by the filter pads (5). An air filter according to any of claims 1 to 5, in which the high voltage power supply (8) supplies voltage to the inside screen (4) through a high voltage probe (13,35) which extends from the high voltage power supply (8) for engaging the inside screen (4) of the air filter cartridge (23), and the air filter cartridge (23) is provided with an opening (16) in the back of the frame (1) positioned to receive the high voltage probe (13,35) so that the probe can contact the inside screen (4) when the high voltage power supply (8) is connected to the cartridge frame (1). An air filter according to claim 6, in which a spring element (17) is electrically attached to the electrically conducting inside screen (4), the spring element (17) being supported within the cartridge frame (1) so that the spring contacts the back of the cartridge frame (1) when the high voltage power supply (8) is disconnected from the cartridge frame (1), and so that the high voltage probe (13,35) contacts the spring element (17) and lifts it from contact with the cartridge frame (1) when the high voltage power supply (8) is connected to the cartridge frame (1) to thereby supply voltage to the inside screen (4); the spring element (17) thereby automatically discharging any electrical charge on the electrically conducting inside screen (4) when the high voltage power supply (8) is disconnected from the cartridge frame (1) and the spring element (17) makes resulting contact with the cartridge frame (1). An air filter according to claim 2, in which the high voltage power supply (8) is mechanically attached to the filter cartridge by way of a pair of retainer clips (6,7) which are affixed to opposite ends of a long and slender metal box (8a) that houses the high voltage power supply, the retainer clips (6,7) mechanically engaging opposite sides of the cartridge frame (1) when the high voltage power supply (8) is attached thereto. An air filter according to claim 8, in which the retainer clips (6,7) mechanically engage the opposite sides of the cartridge frame (1) with retaining pins (6a,7a) affixed to the retainer clips (6,7), the retaining pins (6a,7a) respectively engaging a corresponding aperture (la) in the opposite side of the cartridge frame (1). An air filter according to claim 2, or any claim when dependent on claim 2, in which the air filter cartridge (23) further includes an auxiliary high voltage probe (26) which extends from the cartridge frame (1) on the front side, opposite the back side to which a high voltage power supply (8) is mechanically attached to the cartridge frame (1), and the air filter cartridge (23) further includes retainer clips (6,7) affixed to opposite ends of that side of the air filter cartridge (23) so that a second air filter cartridge (23) can be mechanically attached to the first air filter cartridge (23) in a supported manner and the auxiliary high voltage probe (26) charges the inside screen (4) of the second air filter cartridge (23), thereby providing a tandem of air filter cartridges which cover a larger area in an air duct and which is electrically driven solely by the one high voltage power supply (8). An electronic air filter according to claim 1 or claim 4, or any claim when dependent thereon, in which the air filter cartridge (23) is supported in an air handling system by a frame (30) which includes three U-shaped channel frame members (31,32,33) and a fourth open frame member (34), the air filter cartridge being slidably received in the frame (30) via open frame member (34), the frame (30) further including a voltage probe (35) which is connected by a cable (36) to the high voltage power supply (8) and so positioned that when the air filter cartridge (23) is slid into the frame (30) the high voltage probe (35) penetrates an opening (16) in the air filter cartridge frame (1) and contacts the inside screen (4) to supply the inside screen (4) with high voltage.

Inventors: JOANNOU, CONSTANTINOS J.
Applicants: JOANNOU, CONSTANTINOS J.
Application year: 1988
Main classification: B03C3
IPC codes: B03C3