MXPA99003557A - High efficiency permanent air filter - Google Patents

Abstract

An air filter for use in residential and commercial heating and air conditioning systems including a laminated unit (100) having a filter media (102) where either side of the filter media (102) has a porous layer (104, 106) of passive electrostatic netting. The air filter has a corrugation configuration (142, 144) to increase the available surface area when compared to conventional flat filters.

Description

HIGH EFFICIENCY PERMANENT AIR FILTER Field of the Invention The present invention relates to filters capable of being cleaned by washing or vacuuming or the like for the intake air in heating and air conditioning systems used in residential or commercial buildings and, more particularly, this invention relates to a electrostatic filter for such systems and that has a long lifespan.

BACKGROUND OF THE INVENTION The intake air filters for heating and air conditioning systems have been used for decades. The intake air filter or primary filter was originally designed to protect heating coils and mechanical devices such as fans from damage by airborne particles. Because the harmful effect that inhaled particles have on the health of humans became public knowledge, the intake air filters were designed to remove these particles from the air. The most popular configuration of the prior art is a disposable rectangular filter. The filter contains fiberglass, animal hair, fibrous foam or polymeric medium or aluminum mesh encapsulated in a cardboard or plastic frame. Prior art filters may comprise polyester panels, urethane foam or animal hair coated with latex. In recent years, filters of the prior art comprising passive or static electrostatic means have been made available to the public. Most residential resistance specifications require that air filters have an initial pressure drop of no more than 0.22 inches of water for an air flow rate of 300 feet per minute. The efficiency of powders for typical air filters of the prior art, tested using ASHRAE 52.1-1992, is 20% or less. The ASHRAE efficiencies of four types of filters that are commercially available are as follows: TABLE 1 Filter Type Environmental Area ASHRAE Disposable Fiberglass 4.0 < 20% Electrostatic (passive) 4.0 20% Electrostatic (fibers) Up to 8.9 30% Polyester Corrugated and Folded Up to 6.9 25% When these filters are first put into use through an air stream, they have a very low filtering efficiency. Typically, the output or powder efficiency is approximately 8%. However, as the dust particles are collected, the dust collection efficiency can be increased up to about 20%. At this point, the filter is ready to be replaced. Prior art filters are usually difficult to clean since the powder particles are embedded in the medium. Another current concern is the recognition that particles below 10 microns are not filtered by the hairs of the nose and are therefore inhaled into the lungs of humans. It is known that fibrous particles such as asbestos and fiberglass are the cause of respiratory diseases. Most current intake air filters for heating and air conditioning systems are not as efficient in capturing these small particles. Filters containing layers of electrostatic media have a better performance within this range of particles but these filters also become plugged. Because they can not be cleaned efficiently they must be replaced.

OBJECTIVES OF THE INVENTION According to the invention it has been discovered that the approach angle of the air current affects the efficiency of the capture of the particles, the life of the filter between cleaning operations and the difficulty of cleaning the filter. The filter of the invention causes a non-perpendicular path of the air flow resulting from the corrugated or folded configuration of the new air filter. Due to the corrugated configuration, there is more surface area than with the standard and flat air filters of the prior art. The increased surface area of the new filter also results in a lower pressure drop than that experienced with electrostatic air filters of the state of the art. The filter has a significantly longer life between cleanings and is very easy to clean. The efficiency of the novel air filter in the removal of particles is also improved over the prior art. The purpose of the invention is to provide a passive electrostatic layer, upstream, disposed on a layer of filter medium wherein both layers are in a corrugated or folded configuration to increase the filtration surface area when compared to an air filter. of flat surface. A large number of alternative configurations can be used that incorporate my novel concept. The following are examples. Modality of Two Layers. A filter media will be composed of fibers of a plastic material such as polyester or nylon held together with a binder, preferably a thermosetting acrylic binder. The filter medium is selected from among material that can capture above 80% of particles of a size of 10 microns or less. The filter media layer is preferably made of polyester having 6-15 Denier fibers, an acrylic resin binder preferably containing an antimicrobial agent. The medium may contain a curable resin such as a thermosetting, light curable or water activated resin. The resin may be dispersed throughout the medium as it is applied as streaks to the medium at locations corresponding to the upper portions of the pleats, before or after folding, preferably after folding. The resin is then cured to a rigid state to keep the folds in shape. Said thermosetting filter medium, in combination with a passive electrostatic layer can be corrugated without the need for metal grills to maintain the corrugated shape. The desired passive electrostatic layer can be described as a network material. The electrostatic layer can be made from medium such as polypropylene, polyester, nylon or polycarbonate. More preferably, the electrostatic layer is made of DELNET RB404-12P, a product of Applied Extrusion Technology, Middletown, Delaware or Equiliuent. In operation, the air filter would be installed with the electrostatic layer facing upstream. In this embodiment, sewing, stapling, thermal welding, adhesives or other means could be used to fix the filter media and the electrostatic layer, one with the other. Additionally, a second electrostatic layer may be disposed on the side downstream of the filter media to increase the efficiency of the filter. Modality of Five Layers. In this configuration, any side of the filter can be placed upstream. This embodiment has a layer of central filter medium of the same material as described above, although the property of thermofixing is not required. Arranged on either side of the central layer is a passive electrostatic layer of the same material as described above. Arranged on the surface facing outward from each of the electrostatic layers is a grill, appropriately formed of expanded metal. The grill is preferably made of metal. More preferably, the grill is made of an anticorroble material such as aluminum. A non-metallic material can also be used for the grill. The purpose of the grill is to provide a deformable material that will make the filter, once corrugated, maintain its corrugated shape. Grid layers are required when using an elastic filter media, which will tend to return to a flat shape. When trying to form the electrostatic layers and the central layer in a corrugated configuration that has angled surfaces, the material comprising these layers has an elastic property that attempts to return to a flat configuration as soon as the forming tool is released from the surface. A further aspect of this invention is a method of forming a flat medium on an angled surface in a manner that prevents the latter from returning to its original configuration. In an alternative of the five-layer mode, the electrostatic medium is placed between sheets of mesh or expanded metal gratings. The end of at least one mesh is wrapped on the opposite side to lock the assembly together and prevent the medium from expanding and returning to its original shape. In a second alternative of the five layer mode, the layers of electrostatic medium, the middle layer and the outer grids are sewn together. In a third alternative of the five-layer mode, a respective grid and the electrostatic layer are adhesively bonded to one another. During the assembly process, a central layer is disposed between two layers of laminated gratings and electrostatic medium. The grill can be washed easily. Any side of the grill can face downstream, provided the layer of the grill is the outer layer. It has been found that if the grate is disposed between the electrostatic and central layers, adhesive can be used to bond the grate to both layers. This has the advantage of overcoming the elastic tendency of the central layer to flatten. The grill, however, can only be arranged between the two layers on the upstream side. Tests have shown that while the airflow tends to force the electrostatic layer into the grate and the central layer on the upstream side, on the downstream side the airflow tends to displace the electrostatic layer away from the layer central. Therefore, it is preferred to place the grill layer as the outer layer on the downstream side. My innovative air filter can also be manufactured in any size. However, as the filter size increases, it is preferred that the size of the grid layers increases. Due to the elastic tendency of the core layer material as described above, the larger the air filter, the heavier gauge material will be required to maintain the corrugated shape of the filter, especially in the central surface area of the filter. filter. Another feature of the invention is the use of two sheets of expanded metal. The prior art used expanded metal grills only for metal filters capable of being cleaned and washed. In the invention, the expanded metal layers are bent in an angled manner at the same time as the electrostatic means and the core layer. The metal layers prevent the electrostatic medium at an angle and the central layer from returning to a flat shape. The metal layers have very wide openings and thin strips that do not contribute to the capture of particles but do not contribute to the pressure drop of the composite medium. The filter of the invention is optimally arranged at an angle to capture the particles. It can be cleaned by shaking and / or by washing. The medium has a low pressure drop and a high efficiency for the range of particles found in the intake air. Because it can be cleaned and reused, my invention can be considered a permanent filter. These and many other features and advantages of the invention will become clearer as the invention is understood with reference to the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a multi-layered, folded or folded filter media for increasing the surface area to 160% of the planar medium; Figure 2 is another cross-sectional view of the filter of Figure 1, shown in operation; Figure 3 is a schematic graph showing the filter efficiency; Figure 4 is a graph showing the efficiency of bent electrostatic filters of the invention in the range of 0.3 to 10 microns; Figure 5 is a graph showing the efficiency of commercial and flat electrostatic filters in the same tested range and under the same conditions; Figure 6 is a schematic view of one embodiment of the novel air filter with five layer media; Figure 7 is a schematic view of one embodiment of the novel air filter with five layer media after securing the ends; Figure 8 is an elevational view of one end of the roller for corrugating the medium in an embodiment of the invention; Figure 9 is a schematic view of one embodiment of a continuous system for the formation of filter media of the invention; and Figure 10 is a schematic view of another embodiment of a continuous system for the formation of filter media of the invention.

Detailed Description of the Invention The passive electrostatic filter contains a core layer of a material capable of being bent, from 0.05 to 0.45 inches thick, selected from polymeric foam of a high-caliber fibrous polymer material, such as air-laid polyester fibers. , which have a density of 0.5 to 5 ounces per square yard (OPSY). Fibers are resins bonded by a resin such as an acrylic resin or spun-bonded or needle-bonded. In a preferred embodiment, the core or core layer is composed of a thermosetting material. This material removes most of the particles from the air stream, typically at least 80% of the particles that enter and that have a size of up to 10 microns. The efficiency in the capture of the particles by the core material is improved by placing a layer of an electrostatic polymeric material on each side of the core material. The material can be woven or non-woven. More preferably, passive electrostatic materials are used which are charged as the air flow passes through the polymers which tend to have natural static charges. These are preferred because the active electrostatic fibrous materials that are available produce an undesirably high pressure drop as a filter medium and are not amenable to cleaning. The passive material is usually formed by casting, extruding or weaving from a polymer of an unsaturated alkene monomer having from 2 to 8 carbon atoms. One type of material is a woven polypropylene net having a thickness of 0.01 to 0.10 inches, usually from 0.02 to 0.06 inches. The diameter of the yarn can be 1-35 denier, preferably 5-20 denier. The ratio of warp to fill yarn is 1.2 / 1 to 3/1 and the net is woven in a shape that resembles a honeycomb structure. A commercially available material is a net woven in the shape of a honeycomb of polypropylene fibers with a thickness of 8,000 that can be obtained in thicknesses of 0.03 and 0.05 inches. The fabric count is 51 warp and 32 fill. The outer grill layer does not contribute to filtration but is present to maintain the medium at an angle after it has been formed. Again, the layer must be able to be bent or deformed with extreme ease during the assembly process. If the sheet of material is too thick then it will be difficult to bend and if it is too thin, it will not be able to keep the three-layer medium in its folded form. Expanded metal, such as steel or aluminum that has a thickness of 0.010 to 0.25 inches, behaves satisfactorily in the filter of the invention. The gauge thickness that is most preferred depends on the size of the air filter. Larger air filters require a heavier or stronger gauge grill. The expanded metal grill should have an open area of at least 70%. The open area may be provided with strips of 0.01 to 0.18 thickness expanded to form rectangular or parallelogram shaped openings that have an area of at least 0.5 square inches. In the design of the filter of the invention, the following five methods of particle capture were considered in providing a filter having the optimum combination of high efficiency with the lowest possible resistance. 1. Casting or screening 2. Interception 3. Impaction or shock 4. Diffusion effects 5. Electrostatic attraction EXAMPLE 1 The outer layers on either side of the air filter medium are comprised of expanded aluminum having a thickness of 0.040 inches and thread thickness of approximately 0.04 inches. The rectangular openings were 1.5 x 0.75 inches. The passive electrostatic layers adjacent to each outer layer are composed of a polypropylene network having a thickness of 0.03 inches, diameters of warp and weft yarn of 8 thousand, a weight of 3 ounces yard and a yarn count of 51 yarns of warp per inch and 32 weft threads per inch. The central layer disposed between the electrostatic layers is a high-caliber hard polyester, which has the following properties: Weight (ounces per square yard) 4.5 +/- 10% Caliber (inches) 0.25 +/- 5% Fiber content: Polyester (6 &15 Denier) Type of binder Acrylic latex (solids 38%) Porosity (cfm / Ftsq . @ 0.5WG): 740 cfm Color: White Texture: Hard / High Antimicrobial: Aegis or Equiliuent The effect of the angle of the medium on the capture efficiency of particles was tested by placing a flat panel of the 5-layer filter medium of Example 1 through a stream of air flowing at 300 feet per minute (FPM). The particles of different sizes were counted with a laser counter of Hiac / Rayco particles both before and after the filter to establish the efficiencies at different micron sizes. The corrugated angle of the filter was changed in increments of 10 degrees from 0 degrees (flat) to 90 degrees.

TABLE 2 The experiment indicates that the optimum efficiencies are with the filter at an angle to the air that penetrates it from 20-75 degrees, preferably from 40 to 60 degrees. The angled surface provides an increase in efficiency. The resistance of the air flow can be lowered by appropriately increasing the surface area of the filter by reciprocating the panel to form opposite angled surfaces. Most filters work with low efficiency only by filtering until enough dust particles have been captured. As the filters become saturated with larger particles, their efficiency in capturing small particles that can be deposited in the respiratory system increases. The ability of a filter to initially capture small particles is improved by adding electrostatic media to the filter, especially when the filter is placed at an angle greater than 10 degrees or less than 80 degrees with respect to the incoming air. Referring now to Figure 1, both an increased area and an angled surface are provided by corrugating the medium 10 to form bends 12 having alternating upper and lower external curved ends 14, 16 and opposite angled walls 18, 20. The ratio of the length of the sum of the two angled surfaces is at least 1.2 to 2.5 times the length of the distance between adjacent curved ends and preferably from 1.4 to 2.0. The junction 24 of the inner walls can form a radius. Referring now to Figure 2, as the incoming air 11 has contact with the bent medium 10, the air will diffuse through the surfaces of the inclined walls 18, 20. The air will look for the path of least resistance to pass through. through the filter 10. At the beginning, the paths of least resistance will be the surfaces of the inclined walls 18, 20 more than the internal ends 26. As shown in Figure 2, the particles 30, especially those having larger diameters, will begin to collect at the bottom of the fold. The air flowing to the bottom of the bend will be deflected causing it to change its direction. The air, entraining smaller particles gradually flows up the walls at an angle 18, 20 of the fold. The walls will be loaded with small dust particles and particles of sizes less than one micron. Larger particles traveling at a higher speed and inertia will be collected at the bottom, increasing the efficiency of collecting particles of sizes smaller than one micron. The same mechanism will occur on the side walls as the lower parts of the folds are loaded with dust. The totality of the filtration mechanisms are improved. Casting and electrostatic deposition become more effective due to the increased residence time. The deviation of the air increases the turbulence of the air flow improving the impaction and interception of both large particles and small particles. The diffusion mechanisms are always in operation capturing particles smaller than a micron. The distance between adjacent outer ends 14 and 16 controls the thickness of the filter. The assembly of the final filter including the outer border frame has a thickness of from 0.5 to 4 inches, usually approximately 0.75 inches in thickness.

EXPERIMENTS Five filters approximately 2 feet wide and one inch thick prepared according to Example 1. Each was tested to determine the dust collection efficiency in the range of 0.3 microns to 10.0 microns of a stream of air flowing to 300 feet per minute. The air temperature was 70.2 ° F and the relative humidity was 55%. The test was performed using the laser counting system previously described. The results of the test are the following: 1. Full filter number 1 0.3 microns 6.8% 0.5 12.3% 5.0 86.4% 10.0 91.63% 2. Full filter number 2 0.3 micron 7.2% 0.5 14.3% 5.0 83.92% 10.0 94.28% 3. Full filter number 3 0.3 micron 6.7% 0.5 15.7% 5.0 85.6% 10.0 90.89% 4. Full filter number 4 0.3 microns 6.8% 0.5 14.6% 5.0 88.6% 10.0 93.51% . Full filter number 5 0.3 microns 7.3% 0.5 13.4% 5.0 84.9% 10.0 92.63% The resistance was 0.15 W.G. and the average of the 5 tests is shown in the following table, as well as the average efficiency of a typical commercial flat electrostatic filter where the resistance was 0.20 W.G. or 33% higher.

Figure 4 is a graphic representation of the previous results for my novel air filter design. Figure 5 illustrates the results for a flat air filter of the prior art. When comparing my new air filter design with the prior art, in the 0.30 micron range the average amount of particles observed by the laser upstream of the filter is 750,000 particles per minute. An efficiency of 2.8% of a filter of the prior art would allow more than 729,000 particles per minute to pass through. Having the radial fold an efficiency of 6.80% would allow less than 30,000 particles per minute. The particle size that has the greatest filtration efficiency difference is one micron. For this size, an upstream laser observed approximately 12,000 particles per minute. With the prior art filter having a 22% efficiency, more than 9.360 particles per minute would pass through the filter. However, my novel filter design has an approximate efficiency of 37% for the filtration of micron sized particles and would allow less than 7,560 particles per minute to pass through my filter design. The radial or corrugated folding air filter has an increased surface area on the flat filter of the prior art. Its ease of cleaning can be attributed to the ability of the filter to allow dust to collect between the folds and not penetrate the filter medium itself. The filter will have a larger dust holding capacity and will last longer between cleaning operations. As the filter collects dust, the efficiency of the filter will increase. Another aspect of the invention is found in the manufacture of the filters. As previously indicated, one embodiment is a five-layer assembly 100 as shown in Figure 6. The middle layer 102 is a thin layer of flexible foam or high-polyester foam. The central layer 102 is covered with layers 104, 106 of the passive electrostatic network. The stack completes the outer grids 108 and 110 of open mesh expanded metal layer. A grill layer, either 108 or 110, is slightly larger at 114 and 116 at 1/8 to 1/2 inch on each side. The longer length of a grill layer is bent over the end of the corrugations and extends over and forms a mechanical joint 130 with the upper expanded metal layer 108. The closed flat assembly 132 prevents the folds from returning to their flat condition . After the corrugation action, the filter is finished by securing a U-shaped metal channel, not shown, such as aluminum, on all four sides of the bent assembly. An adhesive, preferably water-based, can be applied to the U-shaped channel to further secure the filter in place, avoiding in this way that the corrugated folds return to their flat condition and that they leave the frame. Referring now to Figure 8, the rolls 120 contain a plurality of protruding and "V" shaped forming members 122 that are spaced evenly over the surface 124 of the roll 120 with a sufficient distance to form a curved radius in the middle at the bottom of a fold. The pointed tops 126 of the forming members 122 form the inner pointed ends of the five-layer folded assembly. The filter assembly of the invention is suitable for the replacement of filters used for filtering the intake air supplied to residential heating and air conditioning systems. The filters usually have a thickness of 0.5 inches to 3 inches, typically 1 to 2 inches, and are rectangular, usually having a width of 1 to 3 feet and a length of 1 to 3 feet. A 5-layer filter assembly according to Figure 9 and Example 1 and a competitive flat construction filter were tested by an independent testing laboratory at at least a test speed of 300 feet per minute. The results are as follows: TABLE The filter of the invention shows a substantially better capture efficiency in all particle sizes. The filter of the invention will capture substantially all the particles that affect the respiratory or allergic reactions. It should be understood that only preferred embodiments of the invention have been described and that numerous substitutions, modifications and alterations are possible without departing from the spirit and scope of the invention as defined in the following claims.

Claims (21)

1. Novelty of the Invention 1. An air filter capable of washing, to filter the intake air to a heating and / or air conditioning system, which comprises an assembly formed by: a deformable, non-electrostatic cushion of high-caliber polymeric fibers , laid to the air and joined with resin possessing a high filtration efficiency for particles of 10 microns and smaller and having a thickness of 0.05 to 0.45 inches and a density of 0.5 to 5 ounces per yard, said cushion having a front surface and a back surface; a layer of a passive, porous, woven electrostatic fabric disposed on either side of the cushion and having an inner surface in contact with said surfaces, and having an outer surface; a metal grate susceptible to being deformed, arranged in contact with the outer surfaces of the fabric; and said assembly having a folded configuration in which the angle between surfaces of adjacent walls of the folds is from 20 degrees to 75 degrees. An air filter according to claim 1, wherein the passive electrostatic fabric is a woven fabric selected from the group consisting of a polyalkylene of 1 to 8 carbon atoms. 3. An air filter according to claim 2, wherein the passive electrostatic fabric is a woven net. 4. An air filter according to claim 2, wherein the passive electrostatic woven fabric comprises polypropylene. 5. An air filter according to claim 4, wherein the woven fabric has a thickness from 0.01 inches to 0.1 inches. 6. An air filter according to claim 2, wherein the polymer fibers are polyester. 7. An air filter according to claim 6, wherein the bonding resin is an acrylic resin. 8. An air filter according to claim 7, wherein the filter has a periphery and further includes a rigid frame coupling said periphery. 9. An air filter according to claim 8, wherein said filter is sewn around said periphery. 10. An air filter according to claim 3, wherein the thickness of the network material is from 0.02 to 0.06 inches. 11. An air filter according to claim 10, wherein the woven net has a fabric that looks like a honeycomb structure. 12. An air filter according to claim 1, wherein the filter has an efficiency for particles of 0.3 microns of at least 6.8%. 13. A method for manufacturing a filter capable of washing, to filter the flow of intake air to a heating and / or air conditioning system, which comprises the steps of: placing a sheet of passive electrostatic network fabric polyalkylene fibers in contact with the surfaces of a non-electrostatic cushion made of resin-bonded, air-laid fibers of high caliber, having a thickness of 0.05 to 0.45 inches and a density of 0.5 to 5 ounces per yard, and high efficiency for particles of 10 microns or less; placing a layer of porous metal in contact with the outer surfaces of the network to form an assembly; and folding said assembly to form folds in which the angle between the surfaces of the walls is from 20 to 75 degrees. 14. A method according to claim 13, wherein the passive electrostatic network is a woven fabric selected from the group consisting of polyalkylenes of 1 to 8 carbon atoms. 15. A method according to claim 14, wherein the passive electrostatic woven fabric consists of polypropylene. 16. A method according to claim 15, wherein the woven fabric has a thickness from 0.01 inches to 0.1 inches. 17. A method according to claim 16, wherein the polymer fibers are polyester. 18. A method according to claim 17, wherein the binding resin is an acrylic resin. 19. A method according to claim 13, wherein the filter has a periphery and further includes the step of encapsulating said periphery in a metal frame. 20. A method according to claim 19, further including the step of sewing said filter around said periphery. 21. A method for filtering inlet air for an air conditioning and heating system with a permanent filter, which comprises the steps of: placing a filter capable of washing, as defined in claim 1 in the air path of admission; capture particles from the intake air inside a filter cushion; remove the filter from the intake air path; wash the filter cushion to remove particles; and reposition the filter in the path of the intake air stream. Extract of the Description A filter for use in residential and commercial heating and air conditioning systems includes a laminated unit that has a filter medium in which any side of the filter medium has a porous passive electrostatic network layer. The air filter has a corrugated configuration to increase the surface area, compared to conventional flat filters.