A heater

Abstract

A heater (10, fig. 1) comprising an air inlet (14, fig. 1) and an air outlet (18, fig. 1) with an airflow path therebetween. An airflow generator draws air along the flow path and a plurality of heate

Description

Background Fan heaters produce warm air by creating an airflow over a heater element. The heater element may be a positive temperature coefficient heater element. Summary According to a first aspect of the present invention, there is provided a heater, comprising: at least one air inlet and at least one air outlet, wherein an airflow path is defined between the at least one air inlet and the at least one air outlet; an airflow generator configured to draw air through the air inlet and along the airflow path; a plurality of heater elements positioned in the airflow path for heating the air flowing along the airflow path, wherein the plurality of heater elements are positioned in series with respect to each other, in the airflow path; a control unit configured to operate the plurality of heater elements in a first mode in which a first number of the plurality of heater elements are switched on and in a second mode in which a second number of the plurality of heater elements are switched on, the second number being higher than the first number. Heaters which produce an airflow over heater elements allow the heated air to be directed towards a particular part of a room or towards a user. Using more than one heater element enables the heater to be controlled in different modes to produce low and high heating levels. By placing the heater elements in series in the airflow path, the same airflow is heated by each heater element. When more than one heater element is switched on, the air exiting the air outlet is heated more uniformly. Additionally, by positioning the heater elements in series, the profile of the heater elements is relatively narrow. This enables the heater elements to be incorporated into spaces that are physically constrained. The plurality of heater elements may be two heater elements, and the first number may be one and the second number may be two. By using two heater elements, the heater design may be kept relatively simple, while still enabling high and low heating modes. The first mode may be a low-power mode and the second mode may be a high-power mode. Using at least two heating modes enables a low-power mode of operation. This reduces energy consumption when less heating is required. The plurality of heater elements may each have a substantially similar power rating. For example, the power rating of each heater element may differ from a target power rating by 5% or less. As an alternative, the plurality of heater elements may each have identical power ratings. By using a plurality of heater elements having similar or identical power ratings, each of the heater elements can be of the same construction. This may make the device simpler and easier to manufacture. The plurality of heater elements may include a first heater element having a first power rating and a second heater element having a second power rating higher than the first power rating. The plurality of heater elements may include heater elements with different power ratings. This enables a greater number of modes of operation for the same number of heater elements. The first mode may include switching on the first heater element without the second heater element switching on, and the second mode includes switching on the first and second heater elements; wherein the control unit is further configured to operate the plurality of heater elements in a third mode in which the second heater element is switched on without the first heater element switching on. The third mode may be a medium-power mode. The medium-power mode may include switching on one or more heater elements which have a power rating between the low and the high-power modes. The first mode may include switching on only the first heater element, and the third mode may include switching on only the second heater element. By using heater elements with different power ratings, three modes of power may be achieved using only two heater elements. The plurality of heater elements may be a plurality of positive temperature coefficient heater elements. Positive temperature coefficient, PTC, heater elements are well suited to airflow-based heaters. PTC heaters are efficient and heat up quickly, thereby improving the user experience. As an alternative, other types of heating elements such as wire-based heating elements may be used. The heater may further comprise a user interface configured to allow the user to select a mode of operation from a range of user selectable modes of operation comprising at least the first and the second modes. The user interface may be configured to allow the user to switch the heater between at least the first and second modes. The user interface may include at least one physical switch or other physical user interface to enable the user to control the heater. Alternatively, the user interface may include a wireless interface to enable a user to control the heater with a dedicated wireless control device or a mobile device such as a mobile phone. For example, the wireless interface may use WiFi (TM) or Bluetooth (TM) radio protocols. The at least one physical switch may be a plurality of switches configured to allow the user to switch the plurality of heater elements based on a mode of operation. The control unit may includes a plurality of heater switches, coupled to the plurality of heater elements, and configured to switch the plurality of heater elements on or off based on the mode of operation. The plurality of heater switches may be high power MOSFETs or TRIACs. The at least one air outlet may comprise two air outlets, wherein a first airflow path is defined between one of the two air outlets and the at least one air inlet, and a second airflow path is defined between another one of the two air outlets and the at least one air inlet. By providing two air outlets, the heater may provide a wider heating zone than an equivalent single outlet design. For example, this enables the heater to be used with an annular air duct assembly having heater elements on both sides of the heater, thereby making the heater suitable for use fans which incorporate an air amplifier design. In some examples, the heater may include two air inlets, with an airflow path being formed between each air inlet and a respective air outlet. The plurality of heater elements may be a first array of heater elements positioned in the first airflow path, and the heater may further comprise a second array of heater elements positioned in the second airflow path for heating the air flowing along the second airflow path. By providing two heater arrays, each with a plurality of heater elements, each side of the heater may provide at least two levels of heating. For example, when used with an annular air duct assembly, the first array and second array may be positioned on a left and a right side respectively. The second heater element array includes a plurality of heater elements arranged in series in the second airflow path. By providing the plurality of heater elements in series, the airflow is heated more uniformly, in the same manner as the first heater array. The control unit is further configured to operate the second heater element array such that in the first mode the first number of the plurality of heater elements are switched on and in the second mode the second number of the plurality of heater elements are switched on. By controlling the heater elements of the second heater array in the same manner as the heater elements of the first heater array, the overall output from the air outlets of the heater is more uniform. Each of the first and second heater element arrays include a first and a second heater element, and the control unit includes a first switch arrangement, coupled to the first heater elements of the first and second heater element arrays, and a second switch arrangement, coupled to the second heater elements of the first and second heater element arrays. By coupling together the first heater elements of each array and separately coupling together the second heater elements of each array, the heater arrays may be controlled simultaneous and in a synchronised manner. The heater may further comprise an air duct assembly; wherein the at least one air outlet is formed in the air duct assembly, and the air duct assembly defines at least one cavity within which the plurality of heater elements are positioned. By forming the air outlets in an air duct assembly, the air duct assembly defines a cavity which acts as the airflow path from the airflow generator. The heater may further comprise a base supporting the air duct assembly, wherein the airflow generator is positioned within the base, and the airflow path is defined between the base and air duct assembly. The cross-section of the opening in the air duct assembly may be an annular shape, such as a capsule or a ring. A capsule shape is a rectangle with semi-circular ends. The control unit is further configured to control the airflow generator to adjust O O J a rate of flow of the air along the airflow path. The user interface may allow the user to control the rate of air flow and the heating mode independently. Alternatively, the rate of air flow and the heating mode may be controlled together. For example, a low-power mode may be combined with a low-rate of air flow and a high-power mode may be combined with a high-rate of air flow. According to a second aspect of the present invention, there is provided a method of controlling the heater described above, the method comprising: operating, using the control unit, the plurality of heater elements in a first mode in which at first number of the plurality of heater elements are switched on; or operating, using the control unit, the plurality of heater elements in a second mode in which a second number of the plurality of heater elements are switched on; wherein the second number being higher than the first number. According to a third aspect of the present invention, there is provided a fan assembly comprising a first heater element and a second heater element arranged in series in an airflow path of the fan assembly; wherein the fan assembly further comprises an airflow generator configured to move air along the airflow path; wherein the fan assembly is configured to operate in a low-heat mode in which the first heater element is switched on and a high-heat mode in which the first and second heater elements are switched on. The airflow generator may also include an impeller and a motor, coupled to the impeller. The motor may be configured to turn the impeller to draw air through the heater and along the primary airflow path. The heater may also include a control unit coupled to the plurality of heater elements. The control unit may include a user interface. The user interface allows a user to control the heater by switching the heater on / off, controlling the fan speed, or the heating mode. The user interface may comprise physical buttons or switches on the heater, or may be a wireless interface provided via a dedicated wireless control or a mobile device such as a mobile phone. The control unit may be coupled to the plurality of heater elements. The user interface may be coupled to the control unit. Further features and advantages of the invention will become apparent from the following description of preferred examples of the invention, given by way of example only, which is made with reference to the accompanying drawings. Brief Description of the Drawings Figure 1 shows a perspective view of a heater in accordance with an example of the disclosure; Figure 2 shows a front view of the heater of Figure 1; Figure 3 shows a cross-sectional view through the line A-A of Figure 1; Figure 4 shows a block diagram of the heater control system of the heater of Figure 1; Figure 5 shows a method of operation of the heater of Figure 1; and Figure 6 shows an arrangement of the heater elements in an alternative example of the disclosure. Detailed Description The present disclosure relates to a heater. In one example, the present disclosure relates to a heater for creating a warm air current in a room, office, or other domestic or commercial environment. Figures 1 and 2 illustrate external views of a heater 10. The heater 10 is in the form of a portable fan heater. The heater 10 comprises a body 12 comprising an air inlet 14 through which a primary airflow enters the heater 10. The heater also comprises an air duct assembly 16 (sometimes referred to as a nozzle) 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 airflow from the heater 10. In this example, the heater is a standalone fan heater. As an alternative, the heater may be part of an air purifier. The heater includes heater elements, which are not shown in Figure 1 as they are internal to the heater 10. The heater elements will be described in more detail below. The body 12 comprises a substantially cylindrical main body section 20. In this example the body 12 has a height in the range from 300 to 400 mm, and a diameter in the range from 200 to 300 mm. The main body section 20 comprises the air inlet 14 through which the primary airflow enters the heater 10. In this example 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 thereof to allow the primary airflow to be exhausted from the body 12 to the air duct assembly 16. The main body section 20 comprises a user interface 22 of the heater 10. The user interface comprises a plurality of user-operable buttons for enabling a user to control various functions of the heater 10, a display for providing the user with, for example, a visual indication of a temperature setting of the heater 10, and a user interface control circuit connected to the buttons and the display. In this example, the user interface 22 is positioned on the base. In other examples, the user interface 22 could be positioned in alternative locations, such as on the air duct assembly 16. The main body section 20 is mounted on a base 24 for engaging a surface on which the heater 10 is located. The heater 10 also includes a motor and an impeller, housed within the body 12. The impeller is positioned in a primary airflow path. In use, the motor turns the impeller to draw air along the primary airflow path. The air duct assembly 16 has an annular shape, extending about a central axis X to define an opening 26. The air outlets 18 for emitting the primary airflow from the heater 10 are located towards the front of the air duct assembly 16 and arranged to direct the primary airflow towards the front of the air duct assembly 16, through the opening 26. In this example, the air duct assembly 16 defines an elongate opening 26 having a height greater than its width, and the air outlets 18 are located on the opposite elongate sides of the opening 26. In this example the maximum height of the opening 26 is in the range from 400 to 500 mm, whereas the maximum width of the opening 26 is in the range from 50 to 150 mm. The inner annular periphery of the air duct assembly 16 comprises a diffuser surface 28 located upstream of the air outlets 18. Further details of the arrangement shown in Figures 1 and 2 is provided in WO 2013150264 Al, the contents of which are hereby incorporated by reference. Figure 3 shows a cross section through the air duct assembly 16 taken along line A-A from Figure 2. The air duct assembly 16 includes an annular casing which includes a first side 32A and a second side 32B. The first side 32A and the second side 32B of the annular casing respectively define a first air cavity 34A and a second air cavity 34B. The first and second air cavities 34A, 34B are fluidly connected to an opening (not shown) in the base of the air duct assembly 16. The opening in the base of the air duct assembly 16 is fluidly connected to the opening at the upper end of the base 20. The primary airflow exiting the main base 20 may then flow to the first and second air cavities 34A, 34B. The primary airflow is therefore bifurcated into a first airflow through the first air cavity 34A and a second airflow through the second air cavity 34B. The specific arrangement show in Figure 3 is one example and is not intended to be limiting. The air duct assembly could be a casing having any shape suitable for the design of a particular heater. In one example, the casing could include a single airflow path with a single air inlet and a single air outlet. Various positions and orientations could be adopted to direct air in a particular direction. A common feature between different examples is the use of at least two heater elements placed in series, such that the airflow passes through one heater element before the other. In this sense, one heater element is upstream, and one heater element is downstream. Several heater elements (three or more) could be arranged in this manner to provide various levels of heating. In one example, a single airflow path is provided through a series of heater elements, and a single air inlet and a single air outlet is provided. In an alternative example, a single airflow path through the heater elements may include a plurality of air inlets and / or a plurality of air outlets. For example, several air outlets could enable the air to be directed in several directions. The first side 32A of the annular casing includes a first air outlet 18 A. Within the first side 32A a first heater channel 36A is defined by first guide wall 30A and a first internal heater wall 38A. The first airflow flowing through the first air cavity 34A passes along the first heater channel 36A and out of the first air outlet 18A. A first heater array 40A is positioned within the first heater channel 36A. The first heater array 40A includes a first upstream heater element 42A and a first downstream heater element 44A. The first upstream heater element 42A and the first downstream heater element 44A are arranged physically in series. The first airflow flowing through the first heater channel 36A passes firstly through the first upstream heater element 42A and secondly through the first downstream heater element 44A before exiting the air duct assembly 16 the via first air outlet 18A. A similar arrangement is used on the second side 32B of the annular casing. The second side 32B of the annular casing includes a second air outlet 18B. Within the second side 32B a second heater channel 36B is defined by second guide wall 30B and a second internal heater wall 38B. The second airflow flowing through the second air cavity 34B passes along the second heater channel 36B and out of the second air outlet 18B. A second heater array 40B is positioned within the second heater channel 36B. The second heater array 40B includes a second upstream heater element 42B and a second downstream heater element 44B. The second upstream heater element 42B and the second downstream heater element 44B are arranged physically in series. The second airflow flowing through the second heater channel 36B passes firstly through the second upstream heater element 42B and secondly through the second downstream heater element 44B before exiting the air duct assembly 16 the via second air outlet 18B. The heater elements 42A, 42B, 44A, 44B are all electrically coupled to a heater controller. The heater elements 42A, 42B, 44A, 44B may all have the same power rating. The term power rating refers to the maximum value of power that may be delivered by each heater element. In instances where a heater element may only deliver one level of heating, the power rating is the value of power used by the heater element to deliver that level of heating. Alternatively, the upstream heater elements 42A, 42B may share the same power rating, which may be different to the power rating shared by the downstream heater elements 44A, 44B. The heater elements 42A, 42B, 44A, 44B may be formed from positive temperature coefficient, PTC, ceramic material. The heater elements 42A, 42B, 44A, 44B are not limited to the use of PTC ceramic material, and other suitable types of heater elements may be used. The electrical connections and modes of operation will be described in more detail below. Figure 4 is a block diagram sharing a heater control system 50 in accordance with an example of the disclosure. The heater control system 50 includes the first and second heater arrays 40A, 40B. Figure 4 also shows the first and second upstream heater elements 42A, 42B and the first and second downstream heater elements 44A, 44B. All of the heater elements are all coupled to a neutral terminal 52. The neutral terminal 52 is coupled to a neutral line of a local power supply within the main body 20. The heater control system 50 also includes a live terminal 54 which is coupled to a live line of a local power supply within the main body 20. The live terminal 54 is coupled to a power supply unit, PSU, 56 which is configured to convert the incoming supply voltage to a suitable voltage for use with the heater elements 42A, 42B, 44A, 44B. The heater control system 50 also includes a heater controller 58. The heater controller 58 is coupled to the PSU 56 and is configured to deliver power to the heater elements. The heater controller 58 includes a first connection 60A to the first and second upstream heater elements 42A, 42B and a second connection 60B to the first and second downstream heater elements 44A, 44B. The heater controller 58 is therefore able to independently control the upstream and downstream heater elements. The heater control system 50 also includes a system controller 59 and the user interface 22 (also shown in Figure 1). The user interface 22 is coupled to the system controller 59 which is coupled to the heater controller 58. In an alternative example, the heater controller 58 may be coupled to each heater elements independently, therefore allowing all the heater elements to be controlled independently. The heater controller 58 includes a plurality of switches for controlling the heater elements. In one example, the heater controller 58 may include one switch for each heater element. The switches may be any type of power switch suitable for switching heater elements. For example, the switches may be high power MOSFETs or TRIACs. Other suitable arrangements will be apparent. In the examples shown in Figures 3 and 4, the upstream heater elements 42A, 42B have the same or substantially similar power ratings as the downstream heater elements 44 A, 44B. As such, a similar level of heating is achieved with either the upstream heater elements 42A, 42B or the downstream heater elements 44A, 44B. In this context, “substantially similar” accounts for the degree because of manufacture. For example, the upstream heater elements 42A, 42B and downstream heater elements 44A, 44B may all be operated to within 5% of a target power. The user interface 22 includes a number of switches or buttons to enable a user to control the heater 10. For example, the user interface 22 may include an on / off switch and a heating mode switch. When the heater 10 is switched on the motor drives the impeller to draw air along the primary airflow path. The details of the operation off the motor and impeller are omitted here for clarity. Further details of the motor and impeller are provided in WO 2013150264 Al. The user interface 22 may also include a switch or button to enable a user to select the speed of the motor. In the present example, the user interface 22 allows the user to select three heating modes. These modes are: a) no heat; b) low heat; and c) high heat. In one example, the heater 10 may be controlled wirelessly. For example, the heater 10 may include a wireless interface which may use WiFi (TM) or a short-range radio protocol such as Bluetooth (TM). The wireless interface may form part of the user interface 22 and perform the function of the on / off switch or the heating mode switch. A user may therefore control the heater 10 using a dedicated wireless control or a mobile device such as a mobile phone. The operation of the heater 10 will now be described in connection with Figure 5. In a first step SI00 a user switches the heater on using the user interface 22. In response to this, the motor turns the impeller to draw air through the heater 10. Air is expelled by the air outlet 18 causing air to circulate in the room within which the heater 10 is placed. In a next step SI02 the user selects the heating mode using the user interface 22. The user may select a) no heat; b) low power; or c) high power. In an alternative example, the user may be able to select a medium power option. If the user selects no heat, the heater controller 58 turns off all of the heater elements (SI04). If the user selects low power, the heater controller 58 turns on the first and second downstream heater elements 44A, 44B, and turns off the first and second upstream heater elements 42A, 42B (SI06). In an alternative example, in low-power mode the heater controller 58 may tum on the first and second upstream heater elements 44A, 44B, and turn off the first and second downstream heater elements 42A, 42B. If the heater elements all have the same power rating, then either the upstream or downstream heater elements may be turned on. If the upstream and downstream heater elements have different power ratings, this may determine which heater elements are switched on in low-power mode. If the user selects high power mode, all the upstream and downstream heater elements are turned on (SI08). In this arrangement, the air heated by the heater 10 is heated in a more uniform manner. Because the upstream and downstream heater elements are all arranged physically in series within their respective heater channels, all the air flowing in the first and second airflow paths passes through both heater elements. This ensures that all of the air is heated uniformly. In contrast, if the heater elements were arranged physically partially or completely in parallel (i.e. side by side), in high heat mode different parts of the airflow would be heated to different degrees. Figure 6 is a representation of the heater elements 42A, 42B, 44A, 44B the accordance with a further example of the present disclosure. The heater elements shown in Figure 6 are shown schematically and are not intended to accurately represent the size, shape or any other real-world parameters associated with the heater elements. In this example, the first and second upstream heater elements 42A, 42B have a first power rating and the first and second downstream heater elements 44A, 44B have a second power rating. In this example the first power rating is larger than the second power rating. This may be achieved by using larger PTC heater elements for the upstream heater elements 42A, 42B. This is shown in Figure 6 by the larger boxes representing the upstream heater elements 42A, 42B. Assuming a combined power output of 100% the upstream heater elements may contribute 60% or greater of the overall power whereas the downstream heater elements may contribute 40% or less of the overall power. In a further example, the upstream heater elements may contribute 70% or greater of the overall power whereas the downstream heater elements may contribute 30% or less of the overall power. In a further example, the upstream heater elements may contribute 80% or greater of the overall power whereas the downstream heater elements may contribute 20% or less of the overall power. The power rating of the heater 10 will depend on the country in which the product is sold. For example, in the UK, the maximum total heater power may be around 2200 Watts. The minimum total heater power may be around 1100 Watts. In Japan, the maximum total heater power may be 1500 Watts and the minimum total heater power may be around 500 Watts. In a low-power mode the first and second downstream heater elements 44A, 44B are switched on and the first and second upstream heater elements 42A, 42B are switched off. In a medium-power mode the first and second upstream heater elements 42A, 42B are switched on and the first and second downstream heater elements 44A, 44B are turned off. In a high-power mode the first and second upstream heater elements 42A, 42B and the first and second downstream heater elements 44A, 44B are all turned on. In a further example, the downstream heater elements 44A, 44B may provide a greater power contribution than the upstream heats elements in the same ratios as noted above. In a further example, each of the heater arrays 40A, 40B may include three of more heater elements. This arrangement may provide a greater range of heating modes than the above-described examples. 5 The above examples are to be understood as illustrative. Further examples are envisaged. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the examples, or 10 any combination of any other of the examples. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. A heater, comprising:at least one air inlet and at least one air outlet, wherein an airflow path is defined between the at least one air inlet and the at least one air outlet;an airflow generator configured to draw air through the air inlet and along the airflow path;a plurality of heater elements positioned in the airflow path for heating the air flowing along the airflow path, wherein the plurality of heater elements are positioned in series with respect to each other, in the airflow path;a control unit configured to operate the plurality of heater elements in a first mode in which a first number of the plurality of heater elements are switched on and in a second mode in which a second number of the plurality of heater elements are switched on, the second number being higher than the first number.

2. A heater according to claim 1, wherein the plurality of heater elements is two heater elements, and the first number is one and the second number is two3. A heater according to claims 1 or 2, wherein the first mode is a low-power modeand the second mode is a high-power mode.

4. A heater according to any preceding claim, wherein the plurality of heater elements each have a substantially similar power rating.

5. A heater according to any of claims 1 to 3, wherein the plurality of heater elements includes a first heater element having a first power rating and a second heater element having a second power rating higher than the first power rating.

6. A heater according to claim 5, wherein the first mode includes switching on the first heater element without the second heater element switching on, and the second mode includes switching on the first and second heater elements; wherein the control unit is further configured to operate the plurality of heater elements in a third mode inwhich the second heater element is switched on without the first heater element switching on.

7. A heater according to any preceding claim, wherein the plurality of heater elements is a plurality of positive temperature coefficient heater elements.

8. A heater according to any preceding claim, further comprising a user interface configured to allow the user to select a mode of operation from a range of user selectable modes of operation comprising at least the first and the second modes.

9. A heater according to claim 8, wherein the user interface includes at least one physical switch configured to allow the user to switch the heater between at least the first and second modes.

10. A heater according to any preceding claim, wherein the control unit includes a plurality of heater switches, coupled to the plurality of heater elements, and configured to switch the plurality of heater elements on or off based on the mode of operation.

11. A heater according to any preceding claim, wherein the at least one air outlet comprises two air outlets, wherein a first airflow path is defined between one of the two air outlets and the at least one air inlet, and a second airflow path is defined between another one of the two air outlets and the at least one air inlet.

12. A heater according to claim 11, wherein the plurality of heater elements is a first array of heater elements positioned in the first airflow path, and the heater further comprises a second array of heater elements positioned in the second airflow path for heating the air flowing along the second airflow path.

13. A heater according to claim 12, wherein the second heater element array includes a plurality of heater elements arranged in series in the second airflow path.

14. A heater according to claim 13, wherein the control unit is further configured to operate the second heater element array such that in the first mode the first number of the plurality of heater elements are switched on and in the second mode the second number of the plurality of heater elements are switched on.

15. A heater according to any of claims 12 to 14, wherein each of the first and second heater element arrays include a first and a second heater element, and the control unit includes a first switch arrangement, coupled to the first heater elements of the first and second heater element arrays, and a second switch arrangement, coupled to the second heater elements of the first and second heater element arrays.

16. A heater according to any preceding claim, further comprising an air duct assembly; wherein the at least one air outlet is formed in the air duct assembly, and the air duct assembly defines at least one cavity within which the plurality of heater elements are positioned.

17. A heater according to claim 16, further comprising a base supporting the air duct assembly, wherein the airflow generator is positioned within the base, and the airflow path is defined between the base and air duct assembly.

18. A heater according to any preceding claim, wherein the control unit is further configured to control the airflow generator to adjust a rate of flow of the air along the airflow path.

19. A method of controlling the heater of any of claims 1 to 18, the method comprising:operating, using the control unit, the plurality of heater elements in the first mode in which the first number of the plurality of heater elements are switched on; oroperating, using the control unit, the plurality of heater elements in the second mode in which the second number of the plurality of heater elements are switched on; wherein the second number being higher than the first number.

20. A fan assembly comprising a first heater element and a second heater element arranged in series in an airflow path of the fan assembly; wherein the fan assembly further comprises an airflow generator configured to move air along the airflow path; wherein the fan assembly is configured to operate in a low-heat mode in which the first 5 heater element is switched on and a high-heat mode in which the first and second heater elements are switched on.

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