GB2478515A

GB2478515A - Filter holder

Info

Publication number: GB2478515A
Application number: GB0922482A
Authority: GB
Inventors: Darius Rahimi
Original assignee: Greenwood Air Management Ltd
Current assignee: Greenwood Air Management Ltd
Priority date: 2009-12-22
Filing date: 2009-12-22
Publication date: 2011-09-14
Anticipated expiration: 2029-12-22
Also published as: GB0922482D0; GB2478515B

Abstract

A filter holder comprising a first part 10 and a second part 20 which is releasably attachable to the first part, wherein each of the first part and the second part comprise a plurality of substantially parallel bars 11, 21 and wherein when the first part is attached to the second part, the bars of the first part interleave with the bars of the second part. Preferably a set of protrusions formed as teeth 12, 13, 22, 23 is provided on each of the first and second parts and serves to trap a filter material placed in the filter holder. Preferably a handle 30 is provided on the second filter part and is formed from finger recesses 31 or may comprise a flexible strip of material. Advantageously the filter holder is utilised as a filter frame particularly for retaining a corrugated or pleated filter material for use in ventilation systems.

Description

Filter holder The invention relates to particle filters for use in ventilation systems. Such filters are typically used for filtering unwanted particulate matter from an air flow through or within a system.

Ventilation systems can be used to move air around or through buildings. In particular, ventilation systems are normally used to extract air from buildings in order to get rid of unwanted odours or moisture. Whilst some ventilation systems merely extract air from the building and rely on the natural leakiness of the building for replacement air to enter (unbalanced systems), other ventilation systems (balanced systems) actively draw air into the building in order to replace the extracted air and maintain the air pressure within the building, e.g. for breathing or for clean-room environments.

Filters may be used in such systems either to prevent particulate matter (in either the airfiows being drawn in or the airfiows being exhausted from the building) from interfering with the operation of the system, e.g. the fans which move the air, or for filtering particulate matter from the air which is being drawn into the building in order to improve the air quality inside the building.

Filters may be used to block airborne pollutants such as soot and mineral dust or irritants such as pollen from entering the building. Filters may also collect dust from air which is being extracted from the building.

As the system operates, more and more matter is collected in the filters which gradually become blocked thereby increasing resistance to the airflow through them and decreasing the efficiency of the system. It therefore becomes necessary to replace or clean filters on a regular basis. For example, in a typical household system, the filters may need to be changed approximately every three months.

Filter cleaning is not typically a suitable option for the end user (e.g. ordinary households). Only certain types of filter material can be cleaned easily and simple replacement filters can be made relatively inexpensively. Therefore, most manufacturers simply provide replacement filters. This also provides an additional income stream for the manufacturer. The filter(s) can easily be withdrawn from the system and replacement filters can easily be inserted. Typically, the filter is simply fitted into a dedicated slot located somewhere within the system. This could be within a main system component, i.e. alongside other components such as fans or heat exchangers, although filters could be positioned elsewhere in the system ducts.

Filters come in different grades of arrestance and efficiency. Arrestance is a measure of a filter's ability to capture and retain a known weight of synthetic dust, fed into the filter at a specific rate until a final pressure drop across the filter is reached. In other words, arrestance describes how well a filter removes coarse dust from an air stream in terms of the weight trapped before a predetermined pressure drop is reached. Filters of these grades are designed to prevent mechanical system fouling. Example filter grades are: 01 (<65 % arrestance), G2 (65 -80 % arrestance), 03 (80 -90 % arrestance), G4 (>90% arrestance).

Efficiency is a measure of a filter's ability to remove fine dust in terms of the concentrations upstream and downstream of the filter. This is measured by the "atmospheric dust spot efficiency test" in EN779. This test is carried out using atmospheric air only and compares the discolouration of high efficiency filter discs, one upstream and one downstream of the test filter. Filters of these grades are designed to keep buildings and process spaces clean and free from airborne pollution. Example filter grades are: F5 (40 -60 % efficiency), F6 (60 -80 % efficiency), F7 (80 -90 % efficiency), F8 (90 -95 % efficiency), F9 (>95% efficiency).

In preferred embodiments, the filter material may be based on reticulated polyurethane foam, e.g. 01 grade (5 mm thickness, 30 pores per inch) or G2 grade (5 mm thickness, 45 pores per inch) or up to 04 grade of a polyester poiyol material. Other available materials include a filter material fabric blend of 100% polyester and bi-component fibres.

The filter typically comprises a sheet of filter material fitted into or onto a frame.

The frame may be made of metal or plastics or wood. Attaching the filter material onto the frame is often a tricky or fiddly job and it is simpler both for the manufacturer and the consumer if replacement filters are sold in a ready-made filter unit, i.e. the consumer is provided with a replacement frame with new filter material already in place. The consumer then simply has to slot the replacement filter unit into the system in place of the old one.

Simple filters consist of a sheet of filter material stretched onto a frame. However, the contact surface area of the filter can be greatly improved by folding the filter material repeatedly back on itself, so as to form a corrugated or pleated filter. This provides a much greater area of filter material for a given cross-section of the airflow path.

Corrugated or pleated filters necessarily have a more complicated frame to support the filter material and hold it in the required corrugated pattern. This makes manufacture of replacement filters more expensive and therefore increases costs for the consumer.

Some filter frames have been made in such a way as to allow replacement of the filter material without having to replace the frame at the same time. Such filter frames have to be designed in such a way as to allow new filter material to be inserted easily onto the frame. One such example provides a filter frame in the form of a metal bar bent into a square U shape, i.e. three sides of a rectangle. The prongs of the U shape can be inserted into an appropriately sized rectangular filter bag so as to hold the filter bag firmly in a rectangular shape. Alternatively, instead of a filter bag, a simple sheet of filter material with sleeves provided on the sides to receive the prongs could be used.

Although such systems allow the user to replace the filter material without purchasing a new filter frame, the filter bag or filter sheet with sleeves is still somewhat specialized and therefore users will still typically need to purchase replacement filter material units which are premade in the appropriate size and shape.

The filter frame described above can only be used for a simple flat filter shape and cannot be used for a corrugated or pleated type of filter due to the required additional structure for holding the material in the corrugated shape. In a corrugated filter, the filter material is held in a corrugated shape by passing the material over and under a series of bars. For example, a series of bars is provided which alternate between high and low positions. The material is then passed over the high bars and under the low bars to form an undulating shape. The bars are permanently fixed in position, e.g. fixed to the side plates of the frame. With the bars fixed in place, the filter material cannot easily be removed or replaced.

According to the invention, there is provided a filter holder comprising a first part and a second part which is releasably attachable to the first part, wherein each of the first part and the second part comprise a plurality of substantially parallel bars and wherein when the first part is attached to the second part, the bars of the first part interleave with the bars of the second part.

By providing the filter in two parts, with interleaving bars, the invention provides a pleated or corrugated filter in which the filter material can easily be removed and/or replaced. One part of the filter holder comprises the bars which push the filter material in one direction, while the other part of the filter holder comprises the bars which push the filter material in the opposite direction. As the bars interleave, the bars of one part push the filter material in between the bars of the other part, thus forming the corrugations.

When the two filter holder parts are separated, the bars are also separated into two groups, one either side of the material, thus freeing the material for easy removal and replacement. In this way, the filter holder is easily reusable. Only the filter material needs to be replaced which can be done very easily. This reduces the cost to the consumer. A further advantage of this arrangement is that the type or grade of filter material can be changed without having to replace the filter holder. For example, if it is desired to filter out smaller particles, a finer grade of filter material can easily be substituted into the same filter holder.

Preferably, each of the first and second parts is provided with a set of protrusions at each of two opposite ends, and each bar extends perpendicularly between a protrusion at one end and a protrusion at the opposite end. The size of the protrusions determines the placement of the bars with respect to the depth of the filter, i.e. the height of the undulations in the corrugated filter material. In order to make the corrugations in the filter material, the bars of each part must extend into the other part, i.e. the bars of one part must pass through between the bars of the other part as the two parts are brought together. The protrusions provide this extension. The size of the protrusions determines the amount of overlap between the interleaved parts and therefore the size of the undulations in the filter material.

Although the bars could be mounted on only a single set of protrusions in a cantilever manner (i.e. each bar extending from a protrusion at one end, but with the opposite end free), providing two sets of protrusions provides greater stability and rigidity to the filter holder.

The protrusions may be formed in any shape. For example, in a simple arrangement they may be just stalks or rods extending out from the frame of the filter holder part.

However, preferably the protrusions are formed as teeth and the profile of the teeth of the first part mates closely with the profile of the teeth of the second part when the two parts are fixed together. With this arrangement, when the filter parts are fixed together, the teeth of the two parts form a substantially solid end face. In use, the filter material abuts the two sets of teeth. Because the teeth are solid, they close off a possible route by which air could bypass the filter material. Because the teeth profiles of the two parts mate closely, there are no gaps through which air could flow around the filter material. This effectively separates the two sides of the filter into an unfiltered side and a filtered (clean) side.

The bars of the filter holder parts may be supported only at the ends. This will be sufficient in smaller filters, but in longer filters, the bars of the first part and/or the second part may be supported at one or more places along their lengths by additional supports. These additional supports help to prevent the bars from bending under the tension of the filter material and help to keep the shape of the undulations and therefore maintain the desired contact area of the filter. Additional supports also help to prevent lateral bend of the bars which could cause adjacent undulations to come close together or into contact which would create resistance to the air flow through the filter and would reduce the efficiency of the filter.

The additional supports may be formed as additional sets of teeth in order to maintain a desired profile of the undulations (for example if it is desired to maintain a consistent square wave or sine wave). However, in a preferred embodiment, the additional supports are simply sets of projections, such as rods or stalks as these are easier to manufacture, weigh less and interfere less with the air flow through the filter. The additional projections are preferably provided on a support bar which lies substantially perpendicularly to the main bars.

Preferably the filter holder further comprising a handle at one end of one of the first and second parts. The handle may take a variety of shapes and forms. For example, in one embodiment the handle may be in the form of two recesses which form finger grips. Filters of this type are normally slotted into a filter unit from the side.

Therefore this arrangement allows the filter to lie substantially flush with the unit while still providing adequate leverage to remove the filter when the filter material needs replacing. In another embodiment, the handle may simply be formed by a flexible strip of material, fixed at each end to the end of one of the first and second parts. The strip thereby forms a handle which can be pulled to remove the filter.

In one embodiment, the first and second parts of the filter holder are entirely separate from each other. This makes the filter holder easy to work with and easy to manufacture. In an alternative arrangement, the first and second parts may be hinged together. This prevents the two parts from getting entirely separated and, if the filter parts are not symmetrical, prevents them from being fitted together the wrong way round.

A fastening means may be provided on one or both of the first and second parts for releasably retaining the other of the first and second parts. Any kind of fastening means may be used, but preferably one or more clips or hooks are used as these can be integrally moulded with the first and second parts and can be easily levered apart when replacement of the material is desired. In one preferred embodiment the assembly is held together with snap clips on the side of the frame halves.

The invention also extends to a filter comprising a filter holder as described above with a piece of filter material positioned between the first and second parts. As described above, the filter material preferably buts at both ends against the teeth of the first part and the teeth of the second part so as to prevent the air flow (and hence particulate matter) from bypassing the filter material. The filter material is preferably also held via barbs on the supports which snag the material and secure it to one of the frame parts.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a filter holder according to an embodiment of the invention; Figure 2 shows an exploded view of a filter holder according to an embodiment of the invention; and Figure 3 shows an exploded view of a filter according to another embodiment of the invention.

The filter holder as shown in figures 1 and 2 is formed of a first part 10 and a second part 20. In the embodiment shown, the second part 20is formed with a handle 30 and has a substantial rectangular frame which provides support and rigidity to the filter. The first part 10 is sized and shaped to fit into the second part 20 and to be releasably attached thereto by means of clips provided along the edges.

The second part 20 comprises a number (seven in the figures) of longitudinal bars 21 which extend along the length of the filter holder. Each of the bars 21 is supported at each end by teeth 22, 23. Each bar is also supported at intervals along its length by additional supports 24 (three shown in the figures). The additional supports 24 are in the form of projections which extend from support bars 25 which themselves extend across the width of the second part 20 perpendicular to the main bars 21.

The first part 10 has a very similar construction to that of the second part 20. First part 10 comprises a number (six in the figures) of longitudinal bars 11 which extend along the length of the filter holder. Each of the bars 11 is supported at each end by teeth 12, 13. Each bar is also supported at intervals along its length by additional supports 14 (three shown in the figures). The additional supports 14 are in the form of projections which extend from support bars 15 which themselves extend across the width of the first part 10 perpendicular to the main bars 11.

In use, a piece of flexible filter material (not shown) is placed over the second part and the first part 10 is pushed down into the second part. Because the bars 11 of the first part extend downwards and the bars 21 of the second part extend upwards (the terms upwards and downwards being used in relation to the orientation shown in the figures), as the two parts 10, 20 are brought together, the bars 11 of the first part pass between the bars 21 of the second part. The bars 11 of the first part 10 therefore push the filter material down into the gaps between the bars 21 of the second part 20 and the bars 21 of the second part 20 push the filter material up into the gaps between the bars 11 of the first part 10. Once the two parts 10, 20 have been fitted together, the filter material between them undulates alternately over the bars 21 of the second part 20 and under the bars 11 of the first part 10, thus creating a corrugated filter which provides a high contact area for filtering an air flow.

As can be seen in figure 1, when the two filter parts 10, 20 are fitted together, the teeth 12, 13 of the first part 10 mesh closely with the teeth 22,23 of the second part 20. In other words, the profiles of the teeth 12 of the first part 10 are complementary to the profiles of the teeth 22 of the second part 20 and the profiles of the teeth 13 of the first part 10 are complementary to the profiles of the teeth 23 of the second part 20. Thus when the two parts 10, 20 are brought together with the filter material between them, the teeth 12, 13, 22, 23 form an effective seal at each end of the filter and thereby prevent the air flow from bypassing the filter material which abuts against them. In an alternative embodiment, the filter material may be trapped between the teeth 12, 13, 22, 23.

At one end of the filter, a handle 30 is provided. In one embodiment (figure 2), the handle 30 is formed in the second filter part 20 and is formed from two finger recesses 31 which provide purchase for a user to remove and insert the filter from and into the system. In another embodiment (figure 3), the handle 30' is formed as a flexible finger strap. The handle 30' comprises a flexible strip of material fixed at both ends to the second filter part 20 so as to provide a loop into which one or more fingers can be inserted for pulling out the filter.

It will be appreciated that other forms of handle may be used in place of these handles.

It will also be appreciated that any shape of tooth profile may be used, for example the teeth may be shaped to produce a sine wave or a square wave profile, or the teeth may be shaped into a symmetrical or an asymmetrical sawtooth profile.

As shown in figure 3, on side of the filter (one of the sides parallel with the main bars 11, 21), the filter material 35 is held in place by barbs 33 on the second filter part 20 (although these barbs could equally well be formed on the first filter part 10.

These barbs 33 snag the filter material 35 and hold it securely in place during assembly or disassembly (e.g. for cleaning or replacement). During assembly, the barbs hold the material 35 in place while the upper frame half 10 is lowered into place. It will be appreciated that barbs 33 may be formed on both sides parallel with themainbarsll,21.

To form the filter, a piece of filter material 35 is attached to the barbs 33 and then laid over the second filter part 20. The piece of filter material 35 is sized so as to abut the teeth 12, 13, 22, 23 at either end of the filter and to form undulations over the bars 21 of the second part 20 and under the bars 11 of the first part 10. To aid the mating of the two halves 10, 20, the filter material 35 may be tucked slightly in between the bars 21 of the second part 20 before fitting the first part 10 to the second part 20.

When the first filter part 10 is brought down onto the filter material 35, the bars 11 of the first filter part 10 pass between the bars 21 of the second filter part 20, thus forming undulations in the filter material 35, The first filter part 10 attaches to the second filter part 20 by snap clips 37 to hold the whole filter together.

It will be appreciated that the embodiments described above are preferred embodiments only and that various modifications could be made to the embodiments which would fall within the scope of the inventionas defined by the appended claims. -11 -

Claims

Claims 1. A filter holder comprising a first part and a second part which is releasably attachable to the first part, wherein each of the first part and the second part comprise a plurality of substantially parallel bars and wherein when the first part is attached to the second part, the bars of the first part interleave with the bars of the second part.
2. A filter holder as claimed in claim 1, wherein each of the first and second parts is provided with a set of protrusions at each of two opposite ends, and wherein each bar extends between a protrusion at one end and a protrusion at the opposite end.
3. A filter holder as claimed in claim 2, wherein the protrusions are formed as teeth and wherein the profile of the teeth of the first part mates closely with the profile of the teeth of the second part when the two parts are fixed together.
4. A filter holder as claimed in claim 1, 2 Or 3, wherein the bars of the first part and/or the second part are supported at one or more places along their lengths by additional supports.
5. A filter holder as claimed in claim 4, wherein the additional supports are formed as additional sets of projections.
6. A filter holder as claimed in claim 5, wherein the additional projections are provided on a support bar which lies substantially perpendicularly to the bars.
7. A filter holder as claimed in any preceding claim, further comprising a handle at one end of one of the first and second parts.
8. A filter holder as claimed in claim 7, wherein the handle is in the form of two recesses which form finger grips.
9. A filter holder as claimed in claim 7, wherein the handle is in the form of a flexible finger strap.
10. A filter holder as claimed in any preceding claim, wherein the first and second parts are separate from each other.
11. A filter holder as claimed in any of claims 1 to 9, wherein the first and second parts are hinged together.
12. A filter holder as claimed in any preceding claim, further comprising fastening means provided on one of the first and second parts for releasably retaining the other of the first and second parts.
13. A filter holder as claimed in any preceding claim, wherein at least one of the first and second parts is provided with barbs for holding filter material in place.
14, A filter holder as claimed in any preceding claim, wherein the filter holder is generally rectangular and wherein two opposite sides are provided with protrusions as claimed in 2 or 3, and wherein at least one of the other two opposite sides is provided with barbs as claimed in claim 13.
15. A filter comprising a filter holder as claimed in any preceding claim and a piece of filter material positioned between the first and second parts.
16. A filter as claimed in claim 15 and claim 3, wherein the filter material buts against the teeth of the first part and the teeth of the second part.
17. A filter as claimed in claim 15 or 16 and claim 13, wherein the filter material is held by the barbs.

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18. A filter holder substantially as hereinbefore described with reference to the accompanying drawings.
19. A filter substantially as hereinbefore described with reference to the accompanying drawings.