Abstract:
A fan assembly includes a motor-driven impeller for creating an air flow, at least one heater for heating a first portion of the air flow, and a casing comprising at least one air outlet for emitting the first portion of the air flow, and first channel means for conveying the first portion of the air flow to said at least one air outlet. To cool part of the casing, the casing includes means for diverting a second portion of the air flow away from said at least one heater, and second channel means for conveying the second portion of the air flow along an internal surface of the casing. This second portion of the air flow may merge with the first portion within the casing, or it may be emitted through at least one second air outlet of the casing.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of United Kingdom Application No. 1013266.0, filed Aug. 6, 2010, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a fan assembly. In a preferred embodiment, the present invention relates to a fan heater for creating a warm air current in a room, office or other domestic environment. 
       BACKGROUND OF THE INVENTION 
       [0003]    A conventional domestic fan typically includes a set of blades or vanes mounted for rotation about an axis, and drive apparatus for rotating the set of blades to generate an air flow. The movement and circulation of the air flow creates a ‘wind chill’ or breeze and, as a result, the user experiences a cooling effect as heat is dissipated through convection and evaporation. 
         [0004]    Such fans are available in a variety of sizes and shapes. For example, a ceiling fan can be at least 1 m in diameter, and is usually mounted in a suspended manner from the ceiling to provide a downward flow of air to cool a room. On the other hand, desk fans are often around 30 cm in diameter, and are usually free standing and portable. Floor-standing tower fans generally comprise an elongate, vertically extending casing around 1 m high and housing one or more sets of rotary blades for generating an air flow. An oscillating mechanism may be employed to rotate the outlet from the tower fan so that the air flow is swept over a wide area of a room. 
         [0005]    Fan heaters generally comprise a number of heating elements located either behind or in front of the rotary blades to enable a user to heat the air flow generated by the rotating blades. The heating elements are commonly in the form of heat radiating coils or fins. A variable thermostat, or a number of predetermined output power settings, is usually provided to enable a user to control the temperature of the air flow emitted from the fan heater. 
         [0006]    A disadvantage of this type of arrangement is that the air flow produced by the rotating blades of the fan heater is generally not uniform. This is due to variations across the blade surface or across the outward facing surface of the fan heater. The extent of these variations can vary from product to product and even from one individual fan heater to another. These variations result in the generation of a turbulent, or ‘choppy’, air flow which can be felt as a series of pulses of air and which can be uncomfortable for a user. A further disadvantage resulting from the turbulence of the air flow is that the heating effect of the fan heater can diminish rapidly with distance. 
         [0007]    In a domestic environment it is desirable for appliances to be as small and compact as possible due to space restrictions. It is undesirable for parts of the appliance to project outwardly, or for a user to be able to touch any moving parts, such as the blades. Fan heaters tend to house the blades and the heat radiating coils within a cage or apertured casing to prevent user injury from contact with either the moving blades or the hot heat radiating coils, but such enclosed parts can be difficult to clean. Consequently, an amount of dust or other detritus can accumulate within the casing and on the heat radiating coils between uses of the fan heater. When the heat radiating coils are activated, the temperature of the outer surfaces of the coils can rise rapidly, particularly when the power output from the coils is relatively high, to a value in excess of 700° C. Consequently, some of the dust which has settled on the coils between uses of the fan heater can be burnt, resulting in the emission of an unpleasant smell from the fan heater for a period of time. 
         [0008]    Our co-pending patent application PCT/GB2010/050272 describes a fan heater which does not use caged blades to project air from the fan heater. Instead, the fan heater comprises a base which houses a motor-driven impeller for drawing a primary air flow into the base, and an annular nozzle connected to the base and comprising an annular mouth through which the primary air flow is emitted from the fan. The nozzle defines a central opening through which air in the local environment of the fan assembly is drawn by the primary air flow emitted from the mouth, amplifying the primary air flow to generate an air current. Without the use of a bladed fan to project the air current from the fan heater, a relatively uniform air current can be generated and guided into a room or towards a user. In one embodiment a heater is located within the nozzle to heat the primary air flow before it is emitted from the mouth. By housing the heater within the nozzle, the user is shielded from the hot external surfaces of the heater. 
       SUMMARY OF THE INVENTION 
       [0009]    In a first aspect the present invention provides a nozzle for a fan assembly for creating an air current, the nozzle comprising an air inlet for receiving an air flow, means for heating a first portion of the air flow, means for diverting a second portion of the air flow away from the heating means, first channel means for conveying the first portion of the air flow to at least one air outlet of the nozzle, the nozzle defining an opening through which air from outside the nozzle is drawn by the air flow emitted from the at least one air outlet, and second channel means for conveying the second portion of the air flow along an internal surface of the nozzle. 
         [0010]    To cool part of the nozzle, the nozzle includes means for diverting a second portion of the air flow away from the heating means, and second channel means for conveying the second portion of the air flow along an internal surface of the nozzle. 
         [0011]    The dividing means may be arranged to divert both a second portion and a third portion of the air flow away from the heating means. The second channel means may be arranged to convey the second portion of the air flow along a first internal surface of the nozzle, for example the internal surface of an inner annular section of the nozzle, whereas third channel means may be arranged to convey the third portion of the air flow along a second internal surface of the nozzle, for example the internal surface of the outer annular section of the nozzle. 
         [0012]    In a second aspect, the present invention provides a nozzle for a fan assembly for creating an air current, the nozzle comprising an air inlet for receiving an air flow, means for heating a first portion of the air flow, means for diverting a second portion of the air flow away from the heating means, and for diverting a third portion of the air flow away from the heating means, first channel means for conveying the first portion of the air flow to at least one air outlet of the nozzle, the nozzle defining an opening through which air from outside the nozzle is drawn by the air flow emitted from the at least one air outlet, and second channel means for conveying the second portion of the air flow along a first internal surface of the nozzle, and third channel means for conveying the third portion of the air flow along a second internal surface of the nozzle. 
         [0013]    It may be found that, depending on the temperature of the first portion of the air flow, sufficient cooling of the external surfaces of the nozzle may be provided without having to emit the both the second and the third portions of the air flow through separate air outlets. For example, the first and the third portions of the air flow may be recombined downstream from the heating means. 
         [0014]    This second portion of the air flow may also merge with the first portion of the air flow within the nozzle, or it may be emitted through at least one air outlet of the nozzle. Thus, the nozzle may have a plurality of air outlets for emitting air at different temperatures. One or more first air outlets may be provided for emitting the relatively hot first portion of the air flow which has been heated by the heating means, whereas one or more second air outlets may be provided for emitting relatively cold second portion of the air flow which has by-passed the heating means. 
         [0015]    The different air paths thus present within the nozzle may be selectively opened and closed by a user to vary the temperature of the air flow emitted from the fan assembly. The nozzle may include a valve, shutter or other means for selectively closing one of the air paths through the nozzle so that all of the air flow leaves the nozzle through either the first air outlet(s) or the second air outlet(s). For example, a shutter may be slidable or otherwise moveable over the outer surface of the nozzle to selectively close either the first air outlet(s) or the second air outlet(s), thereby forcing the air flow either to pass through the heating means or to by-pass the heating means. This can enable a user to change rapidly the temperature of the air flow emitted from the nozzle. 
         [0016]    Alternatively, or additionally, the nozzle may be arranged to emit the first and second portions of the air flow simultaneously. In this case, at least one second air outlet may be arranged to direct at least part of the second portion of the air flow over an external surface of the nozzle. This can keep that external surface of the nozzle cool during use of the fan assembly. Where the nozzle comprises a plurality of second air outlets, the second air outlets may be arranged to direct substantially the entire second portion of the air flow over at least one external surface of the nozzle. The second air outlets may be arranged to direct the second portion of the air flow over a common external surface of the nozzle, or over a plurality of external surfaces of the nozzle, such as front and rear surfaces of the nozzle. 
         [0017]    The, or each, first air outlet is preferably arranged to direct the first portion of the air flow over the second portion of the air flow so that the relatively cold second portion of the air flow is sandwiched between the relatively hot first portion of the air flow and the external surface of the nozzle, thereby providing a layer of thermal insulation between the relatively hot first portion of the air flow and the external surface of the nozzle. 
         [0018]    All of the first and second air outlets are preferably arranged to emit the air flow through the opening in order to maximize the amplification of the air flow emitted from the nozzle through the entrainment of air external to the nozzle. Alternatively, at least one second air outlet may be arranged to direct the air flow over an external surface of the nozzle which is remote from the opening. For example, where the nozzle has an annular shape, one of the second air outlets may be arranged to direct a portion of the air flow over the external surface of an inner annular section of the nozzle so that that portion of the air flow emitted from that second air outlet passes through the opening, whereas another one of the second air outlets may be arranged to direct another portion of the air flow over the external surface of an outer annular section of the nozzle. 
         [0019]    The diverting means may comprise at least one baffle, wall or other air diverting surface located within the nozzle for diverting the second portion of the air flow away from the heating means, and at least one other baffle, wall or other air diverting surface located within the nozzle for diverting the third portion of the air flow away from the heating means. The diverting means may be integral with or connected to one of the casing sections of the nozzle. The diverting means may conveniently form part of, or be connected to, a chassis for retaining the heating means within the nozzle. Where the diverting means is arranged to divert both a second portion of the air flow and a third portion of the air flow away from the heating means, the diverting means may comprise two mutually spaced parts of the chassis. 
         [0020]    Preferably, the nozzle comprises means for separating the first channel means from the second channel means. The separating means may be integral with the diverting means for diverting the second portion of the air flow away from the heating means, and thus may comprise at least one side wall of a chassis for retaining the heating means within the nozzle. This can reduce the number of separate components of the nozzle. The nozzle preferably also comprises means for separating the first channel means from the third channel means. This separating means may be integral with the diverting means for diverting the third portion of the air flow away from the heating means, and thus may also comprise at least one side wall of a chassis for retaining the heating means within the nozzle. 
         [0021]    The chassis may comprise first and second side walls configured to retain a heating assembly therebetween. The first and second side walls may form a first channel therebetween, which includes the heating assembly, for conveying the first portion of the air flow to an air outlet of the nozzle. The first side wall and a first internal surface of the nozzle may form a second channel for conveying the second portion of the air flow along the first internal surface, preferably to a second air outlet of the nozzle. The second side wall and a second internal surface of the nozzle may form a third channel for conveying a third portion of the air flow along the second internal surface. This third channel may merge with the first or second channel, or it may convey the third portion of the air flow to an air outlet of the nozzle. 
         [0022]    As mentioned above, the nozzle may comprise an inner annular casing section and an outer annular casing section surrounding the inner casing section, and which together define the opening, and so the separating means may be located between the casing sections. Each casing section is preferably formed from a respective annular member, but each casing section may be provided by a plurality of members connected together or otherwise assembled to form that casing section. The inner casing section and the outer casing section may be formed from plastics material or other material having a relatively low thermal conductivity (less than 1 Wm −1 K −1 ), to prevent the external surfaces of the nozzle from becoming excessively hot during use of the fan assembly. 
         [0023]    The separating means may also define in part one or more air outlets of the nozzle. For example, the, or each, first air outlet for emitting the first portion of the air flow from the nozzle may be located between an internal surface of the outer casing section and part of the separating means. Alternatively, or additionally, the, or each, second air outlet for emitting the second portion of the air flow from the nozzle may be located between an external surface of the inner casing section and part of the separating means. Where the separating means comprises a wall for separating a first channel means from a second channel means, a first air outlet may be located between the internal surface of the outer casing section and a first side surface of the wall, and a second air outlet may be located between the external surface of the inner casing section and a second side surface of the wall. 
         [0024]    The separating means may comprise a plurality of spacers for engaging at least one of the inner casing section and the outer casing section. This can enable the width of at least one of the second channel means and the third channel means to be controlled along the length thereof through engagement between the spacers and said at least one of the inner casing section and the outer casing section. 
         [0025]    The direction in which air is emitted from the air outlet(s) is preferably substantially at a right angle to the direction in which the air flow passes through at least part of the nozzle. Preferably, the air flow passes through at least part of the nozzle in a substantially vertical direction, and the air is emitted from the air outlet(s) in a substantially horizontal direction. The, or each, air outlet is preferably located towards the rear of the nozzle and arranged to direct air towards the front of the nozzle and through the opening. Consequently, each of the first and second channel means may be shaped so as substantially to reverse the flow direction of a respective portion of the air flow. 
         [0026]    The nozzle is preferably annular, and is preferably shaped to divide the air flow into two air streams which flow in opposite directions around the opening. For example, the nozzle may have an interior passage shaped to divide the air flow into these two streams. In this case the heating means is arranged to heat a first portion of each air stream and the diverting means is arranged to divert at least a second portion of each air stream, preferably both a second portion and a third portion of each air stream, away from the heating means. Therefore, in a third aspect the present invention provides a nozzle for a fan assembly for creating an air current, the nozzle comprising an interior passage for receiving an air flow, and for dividing a received air flow into a plurality of air streams, means for heating a first portion of each air stream, means for diverting a second portion of each air stream away from the heating means, first channel means for conveying the first portions of the air streams to at least one air outlet of the nozzle, the nozzle defining an opening through which air from outside the nozzle is drawn by the air flow emitted from the at least one air outlet, and second channel means for conveying the second portions of the air streams along an internal surface of the nozzle. 
         [0027]    These first portions of the air streams may be emitted from a common first air outlet of the nozzle, or they may each be emitted from a respective first air outlet of the nozzle, and together form the first portion of the air flow. These first air outlets may be located on opposite sides of the opening. The second portions of the air streams may be conveyed along a common internal surface of the nozzle, for example the internal surface of the inner casing section of the nozzle, and emitted either from a common second air outlet of the nozzle, or from a respective second air outlet of the nozzle, and together form the second portion of the air flow. Again, these second air outlets may be located on opposite sides of the opening. 
         [0028]    At least part of the heating means may be arranged within the nozzle so as to extend about the opening. Where the nozzle defines a circular opening, the heating means preferably extends at least 270° about the opening and more preferably at least 300° about the opening. Where the nozzle defines an elongate opening, that is, an opening having a height greater than its width, the heating means is preferably located on at least the opposite sides of the opening. 
         [0029]    The heating means may comprise at least one ceramic heater located within the interior passage. The ceramic heater may be porous so that the first portion of the air flow passes through pores in the heating means before being emitted from the first air outlet(s). The heater may be formed from a PTC (positive temperature coefficient) ceramic material which is capable of rapidly heating the air flow upon activation. 
         [0030]    The ceramic material may be at least partially coated in metallic or other electrically conductive material to facilitate connection of the heating means to a controller within the fan assembly for activating the heating means. Alternatively, at least one non-porous, preferably ceramic, heater may be mounted within a metallic frame located within the interior passage and which is connectable to a controller of the fan assembly. The metallic frame preferably comprises a plurality of fins to provide a greater surface area and hence better heat transfer to the air flow, while also providing a means of electrical connection to the heating means. 
         [0031]    The heating means preferably comprises at least one heater assembly. Where the air flow is divided into two air streams, the heating means preferably comprises a plurality of heater assemblies each for heating a first portion of a respective air stream, and the diverting means preferably comprises a plurality of walls each for diverting a second portion of a respective air stream away from a heater assembly. The diverting means may also comprise a second plurality of walls each for diverting a third portion of a respective air stream away from a heater assembly. 
         [0032]    Each air outlet is preferably in the form of a slot, and which preferably has a width in the range from 0.5 to 5 mm. The width of the first air outlet(s) is preferably different from that of the second air outlet(s). In a preferred embodiment, the width of the first air outlet(s) is greater than the width of the second air outlet(s) so that the majority of the air flow passes through the heating means. 
         [0033]    The nozzle may comprise a surface located adjacent the air outlet(s) and over which the air outlet(s) are arranged to direct the air flow emitted therefrom. Preferably, this surface is a curved surface, and more preferably is a Coanda surface. Preferably, the external surface of the inner casing section of the nozzle is shaped to define the Coanda surface. A Coanda surface is a known type of surface over which fluid flow exiting an output orifice close to the surface exhibits the Coanda effect. The fluid tends to flow over the surface closely, almost ‘clinging to’ or ‘hugging’ the surface. The Coanda effect is already a proven, well documented method of entrainment in which a primary air flow is directed over a Coanda surface. A description of the features of a Coanda surface, and the effect of fluid flow over a Coanda surface, can be found in articles such as Reba, Scientific American, Volume 214, June 1966 pages 84 to 92. Through use of a Coanda surface, an increased amount of air from outside the fan assembly is drawn through the opening by the air emitted from the air outlets. 
         [0034]    In a preferred embodiment an air flow is created through the nozzle of the fan assembly. 
         [0035]    In the following description this air flow will be referred to as the primary air flow. The primary air flow is emitted from the air outlet(s) of the nozzle and preferably passes over a Coanda surface. The primary air flow entrains air surrounding the nozzle, which acts as an air amplifier to supply both the primary air flow and the entrained air to the user. The entrained air will be referred to here as a secondary air flow. The secondary air flow is drawn from the room space, region or external environment surrounding the mouth of the nozzle and, by displacement, from other regions around the fan assembly, and passes predominantly through the opening defined by the nozzle. The primary air flow directed over the Coanda surface combined with the entrained secondary air flow equates to a total air flow emitted or projected forward from the opening defined by the nozzle. 
         [0036]    Preferably, the nozzle comprises a diffuser surface located downstream of the Coanda surface. The diffuser surface directs the air flow emitted towards a user&#39;s location while maintaining a smooth, even output. Preferably, the external surface of the inner casing section of the nozzle is shaped to define the diffuser surface. 
         [0037]    In a fourth aspect, the present invention provides a fan assembly comprising a nozzle as aforementioned. The fan assembly preferably comprises a base housing said means for creating the air flow, with the nozzle being connected to the base. The base is preferably generally cylindrical in shape, and comprises a plurality of air inlets through which the air flow enters the fan assembly. 
         [0038]    The means for creating an air flow through the nozzle preferably comprises an impeller driven by a motor. This can provide a fan assembly with efficient air flow generation. The motor is preferably a DC brushless motor. This can avoid frictional losses and carbon debris from the brushes used in a traditional brushed motor. Reducing carbon debris and emissions is advantageous in a clean or pollutant sensitive environment such as a hospital or around those with allergies. While induction motors, which are generally used in bladed fans, also have no brushes, a DC brushless motor can provide a much wider range of operating speeds than an induction motor. 
         [0039]    The nozzle is preferably in the form of a casing, preferably an annular casing, for receiving the air flow. 
         [0040]    The heating means need not be located within the nozzle. For example, both the heating means and the diverting means may be located in the base, with the first channel means being arranged to receive a relatively hot first portion of the air flow and to convey the first portion of the air flow to the at least one air outlet, and the second channel means being arranged to receive a relatively cold second portion of the air flow from the base, and to convey the second portion of the air flow over an internal surface of the nozzle. The nozzle may comprise internal walls or baffles for defining the first channel means and second channel means. 
         [0041]    Alternatively, the heating means may be located in the nozzle but the diverting means may be located in the base. In this case, the first channel means may be arranged both to convey the first portion of the air flow from the base to the at least one air outlet and to house the heating means for heating the first portion of the air flow, while the second channel means may be arranged simply to convey the second portion of the air flow from the base over the internal surface of the nozzle. 
         [0042]    Therefore, in a fifth aspect the present invention provides a fan assembly for creating an air current, the fan assembly comprising means for creating an air flow, a casing comprising at least one air outlet, the casing defining an opening through which air from outside the fan assembly is drawn by the air flow emitted from the at least one air outlet, means for heating a first portion of the air flow, means for diverting a second portion of the air flow away from the heating means, first channel means for conveying the first portion of the air flow to said at least one air outlet, and second channel means for conveying the second portion of the air flow along an internal surface of the casing. 
         [0043]    The fan assembly is preferably in the form of a portable fan heater. 
         [0044]    Features described above in connection with the first aspect of the invention are equally applicable to any of the second to fifth aspects of the invention, and vice versa. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]    An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0046]      FIG. 1  is a front perspective view, from above, of a fan assembly; 
           [0047]      FIG. 2  is a front view of the fan assembly; 
           [0048]      FIG. 3  is a sectional view taken along line B-B of  FIG. 2 ; 
           [0049]      FIG. 4  is an exploded view of the nozzle of the fan assembly; 
           [0050]      FIG. 5  is a front perspective view of the heater chassis of the nozzle; 
           [0051]      FIG. 6  is a front perspective view, from below, of the heater chassis connected to an inner casing section of the nozzle; 
           [0052]      FIG. 7  is a close-up view of region X indicated in  FIG. 6 ; 
           [0053]      FIG. 8  is a close-up view of region Y indicated in  FIG. 1 ; 
           [0054]      FIG. 9  is a sectional view taken along line A-A of  FIG. 2 ; 
           [0055]      FIG. 10  is a close-up view of region Z indicated in  FIG. 9 ; 
           [0056]      FIG. 11  is a sectional view of the nozzle taken along line C-C of  FIG. 9 ; and 
           [0057]      FIG. 12  is a schematic illustration of a control system of the fan assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0058]      FIGS. 1 and 2  illustrate external views of a fan assembly  10 . The fan assembly  10  is in the form of a portable fan heater. The fan assembly  10  comprises a body  12  comprising an air inlet  14  through which a primary air flow enters the fan assembly  10 , and a nozzle  16  in the form of an annular casing mounted on the body  12 , and which comprises at least one air outlet  18  for emitting the primary air flow from the fan assembly  10 . 
         [0059]    The body  12  comprises a substantially cylindrical main body section  20  mounted on a substantially cylindrical lower body section  22 . The main body section  20  and the lower body section  22  preferably have substantially the same external diameter so that the external surface of the upper body section  20  is substantially flush with the external surface of the lower body section  22 . In this embodiment the body  12  has a height in the range from 100 to 300 mm, and a diameter in the range from 100 to 200 mm. 
         [0060]    The main body section  20  comprises the air inlet  14  through which the primary air flow enters the fan assembly  10 . In this embodiment the air inlet  14  comprises an array of apertures formed in the main body section  20 . Alternatively, the air inlet  14  may comprise one or more grilles or meshes mounted within windows formed in the main body section  20 . The main body section  20  is open at the upper end (as illustrated) thereof to provide an air outlet  23  through which the primary air flow is exhausted from the body  12 . 
         [0061]    The main body section  20  may be tilted relative to the lower body section  22  to adjust the direction in which the primary air flow is emitted from the fan assembly  10 . For example, the upper surface of the lower body section  22  and the lower surface of the main body section  20  may be provided with interconnecting features which allow the main body section  20  to move relative to the lower body section  22  while preventing the main body section  20  from being lifted from the lower body section  22 . For example, the lower body section  22  and the main body section  20  may comprise interlocking L-shaped members. 
         [0062]    The lower body section  22  comprises a user interface of the fan assembly  10 . With reference also to  FIG. 12 , the user interface comprises a plurality of user-operable buttons  24 ,  26 ,  28 ,  30  for enabling a user to control various functions of the fan assembly  10 , a display  32  located between the buttons for providing the user with, for example, a visual indication of a temperature setting of the fan assembly  10 , and a user interface control circuit  33  connected to the buttons  24 ,  26 ,  28 ,  30  and the display  32 . The lower body section  22  also includes a window  34  through which signals from a remote control  35  (shown schematically in  FIG. 12 ) enter the fan assembly  10 . The lower body section  22  is mounted on a base  36  for engaging a surface on which the fan assembly  10  is located. The base  36  includes an optional base plate  38 , which preferably has a diameter in the range from 200 to 300 mm. 
         [0063]    The nozzle  16  has an annular shape, extending about a central axis X to define an opening  40 . The air outlets  18  for emitting the primary air flow from the fan assembly  10  are located towards the rear of the nozzle  16 , and arranged to direct the primary air flow towards the front of the nozzle  16 , through the opening  40 . In this example, the nozzle  16  defines an elongate opening  40  having a height greater than its width, and the air outlets  18  are located on the opposite elongate sides of the opening  40 . In this example the maximum height of the opening  40  is in the range from 300 to 400 mm, whereas the maximum width of the opening  40  is in the range from 100 to 200 mm. 
         [0064]    The inner annular periphery of the nozzle  16  comprises a Coanda surface  42  located adjacent the air outlets  18 , and over which at least some of the air outlets  18  are arranged to direct the air emitted from the fan assembly  10 , a diffuser surface  44  located downstream of the Coanda surface  42  and a guide surface  46  located downstream of the diffuser surface  44 . The diffuser surface  44  is arranged to taper away from the central axis X of the opening  38 . The angle subtended between the diffuser surface  44  and the central axis X of the opening  40  is in the range from 5 to 25°, and in this example is around 7°. The guide surface  46  is preferably arranged substantially parallel to the central axis X of the opening  38  to present a substantially flat and substantially smooth face to the air flow emitted from the mouth  40 . A visually appealing tapered surface  48  is located downstream from the guide surface  46 , terminating at a tip surface  50  lying substantially perpendicular to the central axis X of the opening  40 . The angle subtended between the tapered surface  48  and the central axis X of the opening  40  is preferably around 45°. 
         [0065]      FIG. 3  illustrates a sectional view through the body  12 . The lower body section  22  houses a main control circuit, indicated generally at  52 , connected to the user interface control circuit  33 . The user interface control circuit  33  comprises a sensor  54  for receiving signals from the remote control  35 . The sensor  54  is located behind the window  34 . In response to operation of the buttons  24 ,  26 ,  28 ,  30  and the remote control  35 , the user interface control circuit  33  is arranged to transmit appropriate signals to the main control circuit  52  to control various operations of the fan assembly  10 . The display  32  is located within the lower body section  22 , and is arranged to illuminate part of the lower body section  22 . The lower body section  22  is preferably formed from a translucent plastics material which allows the display  32  to be seen by a user. 
         [0066]    The lower body section  22  also houses a mechanism, indicated generally at  56 , for oscillating the lower body section  22  relative to the base  36 . The operation of the oscillating mechanism  56  is controlled by the main control circuit  52  upon receipt of an appropriate control signal from the remote control  35 . The range of each oscillation cycle of the lower body section  22  relative to the base  36  is preferably between 60° and 120°, and in this embodiment is around 80°. In this embodiment, the oscillating mechanism  56  is arranged to perform around 3 to 5 oscillation cycles per minute. A mains power cable  58  for supplying electrical power to the fan assembly  10  extends through an aperture formed in the base  36 . The cable  58  is connected to a plug  60 . 
         [0067]    The main body section  20  houses an impeller  64  for drawing the primary air flow through the air inlet  14  and into the body  12 . Preferably, the impeller  64  is in the form of a mixed flow impeller. The impeller  64  is connected to a rotary shaft  66  extending outwardly from a motor  68 . In this embodiment, the motor  68  is a DC brushless motor having a speed which is variable by the main control circuit  52  in response to user manipulation of the button  26  and/or a signal received from the remote control  35 . The maximum speed of the motor  68  is preferably in the range from 5,000 to 10,000 rpm. The motor  68  is housed within a motor bucket comprising an upper portion  70  connected to a lower portion  72 . The upper portion  70  of the motor bucket comprises a diffuser  74  in the form of a stationary disc having spiral blades. 
         [0068]    The motor bucket is located within, and mounted on, a generally frusto-conical impeller housing  76 . The impeller housing  76  is, in turn, mounted on a plurality of angularly spaced supports  77 , in this example three supports, located within and connected to the main body section  20  of the base  12 . The impeller  64  and the impeller housing  76  are shaped so that the impeller  64  is in close proximity to, but does not contact, the inner surface of the impeller housing  76 . A substantially annular inlet member  78  is connected to the bottom of the impeller housing  76  for guiding the primary air flow into the impeller housing  76 . 
         [0069]    A flexible sealing member  80  is mounted on the impeller housing  76 . The flexible sealing member prevents air from passing around the outer surface of the impeller housing to the inlet member  78 . The sealing member  80  preferably comprises an annular lip seal, preferably formed from rubber. The sealing member  80  further comprises a guide portion in the form of a grommet for guiding an electrical cable  82  to the motor  68 . The electrical cable  82  passes from the main control circuit  52  to the motor  68  through apertures formed in the main body section  20  and the lower body section  22  of the body  12 , and in the impeller housing  76  and the motor bucket. 
         [0070]    Preferably, the body  12  includes silencing foam for reducing noise emissions from the body  12 . In this embodiment, the main body section  20  of the body  12  comprises a first annular foam member  84  located beneath the air inlet  14 , and a second annular foam member  86  located within the motor bucket. 
         [0071]    The nozzle  16  will now be described in more detail with reference to  FIGS. 4 to 11 . With reference first to  FIG. 4 , the nozzle  16  comprises an annular outer casing section  88  connected to and extending about an annular inner casing section  90 . Each of these sections may be formed from a plurality of connected parts, but in this embodiment each of the casing sections  88 ,  90  is formed from a respective, single molded part. The inner casing section  90  defines the central opening  40  of the nozzle  16 , and has an external surface  92  which is shaped to define the Coanda surface  42 , diffuser surface  44 , guide surface  46  and tapered surface  48 . 
         [0072]    The outer casing section  88  and the inner casing section  90  together define an annular interior passage of the nozzle  16 . As illustrated in  FIGS. 9 and 11 , the interior passage extends about the opening  40 , and thus comprises two relatively straight sections  94   a ,  94   b  each adjacent a respective elongate side of the opening  40 , an upper curved section  94   c  joining the upper ends of the straight sections  94   a ,  94   b , and a lower curved section  94   d  joining the lower ends of the straight  94   a ,  94   b . The interior passage is bounded by the internal surface  96  of the outer casing section  88  and the internal surface  98  of the inner casing section  90 . 
         [0073]    As also shown in  FIGS. 1 to 3 , the outer casing section  88  comprises a base  100  which is connected to, and over, the open upper end of the main body section  20  of the base  12 . The base  100  of the outer casing section  88  comprises an air inlet  102  through which the primary air flow enters the lower curved section  94   d  of the interior passage from the air outlet  23  of the base  12 . Within the lower curved section  94   d , the primary air flow is divided into two air streams which each flow into a respective one of the straight sections  94   a ,  94   b  of the interior passage. 
         [0074]    The nozzle  16  also comprises a pair of heater assemblies  104 . Each heater assembly  104  comprises a row of heater elements  106  arranged side-by-side. The heater elements  106  are preferably formed from positive temperature coefficient (PTC) ceramic material. The row of heater elements is sandwiched between two heat radiating components  108 , each of which comprises an array of heat radiating fins  110  located within a frame  112 . The heat radiating components  108  are preferably formed from aluminium or other material with high thermal conductivity (around 200 to 400 W/mK), and may be attached to the row of heater elements  106  using beads of silicone adhesive, or by a clamping mechanism. The side surfaces of the heater elements  106  are preferably at least partially covered with a metallic film to provide an electrical contact between the heater elements  106  and the heat radiating components  108 . This film may be formed from screen printed or sputtered aluminium. Returning to  FIGS. 3 and 4 , electrical terminals  114 ,  116  located at opposite ends of the heater assembly  104  are each connected to a respective heat radiating component  108 . Each terminal  114  is connected to an upper part  118  of a loom for supplying electrical power to the heater assemblies  104 , whereas each terminal  116  is connected to a lower part  120  of the loom. The loom is in turn connected to a heater control circuit  122  located in the main body section  20  of the base  12  by wires  124 . The heater control circuit  122  is in turn controlled by control signals supplied thereto by the main control circuit  52  in response to user operation of the buttons  28 ,  30  and/or use of the remote control  35 . 
         [0075]      FIG. 12  illustrates schematically a control system of the fan assembly  10 , which includes the control circuits  33 ,  52 ,  122 , buttons  24 ,  26 ,  28 ,  30 , and remote control  35 . Two or more of the control circuits  33 ,  52 ,  122  may be combined to form a single control circuit. A thermistor  126  for providing an indication of the temperature of the primary air flow entering the fan assembly  10  is connected to the heater controller  122 . The thermistor  126  may be located immediately behind the air inlet  14 , as shown in  FIG. 3 . The main control circuit  52  supplies control signals to the user interface control circuit  33 , the oscillation mechanism  56 , the motor  68 , and the heater control circuit  124 , whereas the heater control circuit  124  supplies control signals to the heater assemblies  104 . The heater control circuit  124  may also provide the main control circuit  52  with a signal indicating the temperature detected by the thermistor  126 , in response to which the main control circuit  52  may output a control signal to the user interface control circuit  33  indicating that the display  32  is to be changed, for example if the temperature of the primary air flow is at or above a user selected temperature. The heater assemblies  104  may be controlled simultaneously by a common control signal, or they may be controlled by respective control signals. 
         [0076]    The heater assemblies  104  are each retained within a respective straight section  94   a ,  94   b  of the interior passage by a chassis  128 . The chassis  128  is illustrated in more detail in  FIG. 5 . The chassis  128  has a generally annular structure. The chassis  128  comprises a pair of heater housings  130  into which the heater assemblies  104  are inserted. Each heater housing  130  comprises an outer wall  132  and an inner wall  134 . The inner wall  134  is connected to the outer wall  132  at the upper and lower ends  138 ,  140  of the heater housing  130  so that the heater housing  130  is open at the front and rear ends thereof. The walls  132 ,  134  thus define a first air flow channel  136  which passes through the heater assembly  104  located within the heater housing  130 . 
         [0077]    The heater housings  130  are connected together by upper and lower curved portions  142 ,  144  of the chassis  128 . Each curved portion  142 ,  144  also has an inwardly curved, generally U-shaped cross-section. The curved portions  142 ,  144  of the chassis  128  are connected to, and preferably integral with, the inner walls  134  of the heater housings  130 . The inner walls  134  of the heater housings  130  have a front end  146  and a rear end  148 . With reference also to  FIGS. 6 to 9 , the rear end  148  of each inner wall  134  also curves inwardly away from the adjacent outer wall  132  so that the rear ends  148  of the inner walls  134  are substantially continuous with the curved portions  142 ,  144  of the chassis  128 . 
         [0078]    During assembly of the nozzle  16 , the chassis  128  is pushed over the rear end of the inner casing section  90  so that the curved portions  142 ,  144  of the chassis  128  and the rear ends  148  of the inner walls  134  of the heater housings  130  are wrapped around the rear end  150  of the inner casing section  90 . The inner surface  98  of the inner casing section  90  comprises a first set of raised spacers  152  which engage the inner walls  134  of the heater housings  130  to space the inner walls  134  from the inner surface  98  of the inner casing section  90 . The rear ends  148  of the inner walls  134  also comprise a second set of spacers  154  which engage the outer surface  92  of the inner casing section  90  to space the rear ends of the inner walls  134  from the outer surface  92  of the inner casing section  90 . 
         [0079]    The inner walls  134  of the heater housing  130  of the chassis  128  and the inner casing section  90  thus define two second air flow channels  156 . Each of the second flow channels  156  extends along the inner surface  98  of the inner casing section  90 , and around the rear end  150  of the inner casing section  90 . Each second flow channel  156  is separated from a respective first flow channel  136  by the inner wall  134  of the heater housing  130 . Each second flow channel  156  terminates at an air outlet  158  located between the outer surface  92  of the inner casing section  90  and the rear end  148  of the inner wall  134 . Each air outlet  158  is thus in the form of a vertically-extending slot located on a respective side of the opening  40  of the assembled nozzle  16 . Each air outlet  158  preferably has a width in the range from 0.5 to 5 mm, and in this example the air outlets  158  have a width of around 1 mm. 
         [0080]    The chassis  128  is connected to the inner surface  98  of the inner casing section  90 . 
         [0081]    With reference to  FIGS. 5 to 7 , each of the inner walls  134  of the heater housings  130  comprises a pair of apertures  160 , each aperture  160  being located at or towards a respective one of the upper and lower ends of the inner wall  134 . As the chassis  128  is pushed over the rear end of the inner casing section  90 , the inner walls  134  of the heater housings  130  slide over resilient catches  162  mounted on, and preferably integral with, the inner surface  98  of the inner casing section  90 , which subsequently protrude through the apertures  160 . The position of the chassis  128  relative to the inner casing section  90  can then be adjusted so that the inner walls  134  are gripped by the catches  162 . Stop members  164  mounted on, and preferably also integral with, the inner surface  98  of the inner casing section  90  may also serve to retain the chassis  128  on the inner casing section  90 . 
         [0082]    With the chassis  128  connected to the inner casing section  90 , the heater assemblies  104  are inserted into the heater housings  130  of the chassis  128 , and the loom connected to the heater assemblies  104 . Of course, the heater assemblies  104  may be inserted into the heater housings  130  of the chassis  128  prior to the connection of the chassis  128  to the inner casing section  90 . The inner casing section  90  of the nozzle  16  is then inserted into the outer casing section  88  of the nozzle  16  so that the front end  166  of the outer casing section  88  enters a slot  168  located at the front of the inner casing section  90 , as illustrated in  FIG. 9 . The outer and inner casing sections  88 ,  90  may be connected together using an adhesive introduced to the slot  168 . 
         [0083]    The outer casing section  88  is shaped so that part of the inner surface  96  of the outer casing section  88  extends around, and is substantially parallel to, the outer walls  132  of the heater housings  130  of the chassis  128 . The outer walls  132  of the heater housings  130  have a front end  170  and a rear end  172 , and a set of ribs  174  located on the outer side surfaces of the outer walls  132  and which extend between the ends  170 ,  172  of the outer walls  132 . The ribs  174  are configured to engage the inner surface  96  of the outer casing section  88  to space the outer walls  132  from the inner surface  96  of the outer casing section  88 . The outer walls  132  of the heater housings  130  of the chassis  128  and the outer casing section  88  thus define two third air flow channels  176 . Each of the third flow channels  176  is located adjacent and extends along the inner surface  96  of the outer casing section  88 . Each third flow channel  176  is separated from a respective first flow channel  136  by the outer wall  132  of the heater housing  130 . Each third flow channel  176  terminates at an air outlet  178  located within the interior passage, and between the rear end  172  of the outer wall  132  of the heater housing  130  and the outer casing section  88 . Each air outlet  178  is also in the form of a vertically-extending slot located within the interior passage of the nozzle  16 , and preferably has a width in the range from 0.5 to 5 mm. In this example the air outlets  178  have a width of around 1 mm. 
         [0084]    The outer casing section  88  is shaped so as to curve inwardly around part of the rear ends  148  of the inner walls  134  of the heater housings  130 . The rear ends  148  of the inner walls  134  comprise a third set of spacers  182  located on the opposite side of the inner walls  134  to the second set of spacers  154 , and which are arranged to engage the inner surface  96  of the outer casing section  88  to space the rear ends of the inner walls  134  from the inner surface  96  of the outer casing section  88 . The outer casing section  88  and the rear ends  148  of the inner walls  134  thus define a further two air outlets  184 . Each air outlet  184  is located adjacent a respective one of the air outlets  158 , with each air outlet  158  being located between a respective air outlet  184  and the outer surface  92  of the inner casing section  90 . Similar to the air outlets  158 , each air outlet  184  is in the form of a vertically-extending slot located on a respective side of the opening  40  of the assembled nozzle  16 . The air outlets  184  preferably have the same length as the air outlets  158 . Each air outlet  184  preferably has a width in the range from 0.5 to 5 mm, and in this example the air outlets  184  have a width of around 2 to 3 mm. Thus, the air outlets  18  for emitting the primary air flow from the fan assembly  10  comprise the two air outlets  158  and the two air outlets  184 . 
         [0085]    Returning to  FIGS. 3 and 4 , the nozzle  16  preferably comprises two curved sealing members  186 ,  188  each for forming a seal between the outer casing section  88  and the inner casing section  90  so that there is substantially no leakage of air from the curved sections  94   c ,  94   d  of the interior passage of the nozzle  16 . Each sealing member  186 ,  188  is sandwiched between two flanges  190 ,  192  located within the curved sections  94   c ,  94   d  of the interior passage. The flanges  190  are mounted on, and preferably integral with, the inner casing section  90 , whereas the flanges  192  are mounted on, and preferably integral with, the outer casing section  88 . As an alternative to preventing the air flow from leaking from the upper curved section  94   c  of the interior passage, the nozzle  16  may be arranged to prevent the air flow from entering this curved section  94   c . For example, the upper ends of the straight sections  94   a ,  94   b  of the interior passage may be blocked by the chassis  128  or by inserts introduced between the inner and outer casing sections  88 ,  90  during assembly. 
         [0086]    To operate the fan assembly  10  the user presses button  24  of the user interface, or presses a corresponding button of the remote control  35  to transmit a signal which is received by the sensor of the user interface circuit  33 . The user interface control circuit  33  communicates this action to the main control circuit  52 , in response to which the main control circuit  52  activates the motor  68  to rotate the impeller  64 . The rotation of the impeller  64  causes a primary air flow to be drawn into the body  12  through the air inlet  14 . The user may control the speed of the motor  68 , and therefore the rate at which air is drawn into the body  12  through the air inlet  14 , by pressing button  26  of the user interface or a corresponding button of the remote control  35 . Depending on the speed of the motor  56 , the primary air flow generated by the impeller  52  may be between 10 and 30 litres per second. The primary air flow passes sequentially through the impeller housing  76  and the open upper end of the main body portion  22  to enter the lower curved section  94   d  of the interior passage of the nozzle  16 . The pressure of the primary air flow at the outlet  23  of the body  12  may be at least 150 Pa, and is preferably in the range from 250 to 1.5 kPa. 
         [0087]    The user may optionally activate the heater assemblies  104  located within the nozzle  16  to raise the temperature of the first portion of the primary air flow before it is emitted from the fan assembly  10 , and thereby increase both the temperature of the primary air flow emitted by the fan assembly  10  and the temperature of the ambient air in a room or other environment in which the fan assembly  10  is located. In this example, the heater assemblies  104  are both activated and de-activated simultaneously, although alternatively the heater assemblies  104  may be activated and de-activated separately. To activate the heater assemblies  104 , the user presses button  30  of the user interface, or presses a corresponding button of the remote control  35  to transmit a signal which is received by the sensor of the user interface circuit  33 . The user interface control circuit  33  communicates this action to the main control circuit  52 , in response to which the main control circuit  52  issues a command to the heater control circuit  124  to activate the heater assemblies  104 . The user may set a desired room temperature or temperature setting by pressing button  28  of the user interface or a corresponding button of the remote control  35 . The user interface circuit  33  is arranged to vary the temperature displayed by the display  34  in response to the operation of the button  28 , or the corresponding button of the remote control  35 . In this example, the display  34  is arranged to display a temperature setting selected by the user, which may correspond to a desired room air temperature. Alternatively, the display  34  may be arranged to display one of a number of different temperature settings which has been selected by the user. 
         [0088]    Within the lower curved section  94   d  of the interior passage of the nozzle  16 , the primary air flow is divided into two air streams which pass in opposite directions around the opening  40  of the nozzle  16 . One of the air streams enters the straight section  94   a  of the interior passage located to one side of the opening  40 , whereas the other air stream enters the straight section  94   b  of the interior passage located on the other side of the opening  40 . As the air streams pass through the straight sections  94   a ,  94   b , the air streams turn through around 90° towards the air outlets  18  of the nozzle  16 . To direct the air streams evenly towards the air outlets  18  along the length of the straight section  94   a ,  94   b , the nozzle  16  may comprises a plurality of stationary guide vanes located within the straight sections  94   a ,  94   b  and each for directing part of the air stream towards the air outlets  18 . The guide vanes are preferably integral with the internal surface  98  of the inner casing section  90 . The guide vanes are preferably curved so that there is no significant loss in the velocity of the air flow as it is directed towards the air outlets  18 . Within each straight section  94   a ,  94   b , the guide vanes are preferably substantially vertically aligned and evenly spaced apart to define a plurality of passageways between the guide vanes and through which air is directed relatively evenly towards the air outlets  18 . 
         [0089]    As the air streams flow towards the air outlets  18 , a first portion of the primary air flow enters the first air flow channels  136  located between the walls  132 ,  134  of the chassis  128 . Due to the splitting of the primary air flow into two air streams within the interior passage, each first air flow channel  136  may be considered to receive a respective first sub-portion of the primary air flow. Each first sub-portion of the primary air flow passes through a respective heating assembly  104 . The heat generated by the activated heating assemblies is transferred by convection to the first portion of the primary air flow to raise the temperature of the first portion of the primary air flow. 
         [0090]    A second portion of the primary air flow is diverted away from the first air flow channels  136  by the front ends  146  of the inner walls  134  of the heater housings  130  so that this second portion of the primary air flow enters the second air flow channels  156  located between the inner casing section  90  and the inner walls of the heater housings  130 . Again, with the splitting of the primary air flow into two air streams within the interior passage each second air flow channel  156  may be considered to receive a respective second sub-portion of the primary air flow. Each second sub-portion of the primary air flow passes along the internal surface  92  of the inner casing section  90 , thereby acting as a thermal barrier between the relatively hot primary air flow and the inner casing section  90 . The second air flow channels  156  are arranged to extend around the rear wall  150  of the inner casing section  90 , thereby reversing the flow direction of the second portion of the air flow, so that it is emitted through the air outlets  158  towards the front of the fan assembly  10  and through the opening  40 . The air outlets  158  are arranged to direct the second portion of the primary air flow over the external surface  92  of the inner casing section  90  of the nozzle  16 . 
         [0091]    A third portion of the primary air flow is also diverted away from the first air flow channels  136 . This third portion of the primary air flow by the front ends  170  of the outer walls  132  of the heater housings  130  so that the third portion of the primary air flow enters the third air flow channels  176  located between the outer casing section  88  and the outer walls  132  of the heater housings  130 . Once again, with the splitting of the primary air flow into two air streams within the interior passage each third air flow channel  176  may be considered to receive a respective third sub-portion of the primary air flow. Each third sub-portion of the primary air flow passes along the internal surface  96  of the outer casing section  88 , thereby acting as a thermal barrier between the relatively hot primary air flow and the outer casing section  88 . The third air flow channels  176  are arranged to convey the third portion of the primary air flow to the air outlets  178  located within the interior passage. Upon emission from the air outlets  178 , the third portion of the primary air flow merges with this first portion of the primary air flow. These merged portions of the primary air flow are conveyed between the inner surface  96  of the outer casing section  88  and the inner walls  134  of the heater housings to the air outlets  184 , and so the flow directions of these portions of the primary air flow are also reversed within the interior passage. The air outlets  184  are arranged to direct the relatively hot, merged first and third portions of the primary air flow over the relatively cold second portion of the primary air flow emitted from the air outlets  158 , which acts as a thermal barrier between the outer surface  92  of the inner casing section  90  and the relatively hot air emitted from the air outlets  184 . Consequently, the majority of the internal and external surfaces of the nozzle  16  are shielded from the relatively hot air emitted from the fan assembly  10 . This can enable the external surfaces of the nozzle  16  to be maintained at a temperature below 70° C. during use of the fan assembly  10 . 
         [0092]    The primary air flow emitted from the air outlets  18  passes over the Coanda surface  42  of the nozzle  16 , causing a secondary air flow to be generated by the entrainment of air from the external environment, specifically from the region around the air outlets  18  and from around the rear of the nozzle. This secondary air flow passes through the opening  40  of the nozzle  16 , where it combines with the primary air flow to produce an overall air flow projected forward from the fan assembly  10  which has a lower temperature than the primary air flow emitted from the air outlets  18 , but a higher temperature than the air entrained from the external environment. Consequently, a current of warm air is emitted from the fan assembly  10 . 
         [0093]    As the temperature of the air in the external environment increases, the temperature of the primary air flow drawn into the fan assembly  10  through the air inlet  14  also increases. A signal indicative of the temperature of this primary air flow is output from the thermistor  126  to the heater control circuit  124 . When the temperature of the primary air flow is above the temperature set by the user, or a temperature associated with a user&#39;s temperature setting, by around 1° C., the heater control circuit  124  de-activates the heater assemblies  104 . When the temperature of the primary air flow has fallen to a temperature around 1° C. below that set by the user, the heater control circuit  124  re-activates the heater assemblies  104 . This can allow a relatively constant temperature to be maintained in the room or other environment in which the fan assembly  10  is located.