Air-treatment apparatus and methods

Air-treatment apparatus and methods are disclosed that are especially suitable for treating the air in a room or other dwelling or working space. An apparatus embodiment of the subject apparatus includes a housing having air-intake and air-output openings. A gas-filter assembly inside the housing receives air entering the air-intake opening and includes a dual-media filter element having a matrix of fibers to which particles of activated carbon are adhered at mutual points of contact without using an extraneous binder. As air passes through the gas-filter assembly, the carbon particles adsorb odor compounds from the air. At least one electrostatic 3-dimensional (E3D) filter assembly downstream of the gas-filter assembly includes a respective charging element sandwiched between dielectric-fiber filters sandwiched between two respective electrically conductive screens. The screens are electrically grounded while the charging element (which is conductive) is connected to a source of high-voltage DC power. The resulting charges on fibers of the dielectric-fiber filters polarize and attract particles in air passing therethrough.

FIELD

This disclosure pertains to apparatus and methods for treating air, typically air contained in an interior space such as one or more rooms of a dwelling, in a manner resulting in removal of undesired substances and particulates from the air.

BACKGROUND

Air treatment, i.e., any of various processes aimed at removing undesired substances from the air, is of great interest especially in human dwellings and workplaces. Attention to the quality of air in rooms and other spaces is increasing from research indicating that breathing purer air provides tangible health benefits. For example, many people live in or otherwise spend large amounts of time in single rooms or other relatively confined spaces in which the air available for breathing can become excessively laden over time with potentially harmful particulates, volatile compounds, and other contaminants. Also, with the increased emphasis on making living spaces and workspaces more environmentally tight, the air contained in such spaces can become more rapidly laden with levels of particulate and volatile contaminants that pose unacceptable health risks to the person or persons who occupy such spaces.

One conventional approach to air treatment is passing the air through a filter. For example, most residential forced-air heating units include a passive filter configured to remove larger, easily entrapped particulates such as pet hair and aggregates of lint and dust, principally for the purpose of protecting the heating equipment (e.g., the blower) from becoming overly burdened with accumulated debris from the air. Air passes through the filter whenever the heating unit is running. A disadvantage of this approach is that these filters have large interstitial spaces to ensure that the filter exhibits a very low pressure drop. As a result, these filters (while being better than no filter at all) are notoriously ineffective in capturing small particulates and volatile contaminants. If the pore size of these filters were reduced sufficiently to capture a large percentage (by count) of particulates in the air passing through the filter, then the filter would have too high a pressure drop (i.e., exhibit too high a flow resistance) to be usable with the forced-air heating unit. Also, filters having very small pore sizes are easily and rapidly clogged due to debris accumulation on upstream surfaces, which causes a rapid decline in the ability of the filters to pass air without having to apply a prohibitively high pressure gradient across the filter.

Another air-treatment approach involves passing the air through a region in which the air is ionized or subjected to generated electrons. This approach utilizes a source of electricity to produce an electrical charge in the region. The charge has sufficient amplitude to generate negative ions from the molecules of air gases exposed to the charge in the region. Particulate contaminants suspended in air, such as dust, smoke, and pollen, are usually made up of small, positively-charged particles. The generated negative ions combine with airborne positively charged particles and electrically neutralize them. The resulting neutral-charged particles fall to the earth or floor under the action of gravity. Thus, “ionized” air tends to reduce the concentration of suspended particles in the air. Unfortunately, most devices that produce ionized air also produce ozone, which has become generally recognized as an undesirable contaminant especially in room air. Ionizers also tend to overcharge airborne particles, thereby rendering them attractive to oppositely charged surfaces. This can result in an increased particulate accumulation on various surfaces in the room such as walls, furniture, and draperies.

Another known type of air treatment, called “photo-ionization,” also produces ozone. In photo-ionization, the air is routed past a light source that produces ultraviolet light at a wavelength (about 185 nm) at which oxygen in the air is ionized to produce ozone. Ozone in sufficient concentration is an effective oxidizer of many types of organic compounds including the compounds that make up biological structures on microorganisms such as bacteria, algae, mildews, and molds. Thus, ozone destructively reacts with these microorganisms, which is effective especially in eliminating odors otherwise caused by them. Unfortunately, photo-ionization is not effective or at most poorly effective in physically removing fine particles such as soot, smoke, animal dander, and certain microorganisms from air. Also, as noted above, producing and discharging ozone into room air is not desirable.

Yet another known type of air treatment involves passing air through a gas-absorbing material such as granules of activated carbon (charcoal), wherein activated carbon is an effective adsorber of gaseous and certain molecular airborne contaminants. Conventional carbon gas-phase filters typically are configured for industrial use, and frequently exhibit any of various undesirable traits such as production of excessive amounts of carbon dust, and short service life. Reducing dust production can be achieved by attaching the granules of activated carbon to a matrix, but many such efforts tend to mask most of the surface of the carbon granules with adhesives or binders, which substantially reduces the effectiveness of the granules.

Hence, effective air treatment poses substantial challenges in the application of effective techniques. Whereas there have been various efforts to combine multiple air-treatment techniques in a single apparatus, these efforts heretofore have yielded disappointing results.

DETAILED DESCRIPTION

The subject apparatus and methods are described below in the context of representative embodiments that are not intended to be limiting in any way.

FIGS. 1A–1Cdepict general exterior aspects of a representative embodiment of an air-treatment unit10. The depicted air-treatment unit10comprises a base12and a housing14extending vertically upward from the base12. The housing14includes a front panel16, side panels18a,18b, an intermediary portion19, a rear panel20, and a top surface22. The front panel16defines an air-output grille24, and the rear panel20(FIG. 1B) defines an air-intake grille26. As seen inFIG. 1C, the housing14has a generally triangular profile transversely as a result of the particular manner in which filter assemblies, discussed in detail below, are disposed inside the housing14in this particular embodiment. The housing14also defines a control and display panel28adjacent the top surface22. The control and display panel28desirably is sloped forwardly for ease of use by an operator. A power cord30enters the unit10from the rear or either side of the base12. In this embodiment, and not intending to be limiting in any way, the housing is 36 inches high, 16 inches wide at the rear panel20, and 10 inches deep.

Turning now toFIG. 2, and further with respect to the exemplary embodiment, certain assemblies and components mounted inside the housing14are shown.FIG. 2shows the rear panel20opened and displaced to the left (arrow32). As noted above, the rear panel20defines an air-intake grille26(FIG. 1(B)) that, inFIG. 2, is obscured by a gas-filter assembly34and inner louver panel36. Also attached to the rear panel20inwardly of the inner louver panel36is a reflector strip38extending up the vertical midline of the louver panel36by which the gas-filter assembly is mounted to the rear panel20. The reflector strip38is held by ribs39, which also rigidify the louver panel36. The rear panel has an extension40that becomes the top surface22when the housing14is closed up.

The right-hand portion ofFIG. 2depicts assemblies mounted on the inside surface of the intermediary portion19of the housing14. These assemblies include a pair of electrostatic 3-dimensional (“E3D”) filter assemblies42a,42bflanking a vertically disposed, ultraviolet (UV) lamp tube44mounted in a lamp socket46. The lamp socket46comprises an upper portion46aand a lower portion46bthat are mounted on respective arms47a,47bextending toward the rear panel20between the E3D filter assemblies42a,42b. Frontwardly of the UV lamp tube44and mounted in a vertically stacked manner on the intermediary portion19are three fans48a–48c. Frontwardly of the E3D filter assembly42a(and mounted to the intermediary portion19) are a high-voltage transformer50, a power electronics board52, and a high-voltage probe54a(a similar high-voltage probe54bis situated frontwardly of the other E3D filter assembly42b). During operation of the unit10, the high-voltage transformer50supplies a high electrostatic potential via the respective probe54a,54bto the E3D filter assemblies42a,42b, as discussed in detail later below, and the UV lamp tube44irradiates UV light on the surfaces of the E3D filter assemblies (i.e., the upstream-facing surfaces) that face the UV lamp tube44.

The air-treatment unit10desirably is run continuously during use, with the air-output grille24facing the area in a room or the like in which treated air is to be discharged. Because air enters the rear of the unit10, the unit can be placed near a wall. In the depicted embodiment the base12has a slight flare to prevent the unit10from being placed with zero clearance against a wall.

The unit10will treat the air in a room or other space more quickly at higher fan speeds. Continuous operation is desirable because room air tends to acquire contaminants continuously, for example, by human and pet traffic into and out of the room, by other ventilation equipment discharging air into the room, around door frames and window frames, and through cracks and other imperfections in floors, walls, and ceiling. Also, particulate contamination and volatiles are continuously being added to the room air by the daily activity of the room occupant(s) and from furnishings and other things in the room. In addition, imparting movement to air in a dwelling structure can generate one or more areas of slightly negative pressure that pull air in through other openings such as vents, cracks, etc.

The unit10desirably is portable to allow movement to and placement at any of various locations where air cleaning is needed. Placing the unit10in a central location in a room or the like will provide clean air to surrounding locations in the room. The degree of cleaning will be greatest near the unit10, with less-clean air generally existing at progressively greater distances from the unit. Any of various factors can affect these general performance parameters, such as air currents in the room, the configuration of the room (doors, windows, and walls), activity in the room, furnishings, etc.

Further with respect to the representative embodiment, air entering the unit10flows through the air-intake grille26and the gas-filter assembly34, then flows through the E3D filter assemblies42a,42bas a germicidal wavelength of UV light from the UV lamp tube44irradiates the surfaces of the E3D filter assemblies42a,42b. The resulting purified air then passes through the fans48a–48cand through the air-output grille24in the front panel16back into the room. Because the fans48a–48care located downstream of the gas-filter assembly34and E3D filter assemblies42a,42b, particle accumulation on the fans is minimized. Also, the action of the gas-phase filter34on air passing through the unit10keeps the UV lamp tube44and E3D filter assemblies clean.

The fans48a–48cdesirably run continuously so long as the unit10is on. Running of the fans48a–48ccreates a reduced pressure inside the housing14, which draws air into the unit through the air-intake grille26in the rear panel20. In a particular embodiment the fans48a–48chave five selectable speeds (discussed later below) to suit a user's preference in terms of air-movement velocity in the room.

An exemplary UV lamp tube is a 25-Watt germicidal UV lamp tube, type TUV25, manufactured by Phillips. The UV lamp tube44is powered by a lamp-driving circuit (as known in the art) on the power electronics board52, and desirably is illuminated continuously so long as the unit10is running. The UV lamp tube44produces UV light at a germicidal wavelength suitable for killing microorganisms such as bacteria and fungi (molds) in air near the tube and that become lodged on the surfaces of the E3D filter assemblies42a,42bfacing the UV lamp tube44. In this regard, a particularly desirable wavelength of UV light is 254 nm. The UV lamp tube44desirably does not produce ozone-generating wavelengths of UV light, such as 185-nm light (185-nm UV light splits molecular oxygen to form ozone). To such end, a particularly advantageous UV lamp tube44is made with a quartz tube doped to block transmission of 185-nm light while remaining transmissive to 254-nm light. Consequently, production of significant amounts of ozone by the unit10is prevented. As noted above, although the light produced by the UV lamp tube44can kill microorganisms in air near (i.e., passing by) the tube, the exposure time of microorganisms in air passing by the tube is usually very short. In contrast, the exposure time of microorganisms lodged on the facing surfaces of the E3D filter assemblies42a,42bis very long (potentially unlimited), which ensures thorough killing of the lodged microorganisms.

Referring now toFIG. 3, a transverse section through the housing14of the representative embodiment is shown. The sectioned portions of the housing14include the intermediary portion19, the front panel16, the side panels18a,18b, and the rear panel20. Shown also are spatial relationships of the air-intake grille26, the gas-filter assembly34, the louver panel36, the reflector strip38, the UV lamp tube44, the lamp socket46, the E3D filter assemblies42a,42b, the fans48a–48c, and the air-output grille24. Air passing through the gas-filter assembly34enters a first space56asituated between the louver panel36and the E3D filter assemblies42a,42bmounted to the intermediary portion19. While the air passes through the first space56a, the air is exposed to the UV light produced by the lamp tube44and thus experiences some disinfection by the UV light. The air then passes through the E3D filter assemblies42a,42band enters a second space56bsituated between the E3D filter assemblies and the side panels18a,18band front panel16as the air moves toward the fans48a–48c. Air passing through the fans48a–48cpasses out of the unit10through the air-output grille24in the front panel16. As shown inFIG. 2, the second space56baccommodates the high-voltage transformer50and the power-electronics board52mounted to the intermediary portion19.

The gas-filter assembly34and E3D filter assemblies42a,42bdesirably are mounted inside the housing14in a manner allowing easy replacement of the respective filters. The usable lifetime of these filters is a function of the degree of contamination of air in the space to be treated using the unit10. In a space in which the contaminant load of the air is heavier than normal (e.g., particles, gases, and/or odors), the filters may need replacement more frequently than normal. By way of example, certain specific filters should be replaced after 6 months (approximately 4400 hours) of continuous use.

Similarly, the UV lamp tube44has a useful lifetime and desirably is mounted for ease of replacement as required. For example, to ensure optimum germicidal activity of the UV light, it is desirable to replace a particular UV lamp every year (approximately 8800 hours) of continuous use, even though the UV lamp tube44likely will illuminate for a longer period before burning out.

Turning now toFIG. 9, the control and display panel28in the depicted embodiment includes a power on-off push-button switch58, a reset push-button switch60for the filter-replacement clock, a reset push-button switch62for the UV lamp-replacement clock, a fan-speed-decrease push-button switch64, and a fan-speed-increase push-button switch66. The control and display panel28also includes a display68, which can be a liquid-crystal display (LCD). The display68illustrates fan speed with a numerical indication70(with “1” corresponding to the slowest fan speed and “5” corresponding to the fastest fan speed) and with a bar graph72. The display68also includes a bar graph74indicating remaining useful lamp life, and bar graph76indicating remaining useful filter life. In each bar graph74,76, each displayed bar represents an available 20% of the life of the respective component. For example, a display of two bars indicates that approximately 40% of the useful life remains for the respective component. Thus, the bar graphs74,76provide continuous feedback to the operator on the remaining lives of the respective components, which allows the operator to predict accurately when replacement of the respective components should be performed. On a particular bar graph, when the last bar is no longer displayed, a “Replace” message is displayed on the display68. Upon replacing the respective component (lamp or filters), the respective push-button switch60,62is depressed for five seconds to reset the respective replacement clock. Upon actuating any of the push-button switches58,60,62,64,66, the display68will become back-lit and will remain so for 30 seconds if no other push-button switches on the unit are pressed. The display68also includes an LED indicator light (not shown) that remains illuminated so long as the unit10is plugged in to a source of household current.

As shown inFIGS. 4A–4B, an exemplary embodiment of the gas-filter assembly34comprises a filter frame80, a dual-media filter element82, and a pre-filter84, and is made by Filtration Group, Inc., Joliet, Ill. The gas-filter assembly34is mounted, with the major dimension extending vertically, between the rear panel20and the louver panel36such that air passes through the pre-filter84before passing through the dual-media filter element82.

The pre-filter84desirably is configured as a non-woven, spun-fiber open matrix having interstitial spaces sized and configured so as to impose very low flow resistance to air passing through the pre-filter. In a particular embodiment, the fibers in the pre-filter84are of spun polypropylene. Alternatively, any of various other spun polymeric or glass fibers, for example, or mixtures of such fibers could be used. The primary role of the pre-filter84is to remove large, particulate matter from air passing through the pre-filter, so as to prevent such matter from clogging the downstream dual-media filter element82and to extend the life of the E3D filter assemblies42a,42b. By way of example, the pre-filter is approximately ⅜-inch to ½-inch thick and blocks passage therethrough of airborne particles that are 20 micrometers or larger, which is effective for removing hair, lint aggregates, and other large particulate matter from the air propagating toward the dual-media filter element82.

The dual-media filter element82is a three-dimensional matrix (exemplary thickness is 3/16 inch) of non-woven fibers and functional particles that are adhered to the fibers. The particles are adhered to the fibers without using an extraneous binder or adhesive but rather by the fibers themselves. The non-woven fibers desirably are of a “bicomponent” type, comprising a high-strength core and a low-melt sheath. The functional particles desirably are activated carbon (also termed “activated charcoal”). A particularly advantageous filter element of this type is an “AQF®” filter element manufactured by AQF Technologies LLC, Charlotte, N.C. As shown inFIG. 5, the bicomponent fibers86form a non-woven, generally uniform web85of interconnected fibers that are thermally bonded to each other by localized fusing of the low-melt sheaths at points of contact of the fibers. Also, the functional particles88are thermally bonded (by the low-melt sheath) to the fibers86at respective points of contact of the fibers86with the particles88. Thus, the functional particles88are strongly bonded to the web85and distributed three-dimensionally throughout the web85. The bonding of the functional particles88to the web85prevents migration of the particles88out of the web85. In addition, bonding of the particles88to the fibers86is achieved without substantially reducing the surface area of the particles88available for interaction with air. In other words, the effective surface area of the particles88in the web85is not substantially reduced by bonding of the particles88to the fibers86, which allows the dual-media filter element82to exhibit much greater VOC-removal efficiency than conventional activated-carbon filters. Consequently, less activated-carbon material is required, which reduces the pressure drop across the dual-media filter element82, which permits improved air flow at a lower applied pressure. This, in turn, allows the fans48a–48cto be reduced in size and flow rate, which lowers air turbulence, which reduces air noise. A dual-media filter element is discussed in U.S. Pat. No. 5,486,410 to Groeger et al., incorporated herein by reference.

The filter frame80can be made inexpensively of cardboard or the like, or other suitable material offering comparable strength and rigidity. The filter frame80desirably includes struts90that extend on both sides of the frame. The dual-media filter element82and pre-filter84are placed together superposedly and held in intimate contact with each in this manner by being mounted in the filter frame80.

The gas-filter assembly34effectively removes not only many types of large particles (e.g., hair, lint, visible dust) but also gases and volatile organic compounds (VOCs) from the air. Exemplary VOCs include, but are not limited to, formaldehyde, nicotine, acrolein, benzene, valeraldehyde, 4-methyl-2-pentanone, toluene, n-butyl acetate, tetrachloroethylene, styrene, α-pinene, 1,4-dichlorobenzene, d-limonene, and 2-butoxyethanol. Thus, the gas-filter assembly34is effective in reducing common room odors such as pet smells, tobacco smoke, and cooking odors.

In a typical embodiment subjected to normal-use conditions, the gas-filter assembly34should be replaced after it has been used for the prescribed length of time (e.g., 6 months). Desirably, the bottom edge of the louver panel36is provided with one or more latch clips (not shown) that can be released by an operator to allow the expired gas-filter assembly34to be removed for disposal. To facilitate ease of removal of the gas-filter assembly, a pull tab81is attached to the filter frame80.

Electrostatic 3-Dimensional Filter Assembly

The electrostatic 3-D (E3D) filter assemblies42a,42bare located fluidically downstream of the gas-filter assembly34. Although the representative embodiment depicted herein includes two E3D filter assemblies42,42b, only one or more than two alternatively can be used. In the depicted embodiment, the E3D filter assemblies42a,42bare mounted adjacent each other, with each one's major dimension oriented vertically. Desirably, the two E3D filter assemblies42a,42bare oriented in a book-like manner as shown (seeFIG. 3) so as to partially face the UV lamp tube44. Certain aspects of an E3D filter assembly42a,42bare discussed in U.S. Pat. No. 5,108,470 to Pick and U.S. Pat. No. 4,886,526 to Joannou, both incorporated herein by reference. Filter assemblies of this type can be obtained from Environmental Dynamics Group, Princeton, N.J.

Turning now toFIGS. 6 and 7, each E3D filter assembly42a,42bin the representative embodiment comprises an upstream electrically conductive screen94, a downstream electrically conductive screen96, upstream and downstream dielectric filters98,100, respectively (sandwiched between the screens94,96), and an electrically conductive charging element102sandwiched between the dielectric filters98,100. Each screen94,96, in a manner similar to a window screen, desirably is made of woven metal (e.g., aluminum) wires, which can be dielectric-coated if desired. Each screen94,96is mounted peripherally in a respective electrically conductive frame104,106, respectively. The frames104,106can be made, e.g., of the same metal used to make the screens94,96. Each dielectric filter98,100desirably is configured as a non-woven, continuous-filament, spun-fiber matrix having interstitial spaces sized and configured so as to impose very low flow resistance to air passing through the respective filter. Desirably, the fibers in each of the dielectric filters98,100are spun glass, but any of various other dielectric fibers can be used instead. An exemplary thickness of each dielectric filter98,100is ¼ to ⅜ inch. The charging element102can be, for example, an open-celled dielectric foam or non-woven matrix of dielectric fibers coated and/or impregnated with fine carbon (graphite or finely powdered charcoal) so as to make the charging element102electrically conductive. An exemplary thickness of the charging element102is 1/16 to ⅛ inch.

As shown inFIG. 7, the charging element102in the depicted embodiment is sandwiched between the dielectric filters98,100. The length and width dimensions of the charging element102desirably are one to two inches less than corresponding dimensions of the dielectric filters98,100(seeFIG. 6), such that, while sandwiched, the charging element102is centered relative to and isolated inside the dielectric filters98,100. The charging element102desirably is immobilized between the dielectric filters98,100in the filter “sandwich”108(FIG. 6) by applying a suitable adhesive (e.g., a hot-melt adhesive) at least peripherally to the facing sides of the dielectric filters to form an integrated unit. Thus, the charging element102is suspended in all three of the length, width, and thickness dimensions by the dielectric filters98,100. The sandwich108is interposed between the screens94,96to form the respective E3D filter assembly42a,42b.

Desirably, in each E3D assembly42a,42b, the respective screen frames104,106are mounted to each other along respective longitudinal sides by hinges110(FIG. 6). Thus, the frames104,106can be opened in the manner of a book for easy removal or insertion of a filter sandwich108. On at least one of the frames104are mounted latches112. For use, the frames104,106(with a filter sandwich108interposed between the respective screens94,96) are closed and held together firmly using the latches112. Desirably, one of the frames104,106of each E3D filter assembly42a,42bis mounted to posts115extending rearwardly from the intermediary portion19of the housing14(seeFIG. 3), leaving the other frame free to pivot on the hinges110whenever the latches112are opened.

With respect to each E3D filter assembly42a,42b, to energize the charging element102electrically without charging the screens94,96, a respective high-voltage probe54a,54bis used. As shown inFIG. 8, each high-voltage probe54a,54bcomprises an electrically insulative (e.g., plastic) flange120and electrical conductor122(made, e.g., of titanium) extending axially through the flange120. The distal end of the conductor122terminates in a pointed tip124, and the opposite end of the conductor122serves as a connector pin126. The probe54a,54bis mounted to the intermediary portion19via a compliant mounting such as a closed-cell foam cylinder128, which orients the conductor122at a normal angle toward the respective E3D filter assembly42a,42b. Specifically, the cylinder128positions the flange120so as to contact the downstream screen96whenever the screen is mounted to the intermediary portion19. The conductor122has a length that allows the tip124, when properly positioned, to penetrate the downstream dielectric filter100and contact the charging element102without extending significantly into the upstream dielectric filter98. Meanwhile, the connector pin126of the conductor122is connected to a wire130from the high-voltage transformer50. To ensure proper penetration of the probe tip124, a button132is mounted to the upstream screen94. Whenever the frames104,106of the screens94,96, respectively, are latched together at the time of mounting a fresh filter sandwich108between the screens94,96, the operator presses the button132(which is made of a suitable rigid dielectric such as a rigid plastic) directly toward the respective probe54a,54b. Depression of the button132is sufficient to collapse the upstream dielectric filter98locally until the button132actually is urged against the probe tip124, thereby achieving penetration of the probe tip124through the downstream dielectric filter100and into the thickness dimension of the charging element102. Upon releasing the button132, the upstream dielectric filter98returns to full thickness. With the probe tip124positioned in this manner, electrical charging of the screens94,96is prevented.

As noted, during use, the probes54a,54bare connected to a secondary winding of the high-voltage transformer50. The transformer50is part of an electrical circuit (not shown but understood in the art) that converts 110 VAC line voltage (supplied by the power cord30) to approximately −6000 VDC at very low current. In an exemplary embodiment, the transformer50is a type CS2080A3, obtained from High Voltage Power Systems, Inc., Carrollton, Tex., and having a nominally 120 VAC input and nominally −6 KVDC output as rectified by an integral rectifier and filter. This high negative voltage is connected by the probes54a,54bto the respective charging elements102in the E3D filter assemblies42a,42b. Meanwhile, the screens94,96and their respective frames104,106are electrically grounded, thereby placing the charging elements102at a −6000 VDC electrostatic potential relative to the screens and frames. The dielectric filters98,100are not directly charged. However, being dielectric and in close proximity to the charging element102, the fibers of the dielectric filters98,100acquire various electrostatic polarized charges proximally from the charging element102being at −6000 VDC and from charged particles adhering to the fibers.

The E3D filter assemblies42a,42brely upon at least three principles to trap airborne dust particles: impingement, polarization, and agglomeration. Impingement is the entrapment of an airborne particle that occurs as the particle impacts and becomes attached to a fiber of one of the dielectric filters98,100or of the charging element102. However, filtration by impingement represents a very small contribution to the overall filtration effectiveness of the E3D filter assembly. Polarization is a phenomenon that occurs when airborne particles as well as the fibers of the filters98,100are in close proximity to the electrostatically charged charging element102. Under such conditions, locations on dust particles and on the fibers become charged by being closely proximal to the applied electrostatic charge. According to the principles of electrostatic attraction (between opposite charges) and repulsion (between like charges), airborne particles entering the E3D filter assembly42a,42bacquire localized charges themselves and are attracted to oppositely charged regions on proximal regions of the dielectric filters98,100and charging element102. Because the effects of electrostatic attraction and repulsion act over distances, the particle-collecting effectiveness of each fiber of the filters98,100is increased many times over the effectiveness of an otherwise similarly configured but uncharged fiber. In other words, many more dust particles are influenced by a single fiber of a filter98,100when the fiber is electrically polarized versus when it is not polarized. This allows the E3D filter assembly42a,42bto be configured with a very low pressure drop (and hence very low flow resistance) while exhibiting excellent removal of particles from the air passing through the assembly.

Since polarized particles from the air remain polarized only so long as they are being influenced by a static charge, if any such particles leave the E3D filter assembly, they carry no residual charge and thus are free to be captured on a subsequent pass through the air-treatment unit10. Also, because the particles leaving the E3D filter assembly42a,42bare uncharged, they are not electrostatically attracted to other surfaces in the room, for example, which allows the particles to be captured by the air-treatment unit10later.

The third principle is agglomeration. As discussed above, as airborne particles enter the air-treatment unit10, they become polarized by the E3D filter assemblies42a–42b. This causes the particles to behave as individual airborne miniature magnets. As a result: (a) the particles are attracted to and captured on oppositely polarized fibers or regions of the E3D filter assemblies42a,42b, (b) the particles strike or are attracted to each other, causing self-adhesion and formation of larger particles (“agglomeration”), which are more easily captured by the air-treatment unit10, (c) the agglomerated particles can pass through the E3D filter assemblies42a,42b, but because they are now larger particles (as a result of agglomeration), the particles can be captured on a subsequent pass, and (d) the dust particles may pass unchanged and uncharged through the air-treatment unit10, which leaves them available for charging, agglomeration, and/or capture on a subsequent pass.

Operation

The representative embodiment of the air-treatment unit10is configured to operate on normal household AC current (115 VAC in the U.S.). Power is supplied to the air-treatment unit10by the power cord30, which provides power for the fans48a–48c, the power electronics board52, the control and display panel28, and the primary winding of the high-voltage transformer50. The high-voltage transformer50includes a rectifier and filter on its secondary winding to produce the −6000 VDC output to the high-voltage probes54a,54b. The power on-off button58on the control and display panel28turns the air-treatment unit10ON and OFF. Whenever the air-treatment unit10is OFF, the fans48a–48care not running, the UV lamp tube44is off, and no power is being applied to the high-voltage transformer50. Upon turning the air-treatment unit10ON, the fans run at the previously set fan speed. If the air-treatment unit10had been unplugged during the time it was OFF, the fans48a–48cwill operate at a default speed of “3” (the median speed) when the air-treatment unit10is turned back ON.

Referring now toFIG. 10, whenever the air-treatment unit10is ON, “dirty” air enters and passes first through the gas-filter assembly34(passing first through the pre-filter84and then through the dual-media filter element82). As the air passes through the gas-filter assembly34, the pre-filter84traps lint, hair, and other large airborne particles, and the dual-media filter element82removes VOC contaminants (small, volatile organic compounds of some contaminant gases and many odors) as well as some particulates. (Small particles such as particles of soot, smoke, bacteria, and mold generally pass through the gas-filter assembly34, but many of these particles are captured by the downstream E3D filter assemblies.) The air exiting the dual-media filter element82passes by the UV lamp tube44and enters the E3D filter assemblies42a,42b. As the air enters the E3D filter assemblies42a,42b, many small particles and microorganisms entrained in the air are captured by the upstream dielectric filters98. Meanwhile, the UV lamp tube44continuously irradiates the upstream dielectric filters98and screens94with germicidal UV light140and thus kills the microorganisms captured on these upstream surfaces. Also, as the air enters the E3D filter assemblies42a,42b, particles entrained in the air are polarized and thus are highly attracted to the fibers of the filter sandwich108. As a result of these actions, air exiting the E3D filter assemblies42a,42bis substantially cleaner than upstream air. This “clean” air is discharged from the air-treatment unit10via the fans48a–48c.

Except as specifically noted, the various components of the air-treatment unit10can be made of any of various suitable materials. In a specific implementation, and by way of example, the base12and various panels of the housing14are made of a rigid polymeric plastic such as polycarbonate or UV-stabilized ABS.

It will be understood that the appended claims are not limited to the representative embodiments disclosed herein, but rather encompass all modifications, alternatives, and equivalents that are within the spirit and scope of the following claims.