A Fan assembly

Abstract

A fan assembly 100 comprises a nozzle 11 having an opening 14 extending there through and one or more primary airflow outlets 15, and an airflow generator which supplies a primary airflow to the prima

Description

BACKGROUND Fans are known for moving air in a space. Typically, fans are used to provide a cooling effect (i.e. making a user feel cooler due to the movement of the air). Some fans are also configured to treat air by e.g. heating, cooling, humidifying, dehumidifying, and / or purifying the air. SUMMARY In a first aspect there is disclosed a fan assembly comprising: a nozzle having an opening extending through the nozzle and one or more primary airflow outlets; and an airflow generator arranged to generate a primary airflow for supply to the one or more primary airflow outlets, such that discharge of the primary airflow from the one or more primary airflow outlets is capable of drawing an external airflow through the opening; wherein the fan assembly is configured to selectively obstruct the external airflow through the opening. The provision of one or more primary airflow outlets that are capable of drawing an external airflow through the opening of the nozzle means that, in use, a larger volume of air can be supplied to a user (i.e. than would be the case if air was supplied only by the one or more primary airflow outlets). The ability to selectively obstruct the external airflow can provide a user with a way to change the nature of the airflow being discharged from the fan assembly in a manner that minimises additional complexity. Selectively obstructing external airflow through the opening, for example, allows switching between a diffuse airflow pattern and a more targeted airflow pattern. In other words, the ability to selectively obstruct the external airflow allows a user to switch between a high-entrainment mode in which there is high-entrainment of external air (i.e. in which a greater volume of air is drawn through the opening and then entrained in the primary airflow) and a low-entrainment mode in which there is a lower entrainment of external air (i.e. in which a lower volume of air is drawn through the opening and then entrains in the primary airflow). Optional features of the first aspect will now be set out. These are applicable singly or in any combination with any aspect. The fan assembly may comprise an air treatment device for treating air. In this respect, the fan assembly may be referred to as an air treatment assembly. The air treatment device may be arranged to treat the primary airflow before the primary airflow is discharged (via the one or more primary airflow outlets). The air treatment device may be upstream of the airflow generator (this may ensure only treated air flows through the airflow generator). In other embodiments the air treatment device may be downstream of the airflow generator. The air treatment device may comprise at least one of a heater, cooler, filter, humidifier, dehumidifier, ionizer, air purifier or e.g. a device that adds or removes volatile organic compounds (VOCs) and / or volatile inorganic compounds (VICs). When the fan assembly includes an air treatment device, the ability to selectively obstruct the external airflow may improve the effectiveness of such air treatment. While the ability to draw external air through the opening of the nozzle is desirable for providing a user with a greater volume of air, when the fan assembly is for supplying treated air, the induced external airflow (which is untreated) can dilute treated air discharged from the one or more primary airflow outlets. For example, when the air treatment device comprises a heater, the heated primary airflow can be cooled by the external airflow that is drawn through the opening, which means a user in the path of the discharged (combined) airflow may receive air that is cooler than would otherwise be the case in the absence of the external airflow. The ability to selectively obstruct the external airflow through the opening may allow adjustment of the amount of such dilution. In some cases, such obstruction may substantially eliminate the dilution. This can improve the effectiveness of the fan assembly when used to treat an airflow. When the opening is unobstructed (as in the high-entrainment mode mentioned above) there is a greater volume of air supplied to a user (i.e. providing a more effective fan function), but greater dilution of treated air. When the opening is at least partly obstructed (as in the above-mentioned low-entrainment mode), there may be a smaller volume of air supplied to a user, but less dilution of the treated air (i.e. a more effective treatment function). Such an arrangement may be particularly suited to fan assemblies in which the air treatment device has a limited operating time (e.g. where the air treatment device is battery powered or can otherwise be depleted). In such arrangements, a user can use the fan assembly in the low-entrainment mode when the air treatment device is operable, and switch to the high-entrainment mode when the air treatment device is non-operable (for example, when the air treatment device has depleted a battery on which the air treatment device is reliant). As may be appreciated, the treatment of airflow may vary between the high-entrainment and low-entrainment modes. For example, the air treatment device may be inactive in the high-entrainment mode. Likewise, when the fan assembly includes both primary and secondary airflow outlets (as will be discussed further below) the fan assembly may be configured such that treated air is supplied only to either the primary outlet(s) or the secondary outlet(s). For example, in embodiments where air is discharged from both the primary outlet(s) and secondary outlet(s) in the low-entrainment mode, the fan assembly may be configured such that in the low-entrainment mode treated air (from the air treatment device) is supplied to the secondary outlet(s) but not the primary outlet(s). The one or more primary airflow outlets may be arranged to discharge the primary airflow away from the opening. The opening in the nozzle may comprise a central axis. The one or more primary airflow outlets may be arranged to discharge the primary airflow in a direction that is substantially parallel to the central axis. The one or more primary airflow outlets may be arranged at a periphery of the opening. The one or more primary airflow outlets may extend at least partly about a periphery of the opening. The one or more primary airflow outlets may extend substantially fully about a periphery of the opening. The nozzle may have front and rear sides. The opening may extend from the front side to the rear side. The one or more primary airflow outlets may be provided at or proximate to the front side of the nozzle. The one or more primary airflow outlets may be provided within the opening in the nozzle. The one or more primary airflow outlets may, in some embodiments, be provided proximate to an end of the opening at the rear side of the nozzle. The fan assembly may comprise one or more secondary airflow outlets to discharge a secondary airflow into the opening. The one or more secondary airflow outlets may, for example, be arranged to discharge the secondary airflow inwardly from the nozzle into the opening. Such an arrangement can improve the supply of air to a user when the external airflow through the opening is obstructed (i.e. in the low-entrainment mode). In the low-entrainment mode, for example, the secondary airflow can be discharged from the one or more secondary airflow outlets into the opening to flood the opening (e.g. to substantially fill the opening with air from the one or more secondary airflow outlets). Flooding the opening in this way means that the opening itself acts as an outlet or jet of the fan assembly. This effective “jet” has a greater cross-sectional area than that provided by the primary airflow outlets and so provides a much greater projection (or throw) of treated air towards a user. Hence, one result of providing the described one or more secondary airflow outlets is that (at least in the low-entrainment mode) the treated air is pushed further from the fan assembly. Thus, a user is able to receive a greater proportion of treated air than would otherwise be the case without the one or more secondary airflow outlets. The secondary airflow may be supplied to the one or more secondary airflow outlets from the airflow generator. For example, the fan assembly may comprise an airflow director to adjust a proportion of the secondary airflow relative to the primary airflow (i.e. the airflow supplied from the airflow generator to the one or more secondary outlets relative to the one or more primary outlets. The air flow director may comprise or may be a valve. In other embodiments, the secondary airflow may be supplied by a further airflow generator. That is, the fan assembly may comprise a primary airflow generator arranged to supply the primary airflow to the one or more primary outlets, and a secondary airflow generator arranged to supply the secondary airflow to the one or more secondary airflow outlets. The or each airflow generator may comprise a motor and an impeller (and may be referred to as a compressor, blower or fan). The one or more secondary airflow outlets may be positioned upstream (relative to a direction of the external airflow through the opening) of the one or more primary airflow outlets. When the nozzle includes front and rear sides, the one or more secondary airflow outlets may be positioned rearwardly of the one or more primary airflow outlets (i.e. the one or more secondary airflow outlets may be between the rear side of the nozzle and the one or more primary airflow outlets). The one or more secondary airflow outlets may be arranged to discharge the secondary airflow at an angle to the central axis of the opening. The one or more secondary airflow outlets may be arranged to discharge the secondary airflow in an inward-forward direction (i.e. a direction that has an inward component towards the central axis of the opening and a forward component towards the front side of the nozzle). The one or more secondary airflow outlets may be arranged to discharge the secondary airflow in an inward-rearward direction (i.e. in a direction that has an inward component towards the central axis of the opening and a rearward component towards the rear side of the nozzle). The one or more secondary airflow outlets may be arranged to discharge the secondary airflow in an inward direction that is substantially perpendicular to the forward direction and an opposite rearward direction. As may be appreciated, the one or more secondary airflow outlets may be arranged to discharge the secondary airflow in a combination of two or more of the above described inward-forward direction, inward-rearward direction, and inward direction. The one or more secondary airflow outlets may comprise a slot, a plurality of slots and / or a plurality of apertures that extend around (e.g. partly or fully around) a periphery of the opening. The one or more secondary airflow outlets may extend circumferentially around the opening. The one or more secondary airflow outlets may be arranged in a plurality of rings that extend at least partly around the opening and that are spaced along the opening from one another. The one or more primary airflow outlets may comprise a slot, a plurality of slots and / or a plurality of apertures that extend around (partially or fully) a periphery of the opening, e.g. at the front side of the nozzle. In general, the one or more primary airflow outlets may be configured to discharge an annular jet of air in a forward direction. The (transverse) cross-sectional area of the opening may be greater than a total cross-sectional area of the one or more primary airflow outlets. The cross-sectional area of the opening may, for example, be taken at a front opening of the opening, where the opening opens to the front side of the nozzle. The cross-sectional area of the opening may be at least 0.01 m2, e.g. at least 0.05 m2, e.g. at least 0.1 m2. The opening may have a width (e.g. diameter) that is from 60 to 180 mm, or e.g. from 80 to 160 mm, or e.g. from 100 to 140 mm. The opening may have a width (e.g. diameter) from 200 mm to 400 mm, or e.g. from 250 mm to 350 mm, or e.g. about 300 mm. More generally, the opening may have a width (e.g. diameter) that is from 60 mm to 400 mm. The opening may have a length (i.e. in a direction along the central axis of the opening) that is at least 0.5 times a width (e.g. diameter) of the opening, or e.g. at least 0.8 times the width (e.g. diameter), or e.g. at least greater than the width (e.g. diameter). When the nozzle includes front and back sides and the opening extends from the back side to the front side, the length of the opening may be the distance from the back side to the front side. The opening may have a circular transverse cross-sectional shape (i.e. taken transverse to a direction extending between the front and rear sides of the nozzle). The opening may, for example, have an elliptical, obround, rectangular, square, or triangular transverse cross-sectional shape. The nozzle may have a shape that is complementary to the shape of the opening. For example, the nozzle may have a circular or obround annular shape. The fan assembly may comprise a controller configured to control the fan assembly. The controller may be configured to control the fan assembly according to a high-entrainment mode and a low-entrainment mode. The high-entrainment mode may be suitable for use when the fan assembly is not obstructing the external airflow. The low-entrainment mode may be suitable for use when the fan assembly is at least partly obstructing the airflow. The fan assembly may comprise a user input device configured to receive a user input. The user input device may be provided on (e.g. mounted to) the nozzle of the fan assembly or may be separate to the nozzle (e.g. may be in the form of a remote-control device, including e.g. a mobile phone). The user input device may comprise e.g. a touch screen, a microphone, a push button, etc. The user input device may be operatively connected to the controller. The user input device may be configured to generate a mode-switch signal in response to receipt of a user input. The controller may be configured to respond to the mode-switch signal by switching (e.g. toggling) between the high-entrainment mode and the low-entrainment mode. In this way, a user may be able to select the operating mode of the fan assembly. Such switching may be performed in other ways. For example, a mode-switch signal may be generated upon detection of a person in proximity to the nozzle (e.g. via a proximity sensor) and / or may be generated upon detection of a threshold temperature. Alternatively, or additionally, a mode-switch signal may be generated based on air quality (e.g. in combination with proximity of a person). In the high-entrainment mode the secondary airflow comprises a first flow rate (i.e. a first flow rate of air may be discharged from the one or more secondary air outlets). In the low-entrainment mode the secondary airflow comprises a second flow rate (i.e. a second flow rate of air may be discharged from the one or more secondary air outlets). The second flow rate may be greater than the first flow rate. For example, the controller may be configured to control the fan assembly in the high-entrainment mode such that the secondary airflow (discharged from the one or more secondary airflow outlets) is negligible. For example, the secondary airflow may be negligible compared to the primary airflow in the high-entrainment mode. In some embodiments, air may not be discharged from the one or more secondary airflow outlets in the high-entrainment mode (but may be discharged from the one or more secondary airflow outlets in the low-entrainment mode). That is, in some embodiments, the secondary airflow outlets may be e.g. disabled or obstructed. In such embodiments, in the high-entrainment mode air may substantially only be discharged from the one or more primary airflow outlets. These differences in flow rate of air may be controlled by the controller, which may control, for example, one or more of the airflow generator, further airflow generator and / or the airflow director (when present). Control of the fan assembly in this way, means the one or more secondary airflow outlets may flood (e.g. substantially fill with air) the opening in the low-entrainment mode, but in the high-entrainment mode may not discharge air (or may discharge negligible air) so as to avoid disrupting the entrainment of external airflow through the opening. A flow rate of the primary airflow discharged from the one or more primary air outlets (e.g. as controlled by the controller) may be greater in the high-entrainment mode than in the low-entrainment mode. For example, the controller may be configured to control the fan assembly in the low-entrainment mode such that the primary airflow (discharged from the one or more primary airflow outlets) is negligible. For example, the primary airflow may be negligible compared to the secondary airflow in the low-entrainment mode. That is, in some embodiments, the primary airflow outlets may be e.g. disabled or obstructed. In such embodiments, in the low-entrainment mode air may substantially only be discharged from the one or more secondary airflow outlets. In general, the fan assembly may be configured such that in the low-entrainment mode (which may be when the opening is obstructed), air is discharged from the primary outlet(s) only (e.g. when no secondary outlet(s) are present), from the secondary outlet(s) only, or from both the primary outlet(s) and secondary outlet(s). As will be described further below, in any of these scenarios the opening may be obstructed (which may be a physical barrier or an aerodynamic obstruction as is discussed below). The fan assembly may comprise a physical barrier to selectively physically obstruct the external airflow through the opening. The barrier may form part of, or be connectable (e.g. mountable) to, the nozzle. The barrier may fully obstruct the opening (e.g. substantially fully prevent external air from passing into and through the opening). In other embodiments, the barrier may only partially obstruct the opening (e.g. some external air may be able to pass into and through the opening.) The physical barrier may be releasably mountable to the nozzle. The physical barrier may be mountable to the nozzle so as to be upstream (relative to the direction of the external airflow through the opening) of the primary and / or secondary airflow outlets when mounted. The physical barrier may be mountable to the nozzle so as to be at the rear side of the nozzle when mounted. The releasable mounting may be provided, for example, by way of magnets (and corresponding ferrous elements), snap engagement, clips, push-fit (e.g. interference fit), etc. The releasable mounting may allow a user to selectively obstruct the opening with the physical barrier. The physical barrier may be complementary in shape to the opening. The physical barrier may be complementary in shape to the nozzle. The physical barrier may be disc shaped. The physical barrier may be planar. The physical barrier may be flexible or may be rigid. The barrier may comprise a plate, sheet, membrane, panel, etc. configured to extend at least partly across the opening. The physical barrier may be porous. The physical barrier may comprise a porous media (e.g. may be formed of a fibrous material). The physical barrier may be in the form of a filter (i.e. for filtering air passing through the opening). The physical barrier may be moveable across the opening between a retracted position and an extended position. In the retracted position the opening may be less obstructed by the physical barrier (i.e. than in the extended position). In the extended position, the opening may be more obstructed by the physical barrier (i.e. than in the retracted position). The fan assembly may comprise an actuator configured to move the physical barrier between the retracted position and the extended position (i.e. in an automated manner). The actuator may comprise e.g. a motor. The actuator may be operatively connected to the controller for control by the controller. The controller may be configured to control the actuator to move the physical barrier to the retracted position in the high-entrainment mode (e.g. when toggled via the user input device). The controller may be configured to control the actuator to move the physical barrier to the extended position in the low-entrainment mode (e.g. when toggled via the user input device). In other embodiments, the physical barrier may be configured to be manually moved (e.g. by a user) between the retracted and extended positions. The physical barrier may, for example, comprise a retractable roller blind. In this respect, the physical barrier may be flexible so as to be able to be rolled up in the retraced position. The physical barrier may comprise a curtain (e.g. a flexible nozzle that is slideably mounted to the nozzle). The physical barrier may comprise shutters. For example, the physical barrier may comprise a plurality of vanes / blades / louvers that are rotatably mounted to the nozzle (i.e. such that their respective rotational axes extend transverse to the opening). The physical barrier may comprise a diaphragm mechanism, sometimes referred to as an iris valve. Thus, the physical barrier may comprise (e.g. overlapping) blades, which may collectively define a central aperture. The blades may be moveable (e.g. slideable) to vary the size of the aperture. In this way, movement of the blades may provide adjustment of the amount of external air that is able to flow into the opening. The central apertures may be e.g. circular, hexagonal, triangular, etc. The central aperture may be defined by inner edges of the blades (i.e. a portion of each inner edge defining part of the periphery of the central aperture). Movement of each blade adjusts the size of the portion of the inner edge of each blade defining the periphery of the aperture (such that the aperture increases and decreases in size with such movement). The physical barrier may comprise one or more apertures therethrough or may be configured to extend only partway across the opening. In this way, the physical barrier may provide only partial obstruction of the opening. As set forth above, the physical barrier may be porous (and such partial obstruction may thus be provided in this manner). The fan assembly may comprise a barrier sensor configured to detect whether the physical barrier is at least partially obstructing the opening. For example, in the case of a releasably mounted physical barrier the sensor may be configured to detect whether the barrier is mounted. For example, the fan assembly may comprise a hall effect sensor (or optical sensor) for detecting the presence of the barrier when mounted to the nozzle. The controller may be operatively connected to the barrier sensor. The controller may be configured to toggle between the high- and low-entrainment modes in response to detection of the physical barrier at least partially obstructing the opening by the barrier sensor. As an alternative to (or in addition to) a physical barrier, selective obstruction of the external airflow through the opening may be provided aerodynamically (i.e. by the provision of airflows that provide such obstruction). For example, the one or more secondary airflow outlets may be configured to selectively aerodynamically obstruct the external airflow through the opening. The one or more secondary airflow outlets may be configured to discharge the secondary airflow across the opening to at least partially obstruct the external airflow through the opening (i.e. such obstruction occurring aerodynamically). The one or more secondary airflow outlets may be configured to form an air curtain (i.e. provided by the secondary airflow) across the opening. In this way, the secondary airflow outlets may have dual functionality: obstruction of external airflow through the opening (optionally to a varying degree) and flooding of the opening. In such embodiments (where the selective obstruction is provided aerodynamically by the one or more secondary airflow outlets), the one or more secondary airflow outlets may be provided upstream of the one or more primary airflow outlets. The one or more secondary airflow outlets may be provided at or near to an upstream end of the opening (e.g. at or near to a rear side of the nozzle). The fan assembly (e.g. the nozzle) may further comprise one or more tertiary airflow outlets arranged to discharge a tertiary airflow into the opening. The one or more tertiary outlets may be spaced from the one or more secondary outlets along the opening (e.g. in a direction parallel to the central axis of the opening). The one or more tertiary airflow outlets may comprise a slot, a plurality of slots and / or a plurality of apertures that extend around (e.g. partly or fully around) a periphery of the opening. The one or more tertiary airflow outlets may extend circumferentially around the opening. The one or more tertiary airflow outlets may be arranged in a plurality of rings that extend at least partly around the opening and that are spaced along the opening from one another. The nozzle may be supported on a base. The base may be cylindrical. The base may house one or more of the airflow generators (and optionally further airflow generator), the airflow director, and / or the air treatment device. The base may comprise an airflow inlet or a plurality of inlets (e.g. for supply of air to the airflow generator, airflow director and / or air treatment device). The air treatment device may be arranged to treat the secondary airflow and / or the tertiary airflow before the respective secondary airflow and / or tertiary airflow is discharged (i.e. respectively discharged via the one or more secondary and / or tertiary airflow outlets). In a second aspect there is disclosed a method of operating a fan assembly, the method comprising: operating the fan assembly in a high-entrainment mode by discharging a primary airflow so as to draw an external airflow through an opening of the fan assembly; and operating the fan assembly in a low-entrainment mode by at least partly obstructing the opening. Optional features of the second aspect will now be set out. These are applicable singly or in any combination with any aspect. The fan assembly may be as described above with respect to the first aspect. The fan assembly may include one or more of the optional features of the first aspect described above. Operating the fan assembly in the low-entrainment mode may comprise discharging a secondary airflow into the opening. The secondary airflow may be such that the secondary airflow at least partly obstructs the external airflow through the opening. Operating the fan assembly in the low-entrainment mode may comprise not discharging the primary airflow (or discharging negligible primary airflow). In other embodiments, operating the fan assembly in low-entrainment mode may comprise discharging the primary airflow. Operating the fan assembly in the high-entrainment mode may comprise not discharging the secondary airflow (or discharging negligible secondary airflow). Obstructing the opening may comprise obstructing the opening with a physical barrier. The barrier may be as described in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A is a perspective view of a fan assembly according to a first embodiment in a high-entrainment mode; Figure IB is a perspective view of the fan assembly of the first embodiment in a low-entrainment mode; Figure 2A is a schematic view of components of the fan assembly of the first embodiment in the high-entrainment mode; Figure 2B is a schematic view of components of the fan assembly of the first embodiment in the low-entrainment mode; Figure 2C is a schematic view of components of the fan assembly of the first embodiment in a further low-entrainment mode; Figure 3 is a front view of a fan assembly according to a second embodiment in a low-entrainment mode; Figure 4 is a schematic top cross-sectional view of a fan assembly according to a third embodiment in a low-entrainment mode; Figure 5 is a schematic top cross-sectional view of a fan assembly according to a fourth embodiment in a low-entrainment mode; Figure 6 is a schematic top cross-sectional view of a fan assembly according to a fifth embodiment in a low-entrainment mode; and Figure 7 is a schematic top cross-sectional view of a fan assembly according to a sixth embodiment in a low-entrainment mode. DETAILED DESCRIPTION Figures 1A and IB illustrate a fan assembly 100 (which in this case is in the form of an air treatment assembly) comprising an annular nozzle 11 having front 12 and rear 13 sides, and an opening 14 extending through the nozzle 11 so as to open at the front 12 and rear 13 sides for flow of an external airflow 30 through the nozzle 11. An inner peripheral surface 18 of the nozzle 11 defines the boundary of the opening 14 extending through the nozzle 11. The fan assembly 100 also includes a primary airflow outlet 15 in the form of an annular slot that is provided on the front side 12 of the nozzle 11 at a periphery of the opening 14 (where the opening 14 opens at the front side 12 of the nozzle 11). In other embodiments the primary airflow outlet 15 may be provided away from the front side of the nozzle 11 (e.g. the primary airflow outlet 15 may be provided within the opening 14). The primary airflow outlet 15 is configured to discharge an annular primary airflow 29 therefrom in a substantially forward direction (i.e. substantially parallel to a central axis 34 of the opening 14 and away from the front side 12 of the nozzle 11). Discharging the primary airflow 29 in this way draws an external airflow 30 into the opening 14 to flow through the opening 14 in a forward direction (i.e. from the rear side 13 to the front side 12 of the nozzle 11). The external airflow 30 is discharged from a front end 36 of the opening 14 at the front side 12 of the nozzle 11 and is entrained in the annular primary airflow 29 discharged from the primary airflow outlet 15. A plurality of secondary airflow outlets 19, in the form of circumferentially spaced apertures, are provided in the inner peripheral surface 18 of the annular portion 16 (to form a ring of apertures). As may be appreciated, further rings of circumferentially spaced apertures (spaced along the opening 14) could be provided. The secondary airflow outlets 19 are arranged to direct a secondary airflow 31 into the opening 14 (in a direction that is substantially perpendicular to the direction of the external airflow 30 through the opening 14 in use). The nozzle 11 is provided on a cylindrical base 17. An airflow generator 20, air treatment device 21 and airflow director 22 are provided in the base 17. These are internal components and are thus not shown in Figures 1A and IB, but are depicted schematically in Figures 2A, 2B and 2C. The airflow generator 20 (which may be a compressor) is in fluid communication with each of the primary outlet 15 and the plurality of secondary outlets 19 and is configured to supply an airflow to these outlets 15, 19. To do so, the airflow generator 20 draws air into the base 17 through a circumferential airflow inlet 23 that extends circumferentially about the base 17, as best seen in Figures 1A and IB (in other embodiments the inlet 23 may not be circumferentially extending). The air treatment device 21 treats air upstream of the airflow generator 20 (but could alternatively be downstream). The air treatment device 21 may comprise, for example, one or more of a heater, cooler, filter, humidifier, dehumidifier, ionizer, air purifier or device that adds or removes VOCs and / or VICs. These functions could also be split between upstream and downstream (e.g. upstream filter and downstream heater). The airflow director 22 is downstream of both the air treatment device 21 and the airflow generator 20. The airflow director 22 is configured to control the flow of air to the primary outlet 15 and the plurality of secondary outlets 19. In Figure 2A, the airflow director 22 is positioned such that all airflow generated by the airflow generator 20 passes to the primary airflow outlet 15. In Figure 2B, the airflow director 22 is positioned such that all airflow generated by the airflow generator 20 passes to the plurality of secondary airflow outlets 19. The airflow director 22 may also split flow partially to the primary outlet 15 and the plurality of secondary outlets 19. This mode is shown in Figure 2C and may be provided as an alternative or in addition to the low-entrainment mode of Figure 2B. Returning to Figures 1A and IB, the fan assembly 100 further comprises a physical barrier 24 which is configured to selectively obstruct external airflow 30 into the opening 14 through the rear side 13 of the nozzle 11. In the illustrated embodiment, the physical barrier 24 is in the form of a panel configured to be releasably mounted to the nozzle 11 (e.g. by magnets, snap fit, etc.) so as to be positioned at the rear side 13 of the nozzle 11. The physical barrier 24 is shown unmounted in Figure 1A and is releasably mounted to the nozzle 11 in Figure IB (e.g. by way of magnets, snap-engagement, push-fit, etc). As is apparent from this figure, the physical barrier 24 extends fully across the rear end 35 of the opening 14 so as to prevent any external air from passing into the opening 14 through the rear side 13 of the nozzle 11. The provision of the releasably mountable physical barrier 24 allows the fan assembly 100 to operate in two alternate modes: a high-entrainment mode (as shown in Figures 1A and 2A) and a low-entrainment mode (such as shown in Figures IB and 2B). The fan assembly 100 is controlled between these modes by a controller 32 which is operatively connected to the airflow director 22 and a user input device 25 in the form of a push button provided on the base of the nozzle (for clarity the operative connection between the controller 32 and these components is not explicitly illustrated). In other embodiments, the user input device 25 may be remote from the nozzle 11 and base 17 (e.g. may be a remote-control, mobile phone, etc.). When pressed by a user, the user input device 25 sends a signal to the controller instructing the controller to toggle between the low-entrainment and high-entrainment modes. The high-entrainment mode is intended for use when the physical barrier 24 is not mounted to the nozzle 11 (i.e. so as not to be obstructing the opening as illustrated in Figure 1A). Thus, for example, a user may manually remove the physical barrier 24 and then depress the user input device 25 to enter the high-entrainment mode. In this mode, the controller controls the flow director 22 to direct airflow from the airflow generator 20 to the primary airflow outlet 15 only. Thus, in the high-entrainment mode substantially all of the airflow supplied by the airflow generator 20 is discharged through the primary outlet 15. Substantially no air is discharged from the plurality of secondary airflow outlets 19. By configuring the fan assembly 100 in this way, the annular primary airflow 29 that is discharged by the primary airflow outlet 15 is able to induce movement of external air through the opening 14 from the rear side 13 of the nozzle 11 to the front side 12 of the nozzle 11. This external airflow 30 is then entrained in the annular jet of air for flow towards a user. The overall effect is that a greater volume of air can be supplied to a user (which may be particularly beneficial for cooling a user). As has been described above, however, one effect of this arrangement is that any treated air, treated by the air treatment device 21, is diluted by the external airflow 30 entrained in the annular jet. The low-entrainment mode addresses this. The low-entrainment mode is a mode of operation of the fan assembly 100 that is intended for use when the physical barrier 24 is releasably mounted to the rear side 13 of the nozzle 11 (so as to obstruct the opening 14 as illustrated in Figure IB). Thus, a user may releasably mount the physical barrier 24 to the nozzle 11 and then press the user input device 25 to switch the fan assembly 100 to the low-entrainment mode. In other embodiments, the fan assembly 100 may be configured to automatically detect the presence of the physical barrier 24 (e.g. by way of a hall effect sensor). In the low-entrainment mode, as is evident from Figures IB and 2B, the controller controls the airflow director 22 to direct substantially all airflow generated by the airflow generator 20 to the plurality of secondary airflow outlets 19. Substantially no air is discharged from the primary airflow outlet 15. By directing airflow into the opening 14 (via the secondary airflow outlets 19) rather than in a forward direction from the primary airflow outlet 15, the opening 14 is able to act as a large-scale jet from which the treated air is discharged. The significantly larger cross-sectional area of the opening 14, compared to that of the primary airflow outlet 15, means that treated air is able to be pushed a greater distance from the nozzle 11 (i.e. such an arrangement has a greater “throw” such that a greater volume of treated air reaches the user). In this way, the fan assembly 100 of Figures 1A to 2C provides a user with the option of receiving a high volume of air for e.g. cooling purposes, or a lower volume of air but with significantly reduced dilution of treated air. As may be appreciated, the physical barrier 24 may take various other forms, such as a blind (e.g. roller blind) or a curtain. A further variation is shown Figure 3. The physical barrier 24 of the fan assembly 200 of Figure 3 is in the form of a diaphragm mechanism, sometimes referred to as an iris valve, which comprises a plurality of blades 26 that extend across the opening 14 so as to surround (and define) a central aperture 27 through which external air is able to pass. The blades 26 are slideably mounted such that sliding the blades 26 increases or decreases the size of the aperture 27 (i.e. depending on the direction in which the blades 26 are moved). In this way, the opening 14 can be selectively obstructed to alter the amount of external airflow 30 that passes through the opening 14. As well as varying the physical barrier 24, the airflows discharged by the fan assembly 200 in the low-entrainment mode may be varied. Figures 4 to 7 schematically illustrate examples of this. These figures are schematic in nature and provide a cross-sectional view taken horizontally through the nozzle of a respective fan assembly (similar to that shown in Figures 1A and IB). In the variation of Figure 4, the fan assembly 300 does not include any secondary airflow outlets. Instead, a primary airflow 29 flows from the primary airflow outlet 15 in both the high-entrainment and low-entrainment modes. This represents a less complex variation than that illustrated in Figures 1A to 2C, but because the opening 14 is not flooded (i.e. is not substantially filled with air by secondary airflow outlets) the fan assembly 300 may not be as effective at pushing treated air to a user. In the variation of Figure 5, the fan assembly 400 includes both primary 15 and secondary airflow 19 outlets and is configured such that in the low-entrainment mode respective primary 29 and secondary 31 airflows are discharged from both the primary 15 and secondary 19 airflow outlets. In the variation of Figure 6, the fan assembly 500 (like that of Figure 5) includes both primary 15 and secondary 19 airflow outlets. In this variation, the selective obstruction of the external airflow 30 is provided by the secondary airflow outlets 19. That is, the secondary airflow outlets 19 are configured so as to obstruct the flow of external air into the opening 14 by creating an air curtain (via a secondary airflow 31) across the rear side of the opening 14. In this respect, the secondary airflow outlets 19 have dual functionality: obstruction of the flow of external air into the opening 14; and flooding the opening 14 with treated air. The variation of Figure 7 is similar to that of Figure 6 except that the fan assembly 600 includes a further (e.g. tertiary) set of airflow outlets 28. In this case, the tertiary airflow outlets 28 are configured to discharge a tertiary airflow 33 in an inward-forward direction to flood the opening 14 with treated air. That is, the tertiary airflow 33 is discharged in a direction into the opening 14 at an angle to a central axis 34 of the opening 14 and towards a front side 12 of the nozzle 11. The secondary airflow outlets 19 are provided rearward of the tertiary airflow outlets 28 and are configured to obstruct external airflow 30 through the opening 14 by discharging air across the opening 14 (i.e. these further airflow outlets 19 provide the obstruction to the external airflow). The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations. Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. It must be noted that, as used in the specification and the appended claims, the singular 5 forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be 10 understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / -10%.

Claims

1. A fan assembly comprising:a nozzle having an opening extending through the nozzle, and one or more primary5 airflow outlets; andan airflow generator arranged to generate a primary airflow for supply to the one or more primary airflow outlets, such that discharge of the primary airflow from the one or more primary airflow outlets is capable of drawing an external airflow through the opening; and,10CXI15a physical barrier configured to selectively physically obstruct the external airflow through the opening;wherein the physical barrier is releasably mountable to the nozzle.

2. A fan assembly according to claim 1, wherein the one or more primary airflow outlets are arranged to discharge the primary airflow away from the opening.

3. A fan assembly according to claim 2, wherein the nozzle comprises one or more secondary airflow outlets to discharge a secondary airflow into the opening.20 4. A fan assembly according to claim 3, wherein the secondary airflow is supplied to theone or more secondary airflow outlets from the airflow generator.

5. A fan assembly according to claim 4, comprising an airflow director to adjust a proportion of the secondary airflow relative to the primary airflow.

256. A fan assembly according to any one of claims 3 to 5, wherein the opening comprises a central axis and the one or more secondary airflow outlets are arranged to discharge the secondary airflow at an angle to the central axis.30 7. A fan assembly according to any one of claims 3 to 6, comprising a controllerconfigured to control the fan assembly according to:a high-entrainment mode wherein the secondary airflow comprises a first flow rate; anda low-entrainment mode wherein the secondary airflow comprises a second flow rate, the second flow rate being greater than the first flow rate.

58. A fan assembly according to claim 7, wherein the controller is configured to control the fan assembly in the high-entrainment mode such that the secondary airflow is negligible.

9. A fan assembly according to claim 7 or 8, wherein the controller is configured to control 10 the fan assembly in the low-entrainment mode such that the primary airflow is negligible.

10. A fan assembly according to any preceding claim, wherein the physical barrier is porous.LOCXI15 11. A fan assembly according to any preceding claim, wherein the physical barrier isconfigurable between:a retracted position in which the opening is substantially less obstructed by the T” physical barrier; andan extended position in which the opening is more obstructed by the physical 20 barrier.

12. A fan assembly according to any preceding claim, wherein the physical barrier comprises a plurality of blades to collectively define a central aperture, and wherein the plurality of blades are moveable to vary a size of the central aperture.2513. A fan assembly according to any one of claims 3 to 9, wherein the one or more secondary airflow outlets are configured to selectively aerodynamically obstruct the external airflow through the opening.30 14. A fan assembly according to claim 13, wherein the nozzle comprises one or moretertiary airflow outlets arranged to discharge air into the opening.17 102515. A fan assembly according to claim 14, wherein the one or more tertiary outlets are spaced from the one or more secondary outlets along the opening.5 16. A fan assembly according to any one of the preceding claims, wherein the one or moreprimary airflow outlets comprises one or more slots extending at least partially around a periphery of the opening.

17. A fan assembly according to any one of the preceding claims, wherein a cross-sectional 10 area of the opening is greater than a total cross-sectional area of the one or more primary airflow outlets.

18. A fan assembly according to any one of the preceding claims, comprising an air treatment device arranged to treat the primary airflow before the primary airflow is 15 discharged from the one or more primary airflow outlets.

19. A fan assembly according to claim 18, wherein the air treatment device comprises at least one of a heater, cooler, filter, humidifier, dehumidifier, ionizer, air purifier or device that adds or removes VOCs and / or VICs.

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