POINT-OF-USE INDUCTION WATER HEATER

Abstract

A point of use induction water heater has a water receiving space arranged between an inlet and outlet, and at least one inductor coil disposed in the water receiving space, arranged to become submerged by water flowing between the inlet and outlet. At least one conductive body is also contained in the water receiving space, and arranged to be inductively heated by the inductor coil upon driving of the coil with a current.

Claims

1. A point of use induction water heater for installation in-line with a water supply pipe, for heating water flowing through the water heater between an inlet and an outlet thereof, the water heater comprising: a water receiving space arranged between the inlet and outlet; at least one inductor coil contained in the water receiving space and being configured, in use, to be in contact with and to be submerged by water flowing between the inlet and the outlet; and at least one electrically conductive body contained in the water receiving space, and configured for magnetic inducement therein of electrical currents through driving of the at least one inductor coil, the electrical currents for heating the conductive body, to thereby heat water flowing in use between the inlet and outlet.

2.-15. (canceled)

16. A water heater as claimed in claim 1, wherein the water heater further comprises a capacitor electrically coupled with the at least one inductor coil, to thereby form a resonant circuit with the at least one inductor coil, the resonant circuit having an electrical resonance frequency.

17. (canceled)

18. (canceled)

19. A water heater as claimed in claim 16, wherein the capacitor is arranged in thermal communication with the water receiving space for transferring heat to water flowing through said water receiving space between the inlet and outlet.

20. A water heater as claimed in claim 19, wherein the water receiving space is enclosed by an electrically conductive housing, an interior surface of the housing arranged to contact water passing through the water receiving space between the inlet and the outlet, and the housing configured to be inductively heated in use by the at least one inductor coil upon driving of current through the at least one inductor coil, and the capacitor is arranged wrapped co-axially around the outside of electrically conductive housing, in thermal communication with, but electrical isolation from, the housing.

21. A water heater as claimed in claim 19, wherein the capacitor is contained within the water receiving space, electrically insulated from water flowing through the space, and in thermal communication with passing water.

22. A water heater as claimed in claim 21, wherein the capacitor defines an annular shape with a central bore, and the capacitor arranged in the water receiving space such that the central bore defines a water flow channel arranged for receiving water flowing between the inlet and the outlet, and optionally wherein the water heater further comprises an array of radial heat dissipation fins within the central bore, thermally coupled to the capacitor, for coupling heat to water passing through the central bore.

23.-25. (canceled)

26. A water heater as claimed in claim 16, wherein: the water heater comprises a power input connector for receiving a DC power input from outside the water heater, the water heater comprises a local DC-AC conversion means configured to receive and transform the DC power input into an AC electrical drive signal for driving the at least one inductor coil, and the water heater is configured to provide said AC electrical drive signal to the resonant circuit for driving the at least one inductor coil.

27. A water heater as claimed in claim 26, wherein said AC electrical drive signal has a frequency matching said electrical resonance frequency of the resonant circuit.

28. A water heater as claimed in claim 26, wherein the DC-AC conversion means comprises one or more transistors, the one or more transistors preferably being insulated gate bipolar transistors (IGBTs).

29. A water heater as claimed in claim 26, wherein: the water heater comprises an electrical filter means electrically connected between the DC-AC conversion means and the power input connector, and configured to inhibit transmission of AC signal components from the DC-AC conversion means toward the power input connector; or the DC power input signal is a pulsed DC power input signal, and the DC-AC conversion means is configured for transforming said pulsed DC power input signal into said AC drive signal for driving the at least one inductor coil.

30. (canceled)

31. A water heater as claimed in claim 26, wherein the water heater includes a heat dissipation means thermally coupled to the DC-AC conversion means, and adapted to dissipate heat generated by the DC-AC conversion means.

32. A water heater as claimed in claim 26, wherein the DC-AC conversion means is arranged in thermal communication with the water receiving space, for transferring heat to water flowing through said water receiving space between the inlet and outlet.

33. A water heater as claimed in claim 32, wherein the DC-AC conversion means is arranged in thermal communication with the water receiving space via a heat transfer element of which at least a portion is arranged for making contact with the water flowing in use between the inlet and the outlet.

34. A water heater as claimed in claim 33, wherein the heat transfer element is shaped to define a central bore, and arranged such that the central bore defines a water flow channel arranged, in use, for receiving water flowing between the inlet and the outlet, for transferring heat from the DC-AC conversion means to the water passing through the water flow channel.

35. A water heating system comprising: one or more water outlets for providing outflow of water; a respective water heater as claimed in claim 1; installed in-line with each of said one or more water outlets for supplying each water outlet with heated water; and a remote generator arrangement, arranged in electrical communication with each of the respective water heaters, and configured to provide a power supply signal to each of the respective water heaters for electrically powering at least the driving of the at least one inductor coil of each water heater.

36. A water heating system as claimed in claim 35, wherein the remote generator arrangement is configured to output a DC power supply signal to each respective water heater, and preferably wherein the remote generator arrangement is arranged to receive an AC power input and comprises AC-DC conversion means configured to convert said AC power input into an output DC power supply signal for provision to each of the respective water heaters.

37. (canceled)

38. A water heating system as claimed in claim 35, wherein: the remote generator arrangement comprises a primary power input for receiving input power from outside the generator, and further comprises one or more batteries; and the remote generator arrangement comprises control means configured for selectively implementing: a charging mode in which a battery is charged via power received through the primary power input, and said primary power input is used for generating each of said power supply signal(s) for provision to each of the respective water heaters; and a battery draw mode in which stored power in the battery is used as a secondary power input for use in generating each of said respective power supply signals, either alone or in addition to the primary power input.

39. A water heating system comprising: a plurality of water outlets for providing outflow of water; and a respective point-of-use water heater as claimed in claim 1 installed in-line with each of said water outlets for supplying each water outlet with heated water.

40. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0187] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0188] FIG. 1 shows an isometric view of an example water heater according to one or more embodiments;

[0189] FIG. 2 shows a cross-section through the example water heater of FIG. 1;

[0190] FIG. 3 shows an exterior view of the example water heater of FIG. 1;

[0191] FIGS. 4-5 illustrate an example inductor coil arrangement for use in a water heater according to one or more embodiments;

[0192] FIG. 6 shows an exploded view of the example water heater of FIG. 1;

[0193] FIGS. 7-9 illustrate the magnetic field strength distribution around an example inductor coil as implemented in one or more embodiments;

[0194] FIG. 10 illustrates water flow velocity through a water flow channel of an example water heater according to one or more embodiments;

[0195] FIG. 11 illustrates advantageous flow channel widths for a heater according to one or more embodiments;

[0196] FIGS. 12 and 13 illustrate a further example water heater according to one or more embodiments, the heater incorporating a resonant capacitor;

[0197] FIGS. 14-16 show views of an example capacitor for inclusion within an example water heater according to one or more embodiments;

[0198] FIGS. 17-18 illustrate electrical connection of an example inductor coil arrangement to a capacitor for use in a water heater according to one or more embodiments;

[0199] FIGS. 19 and 20 illustrate a further example water heater according to one or more embodiments, the heater incorporating a DC-AC conversion means;

[0200] FIG. 21 shows a further view of electrical components of the heater embodiment of FIGS. 19 and 20;

[0201] FIG. 22 shows the DC-AC conversion means of the heater of FIGS. 19-20;

[0202] FIG. 23 shows a further view of electrical components of the heater embodiment of FIGS. 19 and 20; and

[0203] FIG. 24 schematically illustrates the electrical arrangement of an example water heating system in accordance with one or more embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0204] The invention will be described with reference to the Figures.

[0205] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0206] The invention provides a point of use induction water heater having a water receiving space arranged between an inlet and outlet, and at least one inductor coil disposed in the water receiving space, arranged to contact water flowing between the inlet and outlet. At least one conductive body is also contained in the water receiving space, and arranged to be inductively heated by the inductor coil upon driving of the coil with a current.

[0207] As noted above, typical heaters have the induction coil external to the water heating space. By locating the inductor coil inside the fluid receiving space, two main benefits are achieved. First, Joule heat generated by the coil can be usefully used for heating water, as it is directly transferred to water passing over the coil as it journeys from the inlet to the outlet. Second, there is enabled the possibility, according to certain embodiments, of providing coils in close proximity to more than one target conductor, or even interleaving coils and conductor bodies, which enables greatly enhanced heating density and output.

[0208] Furthermore, typical heaters with the inductor coil external to the water receiving space require auxiliary means for cooling the induction coil, or dissipating the heat generated, e.g. with a heat sink. By locating the coil in fluid contact with flowing water, the water itself performs the heat sink function.

[0209] FIGS. 1-3 illustrate a first example point of use induction heater in accordance with one or more embodiments of the present invention. FIG. 1 shows a cut away isometric view illustrating an interior of the unit. FIG. 2 shows a cross-sectional view along an axial plane of the heater. FIG. 3 shows an isometric view of an exterior of the unit.

[0210] The heater 12 comprises an inlet 18 and an outlet 20 with a water receiving space 22 defined between the inlet and outlet. In the example of FIG. 1, the water receiving space 22 is formed by an inner cavity or chamber defined within an outer housing 14, the outer housing being formed by an electrically conductive tubular body 32, the tubular body being covered at each axial end by respective cover members 33a, 33b. The inlet 18 and outlet 20 fluidly connect to respective axial ends of the tubular housing, each extending through a respective one of the cover members.

[0211] In some examples there may further be provided an electrically insulative outer casing which wraps around the (electrically conductive) housing 14 enclosing the water receiving space. This may include for instance a plastic insulating layer wrapping around the housing 14. This may further be covered by a metal outer shell. The metal outer shell is preferably grounded when installed, for safety.

[0212] Mounted within the water receiving space 22 are two inductor coils 26a, 26b, having differing outer (helical) diameters and co-axially arranged with respect to one another. The inductor coils are arranged in the water receiving space so as to make contact with water flowing in use between the inlet 18 and the outlet 20. As shown, the windings (i.e. turns) of each coil are axially spaced from one another, forming water flow spaces between neighbouring windings.

[0213] Although in the particular example of FIG. 1, there are two inductor coils, this is not essential, and the heater may in other examples comprise any other number of conductor coils, greater or fewer. The coils are co-axially arranged in the example of FIG. 1, providing a particularly space efficient arrangement. However, this arrangement is not essential, and in other examples, different arrangements may be provided.

[0214] Also mounted in the water receiving space are two co-axially arranged electrically conductive tubes 30a, 30b. These, in combination with the tubular body 32 of the housing 14, define within the water receiving space an arrangement of outer annular flow channels 28a, 28b, co-axially arranged with respect to one another, surrounding an inner axial flow channel 34. In each of the annular flow channels is disposed a separate one of the inductor coils 26a, 26b. In this way, the inductor coils are arranged co-axially inset between the conductor tubes, and arranged in respective annular flow channels formed by the conductor tubes.

[0215] Although only two inner submerged conductor tubes 30a, 30b are shown in the example of FIG. 1, in further examples any number of conductor tubes, one or more, may be provided. For example, more conductor tubes may be added, each additional conductor tube providing an additional annular flow channel defined with respect to a neighbouring tube.

[0216] A first (and radially outer-most) annular flow channel 28a is formed by a radial spacing between an inner wall of the tubular body 32 of the housing 14, and an outer wall of the first conductor tube 30a. A second annular flow channel is formed by a radial spacing between an inner wall of the first conductor tube 30a and an outer wall of the second conductor tube 30b. The axial inner channel 34 is formed by a tubular interior space of the second conductor tube 30b.

[0217] The conductor tubes 30a, 30b, and in this example the tubular body 32 of the outer housing 14, are each tubular bodies of an electrically conductive material. They act as targets for the inductor coils 26a, 26b and are arranged to become inductively heated by the inductor coils upon driving of the inductor coils with alternating current. In particular, they are arranged such that driving of the inductor coils induces electric currents (eddy currents) in the conductor tubes. These currents act to heat the conductor tubes, thereby heating water flowing through the various flow channels 28a, 28b, 34.

[0218] As illustrated in FIG. 1 and FIG. 2, the annular flow channels 28a, 28b and the inner axial flow channel 34 are connected in fluid series with one another, defining a single continuous flow path between the inlet and outlet via the plurality of connected channels. More particularly, the channels are connected end-to-end to, thereby defining a labyrinthine flow path between the inlet and outlet.

[0219] To facilitate this labyrinthine flow arrangement, and end cap 36 is provided closing one end of the first tubular conductor body 30a. In particular, the end cap closes an upper end, adjacent the inlet 18. The lower end of the first inner tubular conductor 30a is open, and arranged to stop short of a base of the water receiving space 22, thereby defining a fluid connection path between a radial outer-most 28a of the annular flow channels and a next radially adjacent annular flow channel 28b.

[0220] The second 30b of the inner conductor tubes (co-axially inset within the first 30a) is directly connected at a lower end to the outlet 20. This end is thus effectively closed or sealed to the immediate water receiving space around it. The upper end of the second inner conductor tube is open, and extends to a point axially short of the capped upper end 36 of the first conductor tube 30a, thereby forming a clearance space between the two and defining a fluid connection path between the second annular flow channel 30b and the inner axial flow channel 34.

[0221] A flow route of water through the water receiving space 22 during operation is illustrated in FIG. 2. In use, water is received into the water receiving space 22 via the inlet 18. The water is directed around the outside of the first conductor tube 30a (being baffled by the end cap 36) and into the (radially outer-most) first annular 28a flow channel. The water flows through the first annular flow channel, making contact with, and fully submerging, the first inductor coil 26a. The water then flows to the second annular flow channel 28b via the connected lower ends of the two channels, and makes contact with and submerges the second inductor coil 26b as it flows through the second annular flow channel. The water then flows to the inner axial flow channel 34 via the connected upper ends of the two channels 28b, 34, and flows along this axial channel directly to the outlet 20 of the water receiving space, the axial channel lower end being directly connected to the outlet.

[0222] Hence the water passes along a labyrinthine flow path through the water receiving space, making contact both with the walls of conductor tubes and the inductor coils as it passes. Hence heat is transferred to the water from both of these elements.

[0223] FIGS. 4-5 show the inductor coils 26a, 26b in more detail. FIG. 4 shows a perspective view of the inductor coils. FIG. 5 shows a second perspective view.

[0224] The two inductor coils 26a, 26b are each formed by a conductive wire or winding which winds helically between lower and upper axial ends. This may be formed of an electrically conductive core, e.g. a wire or other conducting strand. The coil should be rigid enough to retain its shape.

[0225] The two inductor coils 26a, 26b are connected in electrical series via a bridge section 52 at a lower end of the coils. This bridge section is shaped so as (in the assembled device) to loop down and underneath a lower circumferential rim of the first inner conductor tube 30a positioned between the two inductor coils.

[0226] Although not shown in FIG. 1, 2 or 4, in the assembled heater unit 12, the upper ends 21 of the two inductor coils 26a, 26b are connected to upper connecting parts which provide for electrical connection of the coils to outside of the heater unit. These connecting parts are arranged to extend to outward of the water receiving space through the wall of the outer housing 14 via an opening 27. This allows for electrical connection to the coils.

[0227] FIG. 6 shows an exploded view of the example water heater of FIGS. 1-5 above. It can be seen how the simple construction of coaxially inset tubes and coils provides for very straightforward assembly. The various annular components can be installed or mounted one by one, each part fitting co-operatively in annular fashion within or around the other components. Despite the simple construction, a relatively complex flow path arrangement is nonetheless created.

[0228] In use, the coils are each driven with an alternating current of the same frequency. The coils are connected in series in this example, thereby facilitating concurrent driving of the two coils in phase with one another.

[0229] Upon driving the inductor coils 26a, 26b with the oscillating current, an alternating magnetic field is created about each coil. The field runs cyclically around each part of the coil line, and the fields across the whole coil superpose to create a net axially directed field running axially through the centre of the coil spiral. This field is received by the electrically conducting tube(s) 30a, 30b, 32 disposed radially spaced from the coil. The alternating field in turn induces in each of the conductor tubes (by Faraday's law) alternating currents (eddy currents) circulating about the around directionality of the field. These eddy currents cause heating (joule heating) in each conductor tube, which heat is then, during operation, transferred to water passing through the various flow channels 28a, 28b, 34 which the tubes define between them.

[0230] Disposing the conductor tubes 30a, 30b coaxially inset between the inductor coils 26a, 26b makes use of a proximity effect to maximise the strength of induced currents in the conductor tubes. In particular, for each given coil, the regions of minimum field strength are those directly between the different loops of the coil line. This is because the current in each loop runs in the same direction, and hence, the magnetic field created around each loop line circulates in the same direction.

[0231] This is shown schematically in FIG. 7, which illustrates a cross section through a set of four loop turns 25 of a particular coil 26. Radial (r) and axial (z) directions are illustrated. The circulating magnetic fields are illustrated with dotted lines. As can be seen, in the region between each neighbouring pair of turns 25, the fields are directed in opposite directions, and hence destructively superpose and substantially cancel out. The field strength in this region is minimal. By contrast, in the region just radially offset from the coil, the fields are all aligned in the same direction and hence constructively interfere to generate a region of maximal magnetic field (aligned in an axial direction).

[0232] The simulated field strength (intensity) distribution for the example portion of the inductor coil shown in FIG. 7 is illustrated in FIG. 8. FIG. 9 shows the same field strength distribution chart with slightly different shade gradations, for clarity. The magnetic field strength for each shade of grey (in units of Amperes per metre) is indicated in the respective accompanying key for each chart.

[0233] It can be seen that the highest field strength is in the region immediately radially adjacent the coils (to the left and right in the figure), with minimal field strength being in the region between coils.

[0234] In embodiments of the present invention, the conductor tubes 30a, 30b and preferably also the tubular body 32 of the housing 14 are placed in positions slightly radially offset from the inductor coils 26a, 26b, and hence in positions of maximal field strength. The field strength declines with increasing radial distance from the coil. Hence by placing each tube immediately radially adjacent a respective inductor coil, each tube is exposed to a field of maximal field strength and induced heating eddy currents in each tube have maximal strength. Hence inductive heating is maximised.

[0235] It is possible according to embodiments of the present invention to place multiple interior conductor tubes 30a, 30b each immediately radially adjacent a respective inductor coil 26a, 26b because the inductor coils are disposed inside the water receiving space 22. This therefore allows for coaxial stacking of inductor coils immediately adjacent coaxially arranged conductor tubes within the heating space—something not possible when all inductor coils are confined outside the chamber, and hence disposed remote from the interior conductor tubes.

[0236] Furthermore, the arrangement of coaxially inset inductor coils 26a, 26b and conductor tubes 30a, 30b, 32 of embodiments of the present invention means that for at least a subset of the conductor tubes, the tube is arranged sandwiched between a pair of respective inductor coils. Advantageously, the coaxially arranged coils 26a, 26b may be electrically supplied and/or configured or designed such that a current supplied through radially neighbouring coils runs in circumferentially opposite directions. In this way, the fields of the radially neighbouring coils constructively interfere within the radial spacing between the coils. This then leads to a double proximity effect for the conductor tube, as the conductor tube is placed in a region of maximal field strength of two inductor coils, where the two fields combine constructively.

[0237] As discussed above, the conductor tubes 30a, 30b, in combination with the outer housing 14 define within the water receiving space 22 an arrangement of annular flow channels through which water is forced to flow en route between the inlet and outlet. This narrow labyrinthine flow path increases flow velocity of water past the heating elements.

[0238] This is advantageous for purposes of heat transfer to the water, as heat transfer rate into a fluid increases as the velocity of the fluid increases. By way of illustration, FIG. 10 shows a simulated velocity flow diagram for water flowing through a section of one annular flow channel 28, the channel having an inductor coil 26 disposed centrally therein. The figure shows a cross-section through the example flow channel, with the cross-sections through a set of four loops 25 of the coil illustrated.

[0239] As shown, the flow velocity through the flow channel 28 is greatest in the outer regions of the flow channel, radially adjacent the inductor coil 26, and lowest in the regions between respective inductor coil loops 25. This is beneficial, since this outer region of the flow channel is disposed between both the inductor coil 26 and the conductor tube 30, 32 bounding the channel. Hence water flowing through this part of the channel makes contact with both the conductor tube wall and inductor coil outer surface. Hence the fastest flow region (and hence that for which heat absorption rate into water is greatest) is the region in which water makes contact with both heat source surfaces at the same time.

[0240] In advantageous examples, annular cross-sections of the annular flow channels 28 are adapted to provide uniform flow velocity through each channel, i.e. the cross-sections are configured such that there is equal flow velocity through each channel. This is advantageous to ensure balancing of water pressure drop through the different channels, and also to ensure equalising of heat absorption rate in each channel (since heat transfer rate is dependent on water flow speed). Preferably, the flow velocity through the annular flow channels and also the axial flow channel are all rendered the same. In this way, velocity is constant throughout the heater.

[0241] The flow velocity is primarily a function of the cross-sectional flow area through a given channel. The cross-sectional flow area means the cross-sectional area through each channel through which water flows in use. To provide substantially equal flow velocity through each flow channel 28, the flow channels may be provided having substantially equal cross-sectional flow area.

[0242] The cross-sectional flow area may in examples be approximated as the total cross-sectional area of a channel minus the cross-sectional area occupied by the respective inductor coil 26 in the given flow channel (since water cannot flow through this region).

[0243] Since the circumferences of the flow channels 28, 34 declines for channels more radially inward, maintaining constant cross-sectional flow area requires that annular radial widths of channels more radially inward are larger than those more radially outward.

[0244] This is illustrated schematically in FIG. 11 which shows a cross-section through the heater arrangement of FIGS. 1 and 2 above. The radially outer annular flow channel 28a having larger circumference is provided having a smaller radial width than the radially more inward annular flow channel 28b, i.e. r.sub.2>r.sub.1.

[0245] By way of simple example, where each channel is approximately circular in cross-section, for equal cross-sectional area through each channel, the following should hold: r.sub.3.sup.2=r.sub.5.sup.2−r.sub.4.sup.2=r.sub.7.sup.2−r.sub.6.sup.2.

[0246] To then ensure equal cross-sectional flow area, the area occupied in each channel by the respective inductor coil 26 should also be taken into account, i.e. subtracted from the area of each channel, i.e. r.sub.3.sup.2=(r.sub.5.sup.2−r.sub.4.sup.2)−(coil 26b area)=(r.sub.7.sup.2−r.sub.6.sup.2)−(coil 26a area).

[0247] By way of one advantageous example, the flow channel cross-sections may be adapted to provide a flow velocity through each channel of around 1.0-1.5 m/s. This provides an ideal balance between pressure drop across each channel and also efficient heat transfer.

[0248] By way of one example, each flow channel 28, 34 may be provided with a cross-sectional area of between 1.2 cm.sup.2 and 2.2 cm.sup.2 (0.00012-0.00022 in.sup.2).

[0249] According to an advantageous set of embodiments, the dimensions of the coil and the electrically conductive tubes are adapted such that the heat transfer rate (power deposition) per unit area to the water from the conductive tubes substantially matches the heat transfer rate per unit area from the inductor coils. This has the effect that the surface temperature of each coil across all points is substantially equal to the surface temperature of each of the conductive tubes at every point. This equalises the heat transfer into the water by each of the coils and conductive tubes and avoids occurrence of local hot-spots which might lead to local water boiling.

[0250] This may be achieved by providing the inductor coils 26 and conductive tubes 30a, 30b, 32 such that the ratio of the total water-contacting surface area of the set of inductor coils to the total water-contacting surface area of the set of conductive tubes 30a, 30b, 32 is equal to the ratio of the total power deposition (to the water) of the set of inductive coils to the total power deposition of the set of conductive tubes. The total power deposition of the coils means the total heat transfer (to the water) per unit time of the set of inductive coils. The total power deposition of the inductive tubes means the total heat transfer (to the water) per unit time of the set of conductive tubes.

[0251] By way of example, simulations performed for one embodiment of the heater have found that the relative effective power deposition (to water) of the inductor coils 26a, 26b is larger than that of the conductive tubes 30a, 30b, 32, by approximately 20-30%.

[0252] Hence, according to one or more examples, the inductor coils 26a, 26b may be provided such that the set of coils together have a total water contacting surface area larger than a total water contacting surface area of the set of conductive tubes 30a, 30b, 32. In particular, in preferred examples, the set of coils together have a total water contacting surface area between 20-30% larger than a total water contacting surface area of the set of conductive tubes 30a, 30b, 32.

[0253] This means that for each unit of supplied power, that power is spread over a substantially equal water-contacting area for the coils and for the tubes. Hence the higher power deposition of the coils is balanced by a larger surface area across which that power is spread.

[0254] Maintaining the power deposition ratio and the total surface area ratio aligned ensures substantially equal surface temperature on the coil and conductive tube heat transfer surfaces. This substantially avoids the risk of water boiling due to surface temperature hot-spots caused by a large power deposition in a relatively small area.

[0255] According to advantageous embodiments, the heating unit 12 may further comprise a capacitor coupled to the inductor coil(s) 26 to form with the coil(s) a resonant circuit having a resonance frequency. For ease of reference, such a capacitor, forming part of a resonant circuit in combination with the at least one coil, may be referred to in this disclosure as a resonant capacitor.

[0256] The coupled coils 26a, 26b and capacitor together form a resonant LC circuit.

[0257] As discussed above, coupling an inductor coil with a capacitor to form a resonance circuit significantly increases electrical efficiency of the device. In use, energy can oscillate or resonate back and forth between the storage capacities of the coil and the resonant capacitor. This means that energy input into the inductor coil (to drive generation of a field) is not lost upon its discharge from the coil. Instead the energy is transferred to the resonant capacitor before being discharged back again to the inductor coil. Only ‘top-up’ energy need be supplied to the circuit, to compensate the energy actively transferred into the conductive bodies by magnetic induction, and resistive losses in the wires.

[0258] The resonance frequency is a function of both the capacitance, C, of the capacitor and the inductance, L, of the inductor. The angular resonance frequency, coo, in a simple circuit may for instance be determined from the standard equation ω.sub.0=1/√{square root over (LC)}, where C is capacitance of the capacitor and L is inductance of the inductor coil.

[0259] Resonance of the circuit, and thus the energy conservation, is only achieved when the circuit is driven at its resonance frequency.

[0260] Hence, in accordance with one or more embodiments, the heating unit 12 may further comprise a local generator or controller adapted to drive the inductor coil at said resonance frequency, i.e. drive the coil with an alternating current having a frequency equal to said resonance frequency. Alternatively, the heater 12 may be arranged to receive from outside the heater an alternating drive signal suitable for driving the inductor coil at resonance.

[0261] Different arrangements are possible for the resonant capacitor.

[0262] In advantageous arrangements, the water heater may comprise an electrically insulative outer casing, the casing housing or encasing the water receiving space, and the resonant capacitor being contained also within the casing.

[0263] The resonant capacitor may be contained within the water receiving space itself, or may be outside of the water space but still within the insulative casing, for instance in an isolated cavity formed within the casing, separated from the water receiving space.

[0264] In either case, by locating the capacitor within the electrically insulated outer casing, all of the reactive power of the heating device is confined within the outer housing or casing. The only power which need be supplied from outside the heating unit outer housing are those required to ‘top-up’ the resonant circuit with power lost through actual heating of the water and those required to initially charge the resonant circuit (i.e. ‘active power’).

[0265] In known arrangements, the capacitor is typically positioned outside or remote from the heater 12, (for example close to a generator unit). However, this necessitates that the connecting cable transport not only the active electrical loads (associated with the energy transferred into the water), but also the reactive electrical loads, passing between the capacitor and the inductor. This incurs associated safety and cost issues.

[0266] Enclosing all reactive power within the heater unit casing enables safer power transfer from the mains power source to the point of use, as only active power need be transferred.

[0267] In advantageous examples, the capacitor is arranged to be in thermal communication with the water receiving space 22 for transferring heat to water flowing through said space between the inlet and outlet.

[0268] Charging and discharging of the capacitor leads to internal heat generation within the capacitor. In typical inductive heating devices, this heat is wasted, and furthermore causes problems as it must be dissipated to avoid overheating, e.g. with a heat sink or other cooling means. By arranging the capacitor such that it is thermally coupled with the water receiving space, this heat may instead be usefully captured and utilized for contributing to water heating. The thermal coupling with the water also solves the problem of heat dissipation, providing integrated heat sinking via the water.

[0269] In one set of examples, the capacitor may be arranged inside the water receiving space, electrically insulated from water flowing through the space, and in thermal communication with passing water.

[0270] One example water heater 12 according to such an embodiment is illustrated in FIG. 12 and FIG. 13. FIGS. 14-16 show the example capacitor employed in this example. FIGS. 17 and 18 show the inductor coils 26a, 26b and the electrical connection arrangement between the coils and the capacitor.

[0271] The example water heater 12 is substantially the same as that described above with reference to FIGS. 1 and 2, apart from the further inclusion in the water receiving space 22 of a capacitor 62, and the additional electrical connections provided between the inductor coils 26a, 26b and this capacitor. There is also provided an electrically insulative outer casing 64 which wraps around the (electrically conductive) housing 14 enclosing the water receiving space.

[0272] The outer housing 14 has been extended slightly at the end adjacent the inlet 18, to provide space to fit the capacitor. The arrangement of the conductor tubes 30a, 30b, and inductor coils 26a, 26b and also the flow channel arrangement defined by the conductor tubes within the water receiving space 22 are all the same as in the example of FIGS. 1 and 2. These will therefore not be discussed in detail again here. All details and options described above in relation to the example of FIGS. 1 and 2 may be applied also to the present embodiment.

[0273] The outer casing 64 provides an electrically insulative enclosure to ensure safe electrical isolation of all electrical parts inside. For example, the casing wall may include a plastic insulating layer wrapping around the housing 14 enclosing the water receiving space. This may further be covered by a metal outer shell. The metal outer shell is preferably grounded when installed, for safety.

[0274] The capacitor 62 is arranged in the water receiving space 22 immediately adjacent the inlet 18. The capacitor has an annular shape, extending annularly around a central bore 66 defined through the capacitor, this bore forming a water flow channel through which water received into the water receiving space may flow, making thermal contact with the capacitor as it passes. An array of radial heat dissipation fins is provided within the central bore 66 for improving thermal transfer between the capacitor and the passing water. These can be seen more clearly in FIG. 14 for instance. The fins may be formed of any thermally conductive material, such as metal.

[0275] The capacitor 62 is arranged with the water flow channel formed by the central bore 66 directly connected with the inlet 18 of the water receiving space 22. In this way, the capacitor receives and makes contact with the water when it first enters the water receiving space, and hence when it is at its coolest. This is preferred in this case, since heat transfer into a fluid is maximal when the temperature difference between the fluid and the heat source is greatest. In general, the heat generated by the capacitor will be lower than that generated by the coil 26 and the inductively heated tubes 30a, 30b. Hence, this less hot component should make contact with the water when it too is less hot, to optimise overall heat transfer into the water. The hotter coil 26 and tubes 30 will be able to transfer heat to the water even after it is warmed by the capacitor.

[0276] As the water flows in through the inlet 18 and through the capacitor 62 bore 66, heat is transferred from the capacitor to the water. Upon flowing out of the bore 66, the water follows the same fluid flow path as in the example of FIGS. 1 and 2. This flow route is schematically illustrated in FIG. 13. The route is described in detail above, with reference to FIG. 2.

[0277] The capacitor is encased in a water-tight sealing or casing to prevent ingress of water internally into the capacitor. The casing or sealing is also electrically insulative, i.e. including an electrically insulating material.

[0278] The capacitor 62 is shown in detail in FIGS. 14-16. FIGS. 14 and 15 show isometric and cross-sectional views respectively through a centre of the capacitor. FIG. 16 shows an exterior view of the capacitor.

[0279] The central bore 66 is visible more clearly in FIG. 14. The array of radial fins 68 is also shown. The fins each are coupled to an interior wall of the capacitor bore 66.

[0280] The water-tight casing 70 or sealing of the capacitor 62 can be seen more clearly in FIGS. 14 and 16. This forms a fluid tight and electrically insulative shell around the capacitor.

[0281] Protruding from an axial end of the capacitor 62 are two electrical connectors 82a, 82b for electrically coupling the capacitor to the inductor coils 26a, 26b and the power source.

[0282] Electrical connection between the inductor coils 26a, 26b and the capacitor 62 is illustrated in FIGS. 17 and 18. The inductor coils themselves and their arrangement relative to one another is the same as in the example of FIGS. 1-2 and 4. The only difference is in the arrangement of the electrical connecting parts. In the present embodiment, the coil 26b is coupled directly to the capacitor electrical connector 82b via a connection loop 84b. The capacitor electrical connector with opposite polarity 82a connects to the connection loop 84a which is then routed out of the heater through an opening 27. The inner induction coil 26a is routed out of the heater via an arcuate connecting arm 83 and through opening 27. In alternative examples, the inner induction coil and/or connection loop 84a may be routed to a further space within the heater for connection for instance to further electrical components in the heater, e.g. DC-AC conversion means.

[0283] In the particular example of FIGS. 12-13, the capacitor 62 is provided disposed within the water receiving space 22. This maximises heat transfer efficiency. However, this arrangement is not essential. In other examples, the capacitor may for example be disposed inside an electrically insulative outer housing and separated from the water receiving space. The capacitor may be thermally coupled with water flowing through the water receiving space 22. For example, in some arrangements for instance the water receiving space may be contained within a water heating chamber, at least a portion of an outer wall of the chamber being thermally conductive, and the capacitor arranged thermally coupled to, i.e. in direct contact with, said at least portion of the chamber wall. For instance the capacitor may wrap around the outside of this chamber wall.

[0284] By way of one example, a suitable capacitor may be provided having a capacitance of between 0.2-1.2 μF, preferably between 0.3-0.5 μF, even more preferably, 0.35-0.45 μF, for example 0.41 μF. Any suitable conductive material may be used for the capacitor conductor, such as copper. Any suitable dielectric may be used, for example Polyamide. Suitable layer thickness for the conductor may be for instance be in the order of 0.05 mm, for instance, 0.02-0.08 mm. Suitable layer thickness for the conductor may be for instance be in the order of 0.02 mm, for instance, 0.01-0.07 mm.

[0285] A further example water heater in accordance a further set of embodiments is shown in FIGS. 19-23. FIG. 19 and FIG. 20 show isometric part cut-away and sectional views respectively of the heater. FIGS. 21-23 shows further views illustrating the DC-AC conversion means, the inductor coils and the capacitors.

[0286] The example water heater 12 is substantially the same as that shown in FIG. 12 and FIG. 13 apart from the further inclusion in the heater of a DC-AC conversion means and a filter capacitor 118 connected between a power input connector 114 and the DC-AC conversion means, and also the rearrangement of the resonant capacitor 62 within the heater housing. These features will be further explained below.

[0287] In accordance with this set of embodiments, the water heater 12 further comprises a DC-AC conversion means 110 located inside the outer housing or casing 64 of the heater, for converting a received DC power input signal into an AC drive signal for driving the at least one inductor coil 26a, 26b at resonance.

[0288] The DC-AC conversion means in this example takes the form of a set of four insulated gate bipolar transistors (IGBTs) 110 connected together in H-bridge configuration. However other DC-AC conversion means may alternatively be used. The DC-AC conversion means is located at one axial end of the water heater, axially adjacent the water receiving space 22.

[0289] The heater 12 comprises a power input connector 114 which extends from outside the insulative outer casing 64 of the heater 12 to inside the heater enclosure. The power input connector is for example for receiving a DC power input signal from outside of the heater. The power input connector is electrically connected to a filter capacitor 118, which in this example is advantageously arranged extending co-axially around the outside of housing 14 which encloses the water receiving space 22. As discussed in relation to embodiments above, this housing is preferably electrically and thermally conductive, and preferably forms one 32 of the conductive tubes arranged to become inductive heated upon driving of the inductor coils 26a, 26b.

[0290] The filter capacitors 118 filter the high frequency pulsations generated by the DC-AC conversion means 110, isolating these from the power input connector 114, and in use, any electrically upstream components from the power input connector, such as a generator.

[0291] As a result, a stable, non-pulsating DC electrical signal will then be transported through the power cable toward the point of use heater 12.

[0292] The filter capacitor 118 is however optional and may be omitted in alternative examples, in which case the input DC power signal may be routed straight to the DC-AC conversion means 110.

[0293] The filter capacitor 118 is electrically connected to the DC-AC conversion means 110, such that the DC-AC conversion means receives from the filter capacitors the filtered DC power input signal. The DC-AC conversion means converts this received DC signal into an output AC drive signal for actively driving the inductor coils 26a, 26b. More particularly it preferably generates an output AC drive signal having a frequency substantially matching the resonance frequency of the resonance circuit comprised of the inductor coils 26a, 26b, and the connected capacitor 62 (referred to herein as a resonant capacitor).

[0294] The AC drive signal generated by the DC-AC conversion means 110 is routed to the resonant circuit comprising the inductor coils 26a, 26b and connected resonant capacitor 62, to thereby drive the inductor coils for thereby causing inductive heating of the conductive tubes 30a, 30b, 32 in use.

[0295] Electrical connections between components of the heater are facilitated at least in part by means of a PCB 122, to which at least a portion of the components are connected.

[0296] This heater is thus suitable for receiving a DC power input signal, and generating an AC drive signal for driving the coils. The water heater in accordance with this set of embodiments may be suitable for example for use within a water heating system which comprises a generator arrangement located remote from each of one or more point of use heaters (for example remote from the point of use area of each heater unit), and wherein the central generator performs some or all of the electrical processing required in generating the drive signal for supply to the at least one inductor coil, for driving the coil at resonance.

[0297] For example this heater may be suitable for use within a heating system having a remote generator in which the remote generator for example processes an incoming mains supply into a rectified DC signal, and then supplies this DC signal as a DC power input signal for each of one or more point of use heaters comprised by the system.

[0298] Similar to the filter capacitors 118, the resonant capacitor 62 is in this example advantageously arranged wrapped co-axially around the outside of the conductive outer housing 14, this housing forming an outer-most one 32 of the conductive tubes.

[0299] The resonant capacitor 62 and filter capacitors 118 are thermally coupled with the water receiving space 22 via the thermally and electrically conductive outer housing 14. They are thermally coupled to, but electrically isolated from the outer housing. They may be arranged in direct physical contact with the outer housing, with, for example an electrically insulative outer covering of the capacitor electrically isolating it from the housing.

[0300] There may also be provided a mechanical protective casing 120 for the capacitors 62, 118 located within the electrically insulative outer casing 64. The outer casing 64 encloses around the full assembly of electrical components and the water receiving space.

[0301] The IGBTs of the DC-AC conversion means 110 are arranged in thermal communication with the water receiving space 22, for transferring heat to water flowing through said water receiving space between the inlet 18 and outlet 20.

[0302] More particularly, IGBTs 110 are arranged in thermal communication with the water receiving space via a heat transfer element 112 having at least a portion arranged for making contact with the water flowing in use between the inlet and the outlet. The heat transfer element comprises a thermally conductive body which has a heat output surface in contact with water flowing through the heater, and thermally couples the IGBTs with the water in use, while keeping the IGBTs electrically isolated from the water. The heat transfer element provides a heat sink for the IGBTs.

[0303] The heat transfer element 112 and the IGBTs 110 of the inverter are shown in more detail in FIG. 22. In this example, the heat transfer element 112 is in the form of a metal block with external square or rectangular cross section. The inverter components (the IGBTs) are coupled to different respective outer surfaces of the block. The heat transfer element features a central longitudinal bore 116, such that the coupled inverter components 110a-110d are arranged annularly around this bore, and thermally coupled to an inner surface of the bore via the heat transfer element body.

[0304] The heat transfer element 112 may, by way of one example, be formed of a stainless steel or aluminium. There may be provided an electrical insulation material between each IGBT (or other transistor elements) and the heat transfer element surface. The heat transfer element, in use, is preferably in thermal connection with the IGBTs and, simultaneously, in thermal communication with the flowing water.

[0305] The heat transfer element 112 is arranged such that the central bore 116 forms a water flow channel arranged for receiving water flowing in from the inlet 18. Thus the incoming relatively cold water flows through the bore of the heat transfer element, prior to entering the water heating space 22 in which the inductor coils 26a, 26b and the conductive tubes 30a, 30b, 32 are located. Heat is thus transferred away from the IGBTs into the water.

[0306] By placing the DC-AC conversion means 110, the resonant capacitor 62 and the filter capacitor 118 in thermal communication with the water, two advantages are achieved. First, cooling of these devices is performed, thus negating the need for any auxiliary cooling means to cool the components. Second, the otherwise wasted heat dissipated by these components is efficiently harnessed for contributing to the heating of the flowing water.

[0307] DC-AC inverters typically present heat losses due to the switching efficiency and due to Joule heating. These losses are typically dependent on the switching frequency, the calibration of the frequency to the required resonant frequency, and the electrical current. In high power applications, these inverters (typically H-bridge IGBTs) often require external means of cooling. These are often fan and heat sinks for low and medium power applications and water coolers for medium to high power applications.

[0308] By advantageously placing the inverter in the point of use heater and in thermal contact with the flowing water via an electrically insulating heat sink, the need for auxiliary active cooling means is avoided.

[0309] In addition to the thermal efficiency benefits, the location of these components at the point of use (and preferably inside the heater outer casing 64) enables important electrical and safety benefits. By placing the inductor coils 26, the resonant capacitor 62, and the DC-AC conversion means within the point of use area, all high frequency alternating currents will be confined to this space.

[0310] The external diameter of the heater housing and electrically insulative outer casing 64 has been increased for the present set of embodiments (compared to that of FIGS. 12-13 for example) to accommodate the two capacitors 62, 118 and the mechanical protection cover 120 over them. This also provides the required space at the inlet end to accommodate the DC-AC inverter heat transfer element 112 and the inverter components 110 as well as the power printed circuit board (PCB) 122 that features power and drive signal connections. This power PCB is advantageously thermally coupled to an exterior surface of the outer housing 14 of the water receiving space, for example the cover member 33a. This provides cooling for the PCB.

[0311] In use, the incoming water in this advantageous embodiment firstly flows through the bore 116 of the heat transfer element 112, efficiently cooling the main DC-AC converter 110 components installed in thermal contact with the heat transfer element 112. It then flows into the water receiving space 22, firstly passing through an initial upper area, arranged in thermal contact with the power PCB 122 via cover member 33a. This enables extraction of waste heat generated by the PCB.

[0312] Water then flows through the outer-most annular flow channel 28a, beneficially cooling the resonant capacitor 62 and the filter capacitor 118 as it passes, these components being arranged in thermal communication with the outer housing 14 (outer conductive tube 32) as discussed. Water will also absorb heat generated by the inductor coil 26a and the two conductive tubes 32, 30a through driving of coils with the AC drive signal. The remainder of the flow path is substantially identical to previously described embodiments, and so will not be described in detail.

[0313] The arrangement of the conductor tubes 30a, 30b, and inductor coils 26a, 26b and also the flow channel arrangement defined by the conductor tubes within the water receiving space 22 are all the same as in the example of FIGS. 1 and 2, and FIGS. 19 and 20. These will therefore not be discussed in detail again here. All details and options described above in relation to the example of FIGS. 1 and 2 may be applied also to the present embodiment.

[0314] Further options will now be described which may be applied to any of the above described embodiments.

[0315] When a wire or conductor is driven with a high frequency alternating current, a so-called skin effect occurs, wherein current density through the wire is concentrated at a radial periphery of the wire. This has the effect that Joule heating in the wire is maximized at regions toward the radial periphery, i.e. toward the radial outer surface (or ‘skin’) of the wire.

[0316] This has two effects. First, the maximum temperature to which the wire is heated is increased as the current is concentrated in a smaller volume toward this periphery, instead of across the whole wire cross-section. Secondly, due to concentration of Joule heating at the periphery, heat transfer out of the wire (both radiative, convective and conductive), is increased as more of the heat is concentrated at areas more thermally proximal the radial surface.

[0317] In typical inductive heating devices, both of these effects cause problems for the inductor coil winding, as they increase the burden on heat dissipation means for keeping the coil cool.

[0318] According to embodiments of the present invention, these effects are beneficial, since the internal heat generated by the coil is actively used for the heating of the water and hence enhanced thermal transfer out of the conductive line of the coil is advantageous. In embodiments of the present invention, the skin effect occurs in both the inductor coil, but also correspondingly in the conductor tubes 30a, 30b inductively stimulated by the coil. Hence both elements benefit from surface-concentrated heating.

[0319] According to one or more particular examples, the at least one inductor coil may be driven with an alternating current having frequency of at least 10 kHz, preferably at least 20 kHz, more preferably at least 40 kHz, even more preferably at least 60 kHz. These high frequencies help facilitate the skin effect.

[0320] As noted above, in typical inductive heating devices, it is desired to minimize the above-described skin-effect in the inductor coil, in which current is concentrated toward a radial surface of the inductor coil wire. At least partially for this end, typically copper is used for the coil material. Copper has high electrical conductivity and is non-magnetic. These two properties minimize the skin effect.

[0321] According to embodiments of the present invention, it may be beneficial to enhance the skin effect. At least partially for this purpose, according to one or more embodiments, the inductor coil may be formed from a magnetic stainless steel material, e.g. martensitic or ferritic stainless steel. Many example materials within the group of martensitic stainless steels will be known to the skilled person.

[0322] More broadly, Joule heating may be enhanced in the inductor coil by providing the inductor coil(s) and/or the conductor tubes (or other conductive bodies) formed of any high resistivity magnetic material (high compared for instance to copper). Martensitic stainless steels represent one group of such materials.

[0323] According to any embodiment of the present invention, the heater may further comprise a temperature sensor for sensing temperature of water within the water receiving unit. Outputs of the sensor may be used by a further provided controller for instance to regulate the drive signal provided to the inductive coils 26a, 26b.

[0324] An example temperature sensor 78 is illustrated in the example of FIG. 12. The temperature sensor is disposed at an outlet 20 end of the water receiving space 22. Two temperature sensing wires or probes 80 are provided extending across the water outlet for sensing the temperature of water as it leaves the heater (i.e. after it has been heated).

[0325] A control loop may be implemented whereby the frequency, duty or power supplied to the inductor coils is varied in dependence upon a sensed temperature of the water, with the power being increased for cooler water, and decreased for hotter water. In this way, over-heating of the water can be avoided. The control loop may be configured to maintain the water at a defined temperature, or within a defined range, for instance defined by a thermostat setting.

[0326] Due to the instantaneous nature of the heating which is provided by point of use heaters, water temperature adjustments can be performed extremely rapidly. There is no lag-time normally associated with tank based systems. Furthermore, the induction based heating mechanism also allows for rapid temperature adjustments, since the main source of heat (induction) can be altered almost instantaneously. Unlike with traditional resistive heating elements for instance, lag time waiting for the heating element to cool after the current is removed is substantially reduced.

[0327] According to one or more embodiments, at least the one or more conductive bodies (e.g. conductive tubes 30a, 30b 32) of the heater may be formed of a magnetic material having a magnetic relative permeability of at least 800. This very high magnetic permeability allows for conductor targets (e.g. tubes 30) to be provided of very low thickness (e.g. less than 1 mm) while still maintaining high magnetic induction responsiveness in the targets.

[0328] By contrast, in known arrangements, the conductive targets are provided of a certain minimum thickness to enable sufficient ‘pick-up’ of magnetic fields in the targets and thereby avoid interaction between opposed inductor coil turns. By instead increasing magnetic permeability, this thin body problem can be avoided, allowing for much thinner conductor targets and thus substantial weight and material use reductions.

[0329] Advantageously, according to one or more embodiments, the water heater 12 may be further powered by a battery capable of powering the inductor coil(s) 26 for a certain period. The battery may be configured to recharge during periods when sufficient mains power is available. Providing a battery connected in parallel with or instead of the mains input allows the unit to run on its own power. This is useful for instance to allow multiple heating units in a given dwelling to run at the same time without overloading the dwelling power draw limit. One or more of the units may run temporarily, either totally or partially, on the battery power.

[0330] The battery may be provided remote from the heater 12 according to certain examples, and electrically connected to the heater for supplying power when needed. A single battery may service more than one heater in a building or dwelling for instance.

[0331] A high performance lithium battery may for example be used.

[0332] In use, a point of use water heater 12 according to any embodiment of the present invention may installed in-line with an existing cold-water feed, or installed within a water tap or water tap unit for instance. The water heater can be installed directly adjacent, i.e. directly upstream from, the particular water outlet point which is to be supplied by the unit. The unit draws water directly from this cold water feed and outputs hot water, heated substantially instantaneously by the unit.

[0333] Examples in accordance with a further aspect of the present invention provide a water heating system comprising: a plurality of water outlets for providing outflow of water; and

[0334] a respective point-of-use water heater in accordance with any embodiment or example described above or in accordance with any claim of this application, the water heater installed in-line with each of said water outlets for supplying each outlet with heated water.

[0335] The plurality of water outlets of the water heating system may be hot water supply points, i.e. supply points where water may be drawn from the system e.g. by a user, for use by the user. Each inductor heater is installed in-line with one of the plurality of water outlets (or water supply points), meaning it is installed for instance in-line with a water supply pipe leading to the water outlet (or supply point) for heating water as it passes through said pipe en route to the respective water outlet of the system.

[0336] Examples in accordance with a further aspect provide a water heating system comprising:

[0337] one or more water outlets for providing outflow of water;

[0338] a respective point-of-use water heater 12 in accordance with any example or embodiment outlined above or described below, or in accordance with any claim of this application, installed in-line with each of said water outlets for supplying each outlet with heated water; and

[0339] a remote or central generator arrangement, arranged in electrical communication with each of the respective point-of-use water heaters, and configured to provide a power supply signal to each of the heaters for electrically powering at least the driving of the at least one inductor coil of each heater.

[0340] The electrical configuration of one example water heating system in accordance with one set of embodiments is schematically illustrated in FIG. 24.

[0341] The system comprises a remote central generator arrangement 130 located in a convenient central location, remote from each of a set of N point of use water heaters, each installed locally in-line with a respective water outlet (not shown). The system comprises at least one water heater, but preferably a plurality of water heaters.

[0342] Each respective water heater 12 and connected water outlet are located within a respective point of use area, and the generator 130 is located in a generator area, the generator area for example being remote from each point of use area. Purely by way of example, it may for instance be spaced from each point of use area by a distance of at least 2 m, for example at least 3 m, for example at least 5 m.

[0343] In the illustrated example, the remote generator arrangement 130 is configured to output a DC power supply signal to each water heater, and each heater is configured for receiving a DC power input signal from the generator and processing this to generate an AC drive signal for driving the inductor coils of the heater. Each heater 12 may by way of example be a heater in accordance with the embodiment of FIGS. 19-23.

[0344] The central generator arrangement 130 receives a mains AC power input. The generator comprises an AC-DC conversion means (an AC-DC rectifier) 134 configured to convert said AC power input into an output DC power supply signal for provision to each of the respective water heaters 12. The generator preferably further comprises a bank of DC smoothing capacitors 136 electrically connected between the AC-DC rectifier 134 and the output connector 140 of the generator arrangement 130. This acts to smooth or even out fluctuations in the output DC signal. A smoothing capacitor is a well-known electrical component, and the skilled person will know how to implement this component.

[0345] The central generator arrangement 130 is electrically connected to each of the one or more point of use heaters 12, preferably by one or more connecting wires 144, such that each heater is arranged to receive the DC power supply signal output from the generator arrangement.

[0346] In this example system, each point of use heater 12 comprises a DC-AC conversion means 110 configured to transform the received DC power supply signal into an AC drive signal having a frequency suitable for driving the inductor coils 26. The inductor coils are coupled to a capacitor 62 to form a resonant circuit with the capacitor. The AC drive signal may be generated having a frequency substantially matching a resonance frequency of said resonant circuit.

[0347] Thus, the elements transforming the DC signal into a high frequency AC drive signal are located in close proximity to or within each point of use heater unit 12, rather than located at the central generator. This means that the high frequency alternating electrical signal transmission is limited to the point of use area, more preferably to inside the heater enclosure.

[0348] Furthermore, the AC-DC rectifier is located centrally, meaning that there is no need for a separate high power mains connection to be provided to each heater 12. A single mains connection can be provided to the central generator. The heaters do not include any AC-DC conversion means between the power input connection of each heater and the DC-AC conversion means.

[0349] The cable or any other electrical connection means 144 that transports the electrical power from the induction generator 130 to the point of use heater 12 may, in this described embodiment, transport the power in a DC pulsating form, which limits the potential external electromagnetic induction hazard. The cable or any other electrical transport device may be provided with electromagnetic shielding in this case to prevent the cable causing interference in surrounding devices. High frequency pulsation, despite its DC nature (non-alternating), may induce noise and/or heating into the surrounding equipment and structures.

[0350] In further advantageous examples, each water heater 12 may further comprise an electrical filter means, such as one or more filter capacitors, electrically connected between the DC power input point of the heater and the DC-AC conversion means 110. This inhibits transmission of AC signal components from the DC-AC conversion means toward the input connector.

[0351] In this way the high frequency pulsations will be filtered out from the electrically upstream components of the system, i.e. the cable 144, and the power mains and components of the generator. A stable, non-pulsating DC electrical signal will then be transported through the cable connecting the generator and the point of use heater, advantageously avoiding the need for any specially shielded or coaxial cables. This is also optimal from a safety point of view.

[0352] Although in the particular example system of FIG. 24, the DC-AC conversion means 110 is positioned locally at each point of use heater, this is not essential. In an alternative set of embodiments for example, DC-AC conversion means may be provided at the central generator arrangement 130, such that the generator arrangement generates an AC drive signal suitable for driving the inductor coils 26 of each point of use heater. This signal is then transported to each heater via the electrical connection 144. In this case, the heaters do not include any DC-AC conversion means between the power input connection of each heater and the resonant circuit comprising the inductor coils 26 and the resonant capacitor 62. In this set of embodiments, each heater may be a heater in accordance with the embodiment of FIGS. 12-13 for example.

[0353] In accordance with either embodiment, the central generator may in advantageous examples optionally include an auxiliary battery 138. This may be provided connected in parallel with the smoothing capacitor bank 136. The battery is preferably a lithium battery, preferably having a power rating of at least 12 KW, preferably between 12-16 KW, and preferably having a charge capacity of at least 120 Ah and more preferably between 120-200 Ah.

[0354] The battery 138 can be used to supplement the primary mains power supply during periods of high demand, e.g. when multiple water heaters 12 are drawing power from the generator 130 simultaneously. For example, in a domestic dwelling, at periods of high demand, required total water heating power may be between 18-24 KW. For example a typical domestic gas boiler has a maximum power output of 24 KW. This power draw may exceed the maximum possible mains power draw of the dwelling. The battery thus may allow the mains power to be supplemented at times of peak demand.

[0355] Smart charging of the battery may be implemented. For example, the generator arrangement 130 may comprise control means, e.g. a controller or processor, configured for selectively implementing [0356] a charging mode in which the battery 138 is charged via power received through the primary main power input, and said primary power input is used for generating each of said power supply signal(s) for provision to each of the respective water heaters 12; and [0357] a battery draw mode in which stored power in the battery is used as a secondary power input for use in generating each of said respective power supply signals, either alone or in addition to the primary power input.

[0358] In accordance with preferred embodiments, the water heating system may comprise a control means (either the same or different to the above control means) configured for controlling the AC frequency of the AC drive signal supplied to the resonant circuit of each water heater 12 for driving the at least one inductor coil of each. The AC drive signal is output by a DC-AC conversion means 110 which may be located centrally at the remote generator 130, or a separate DC-AC conversion means may be included as part of each heater. In either case, the control means may control generation of one or more guide signals indicative of a target AC frequency output of the DC-AC conversion means, wherein the DC-AC conversion means is adapted to generate an output AC drive signal in accordance with the guide signal indicated frequency.

[0359] This control means may be centrally located at the remote generator arrangement 130, and wherein the one or more guide signals are communicated to each of the one or more heaters via a wired or wireless connection.

[0360] Alternatively, at least part of the control means 130 may be distributed among the one or more water heaters 12.

[0361] The system may further comprise a user interface device permitting a user to adjust one or more settings related to operation of the heaters. For example, the system may permit a user-controllable maximum power of each heater 12, and/or a maximum water temperature of each heater. These may be implemented by the central generator by means of regulating the power level of the output power supply signal provided to each heater.

[0362] The control means may comprise a processor being loaded with a computer program configured when executed for implementing the various control and/or battery charging functions discussed in this disclosure.

[0363] Optionally, the remote generator arrangement 130 may for example be located in a different room to each of the point of use water heaters 12. It may optionally be located at a minimum distance from each of the water heaters, for instance at least 2 m from each of the water heaters, for example at least 3 m from each of the water heaters, for example at least 5 m from each of the water heaters.

[0364] Examples in accordance with a further aspect of the invention provide a point of use induction water heating method for heating water in-line with a water supply pipe, the method comprising:

[0365] receiving water into a water receiving space 22, the water receiving space arranged between an inlet 18 and an outlet 20;

[0366] driving at least one inductor coil 26a, 26b contained in the water receiving space 22 and arranged for making contact with (and/or to be submerged by) water flowing in use between the inlet 18 and the outlet 20 with a current to thereby magnetically induce electrical currents in at least one conductive body contained in the water receiving space for heating the conductive body, and to thereby heat water flowing in use between the inlet 18 and outlet 20.

[0367] As discussed above, certain embodiments make use of a controller or control means. The controller or control means can be implemented in numerous ways, with software and/or hardware, to perform the various functions required. A processor is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the required functions. A controller may however be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

[0368] Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0369] In various implementations, a processor or controller may be associated with one or more storage media such as volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform the required functions. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller.

[0370] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.