Seat assembly for a vehicle

Abstract

A seat assembly (1) for a vehicle has a seat portion (10) and a back portion (30) for supporting the back of the user. At least one of the seat portion (10) and the back portion (30) has a first plenu

Description

Technical Field The present disclosure relates to a seat assembly for a vehicle. Background Vehicle seats are typically subject to high usage and wear, especially in commercial vehicles. Vehicle seats often have foam to form a cushion, for a user to sit on and / or as a back support. However, the foam, which is a dense sponge-like material and may be for example expanded polyurethane or the like, degrades over time. If the foam needs to be replaced, typically the whole seat assembly has to be removed from the vehicle to allow the foam cushion to be replaced. The time and cost for such replacement can be high. This also means that the vehicle is out of use for an extended period of time whilst the foam cushion is replaced. Further, foam cushions are typically not particularly suitable for recycling after use due to the nature of the foam material. Ventilated seats of various forms are known. Typically, one or more fans may be provided to pull or push air through the foam cushion. Such fans are often embedded in the foam material of the cushion. Summary According to an aspect disclosed herein, there is provided a seat assembly for a vehicle, the seat assembly comprising: a seat portion on which a user sits in use; and a back portion for supporting the back of a user seated on the seat portion; at least one of the seat portion and the back portion comprising: a first plenum plate, a second plenum plate and a mattress; the first plenum plate and the second plenum plate defining a plenum chamber therebetween; the first plenum plate having at least one ventilation through hole through which air can pass into the plenum chamber in use; the second plenum plate having at least one exhaust hole through which air can be drawn out of the plenum chamber in use; the seat assembly being arranged such that, in use with a user seated on the seat assembly, the first plenum plate is located towards the user and the second plenum plate is remote from the user, with the mattress being located on the first plenum plate between the user and the first plenum plate; whereby air can be drawn through the mattress, through the at least one ventilation through hole of the first plenum plate into the plenum chamber, and out of the plenum chamber through the at least one exhaust hole of the second plenum plate. Examples described herein provide a ventilated seat assembly which provides for good ventilation of the seat assembly and which is easily and quickly maintainable and therefore has low maintenance costs. In an example, the first plenum plate and the second plenum plate are detachably connected to each other to define the plenum chamber. This facilitates disassembly of the seat assembly for maintenance purposes In an example, the mattress is a sprung mattress comprising a plurality of mattress springs. A sprung mattress avoids the use of foam and enables better air flow through the seat assembly. In an example, at least one of the first plenum plate and the second plenum plate has a generally bowl shape to at least partially define the plenum chamber. In an example, the first plenum plate has a plurality of ventilation through holes through which air can pass in use. In an example, the second plenum plate comprises at least one projection that projects towards the first plenum plate into the plenum chamber to prevent the first plenum plate collapsing into and blocking the exhaust hole of the second plenum plate. In an example, the seat assembly comprises a cover which is removably fitted over the mattress to secure the mattress to the first plenum plate. In an example, the seat assembly is provided in combination with a fan which is in fluid connection with the at least one exhaust hole of the second plenum plate and which is operable to draw air out of the plenum chamber in use. The fan may be located as part of the seat assembly or located elsewhere away from the seat assembly. In an example, each of the seat portion and the back portion comprises a first plenum plate, a second plenum plate and a mattress, each of the first plenum plate and the second plenum plate defining a perspective plenum chamber therebetween, each first plenum plate having at least one ventilation through hole through which air can pass into the respective plenum chamber in use, and each second plenum plate having at least one exhaust hole through which air can be drawn out of the respective plenum chamber in use. Brief Description of the Drawings To assist understanding of the present disclosure and to show how embodiments may be put into effect, reference is made by way of example to the accompanying drawings in which: Figure 1 shows schematically a side view of an example of a seat assembly according to the present disclosure; Figure 2 shows schematically a lateral cross-sectional view of the seat assembly of Figure 1; Figure 3 shows schematically a perspective view of the seat assembly of Figure 1 with parts of the seat portion shown in exploded view; Figure 4 shows schematically a perspective view of the parts of the seat portion shown in exploded view; Figure 5 shows schematically a lateral cross-sectional view of the seat portion with no mattress present; Figure 6 shows schematically a lateral cross-sectional view of the seat portion with a mattress present; Figure 7 shows schematically a perspective view of the seat assembly of Figure 1 with parts of the back portion shown in exploded view; Figure 8 shows schematically a perspective view of the parts of the back portion shown in exploded view; Figure 9 shows schematically a lateral cross-sectional view of the back portion with no mattress present; and Figure 10 shows schematically a lateral cross-sectional view of the back portion with a mattress present. Detailed Description As mentioned, vehicle seats are typically subject to high usage and wear, especially in commercial vehicles. Vehicle seats often have foam to form a cushion, for a user to sit on and / or as a back support. However, the foam, which may be a sponge-like material and may be for example expanded polyurethane or the like, degrades over time. If the foam needs to be replaced, typically the whole seat assembly has to be removed from the vehicle to allow the foam cushion to be replaced. The time and cost for such replacement can be high. This also means that the vehicle is out of use for an extended period of time whilst the foam cushion is replaced. The foam material is also not well suited for recycling. In addition, ventilated seats of various forms are known. Typically, one or more fans may be provided to pull or push air through the foam cushion. Such fans are often embedded in the foam material of the cushion. In examples described herein, a seat assembly for a vehicle has a seat portion on which a user sits in use and a back portion for supporting the back of a user seated on the seat portion. At least one of the seat portion and the back portion has a first plenum plate, a second plenum plate and a mattress. The first plenum plate and the second plenum plate define a plenum chamber therebetween. The first plenum plate has at least one ventilation through hole through which air can pass into the plenum chamber in use. The second plenum plate has at least one exhaust hole through which air can be drawn out of the plenum chamber in use. The seat assembly is arranged such that, in use with a user seated on the seat assembly, the first plenum plate is located towards the user and the second plenum plate is remote from the user, with the mattress being located on the first plenum plate between the user and the first plenum plate. Air can be drawn through the mattress, through the at least one ventilation through hole of the first plenum plate into the plenum chamber, and out of the plenum chamber through the at least one exhaust hole of the second plenum plate. The seat assembly described herein allows for efficient ventilation of the seat assembly, particularly the seat portion and / or the back portion. This provides increased comfort for the user, whether the driver or a passenger. The seat assembly can be easily and quickly disassembled to allow maintenance and replacement of worn parts, including in particular the mattress. This can be carried out with the seat assembly still in position in the vehicle, and so avoids having to remove the seat assembly from the vehicle, which reduces the time and cost of maintenance and reduces the downtime of the vehicle. Referring now to the drawings, an example of a seat assembly according to the present disclosure will be described. Referring first to Figures 1 and 2, in overview, a seat assembly 1 has a seat portion 10 and a back portion 30. In use, a user sits on the seat portion 10 and the user’s back is supported by the back portion 30. The seat portion 10 is sometimes referred to generically as the “cushion” and the back portion 30 is sometimes referred to generically as the “squab”. In use when installed in a vehicle, the seat assembly 1 may be fitted to a base or plinth 2. The plinth 2 may for example be fixed to or integrally formed with a floor of the vehicle. A slide mechanism 3 may be provided to allow the seat assembly 1 to be moved back and forth. A height adjustment mechanism 4 may be provided to allow the seat assembly 1 to be moved up and down. Suitable slide mechanisms 3 and height adjustment mechanisms 4 are known per se. The illustrated height adjustment mechanism 4 is in the form of a scissor mechanism. As mentioned, at least one of the seat portion 10 and the back portion 30 has a first plenum plate, a second plenum plate and a mattress, the first plenum plate and the second plenum plate defining a plenum chamber therebetween. In the example shown in Figures 1 and 2, both the seat portion 10 and the back portion 30 have such an arrangement. In other examples, only one of the seat portion 10 and the back portion 30 has such an arrangement. Referring to Figure 3, this shows schematically a perspective view of the seat assembly 1 of Figures 1 and 2 with parts of the seat portion 10 shown in exploded view. Figure 4 shows schematically a perspective view of the parts of the seat portion 10 shown in exploded view. The seat portion 10 has a first plenum plate 11 and a second plenum plate 12. For the seat portion 10, the first plenum plate 11 and the second plenum plate 12 are arranged generally horizontally in use with the first plenum plate 11 uppermost, towards the user when seated on the seat assembly 1. The seat portion 10 has a mattress 13 which provides cushioned support for the user. In this example, a cover 14 is located over the mattress 13. In use, the seat portion 10 is fitted to a generally square or rectangular lower main seat frame 15, which is open at its centre. In the example shown, the second plenum plate 12 is fastened to a rigid plate 16, which in turn is suspended to and in the centre of the open lower main seat frame 15 by a plurality of springs 17. In this example, the springs 17 are arranged along two opposed sides of each of the lower main seat frame 15 and the rigid plate 16. This arrangement with the rigid plate 16 and the springs 17 acts as a form of suspension or vibration isolation, to reduce jars and impact to the user. The lower main seat frame 15 is fitted to the height adjustment mechanism 4 to allow the whole seat assembly 1 to be moved up and down. The rigid plate 16 may be formed of for example a metal, such as steel, aluminium, etc., or a plastics material, such as high impact polystyrene, ABS (acrylonitrile butadiene styrene), HDPE (high-density polyethylene), etc. The second plenum plate 12 in this example is removably fastened to the rigid plate 16 using one or more connectors, such as bolts, clips, rivets or releasable fasteners, etc. (not shown). The lower main seat frame 15, plinth 2, slide mechanism 3 and height adjustment mechanism 4 are formed of a metal in this example for strength, though other materials may be additionally or alternatively used. The first plenum plate 11 and the second plenum plate 12 are each formed of a rigid material. Suitable materials include a metal, such as steel, aluminium, etc., and / or a plastics material, such as high impact polystyrene, ABS (acrylonitrile butadiene styrene), HDPE (high-density polyethylene), etc. The first plenum plate 11 and the second plenum plate 12 may each be formed by vacuum forming a plastics material. The mattress 13 is located on and supported by the first plenum plate 11. As shown most clearly in Figures 4, 5 and 6, the first plenum plate 11 in this example is formed to be shaped or contoured on its upper surface. This contouring or shaping defines the final shape that will be assumed by the mattress 13 and so is shaped ergonomically to provide comfort for the user. For example, the upper surface of the first plenum plate 11 may be relatively deeper towards the rear in order for the mattress 13 to accommodate and support the user’s buttocks, rising somewhat towards the front in order for the mattress 13 to accommodate and support the upper parts of the user’s legs. The second plenum plate 12 has a generally dish or bowl shape. In this way, when the first plenum plate 11 is located over and fitted to the second plenum plate 12, a cavity or plenum chamber 18 is defined between the first plenum plate 11 and the second plenum plate 12. The outer edge 19 of at least the first plenum plate 11 and optionally also the outer edge 20 of the second plenum plate 12 curve over, with the outer edge 19 of the first plenum plate 11 curving over in a return shape to curve under the edge 20 of the second plenum plate 12. This facilitates locating the first plenum plate 11 over and to the second plenum plate 12 and helps to ensure an at least approximate airtight seal between the first plenum plate 11 and the second plenum plate 12. The first plenum plate 11 may be removably fastened to the second plenum plate 12, for example using one or more connectors, such as bolts, clips, rivets or releasable fasteners, etc. (not shown). The first plenum plate 11 has at least one ventilation through hole 21 through which air can pass into the plenum chamber 18 in use. In the example shown, the first plenum plate 11 has a plurality of ventilation through holes 21 through which air can pass into the plenum chamber 18 in use. The ventilation through holes 21 may be arranged in an array across at least a major part of the surface of the first plenum plate 11 to maximise air flow. The second plenum plate 12 has at least one exhaust hole 22 through which air can be drawn out of the plenum chamber 18 in use. In this example, the rigid plate 16 to which the second plenum plate 12 is connected has a corresponding exhaust hole 23 which aligns with and mates with the exhaust hole 22 of the second plenum plate 12. A fan 24 is provided in fluid communication with the exhaust hole 23 in the rigid plate 16. The fan 24 may be located as part of the seat assembly 1 or located elsewhere away from the seat assembly 1. In the example shown, the fan 24 is shown located within the plinth 2 though other locations on the vehicle are possible. The fan 24 may be connected to the exhaust hole 23 in the rigid plate 16 using one or more tubular air ducts (not shown). In use, the fan 24 is switched on, optionally by a user-operated manual control switch or automatically. This causes air to be drawn in through the ventilation through holes 21 of the first plenum plate 11, into the plenum chamber 18, and out of the exhaust hole 22 of the second plenum plate 12 and the exhaust hole 23 of the rigid plate 16. The exhausted air can be vented into the vehicle compartment or cab generally or vented to the exterior of the vehicle. As the mattress 13 is located on the first plenum plate 11, and the cover 14 is located on the mattress 13, this means that air is drawn in through cover 14 and the mattress 13 and then through the ventilation through holes 21 of the first plenum plate 11. This provides ventilation for the seat portion 10 generally and particularly in the region of the user’s buttocks and upper parts of the user’s legs. As mentioned, the mattress 13 is located on and supported by the first plenum plate 11. In many known vehicles, the seat has foam to form a cushion for the user. However, a problem with foam is that it can degrade over time, especially when subjected to heavy use. In addition, the foam is often dense in order to provide proper support for the user, at least initially. Such dense foam allows for poor air flow through the cushion at best and no airflow at worst. An advantage of using a mattress 13 is that airflow is significantly better than if foam is used. In this regard, the term mattress is used herein to mean a case containing a spring material and little, and preferably, no foam. For example, the mattress 13 may be a spring mattress containing at least one compression spring and preferably plural compression springs. The mattress may be for example an open coil mattress or a pocket sprung mattress which typically include a number of springs encased in layers of padding. An advantage of using a mattress 13, particularly a spring mattress 13, is that air can flow much more easily through the mattress 13 than in the case of a foam cushion. The air can therefore flow much more easily through the mattress 13 and into the ventilation through holes 21 of the first plenum plate 11. This provides improved ventilation for the seat portion 10 of the seat assembly 1. Further, a spring mattress 13 will typically last (much) longer than a foam cushion, which reduces the time and cost of maintenance and reduces the downtime of the vehicle. Further, the flow of air is encouraged by the use of the plenum chamber 18, which allows air to easily flow through the ventilation through holes 21 of the first plenum plate 11 and out of the exhaust hole 22 of the second plenum plate 12 and the exhaust hole 23 of the rigid plate 16. The plenum chamber 18 assists in ensuring airflow is well distributed across the whole of the mattress 13. As well as improved ventilation, the present seat assembly 1 allows much quicker and easier maintenance. To assemble the seat portion 10, in an example the first plenum plate 11 is located on and removably fastened to the second plenum plate 12. The mattress 13 is then located on the first plenum plate 11. The cover 14 is then located over the mattress 13. The cover 14 is air-permeable. The cover 14 may be a fabric cover or a heat-and-vacuum formed material which allows the cover 14 to take the correct ergonomic shape more easily.. The cover 14 may be perforated with through holes and / or formed of an open, mesh-like, material to encourage the flow of air through the cover 14. The cover 14 can be wrapped around the mattress 13 and fastened under the first plenum plate 11 in the gap between the edges of the first plenum plate 11 and the second plenum plate 12. This secures the mattress 13 in position on the first plenum plate 11. The cover 14 can be fastened to the first plenum plate 11 using an adhesive and / or one or more staples, fasteners or the like. This means that if the mattress 13 needs to be replaced, all that is required is that the cover 14 is removed. The old mattress 13 can then be simply lifted away, a new mattress 13 fitted, and the cover 14 or a new cover 14 refitted to secure the new mattress 13 in place. Similarly, if one or both of the first plenum plate 11 and the second plenum plate 12 needs to be replaced, again it is a simple matter of removing the cover 14 and lifting off the mattress 13. This provides access to the first plenum plate 11 which can be detached from the second plenum plate 12. The first plenum plate 11 can then be replaced with a new first plenum plate 11. Alternatively or additionally, once the first plenum plate 11 has been detached from the second plenum plate 12, the second plenum plate 12 can be detached from the rigid plate 16 and lower main seat frame 15. The second plenum plate 12 can then be replaced with a new second plenum plate 12. Again similarly, if the rigid plate 14 or its springs 17 need to be replaced, then the cover 14 is removed, the mattress 13 is lifted off, the first plenum plate 11 is detached from the second plenum plate 12 and the second plenum plate 12 detached from the rigid plate 14. The rigid plate 14 and / or one or more of its springs 17 can then be replaced. Notably, all of the above mentioned maintenance can be carried out with the seat assembly 1 in situ in the vehicle as all of the relevant parts can be accessed and removed without having to remove the seat assembly 1 as a whole from the vehicle. This greatly reduces the maintenance time and therefore maintenance costs. Further, each of the first plenum plate 11, the second plenum plate 12, the mattress 13, the cover 14 and even the fan 24 (which is located outside of the mattress 13) can be replaced independently of any of the other parts. In the example shown, the second plenum plate 12 has at least one bump or projection 25 adjacent the exhaust hole 22. In the example shown, the second plenum plate 12 has plural projections 25 spaced adjacent the exhaust hole 22. The or each projection 25 projects towards the first plenum plate 11 into the plenum chamber 18 when the first plenum plate 11 is located on the second plenum plate 12. The or each projection 25 serves to prevent the first plenum plate 11 collapsing into and blocking the exhaust hole 22 of the second plenum plate 12, for example in the case that a heavy load is placed on the seat portion 10. The second plenum plate 12 also has one or more ribs 26. These add stiffness and strength to the seat portion 10 and to the assembly of the first plenum plate 11 and second plenum plate 12. It is also possible for one or both of the first plenum plate 11 and the second plenum plate 12 to be provided with air flow ribs or channels which are shaped and configured to assist in guiding air flow through the plenum chamber 18 to the exhaust hole 22 of the second plenum plate 12. Referring now to Figure 7, this shows schematically a perspective view of the back portion 30 of Figures 1 and 2 with parts of the seat portion 10 shown in exploded view. Figure 8 shows schematically a perspective view of the parts of the back portion 30 shown in exploded view. Figure 5 shows schematically a lateral cross-sectional view of the seat portion 10 with no mattress present and Figure 6 shows schematically a lateral cross-sectional view of the seat portion 10 with a mattress present. The arrangement of the back portion 30 is substantially the same as the arrangement of the seat portion 10, albeit with differently shaped parts suitable to support the back of the user. A detailed description of the parts will be omitted for brevity. All of the features and options are in substance the same as above for the seat portion 10 except where described below. In brief, the back portion 30 has a first plenum plate 31 and a second plenum plate 32. For the back portion 40, the first plenum plate 31 and the second plenum plate 32 are arranged generally vertically in use, with the first plenum plate 31 located towards the front part of the back portion 30, that is, towards the user when seated on the seat assembly 1. The back portion 30 has a mattress 33 which provides cushioned support for the user. In this example, a cover 34 is located over the mattress 33. In use, the back portion 30 is fitted to a generally rectangular rear main seat frame 35. Whereas for the seat portion 10, the second plenum plate 12 is fastened to a sprung rigid plate 16 which in turn is suspended to the lower open main seat frame 15, for the back portion 30, the second plenum plate 32 is fastened directly to the rear main seat frame 35. This is because the additional suspension and cushioning provided for the seat portion 10 by the suspended sprung rigid plate 16 is not generally necessary or desirable for the back portion 30. The rear main seat frame 35 is fitted to the height adjustment mechanism 4, or to the lower main seat frame 15 which in turn is fitted to the height adjustment mechanism 4, to allow the whole seat assembly 1 to be moved up and down. The second plenum plate 32 has a generally dish or bowl shape. In this way, when the first plenum plate 31 is located over the second plenum plate 32, a cavity or plenum chamber 38 is defined between the first plenum plate 31 and the second plenum plate 32. The second plenum plate 32 has at least one exhaust hole 42 through which air can be drawn out of the plenum chamber 38 in use. A fan, which may be the same fan 24 which is connected to the exhaust hole 23 in the rigid plate 16 of the seat portion 10 or a separate fan, is in fluid communication with the exhaust hole 42 by one or more tubular air ducts (not shown). The second plenum plate 32 also has one or more ribs 46 to stiffness and strength to the back portion 10 and to the assembly of the first plenum plate 31 and second plenum plate 32. For the back portion 10, in addition to the one or more ventilation through holes 41, the first plenum plate 31 has additional through holes 36. Rivets or other fasteners may be passed through the additional through holes 36 into corresponding through holes 37 in the second plenum plate 32 to secure the first and second plenum plates 31,32 together. The outer edge 39 of at least the first plenum plate 31 and optionally also the outer edge 40 of the second plenum plate 32 curve over, with the outer edge 39 of the first plenum plate 31 curving over in a return shape to curve under the edge 40 of the second plenum plate 32.. This facilitates locating the first plenum plate 31 over and to the second plenum plate 32 The mattress 33 is located on and supported by the first plenum plate 31, forwardly of the back portion 30 as a whole (towards the user’s back). As shown most clearly in Figures 8, 9 and 10, the first plenum plate 31 in this example is formed to be shaped or contoured on its forward facing surface. This contouring or shaping defines the final shape that will be assumed by the mattress 33 and so is shaped ergonomically for the mattress 33 to provide comfort for the user’s back, particularly to provide good lower back and lumbar support. The mattress 33 is again a case containing a spring material and little, and preferably, no foam. For example, the mattress 33 may be a spring mattress containing at least one compression spring, and preferably plural compression springs. Assembly of the back portion 30 and disassembly for maintenance and replacement of one or more parts of the back portion 30 is in substance the same as for the seat portion 10 described above. Examples described herein provide a ventilated seat assembly 1 which is easily maintainable and therefore has low maintenance costs. The seat assembly 1 can be easily and quickly disassembled to allow maintenance and replacement of worn parts, including in particular the mattress or mattresses 13, 33. This can be carried out with the seat assembly 1 still in position in the vehicle, and so avoids having to remove the seat assembly 1 from the vehicle, which reduces the time and cost of maintenance. Using a mattress or mattresses 13, 33 means that the ventilation is much improved compared to the ventilation that can be achieved with a foam cushion. The fan or fans 14 can be located away from the seat assembly 1, which makes maintenance and 5 replacement of the fan or fans 14 quicker and easier. The examples described herein are to be understood as illustrative examples of embodiments of the invention. Further embodiments and examples are envisaged. Any feature described in relation to any one example or embodiment may be used 10 alone or in combination with other features. In addition, any feature described in relation to any one example or embodiment may also be used in combination with one or more features of any other of the examples or embodiments, or any combination of any other of the examples or embodiments. Furthermore, equivalents and modifications not described herein may also be employed within the scope of the 15 invention, which is defined in the claims.

Claims

1. A seat assembly for a vehicle, the seat assembly comprising:a seat portion on which a user sits in use; anda back portion for supporting the back of a user seated on the seat portion;at least one of the seat portion and the back portion comprising:a first plenum plate, a second plenum plate and a mattress;the first plenum plate and the second plenum plate defining a plenum chamber therebetween;the first plenum plate having at least one ventilation through hole through which air can pass into the plenum chamber in use;the second plenum plate having at least one exhaust hole through which air can be drawn out of the plenum chamber in use;the seat assembly being arranged such that, in use with a user seated on the seat assembly, the first plenum plate is located towards the user and the second plenum plate is remote from the user, with the mattress being located on the first plenum plate between the user and the first plenum plate;whereby air can be drawn through the mattress, through the at least one ventilation through hole of the first plenum plate into the plenum chamber, and out of the plenum chamber through the at least one exhaust hole of the second plenum plate.

2. A seat assembly according to claim 1, wherein the first plenum plate and the second plenum plate are detachably connected to each other to define the plenum chamber.

3. A seat assembly according to claim 1 or claim 2, wherein the mattress is a sprung mattress comprising a plurality of mattress springs.

4. A seat assembly according to any of claims 1 to 3, wherein at least one of the first plenum plate and the second plenum plate has a generally bowl shape to at least partially define the plenum chamber.

5. A seat assembly according to any of claims 1 to 4, wherein the first plenum plate has a plurality of ventilation through holes through which air can pass in use.

6. A seat assembly according to any of claims 1 to 5, wherein the second plenum plate comprises at least one projection that projects towards the first plenum plate into the plenum chamber to prevent the first plenum plate collapsing into and blocking the exhaust hole of the second plenum plate.

7. A seat assembly according to any of claims 1 to 6, comprising a cover which is removably fitted over the mattress to secure the mattress to the first plenum plate.

8. A seat assembly according to any of claims 1 to 7, in combination with a fan which is in fluid connection with the at least one exhaust hole of the second plenum plate and which is operable to draw air out of the plenum chamber in use.

9. A seat assembly according to any of claims 1 to 8, wherein each of the seat portion and the back portion comprises a first plenum plate, a second plenum plate and a mattress, each of the first plenum plate and the second plenum plate defining a perspective plenum chamber therebetween, each first plenum plate having at least one ventilation through hole through which air can pass into the respective plenum chamber in use, and each second plenum plate having at least one exhaust hole through which air can be drawn out of the respective plenum chamber in use.s

Images