Field of the Invention
The present invention relates to high flow HEPA filter for providing aseptic and clean environmental conditions for manufacturing of pharmaceutical products, electronic products, high precision mechanical assemblies, hospitals and many other industries. Particularly, the invention relates to design of the HEPA filter for air handling units and high flow bio-safety units. More specifically, the invention relates to a method for designing mini pleat bank green HEPA filter for air handling units and high flow bio-safety units for providing aseptic and clean environmental conditions for manufacturing industries.
Background and Prior Art of the Invention
Particulate air filtration for Collective Protection Systems (CPS) use high efficiency particulate air (HEPA) filters. These filters are excellent at removing an extremely high percentage of biological and particulate material from the air, with relatively low pressure drop and energy consumption. These filters have been in use for decades and have proven themselves over the years as a valuable tool in various high technology industries, such as aerospace, pharmaceutical processing, hospitals, health care, nuclear fuels, nuclear power and electronic microcircuitry (computer chips).
In biological applications, laboratory personnel regularly work with microorganisms in biological safety cabinets. HEPA filters used in these cabinets must effectively trap hazardous bacterium and viruses for providing protection to the personnel. The size of an individual virus particle ranges from 0.005 to 0.1 micron, viruses generally travel through the air only as part of large particles (0.3 micron or larger), for example, attached to mucous particles. As it is difficult to disperse or aerosolize single viral particles and because of the particle collection mechanisms of HEPA filters, particles larger (and smaller) than a filter's most penetrating size are collected with greater efficiency.
As air passes through a HEPA filter, the air is not simply strained, rather a number of actions take place. First, as the air comes into contact with the bends and folds of the pleated filter media, the volume of airflow breaks off into numerous smaller air streams, as its own velocity and the velocity of the air upstream forces the air through the filter. Some particles become trapped because they are larger than the pores of the filter media, and cannot pass through. This takes place throughout the filter media, not solely at the surface of the filter. For large particles greater than 1.0 micron, the primary collection mechanism is impaction.
Impaction occurs when air traveling through the filter and the particles suspended in it, encounter a web of randomly placed fibers in the folded filter media, through which it must traverse. Although, the air can change direction to weave through the filter fiber maze, the tendency of particles is to continue on the same trajectory and to collide with the filter media, resulting in entrapment. For small particle entrapment in the 1.0 micron or smaller particle size range, diffusion is the primary collection mechanism. Small aerosolized particles behave similarly to gases; in that they move from an area of higher concentration to an area of lower concentration.
Particles are removed from the air stream, as they settle in areas of low air stream concentration at the fiber surface, where other particles are already trapped. The combination of aforementioned collection mechanisms results in effective removal of particles from a HEPA filtered air stream.
A large capacity HEPA filter having a layered filter medium has been disclosed in US7048501, whereby the layered filter medium is shaped as a mini pleat shape in a thickness direction and an entire shape in the thickness direction is a plurality of continuous "Vs. Also, a dust collecting device having such a large
capacity HEPA filter is produced and an air intake device for a gas turbine is provided with such a dust collecting device.
A "V"-bank air filter having a high air flow rate with low pressure drop is provided in US 2009193773 A. In one embodiment, a "V"-bank filter includes, a housing having a first layer and a second layer of pleated filter elements, arranged in a "V" configuration and comprising a unitary disposable filter. A centerline, defined by the first pair of pleated filter elements, defines an acute angle with a centerline defined by the second pair of pleated filter elements.
The design of HEPA filter used in a vent for venting a chamber, containing a radioactive material, has been described in US 5814118. The filter element includes a stainless steel wire mesh tube which supports a sintered stainless filter media thereon. The wire mesh tube has a stainless steel end plate with an exhaust outlet opening at the other end. The outlet opening communicates with a hollow core, defined by the stainless steel wire mesh tube. The sintered stainless steel filter media has its longitudinal edges joined by a tungsten inert-gas weld and is also welded directly to the end plates by completely closed circular welds. An annular housing of stainless steel surrounds the filter element in spaced relation thereto and has an axial inlet. The gas to be filtered flows into the inlet, around the filter element and through the sintered stainless steel filter media, before exiting through the exhaust outlet.
The separator used in a pleated high efficiency particulate air filter for wounding filter media has been described in US 4801317. The separator for providing uniform internal support for the pleats comprises a lattice with tapered struts or spacers. The struts are formed to provide a tapered space between the filter media and the struts after the media is wound around the separators.
These conventional "V" shaped HEPA filters have certain limitations in their design. The probability of air leakage failure during their manufacturing is very
high in these conventional V type HEPA filters. A HEPA filter is defined to have filtration efficiency of > 99.97% for particles of sizes, as low as, 0.3 micron. The existing design which has many media pleat edge joints can render a filter totally useless even, if one joint is left unsealed. In the present V type HEPA filters where horizontal pleat structure is used, there are plurality of packs wherein each pack has hundreds of media edges to be sealed and number of such packs. Further the time associated with the pack manufacturing and filter manufacturing, is very high and conventional HEPA filters have shorter life due to faster clogging of the filters, media content being less in them.
Object of the Invention
The object of the present invention is to provide a high flow mini pleat bank green HEPA filter for use in air handling units for providing clean and aseptic environmental condition.
Another object of the present invention is, to design a mini pleat bank green HEPA filter with least number of media edge sealings for making the manufacturing process less prone to air leak failure, which is the most critical aspect of any filter, specifically so for a HEPA filter.
Yet another object of the present invention is, to simplify the existing design of mini pleat bank green HEPA filter. The present invention design is suitable for low grade filters as well.
Yet another object of the present invention is, to provide a method for designing mini pleat bank green HEPA filter which reduces pack manufacturing time and machine setting time by 50%.
Still another object of the present invention is, to provide energy efficient and compact HEPA filter design, operational at low energy cost while maintaining high air flow at low pressure drop, as compared to existing high flow HEPA filters.
Statement of the Invention
In accordance with the main object of the present invention, a high flow HEPA filter is provided, which comprises of mini pleat packs with vertical pleats arranged in a "W" form and assembled in a frame, to give very high flow at low pressure drop.
In accordance with another object of the present invention, a high flow HEPA filter is provided, which comprises of 50 ±5 mm deep universal mini pleat packs, assembled and arranged in "W" shape, in the filter frame.
In accordance with yet another object of the present invention, a HEPA filter is provided whereby the edges of mini pleat packs are sealed directly to the filter main frame, thereby reducing edge sealing joints by a factor of 2/13.
In accordance with still another object of the present invention, the method for constructing a HEPA filter is provided, which comprises of arranging mini pleat packs in main frame, having channels and sealing the vertical pleat media surface to the channels.
Summary of the Invention
The mini pleat bank green HEPA filter is constructed by manufacturing a frame of metal or plastic or wood in channel, box or flange type design having standard dimensions of 610 ± 1 x 610 ± 1 x 305 ± 1 mm. Six mini pleat packs having 50±5 mm depth and height according to frame are prepared. The frame is provided with special channels to hold the mini pleat packs. The packs are then
arranged in the channels with media edges facing the upper and lower frame surfaces. The packs used in the filter are such that the mini pleats are in vertical orientation. The one side of all the pack edges is then sealed by plotting the sealant at the frame base in one round. It is then allowed to dry. After the sealing has dried, the filter is turned upside down so as to expose the other side of filter having pleated edge. Then the sealant is plotted on the other side of the filter and the edges are sealed on the frame. It is then allowed to dry.
The 12 vertical pleat media surfaces (not the edges) of the six pleat packs are then sealed to the channels, by using a sealant, to form a completely leak-proof filter.
Brief Descriptions of figures
Figure 1 illustrates the isometric view of the mini pleat bank green HEPA filter assembly, in accordance with an embodiment of the present invention.
Figure 2 illustrates the horizontal sectional view of the Mini pleat bank green HEPA filter assembly, in accordance with an embodiment of the present invention.
Figure 3 illustrates the vertical sectional view of the Mini pleat bank green HEPA filter assembly, in accordance with an embodiment of the present invention.
Figure 4 illustrates the front view of the Mini pleat bank green HEPA filter assembly, in accordance with an embodiment of the present invention. -
Figure 5 illustrates the back view of the Mini pleat bank green HEPA filter assembly, in accordance with an embodiment of the present invention
Figure 6 illustrates the planar arrangement of the vertical mini pleat packs, in accordance with an embodiment of the present invention.
Detailed Description of the Invention
What is claimed in the present invention can be understood with reference to the foregoing preferred and particular embodiments. Although, the subject matter has been disclosed with reference to particular and specific embodiments, it is not intended that such embodiments should be regarded as limitations to the scope of the invention. Also, unless otherwise specified, all the technical and scientific terms used herein, before and after, have the same meanings as commonly understood, by the person skilled in the art, to which this invention belongs, or assigned.
HEPA filters are primarily used for providing aseptic and clean environmental conditions for the manufacturing of pharmaceutical products, electronic products, high precision mechanical assemblies, hospitals and many other industries
In a large number of cases, the HEPA filter is fitted in an air handling unit, which supplies and distributes clean air-conditioned air to the working areas. In some cases, these filters are fitted in the ceilings of the rooms. To decrease the size of air handling units and make the HEPA filter capacity compatible with other air-filters in the air handling units, HEPA filters with double the air flow capacity as compared to the standard HEPA filters are required.
The primary issues that are always being pursued with particulate filter improvements are: 1) lower energy consumption, 2) longer filter life, 3) greater dust load capacity and 4) easier maintenance without compromising with the filter efficiency.
The operational cost, associated with filtering air, is typically related to the pressure drop across the filter. The filter resistance to flow is known as its pressure drop.
For example, easier the air can pass through the filter, lesser is the energy requirement to drive the air through the filter. The pressure drop is related to the area of media utilized in the filter and the filter's corresponding efficiency. Since selection of the area and type of media is limited, reduction in the resistance of an air filter appears to be limited as well. However, with the ever-increasing cost of energy, it is highly desirable to further reduce the pressure drop across the filter.
In an aspect of the present invention, a mini pleat bank green HEPA filter is provided, which is having lower energy consumption, longer filter life, and reduced lead time due to higher media quantity accommodated and ease of manufacturing due to reduced manufacturing time.
The present invention simplifies the existing design of HEPA filter manifolds, eases manufacturing process, reduces lead time and rejection rate during manufacturing and still provides a filter with better performance. The design is also useable for lower grade filters providing the same benefits.
Figure 1 illustrates the isometric view of the "Mini pleat Bank Green HEPA filter assembly, in accordance with an embodiment of the present invention. Referring to Figure 1, the "W" Bank HEPA filter assembly (100) comprises of a rectangular frame (1) consisting of an upper wall 1(a), a bottom wall 1(b), side walls 1(c) and 1(d), and is selected or made from material selected out of metal, wood oi plastic. The layered filter medium (3) is stacked in form of vertical pleat packs (2) which are then assembled in the filter frame (1) in plurality of numbers, arranged in vertical orientation. These vertical pleat packs (2) are embedded in channels
(5) by sealing it into the channel surface (4) using a specialized resin (6), which can be epoxy/PU resin. The preferred air flow is horizontal through the filter (10).
Figure 2 illustrates the horizontal sectional view of the HEPA filter assembly, in accordance with an embodiment of the present invention. Referring to Figure 2, the horizontal sectional view of the HEPA filter assembly (100) is illustrated, wherein six numbers of vertical mini pleat packs (2) are sealed on the top surface 1(a) and the bottom surface 1(b) of the frame using the resin (6), resulting in the media edges sealing (7) on two frame surface. The vertical pleat packs (2) are arranged in "W" fashion (8) in the filter assembly (100).
Figure 3 illustrates the vertical sectional view of the HEPA filter assembly, in accordance with an embodiment of the present invention. Referring to Figure 3, the vertical sectional view of the HEPA filter assembly (100) is illustrated, wherein vertical mini pleat packs are arranged in "W" configuration resulting in a media flat surfaces (9). The media flat surfaces (9) are then sealed into the channels(5).
Figure 4 illustrates the front view of the Mini pleat bank green HEPA filter assembly, in accordance with an embodiment of the present invention. Referring to Figure 4, three vertical pleat packs (2) are sealed to the top surface 1(b) and the bottom surface 1(a) of the filter frame (1) using the resin (6) resulting in media edge sealing (7).
Figure 5 illustrates the back view of the Mini pleat bank green HEPA filter assembly, in accordance with an embodiment of the present invention. Referring to Figure 5, the vertical media pleat surface (9) of the filter assembly (100) is sealed to the channel surface (4).
Figure 6 illustrates the planar arrangement of vertical mini pleat packs in accordance with an embodiment of the present invention. Referring to Figure 6,
the planar arrangement of the vertical mini pleat packs (2) in the filter frame (1) is illustrated. Twelve media flat surfaces (9) are formed due to conjunction of the vertical pleat packs (2) being sealed to the channel surface (4) using the resin (6) for providing leak proof media surface sealing (12).
In a preferred embodiment of the present invention, the HEPA filter comprises of 50±5 mm deep universal mini pleat packs arranged and assembled in filter frame to form a "W" shape, whereby the mini pleat packs are assembled in such a way that all the pleats are in vertical orientation. The pleat surfaces are sealed directly to the frame surface.
The filters are made of microglass fiber media. The pleat packs are formed by folding the filter media one over another in continuous "V" like forms. When folded, these filters take the form of pleats, arranged in continuous form. The use of mini pleat packs, instead of continuous stretch sheets, increases the surface area of the filter which comes in contact with the air. Thus, due to more accessible surface area than in stretched sheets, the air can be filtered more effectively due to larger surface area available while minimizing the pressure drop. The pleat packs formed from the filter media are 50±5 mm deep.
In a preferred embodiment of the present invention, the mini pleat bank green HEPA filter is constructed by manufacturing a frame of metal or plastic or wood in the channel, box or flange type design in cuboidal symmetry. Six mini pleat packs having a 50±5 mm depth and height, according to the frame, are prepared. The frame is provided with special channels to hold the mini pleat packs. The packs are then arranged in the channels with the media edges facing the upper and the lower frame surfaces. The packs used in the filter are such that the mini pleats are in vertical orientation which is always a preferred structure for a filter. The one side of all the pleat pack edges is then sealed by a sealant at the frame base in one instance. It is then allowed to dry. After the sealing has dried, the filter is turned upside down so as to expose the other side of the filter, having pleat pack
edges. Then the sealant is applied on the other side of the filter and the edges are sealed on the frame. It is then allowed to dry.
The twelve vertical pleat media surfaces are then sealed in seven channels by using a sealant to form a completely leak proof filter.
In another embodiment of the present invention, the mini pleat packs used in the filter are 50±5 mm deep. The conventional "V" bank filters utilize the arrangement of 25±5 mm deep packs. These packs are to be specially made. The 50±5 mm deep mini pleat packs are universally made for the use in high grade clean rooms and clean air equipments and thus, the use of universally available 50±5 mm mini pleat packs eliminates the need of special manufacturing of 25±5 mm deep packs used in "V" Bank filters. Besides the 25±5 mm deep pleat packs in conventional V type filters have pleats in horizontal direction loosing the advantage of vertical pleats system which has much higher strength and can hold larger dust quantity without sagging. This result in slower increase in pressure drop.
The elimination of special manufacturing of 25±5 mm deep packs, eliminates the need of special machine settings and the increase in the size of the packs used, reduces the number of mini pleat packs, to be made for arranging in the filter Both these factors will reduce the manufacturing time and provide an economical manufacturing of filters.
The incorporation of the 50±5 mm deep mini pleat packs in the filter, reduces the number of pleat packs to be inserted in the filter frame by a factor of 1/2 The number of mini pleat packs used in the Mini pleat Bank green HEPA filter is 6 as compared to 12 mini pleat packs used in a conventional "V" Bank filter. Due to decrease in number of pleat packs required for the filter, the assembly of the device will be easier and faster as compared to conventional device, thereby decreasing the assembly time. The use of 50±5 mm deep mini pleat packs reduces the manufacturing time of the filter as compared to 25±5 mm deep,
conventionally used, mini pleat packs. This makes the whole process of filter manufacturing very economical and fast.
The mini pleats are formed by folding the filter media, one over another, in continuous accordion pleats. The assembly of these pleats in vertical form in Mini pleat bank Green HEPA provides a preferred pleating arrangement for air filters. This reduces the resistance to air flow across filters especially when filters are used for long period. Due to less resistance, offered by the filters to air flow, there will be less energy consumption, which reduces operational cost. In vertical pleating system, even de-dusting of the filter can be carried out by shaking the filters, which is not possible in the conventional horizontal pleating arrangement. This increases the life of the filter. The HEPA filter of the present invention has a life of few years.
In another preferred embodiment of the present invention, the mini pleat pack edges are sealed directly to the filter frame. The conventional V type HEPA filter has twelve media edge sealings instead of two in vertical pleat system of mini pleat bank green HEPA. Decrease in number of edge sealing reduces the probability of air leakage in the filter significantly.
The filter has six number of the 50±5 mm deep mini pleat packs with two media edges sealed, as compared to twenty four in a conventional "V" bank filter. This decreases the sealing joint by a factor of 1/12 as compared to a conventional pack sealing. This reduction in sealing joint will reduce the manufacturing failure probability and the filter rejection rate by more than 80%.
The vertically assembled pleat packs structure used in the HEPA filters of the present invention, have twelve media surfaces, to be sealed and two edge sealing, as compared to twenty four media edge sealings and two media surface sealings in conventional V type filters. This also reduces the number of seals by a factor of 1/2, which in turn, not only reduces probability of air leak failure but also reduces the manufacturing time. The time required for assembling the filter
will be half as compared to conventional V type HEPA filters having horizontal pleat structure. The reduction in edges sealing will make the manufacturing process 6 times less prone to air leak failures, which is the most critical aspect of any HEPA filter.
In yet another embodiment of the present invention, the pre-filters having paper media can be designed in same manner to provide high efficiency filters.
In yet another embodiment of present invention, these very high efficiency (99.97% and higher) HEPA filters are usually preceded by Pre and Fine filters HEPA filters can be manufactured in different sizes, but for high air capacity the depth should remain same as standard high flow filters, i.e. 305 mm. However, this design is suitable to give twice the air quantity for any depth.
These high flow, low pressure green HEPA filters are to be used in air handling units and are fitted in a leak proof manner, in the frames provided in the air handling units. The HEPA filters of present invention are needed for low power consumption and longer life by central air-conditioning providers for providing clean rooms/environment, required by pharmaceutical, electronics and other industries and establishment requiring clean or aseptic areas. These filters can also be used in filtered air exhaust in biotech industries and other polluting industries and wherever high velocity of air is required.
The utility of the present invention can be further understood by following example. It is to be noted that the following example is set forth to understand the invention more clearly and should not be in any manner construed to restrict the scope of invention. Example 1
An experiment was conducted for comparing production time taken for manufacturing and assembling a conventional 25±5 mm deep pleat pack "V" bank HEPA filter and the 50±5 mm deep pleat pack mini pleat bank green HEPA
filter. Statistical analyses were carried out, by comparing the time taken for every step of manufacturing the conventional 25±5 mm deep "V" bank HEPA filter and the 50±5 mm deep mini pleat bank green HEPA filter. The manufacturing steps required for assembling the HEPA filter include assembly and sealing of packs into the frame and channel.
During the manufacturing of conventional 25±5 mm deep "V" Bank filters, the time required at different steps in manufacturing the filter was noted and the result was tabulated. The time required at different steps, was as mentioned below. For making of twelve packs, forty eight minutes were consumed. It took sixty minutes to assemble twelve packs in the channel and inserting thirteen channels in the frame. The sealing of twelve packs in channel consumed another twelve minutes. The potting of pack assembly into the frame, further required sixty minutes. Thus it took two hundred and forty eight minutes for manufacturing the conventional 25±5 mm deep "V" HEPA filter.
In the simultaneous analyses conducted on the 50±5 mm deep mini pleat bank green HEPA filter of the present invention, the time taken for making six mini pleat packs on a mini pleat machine was twenty four minutes. It took thirty minutes for assembling six packs in the channel and assembling seven channels in the frame. Further, it took twenty minutes for sealing six packs in the channel. whereas it took sixty minutes for potting the pack assembly into the frame. Hence, the time taken for assembling a 50+5 mm deep mini pleat bank green HEPA filter was one hundred and thirty four minutes.
On comparative analysis, the time required for making a 50±5 mm deep pack mini pleat bank green HEPA is almost half (54%) of the time taken in making a 25±5 mm deep "V" bank HEPA filter (except the outer frame making time, which is 2/3. Frame making, however, is a fabrication job work that does not require special skills as that of making the sophisticated HEPA filters and is a framed out job).

We claim:
1. A mini pleat bank green HEPA filter assembly comprising of:
a plurality of mini pleat packs, constituted of filter matrix, so that the mini pleat packs are vertically oriented in a filter frame.
2. The mini pleat bank green HEPA filter assembly, as claimed in claim 1, wherein the mini pleat packs assembled in the filter frame are having a depth of 50±5 mm.
3. The mini pleat bank green HEPA filter assembly, as claimed in claim 1, wherein the filter matrix comprises of fiber glass mini pleat filter packs.
4. The mini pleat bank green HEPA filter assembly, as claimed in claim 1, wherein the frame of the filter assembly is selected out of the materials such as metal, wood or plastic.
5. The mini pleat bank green HEPA filter assembly, as claimed in claim 1, wherein the mini pleat packs are formed by folding filter media in continuous accordion pleats and separated by hot melt spaces.
6. The mini pleat bank green HEPA filter assembly, as claimed in claim 1, wherein the filter assembly comprises of plurality of the vertically oriented mini pleat packs.
7. The mini pleat bank green HEPA filter assembly, as claimed in claim 1, wherein the edges of vertical pleat packs are sealed to the top and the bottom surfaces of the filter frame.
8. The mini pleat bank green HEPA filter assembly, as claimed in cla;m 1, wherein packs are sealed to the channel surface.
9. A mini pleat bank green HEPA filter assembly as substantially described herein with reference to the accompanying drawings.