WO2008065332A2

WO2008065332A2 - A kitchen ventilation system

Info

Publication number: WO2008065332A2
Application number: PCT/GB2007/004170
Authority: WO
Inventors: Michael Leon Shaw
Original assignee: Michael Leon Shaw
Priority date: 2006-11-27
Filing date: 2007-11-02
Publication date: 2008-06-05
Also published as: GB0623534D0; GB2457003B; GB2457003A; WO2008065332A3; EP2087289A2; GB0910326D0

Abstract

A kitchen ventilation system comprises an extraction hood (8) comprising at least one openable and closable air filter (9). A controllable air extraction means (12) is linked to the extraction hood (8) for drawing air through the filter (9). A sensing means (21) is provided that is adapted to determine whether one or more cooking appliances (2, 3, 4, 5,) in the kitchen are in operation and that is linked to a control means (23). The control means (23) is adapted to control the air extraction means (12) and the opening and closing of each of the air filters (9) such that the operation of one or more cooking appliance (2, 3, 4, 5,) causes at least one air filter (9) to be opened and the air extraction means (12) to be operated to extract air through the air filter (9) at a rate appropriate for the number and/or nature of the cooking appliance or appliances in operation. Preferably, a plurality of openable and closable air filters (9) is provided in the hood (8) and the control means (23) is adapted to open as many air filters (9) as required to extract air through each air filter (9) at a predetermined rate optimal for operation of each filter (9).

Description

A KITCHEN VENTILATION SYSTEM

The present invention relates to a kitchen ventilation system and in particular to a kitchen ventilation system suitable for use in commercial kitchens where a plurality of cooking appliances is installed.

In a commercial kitchen it is usual for a plurality of cooking appliances, such as ovens, griddles, fryers, burners and the like, to be installed in a range either in an island unit in the centre of the kitchen or along a wall. Above these appliances a ventilation system is installed to extract the hot air, steam and fumes generated by use of the appliances. These fumes typically comprise grease droplets, small-scale particulate materials, undesirable odours, including heavy cooking vapours, and, from time to time, smoke.

In accordance with British and European standards, each of the appliances in the kitchen range is rated and a minimum air extraction rate for the area above the appliance is specified. When a plurality of appliances is employed, the total extraction rate is calculated by the addition of the individual extraction rates specified for each appliance. The total extraction rate can be high, for example in a conventional commercial kitchen an extraction rate of 2 m3 of air per second is a typical requirement. As the ventilation system must be in operation throughout the working day whenever any of the cooking appliances are in operation, it will be appreciated that over this period the extracted volume of air can exceed the total volume of the kitchen many times over. The removal of air from the building requires its replacement by air from the exterior of the building and usually an air intake arrangement is provided as part of the ventilation system. Typically, an air intake arrangement will supply between 70% and 80% of the volume of the extracted air with the rest being made up of air from the rest of the building. However, the replacement air is usually a different temperature to that of the air inside the building and the ventilation system usually incorporates a heat exchanger or other means of adjusting the temperature of the replacement air before it is supplied to the kitchen. Controlling the temperature of such large volumes of air is expensive.

A grease filter is a typical component of a kitchen ventilation system as otherwise grease-laden fumes from cooking will rapidly deposit a heavy layer of grease in the hood, on the air extraction means and in any associated ducting. This would create a fire hazard as well as being unhygienic and a source of objectionable odours. The grease filter may be, therefore, the first filter of several that may be encountered by air being drawn through a ventilation system. A grease filter typically comprises a mesh or a series of baffles and is designed to operate by forcing air drawn through it to change its direction of travel abruptly prior to exiting the filter. As the air changes direction, grease and other impurities are propelled away from the air stream and impinge upon the mesh or baffles where they either stick or run into a collection area. To operate effectively and efficiently, the air must be drawn through the grease filter at a predetermined speed and conventional ventilation systems are designed to extract air through all of the grease filters of an installation at the required rate to ensure that the grease filters operate effectively and efficiently despite the fact that not all of the cooking appliances in an installation may be in use. It will be appreciated, however, that, in terms of the energy used and the heat lost from the building, this is inefficient and wastes energy thus increasing the running costs of the establishment.

The object of the present invention is to provide a kitchen ventilation system which operates more efficiently than conventional systems, in particular without compromising the efficient operation and effectiveness of any grease filter forming a part of the system. An additional objective is to provide a grease filter suitable for use in a ventilation system such as a kitchen ventilation system according to the present invention.

According to a first aspect of the present invention there is provided a kitchen ventilation system comprising an extraction hood incorporating at least one openable and closable air filter; a controllable air extraction means linked to the extraction hood for drawing air through the filter; a sensing means adapted to determine whether one or more cooking appliances in the kitchen are in operation; a control means linked to the sensing means and adapted to control the air extraction means and the opening and closing of each of the air filters such that operation of one or more cooking appliance causes at least one air filter to be opened and the air extraction means to be operated to extract air through the opened air filter or filters at a rate dependent on the number and/or nature of the cooking appliances in operation.

Preferably, the extraction hood comprises a plurality of openable and closable air filters and the control means is adapted to opens as many air filters as required to extract air through each air filter at a predetermined rate optimal for operation of the filter.

The sensing means may comprise one or more optical or infra-red sensors adapted to detect respectively when one or more of the cooking appliances are in operation. Alternatively, the sensing means may comprise a link to the controls of each of the cooking appliances.

Preferably also, each air filter preferably comprises an openable or closable grease filter.

Hitherto, grease filters have not been made capable of being opened or closed. Therefore, according to a second aspect of the present invention there is provided a grease filter assembly for use within a ventilation system such as that according to the first aspect of the invention comprising a frame, a perforated arrangement which is mounted in the frame and which defines one or more air pathways therethrough that force the air to change its direction of travel abruptly prior to exiting the arrangement, a closure means movable between a first position wherein the air pathway or pathways are open and a second position wherein the air pathway or pathways are closed, and an operating means for the closure means to move the closure means between the first and second positions.

In addition to a grease filter, a kitchen ventilation system may incorporate a fire damper. The fire damper is adapted to be closed on detection of a fire within a kitchen to prevent air from outside the building being drawn through the ventilation ductwork to feed the fire. The fact that the grease filter of the present invention can be controllably opened or closed means that it can be also be used as a fire damper, obviating a requirement for an additional fire damping means.

According to a third aspect of the present invention there is provided a method of operating a kitchen ventilation system comprising an extraction hood incorporating at least one openable and closable air filter, the method comprising the steps of determining if one or more cooking appliances in the kitchen are in operation; opening at least one air filter if one or more cooking appliances are in operation; and extracting air through the open filter or filters at a rate dependent on the number and/ or nature of the cooking appliances in operation.

Preferably, the extraction hood comprises a plurality of openable and closable air filters and the number of air filters opened at any given time is that number required for the extraction of air through each air filter to be at a predetermined rate optimal for operation of that filter.

Preferred but non-essential features of the various aspects of the present invention are further described in the dependent claims appended hereto. Embodiments of the various aspects of the present invention will now be described by way of example with reference to the accompanying drawings, in which:-

Fig. i is a diagram showing a front elevation of a kitchen range and the general arrangement of a kitchen ventilation system for the kitchen range according to the present invention;

Fig. 2 is an end elevation, to an enlarged scale, of the kitchen range and the interior of an extraction hood forming part of the ventilation system shown in Fig. l;

Figs. 3a and 3b are a front elevation of a grease filter forming part of the extraction hood shown in Figs 1 and 2 and a cross-section along the line 3b-3b in Fig. 3a respectively, the filter in being in a closed state and to an enlarged scale with regard to those shown in Figs. 1 and 2; and

Figs. 4a and 4b are similar views of the grease filter shown in Figs. 3a and 3b but with the filter shown in an open state.

As shown in Figs, l and 2, a kitchen range 1 may comprise a plurality of cooking appliances such as ovens 2, 3, a griddle 4, a fryer 5 and food preparation tables 6. If any of the appliances 2, 3, 4, 5 are gas powered, a gas proving system 7 may be linked to the gas supply to these appliances. Such a proving system 7 is a conventional safety arrangement that controls the supply of gas to the appliances 2, 3, 4, 5 and its operation will not be further described. Mounted above the kitchen range 1 is an extraction hood 8 which comprises a plurality of grease filters 9. Within the hood 8, two banks of filters 9 are arranged back to back and, as shown by the arrows in Fig. 2, air which passes through the filters is collected in a plenum chamber 10 above the hood 8 and is then led to extraction ductwork 11. The air is sucked through the hood 8 and the ductwork 11 by a controllable air extraction fan 12 which is not only switchable on and off but is also capable of being operated to extract air through the ductwork 11 as desired at any predetermined rate within the limits of its capabilities.

The extraction fan 12 is used to extract air at a predetermined rate from above the range 1 and to draw it through the hood 8 in order that it can be filtered and expelled from the building premises via the extraction ductwork 11. The ventilation system replaces between 70% and 80% of the volume of this air with air from the exterior of the building via air supply ductwork 13 which incorporates an air supply fan 14. The fan 14 is also controllable and capable of being operated to supply air at any desired predetermined rate within the limits of its capabilities. The air supplied back to the kitchen by ductwork 13 is also channeled into the kitchen via the hood 8. The ductwork 13 terminates in plenum chambers 15 located on each side of the hood 8 along its longitudinal axis. The air is then blown into the kitchen through a plurality of vents 16 spaced along the length of the plenum chambers 15. The vents 16 are preferably located on the exterior of the hood 8 but may also be located internally of the hood 8 as shown in Fig. 2.

The two banks of grease filters 9 are centrally located within the hood 8. The filters 9 may be orientated vertically (as shown in Figs. 1 and 2) or be inclined at an angle towards the appliance and below each of them, arranged along the longitudinal axis of the hood 8, is a removable drip tray 17 that is connected to a baffle 18 which closes off the area defined between the two banks of filters 9. Oils and greases collected by the filters 9 can therefore run or drip off the filters 9 into the trays 17 that can be periodically demounted for cleaning along with the filter means themselves, as described below.

Above each of the filters 9 is a motor 19 and cam arrangement 20 which is used to open or close that particular filter 9. The motors 19 may each be located within their individual casing (not shown) to shield them from the extracted air so that they do not become fouled by grease or other contaminants. Located below each filter 9 is a sensor 21 which is set up to detect heat radiated by the cooking appliance or appliances located directly below that filter 9. The sensors 21 may comprise any suitable form of sensor, for example optical or infra-red sensors, and are individually connected leads 22 via to a programmable controller 23, which is operationally linked to and controls the individual operation of the motors 19 via leads 24, the air extraction fan 12 via lead 25 and the air supply fan 14 via lead 26. The controller 23 is used to control operation of the filters 9 and is programmed with the required air extraction rates specified for the filters 9 and for each appliance 2, 3, 4, 5. The controller 23 is also linked to the gas proving system 7 via a lead 28 and to a control panel 27, which preferably incorporates a limited manual override arrangement.

The controller 23 may also be used to control operation of appropriately rated electric lamps 29 suitable for use in an extraction hood, which are mounted on each side of the hood 8 adjacent each of the filters 9. The lamps 29 orientated to shine down on the cooking appliances below them for the convenience of the chef. The lamps 29 may comprise, for example, 12 v halogen lamps.

A conventional fire detection and suppression system (not shown) may also be incorporated into the hood 8 and linked to the controller 23.

The structure of the filters 9 and their method of operation will now be described in more detail below with reference to Figs. 3a, 3b and 4a, 4b.

Each filter 9 comprises a frame 30 in which is mounted a perforated arrangement comprising a series of baffles 31. The baffles 31 have a substantially S-shaped profile and are arranged to inter-engage with one another such that air pathways 32 are defined between them that are also substantially S-shaped and that force the air traveling through them to change its direction of travel abruptly prior to exiting the filter 9. On the side of the filter 9 that is adapted to face outwards towards the kitchen, namely on the air intake side, is a closure means 33. The closure means 33 comprises a plate 34 which defines a series of parallel slots 35 across its width. The plate 34 passes through a slot 36 in the top of the frame 30 and is located in front of the baffles 31. The top of the plate 34 which protrudes from the frame 30 is bent to form a flange 37 which is spring-loaded by a spring means 38 so that the plate is movable between first and second positions within the frame 30. In the first position of the plate 34 the slots 35 align with the air pathways through the baffles 31 so that the air pathways 32 through the filter 9 are open (see Figs. 4a and 4b). However, in the second position of the plate 34 the slots 35 align with the baffles 31 themselves so that the air pathways 32 are closed by the body of the plate 34 (see Figs. 3a and 3b). The opening and closing of the filter 9 is controlled by the motor 19 and cam arrangement 20. Operation of the motor 19 rotates the cam arrangement 20 which will bear down on the flange 37 against the force of the spring means 38 to move the plate 34 into its second position to close the filter 9. It will be appreciated that the arrangement is such that the spring means 38 ensures that operation of the plate 34 fails in the filter's open position and the filter 9 is normally retained in this position and only closes on operation of the motor 19. Also, the spring means 38 is not connected to the flange 37 or any other part of the filter 9 in order that the filter 9 can be demounted from the hood 8 periodically for cleaning.

It will be appreciated that the foregoing description of the filter 9 comprises only one embodiment suitable for use in the present invention and that many variations are possible. For example, other forms of closure means could also be employed in place of the 'hit and miss' plate arrangement described above, such as rotating louvres. The baffles 31 themselves could also be made moveable so that they could be squeezed together to close the filter.

Also, in an alternative embodiment, the controller 23 may be linked directly via one or more leads 39 to each of the cooking appliances 2, 3, 4, 5. This link can be used instead of the sensors 21 to inform the controller 23 when a particular appliance is in use. In the case of electrical equipment, even with the sensors 21 present, the link can be used to control operation of the appliance, for example to switch the appliance off in certain emergencies such as the detection of a fire.

One mode of operating the ventilation system will now be described.

At the start of the working day it will be usual for all of the appliances

² _J 3_> 4_> 5 to be switched off and for the ventilation system to be likewise in a switched off condition. In this state all of the filters 9 adopt an open condition. The operator, typically a chef, will now carry out a 'switch on' procedure comprising the following steps.

1. The controller 23 is switched on.

2. All motors 19 are energized such that all of the filters 9 are fully opened. 3. The extraction fan 12 and the air supply fan 14 are both switched on and run at full capacity for a predetermined time period between five and 10 minutes dependent on the size of the kitchen.

4. Both fans 12 and 14 signal to the controller 23 that they are fully operational. 5. After the predetermined time period, the controller 23 signals to the gas proving system 7 that the ventilation system is full operational and that it is safe to switch on the gas supply. 6. The gas proving system 7 switches on the gas supply to the appliances 2, 3, 4, 5. 7. The appliances 2, 3, 4, 5 are now operational and cooking can commence. If any of the appliances 2,3,4,5 are electrically operated, then the controller 23 can be used to switch on the electricity supply to them via the lead 39.

8. All of the motors 19 bar one are energized to close their associated filters 9 and the extraction fan 12 is powered down to extract between 15% and 20% of the total extraction rate calculated by the addition of the individual extraction rates specified for each appliance 2, 3, 4, 5. Likewise, the air supply fan 14 is powered down to a similar percentage to supply air at a rate between 70% and 80% of that being extracted by the extraction fan 12.

The 'switch on' procedure clears the kitchen of any fumes and is used to check that the ventilation system and power supply systems are both operating satisfactorily. The ventilation system is then powered down to operate at a low level until cooking commences. Strictly, this is not necessary and in some embodiments of the invention, the ventilation system could be arranged to close all of the filters 9 and switch off the fans 12 and 14 until cooking commences.

Once cooking commences, then the ventilation system will operate as follows. First, each sensor 21 detects if a cooking appliance 2, 3, 4, 5 immediately below it is operational and, if so, sends a message to the controller 23. The controller 23 then signals the motors 19 of the filters 9 adjacent the sensors 21 which have reported cooking activity to open the filters 9. Simultaneously, the controller 23 signals the fans 12 and 14 to power up to a rate dependent on the cooking appliances in operation. It will be appreciated that in the most sophisticated ventilation system this rate will be dependent on both the number of appliances in operation and the nature of these appliances as they may not have the same air extraction rating. However, in a less sophisticated system or one where the appliances all have similar air extraction ratings it may be sufficient for the controller 23 simply to know the number of the appliances in operation as the rates of air extraction dependent on the number of appliances in operation will all be multiples of the rating for any one of the appliances.

Should any appliance 2, 3, 4, 5 be subsequently switched off, then the adjacent sensor 21 will signal this fact to the controller 23, which will then take the opposite action and signal the relevant motor 19 to close the filter 9 adjacent the sensor 21 and the fans 12 and 14 to power down by the relevant amount. Hence, the ventilation system only extracts air through the hood 8 at a rate appropriate for the cooking appliance or appliances in operation and not, as in conventional arrangements, at the total extraction rate required for all of the appliances.

In addition to the foregoing, the optimal extraction rate for each filter 9 is preferably programmed into the controller 23, which can then open as many filters 9 as required to extract air through each filter 9 at a predetermined rate optimal for operation of each filter dependent on the number of appliances which are also operational. Hence dependent on which appliances are in operation, the system may open more or fewer filters 9 than the number of these operational appliances.

It will be appreciated that the ventilation system is preferably set up so that the grease filters 9 are of an appropriate size and have an appropriate filtering capacity for the cooking appliances 2, 3, 4, 5 installed in the kitchen in question.

If during cooking, a large volume of steam, fumes or smoke is produced, the controller 23 will permit the chef to override its settings for a predetermined period of time by pressing an override button on the control panel 27. When this happens, the control panel 27 will signal the controller 23, which will operate the motors 19 to open all of the filters 9 and power up both of the fans 12 and 14 to operate to maximum operating capacity. After the predetermined time period, for example ten minutes, the controller 23 will again resume control of the system and operate the motors 19 and the fans 12 and 14 dependent only on the appliances 2, 3, 4, 5 which the sensors 21 detect are in operation.

As mentioned above, the ventilation system can also be linked to a conventional fire detection and suppression system. Such systems normally comprise fire detectors and extinguishing nozzles that are located in the hood 8. The nozzles are adapted to spray fires occurring on or in cooking appliances directly with fire extinguishing gas, such as carbon dioxide. If the ventilation system is linked to such a fire detection and suppression system, then on detection of a fire, the suppression system will operate automatically and signal to the controller 23 that it is operational. The controller 23 will then operate as follows.

1. The controller 23 will signal to the gas proving system 7 to shut off the supply of gas to the appliance 2,3,4,5. If any appliances are electrically operated, the controller 23 will also cause the electricity supply to these appliances cut off.

2. Simultaneously with 1 above, the controller 23 will switch off both of the fans 12 and 14.

3. Simultaneously with 1 and 2 above, the controller 23 will activate the motors 19 so that all of the filters 9 are closed.

4. Simultaneously with 1 to 3 above, the controller 23 will isolate the manual override switch on the control panel 27. 5. Once the fire suppression system has ceased operation the controller 23 will open all of the filters 9 and operate the fan 12 at maximum operating capacity for a predetermined period.

In some cases the suppression system may not operate automatically and in these cases the control panel 27 is provided with a fire control button. This button can also be linked to the controller 23 so that the above steps are immediately initiated.

The reason for the controller 23 operating as above is firstly to prevent the ventilation system from permitting fresh air to enter the kitchen, which may feed the fire, and secondly to clear smoke from the kitchen. In this situation, therefore, the grease filters 9 also act initially as fire dampers and then as smoke dampers. Once the fire suppression system has ceased operation the system assumes that the fire has been extinguished and the controller 23 is programmed to commence automatically a procedure designed to clear smoke from the kitchen. The length of this operation can be preset, for example ten minutes. Thereafter the controller 23 can be programmed to reset to a start of day condition. It will be appreciated, therefore, that the ventilation system according to the invention is set up to operate more efficiently than a conventional system because except in exceptional circumstances it operates to extract air from the kitchen at a rate appropriate for the number and/or nature of cooking appliances in operation at any given time rather than operating as though all of them were operational all of the time This saves considerable energy and reduces the quantity of cold air which must be introduced into the building and which will require heating. The system accomplishes this benefit without compromising the operation of the grease filters as the rate of air extraction through these filters is always arranged to be at the optimal rate for the filter in question. Also, the use of the closable filters forming part of the invention obviates the requirement for separate fire and/or smoke dampers.

The invention also has the additional advantage that it can be retrofitted into most existing kitchen ventilation systems by replacing the grease filter assembly within an existing ventilation hood with one as described above along with a controller 23 which can be linked to the gas proving system 7 and existing air extraction and air supply fans 12 and 14.

Claims

1. A kitchen ventilation system comprising an extraction hood incorporating at least one openable and closable air filter; a controllable air extraction means linked to the extraction hood for drawing air through the filter; a sensing means adapted to determine whether one or more cooking appliances in the kitchen are in operation; and a control means linked to the sensing means and adapted to control the air extraction means and the opening and closing of each of the air filters such that operation of one or more cooking appliances causes at least one air filter to be opened and the air extraction means to be operated to extract air through the opened air filter or filters at a rate dependent on the number and/or nature of the cooking appliances in operation.

2. A system as claimed in Claim i, wherein the extraction hood comprises a plurality of openable and closable air filters and the control means is adapted to opens as many air filters as required to enable the rate of air extraction through each air filter to be at a predetermined rate optimal for operation of the filter.

3 A system as claimed in Claim i or Claim 2, wherein the sensing means comprises one or more optical or infra-red sensors adapted to detect respectively when one or more of the cooking appliances are in operation.

4. A system as claimed in Claim 1, or Claim 2, wherein the sensing means comprises a link to the controls of each of the cooking appliances.

5- A system as claimed in any of Claims i to 4, wherein the control means is linked to a fire detection system and is adapted such that on detection of a fire within the kitchen it closes all of the air filters and ceases operation of the air extraction means.

6. A system as claimed in any of Claims 1 to 5, wherein the control means is linked to a fire suppression system and is adapted such that after operation of the fire suppression system it opens all of the air filters and operates the air extraction means at a maximum operating capacity.

7. A system as claimed in any of Claims 1 to 6, wherein each air filter comprises an openable or closable grease filter.

8. A system as claimed in any of Claims 1 to 7, wherein the controllable air extraction means comprises an air extraction fan.

9. A system as claimed in any of Claims 1 to 8, comprising an air supply fan controlled by the control means and capable of supplying replacement air at a desired predetermined rate.

10. A system as claimed in Claim 9, wherein replacement air supplied by the air supply fan is channeled back into the kitchen through the extraction hood

11. A system as claimed in any of Claims 1 to io, wherein each air filter comprises a frame, a perforated arrangement which is mounted in the frame and which defines one or more air pathways therethrough, a closure means movable between a first position wherein the air pathway or pathways are open and a second position wherein the air pathway or pathways are closed, and an operating means for the closure means which is linked to the control means.

12. A system as claimed in Claim li, wherein the air pathways through the perforated arrangement force the air to change its direction of travel abruptly prior to exiting the arrangement.

13. A system as claimed in Claim 11 or 12, wherein the perforated arrangement comprises a series of baffles each defining a substantially S-shaped profile and which are arranged to inter-engage with one another such that air pathways are defined between them that are also substantially S-shaped.

14. A system as claimed in any of Claims 11 to 13, wherein the closure means comprises a plate that defines a series of slots and that is moveable between a first position wherein the slots align with the air pathways through the perforated arrangement and a second position wherein the body of the plate closes off the air pathways through the perforated arrangement.

15. A system as claimed in Claim 14, wherein movement of the plate is effected by a motor controlled by the control means.

16. A system as claimed in Claim 14 or Claim 15, wherein the plate is spring-loaded and arranged to fail-safe in its first position.

17. A method of operating a kitchen ventilation system comprising an extraction hood incorporating at least one openable and closable air filter, the method comprising the steps of determining if one or more cooking appliances in the kitchen are operation; opening at least one air filter if one or more cooking appliances are in operation; and extracting air through the open filter or filters at a rate dependent on the number and/or nature of the cooking appliances in operation.

18. A method as claimed in Claim 17, wherein the extraction hood comprises a plurality of openable and closable air filters and wherein the number of air filters opened at any given time is that number required for the extraction of air through each air filter to be at a predetermined rate optimal for operation of that filter.

19. A method as claimed in Claim 17 or Claim 18, wherein the kitchen ventilation system is linked to a fire detection system and on detection of a fire within the kitchen is adapted such that all of the air filters are closed and the extraction of air through the filters is stopped.

20. A method as claimed in any of Claims 17 to 19, wherein the kitchen ventilation system is linked to a fire suppression system and after operation of the fire suppression system is adapted such that all of the air filters are opened and air is extracted through all of the filters.

21. A method as claimed in Claim 20, wherein the air is extracted through all of the filters at a maximum operating capacity of the system.

22. A grease filter assembly for use within a ventilation system comprising a frame; a perforated arrangement which is mounted in the frame and which defines one or more air pathways therethrough that force the air to change its direction of travel abruptly prior to exiting the arrangement; a closure means movable between a first position wherein the air pathway or pathways are open and a second position wherein the air pathway or pathways are closed; and an operating means for the closure means to move the closure means between the first and second positions.