HEATER TANK

Abstract

 A heater tank (1; 100) for an instantaneous water heater. The heater tank (1; 100) comprising: a heater tank having a heater tank inlet (12; 112) and a heater tank outlet (14; 114) and a fluid flow path (10; 110) from the heater tank inlet (12; 112) to the heater tank outlet (14; 114); and one or more electric heating elements (16, 18, 20, 22; 116, 118) operable to heat fluid flowing, in use, along the fluid flow path (10; 110). The one or more electric heating elements (16, 18, 20, 22; 116, 118) are each located within a respective heater tube (2, 4, 6, 8; 102; 104) through which the fluid flow path (10; 110) passes. At least part of the fluid flow path (10; 110) is defined by a space between an outer surface (16a) of the heating elements and an inner surface (2a) of the heater tube in which each heating element is located. The fluid flow path (10; 110) comprises a tapered portion in which a separation distance (W) between the outer surface of at least one of the heating elements (16, 18, 20, 22; 116, 118) and an inner surface of the respective heater tube (2, 4, 6, 8; 102; 104) decreases along at least a portion of the length of the heater tube in the direction of fluid flow. The velocity of fluid flow increases along the respective length of the heater tube (2, 4, 6, 8; 102; 104) in the direction of fluid flow.

Description

[0001] This disclosure relates to a heater tank for an instantaneous water heater for use in a plumbing system such as an ablutionary system or a heating system. The disclosure also relates to plumbing systems, including ablutionary systems or heating systems, comprising such a heater tank for an instantaneous water heater.

[0002] An electric shower system is an example of an ablutionary system. Electric showers generally use an instantaneous (or continuous flow) water heater of the type in which a supply of water is heated as it passes through a heater tank to provide a source of hot water on demand. The heater tank receives an input supply of cold mains water which is heated by one or more heating elements before being output to a shower outlet such as a handset.

[0003] A problem associated with known electric water heaters is that the temperature of the water progressively heats as it passes through the heater thank. This means that at the beginning of the flow path through the heater thank the water enters the tank at a relatively cool temperature which can very effectively cool the heating elements. As the water is progressively heated it increases in temperature and becomes less effective in drawing the heat away from the surface of the heater elements. This means that further downstream the heating elements operate at a higher temperature. This effect leads to a significantly uneven rate of heat transfer along the length of the heating elements. A large disparity may be present in the surface temperature of the heating elements whereby a portion of a heater element towards the exit of the tank is significantly higher in temperature than the portion at the start of the water flow path.

[0004] The variation in heating element temperature has two main drawbacks. Firstly, peak surface temperature of the heating elements may be significantly higher than the temperature at which the formation of limescale is promoted. This leads to the formation of limescale at downstream portions of the heating elements at which the surface temperature is higher. This limescale can build up and reduce the lifespan of the heating element.

[0005] Secondly, instantaneous water heaters are also susceptible to "hot shot". Hot shot is the result of an abrupt stopping and restarting of a flow of water from an instantaneous water heater. If the flow is stopped then non-flowing water within the heating chamber may be further heated due to residual heat from the heating element(s) to an elevated temperature that could be unsafe for a user. If a flow of water is then restarted after only a relatively short delay, then the flow of water may be at the elevated temperature. The problem of a hot shot may be exacerbated by downstream portions of the heating elements having a high temperature as they are not cooled effectively during use of the shower.

[0006] In a first aspect, the present application provides a heater tank for an instantaneous water heater, comprising at least one or more of the following features:

a heater tank having a heater tank inlet and a heater tank outlet and a fluid flow path from the heater tank inlet to the heater tank outlet; and

one or more electric heating elements operable to heat fluid flowing, in use, along the fluid flow path, wherein:

the one or more electric heating elements are each located within a respective heater tube through which the fluid flow path passes;

at least part of the fluid flow path is defined by a space between an outer surface of the heating elements and an inner surface of the heater tube in which each heating element is located; and

the fluid flow path comprises a tapered portion in which a separation distance between the outer surface of at least one of the heating elements and an inner surface of the respective heater tube decreases along at least a portion of the length of the heater tube in the direction of fluid flow whereby the velocity of fluid flow increases along the respective length of the heater tube in the direction of fluid flow.

[0007] By using the geometry of the fluid flow path to cause an increase in the local fluid flow velocity as the fluid flows along the flow path the rate of heat transfer from the respective heating element can be progressively increased. This means that although the fluid will increase in temperature as it flows along the fluid flow path any reduction in the cooling of the heating element by the fluid can be offset by the increase in flow velocity (and hence increase in heat transfer rate). This means that an excessively high temperature at positions towards the most downstream part of the heating element can be avoided and/or the surface temperature may more uniform. This may help to avoid the heating element reaching a surface temperature at which limescale production is promoted. It may also reduce the risk of a hot shot occurring if the fluid flow is paused and quickly restarted.

[0008] The separation distance (and hence fluid velocity) is varied along the flow path and as such creates a relationship whereby fluid velocity (and hence heat transfer) is proportional to the water temperature along the flow path. Therefore, the disclosed water heater may be configured to heat a flow of water where downstream water having a higher-temperature flows over the heating elements more quickly and thus reduces the susceptibility to hot spots and limescale formation.

[0009] A laminar flow of fluid may be maintained along the tapered portion of the fluid flow path. The means that heat transfer is increased by the increase in fluid flow rather than by introducing turbulence to the flow.

[0010] The interior of the one or more electric heating elements and exterior of the respective heater tubes may have a circular cross section and are arranged concentrically such that the fluid flow path along each heater tube has an annular cross section. This may allow good thermal contact between the fluid and heating elements.

[0011] The electric heating element(s) and the heater tube(s) may be configured such that the outer surface of the electric heating elements is close to the inner surface of the heater tube. In this way, a small annular clearance between the electric heating elements and the heater tubes provides good heat transfer from the electric heating elements to the flow of water.

[0012] The portion of the inner surface of the heater tube forming the tapered portion of the fluid path may be tapered. The portion of the outer surface of the heating element forming the tapered portion of the fluid path may have a constant cross-sectional size. This means that the tapered shape may be formed by tapering the inner surface of the heater tube while the size of the heating element remains constant. This may aid manufacture.

[0013] In other examples, the portion of the outer surface of the heating element forming the tapered portion of the fluid path may vary over the length of the tapered portion. The heating element may therefore be tapered along its length. In this case, the inner surface of the respective portion of the heater tube may have a constant interior cross section over the length of the tapered portion. The taper may therefore be created by tapering only the heating element, rather than the surrounding heating tube. This may allow a standard heater tube to be used.

[0014] In yet other examples, the taper may be formed by tapering both the inner surface of the heating tube and the outer surface of the respective heating element along the tapered portion. This may allow a greater degree of taper to be created over a short length.

[0015] The one or more heating elements may be configured such that the fluid flowing, in use, along the fluid flow path experiences a reduction in a local electric heating element power as the fluid flows, in use, along the fluid flow path. This may reduce the surface temperature of the heating elements further downstream where the water temperature is relatively higher. This may add to the effect of the tapered portion, or may be used separately, to reduce the maximum surface temperature and/or provide a homogenous surface temperature.

[0016] The electric heating element power for a given electric heating element may be understood as the overall heating power of the given electric heating element considered as a whole. The sum or integral of the local electric heating element powers across a given electric heating element constitutes the electric heating element power for the given electric heating element.

[0017] The power density of the electric heating element(s) may be distributed unevenly along the flow path and as such creates a relationship whereby power density is inversely related to the water temperature along the flow path. Therefore, the disclosed water heater may be configured to heat a flow of water where downstream water having a higher temperature flows over heating elements having a lower power and thus reduces the susceptibility to hot spots and limescale formation.

[0018] The fluid flow path may be configured to bring fluid into contact with a series of two of more electric heating elements, in which at least one of the electric heating elements (a second heating element) has an electric heating element power that is less than that of the electric heating element (a first heating element) immediately upstream thereof. The heating power may therefore be reduced between successive heating elements.

[0019] The fluid flow path may be provided with a first tapered portion along its length spanning at least part of the first electric heating element and a second tapered portion along its length spanning at least part of the second heating element. The first and second tapered portions may be arranged to provide the same reduction in fluid flow velocity as each other. This may allow the same shaped tapered portion to be used for different heater tubes, with the change in electric power compensating for the change in starting temperature of water entering the downstream heater tube. This may aid manufacture as fewer different sizes of the heater tubes may be needed.

[0020] One or more of the electric heating elements may comprise a series of a plurality of electric heating element segments. At least one of the electric heating element segments may have an electric heating element segment power that is less than that of the electric heating element segment immediately upstream thereof.

[0021] One or more of the electric heating elements may comprise a series of up to or at least five electric heating element segments, up to or at least 10 electric heating element segments, up to or at least 20 electric heating element segments or up to or at least 50 electric heating element segments. The sum of the electric heating element segment powers within a given electric heating element may constitute the electric heating element power.

[0022] One or more of the electric heater elements may be configured such that the local electric heating element power varies continuously along at least a portion of the length of the electric heater element(s).

[0023] One or more of the electric heating elements may comprise an internal filament in the form of a helical coil.

[0024] The local electric heating element power may vary along at least a portion of the length of the electric heating element, due to changes in a helical pitch of the internal filament.

[0025] The fluid flow path may pass through a plurality of heater tubes and wherein two or more of the heater tubes may be integrally formed with each other.

[0026] The fluid flow path may pass through a plurality of heater tubes fluidly connected in flow series.

[0027] The heater thank may comprise 10, up to 20 or up to 50 heater tubes fluidly connected in flow series and forming at least a portion of the fluid flow path. The water heater may comprise two, three, four, five, six, seven, eight, nine or 10 heater tubes fluidly connected in flow series and forming at least a portion of the fluid flow path.

[0028] Two or more of the heater tubes may be arranged in parallel with each other at least in part.

[0029] At least one electric heating element many be disposed at least partially within each heater tube. Each electric heating element may be arranged within a heater tube such that fluid, e.g. water, flowing along the flow path contacts an exterior surface of each heating element. In this way, in use, thermal energy may be transferred from each electric heating element to a flow of fluid, e.g. water, flowing along the fluid flow path. One or more of the heater tubes may be straight.

[0030] In some embodiments, one or more heater tubes may not comprise an electric heating element disposed within the heater tube.

[0031] One or more of the electric heating elements may have an outer diameter of up to or at least 3mm, up to or at least 4 mm, up to or at least 5 mm, up to or at least 6 mm, up to or at least 7 mm, up to or at least 8mm, up to or at least 9 mm or up to or at least 10mm. For example, one or more of the electric heating elements may have an outer diameter of approximately 6.25 mm.

[0032] One or more of the heater tubes may have an internal diameter of up to or at least 5 mm, up to or at least 6 mm, up to or at least 7 mm, up to or at least 8 mm, up to or at least 9 mm, up to or at least 10 mm, up to or at least 11 mm, up to or at least 12 mm, up to or at least 13 mm, up to or at least 14 mm or up to or at least 15 mm. one or more of the heater tubes may have an internal diameter of approximately 12.35 mm. These sizes may correspond to the smallest internal diameter of the heater tubes (e.g. the smallest diameter of the tapered portion).

[0033] Each electric heating element may extend along a substantial portion of a given heater tube. Each tapered portion may extend along a substantial portion of its respective heating element.

[0034] A portion of each heater tube may comprise a seal separating a portion of the heater tube from the fluid flow path. A portion of each electric heating element may extend into the portion sealed from the fluid flow path. The portion of each electric heating element arranged to extend into the portion sealed from the fluid flow path may be configured to form an electrical connection to an electrical power source. In this way, each electric heating element may be configured to form an electrical connection to an electrical power source in a sealed environment. The electrical connection between an electrical power supply and each electrical heating element may be disposed in any suitable location. The sealing means may comprise any suitable means for providing a fluid-tight, e.g. watertight, seal such as, for example, one or more O-rings, or a sealant such as a silicone sealant, for example.

[0035] One or more heater tubes may comprise a portion sealed from the fluid flow path at both ends of the heater tube. In this way, each electric heating element may be configured to form an electrical connection with a wire, cable or the like at both ends. Positive connections may be located at either end of each heater tube. Neutral connections may be located at either end of each tube. All the positive connections may be located at one end of the heater tank and all the neutral connections may be located at the opposing end of the heater tank. At least one positive connection and at least one neutral connection may be located at the same end of the heater tank.

[0036] Each electric heating element may be configured to have a different electrical heating element power from any adjacent electric heating elements. Each electric heating element may have a higher electric heating element power than any electric heating elements disposed downstream. In this way, the electrical heating element disposed nearest to the heater tank inlet may have the highest power.

[0037] Each heater tube arranged in flow series may comprise a heating element, wherein each heating element has a lower power than any upstream heating element and a higher power than any downstream heating elements.

[0038] The first electric heating element may have the highest power of any electric heating elements present. Each electric heating element in flow series along the flow path may have a successively lower power than any electric heating elements disposed upstream. In this way, water flowing through the heater tubes along the flow path may be heated, in use, by heating elements having a successively lower electric heating element power.

[0039] The electric heating element(s) may have any suitable electric heating element power. A total heating power of the water heater may constitute the sum of the electric heating element power(s) of the electric heating element(s). The total heating power of the water heater may be up to or at least 4 kW, up to or at least 5 kW, up to or at least 6kW, up to or at least 7 kW, up to or at least 8 kW, up to or at least 9 kW, up to or at least 10 kW, up to or at least 11 kW, up to or at least 12 kW, up to or at least 13 kW, up to or at least 14 kW or up to or at least 15 kW. For example, the total power may be 10.8 kW.

[0040] The relative power of the electric heating elements may be configured in any suitable way. The power of the electric heating elements may be configured to provide an evenly distributed power reduction of the electric heating elements along the flow path. For example, each electric heating element may have a power that is X kW lower than the power of an electric heating element disposed immediately upstream, where X is equal to a constant numerical value. For example, each electric heating element may have a power that is X kW higher than the power of an electric heating element disposed immediately downstream, where X is equal to a constant numerical value.

[0041] The electric heating elements may be configured such that one half of the electric heating elements provide approximately 50% of the total power and the other half provide approximately 50% of the total power. For example, in an embodiment where the heater tank comprises four electric heating elements, the first and fourth electric heating elements in flow series may be configured to provide a combined 50% of the total power and the second and third electric heating elements in flow series may be configured to provide a combined 50% of the total power. In some embodiments, all of the heating elements of the heater tank, or some of the heating elements of the heater tank, may have the same electrical heating power.

[0042] The electrical heating of each electric heating element may be provided by an internal filament located within each electric heating element. Each internal filament may have a resistance and as such may be arranged to increase in temperature when an electric current passes through. Each internal filament may be arranged in a helix shape extending along a substantial portion of the length of each electric heating element.

[0043] Each internal filament may comprise a helical coil having a constant or variable pitch. The pitch of the helix may be defined as the height of one complete helix turn, measured parallel to the axis of the helix. The heating power of any electric heating element may be proportional to the helical pitch of the internal filament. In use, a current may pass through each internal filament and increase in temperature. In this way, thermal energy may be transferred to the external surface of each electric heating element which may then be operable to heat a flow of water flowing within the heater tubes.

[0044] The electrical power of each electric heating element may be determined by the conductive properties and/or configuration of the internal filament. The heating power of any portion of any electric heating element may be proportional to the helical pitch of the internal filament.

[0045] The instantaneous water heater may comprise one or more electric heating elements wherein at least one electric heating element has a variable electric power density along its length. One or more of the electric heating elements may be configured to have a power that progressively reduces along at least a portion of its length.

[0046] For internal filaments having the same conductive properties, an increase in helical pitch may provide a reduction in heating power provided and a decrease in helical pitch may provide an increase in heating power provided.

[0047] One or more electric heating elements may comprise a different internal filament helical pitch to one or more adjacent electric heating elements. Each electric heating element may comprise an internal filament having a greater helical pitch than any upstream electric heating elements. In this way, electric heating elements having different electric power to adjacent electric heating elements may be provided.

[0048] One or more electric heating elements may comprise two or more electric heating element segments. One or more of the electric heating element segments may comprise a different electrical power from one or more adjacent electric heating element segments. Each electric heating element segment may comprise a higher electric heating element segment power than any segments disposed downstream. Each electric heating element segment may have a lower power than the electric heating element segment disposed immediately upstream. The heating power of any electric heating element segment of any electric heating element may be proportional to the helical pitch of the internal filament.

[0049] One or more of the electric heating elements may comprise any suitable number of electric heating element segments, for example, at least 2 segments, or at least 3, 4, 5, 6, 7, 8, 9 or at least 10 electric heating element segments. One or more of the electric heating elements may comprise up to or at least 10 electric heating element segments, up to or at least 20 electric heating element segments or up to or at least 50 electric heating element segments.

[0050] One or more of the electric heating element segments may have a length of at least 5 mm, up to or at least 10 mm, up to or at least 50 mm, up to or at least 100 mm or up to
or at least 200 mm. One or more of the electric heating elements may have an active heated length of up to or at least 100 mm, up to or at least 200 mm, up to or at least 500 mm or up to or at least 1000 mm. The fluid flow path may have a length of at least 100 mm, up to or at least 500 mm, up to or at least 1000 mm, up to or at least 2000 mm, up to or at least 3000 mm or up to or at least 5000 mm.

[0051] The heater tank may comprise a plurality of electric heating elements where each electric heating element is divided into a plurality of electric heating element segments. The electric heating element segment located furthest upstream along the flow path may have the highest power. The electric heating element segment located furthest downstream along the flow path may have the lowest power.

[0052] One or more of the electric heating element segments may comprise a different internal filament helical pitch than one or more adjacent electric heating element segments. The heating power of any electric heating element segment of any electric heating element may be proportional to the helical pitch of the internal filament.

[0053] The internal filament may be arranged such that the helical pitch is constant along the length of each electric heating element segment. Each electric heating element segment may comprise a helical pitch that is greater than the helical pitch of the filament of any adjacent upstream electric heating element segment. In this way, the internal filament extending along each electric heating element segment may have a helical pitch greater than the section of internal filament extending along the electric heating element segment immediately upstream.

[0054] In some embodiments, the helical pitch of the internal filament may be continuously variable along the length of one or more electric heating elements and as such may be configured to provide a continuously variable electrical heating power along the length of one or more electric heating elements. The helical pitch may continuously increase along the length of one or more electric heating elements in a downstream direction.

[0055] The electric heating elements may be configured such that the electric heating element power of any electric heating element is higher than the electric heating element power of any electric heating element disposed downstream.

[0056] A second aspect provides an instantaneous water heater comprising a heater tank of the first aspect.

[0057] The heater tank may be surrounded at least partially by a casing. The casing may surround at least partially further components of the instantaneous water heater. The instantaneous water heater may include control circuitry configured to control operation of the heater tank.

[0058] The instantaneous water heater may comprise a user input means operably connected to the control circuitry configured to control operation of the heater tank.

[0059] A third aspect provides an electric shower comprising a heater tank of the first aspect or an instantaneous water heater of the second aspect.

[0060] The electric shower may be suitable to be mounted on a surface such as a wall located within, for example, a bathroom. The electric shower may be suitable for being mounted within a wall or a ceiling cavity.

[0061] A fourth aspect provides a plumbing system comprising a heater tank of the first aspect, an instantaneous water heater of the second aspect and/or an electric shower of the third aspect.

[0062] The plumbing system may be an ablutionary system. The ablutionary system may be a bath system or a shower system.

[0063] The heater tank inlet may be in fluid communication with a fluid supply, e.g. a water
supply.

[0064] The instantaneous water heater may be operable to deliver fluid, e.g. water, to one or more fluid delivery device(s) at a user-selected temperature and/or flow rate.

[0065] One or more of the fluid delivery devices may comprise a tap, a faucet, a sprayer or a shower head.

[0066] The plumbing system may be an ablutionary system, e.g. an electric shower system.

[0067] The electric shower system may comprise an electric shower unit. The electric shower unit may be configured to be mounted on a wall. The electric shower unit may comprise a casing housing the instantaneous water heater. The instantaneous water heater may be connected to a water supply point such as a plumbing supply. A hose may provide fluid communication from the instantaneous water heater to a spray head located downstream thereof. A shower tray or bath tub may be present to collect the water emitted from the spray head.

[0068] A fifth aspect provides a dishwasher or a washing machine comprising a heater tank according to the first aspect.

[0069] A sixth aspect provides a bath system or a recirculating shower system, in which a heater tank according to the first aspect is operable to heat a recirculated stream of water.

[0070] A seventh aspect provides an electric shower system comprising a waste-water heat-recovery system and a heater tank according to the first aspect or an instantaneous water heater according to the second aspect.

[0071] The waste-water heat-recovery system may be configured to transfer heat from a waste water stream to a stream of cold water, e.g. from a mains supply, being conveyed to the instantaneous water heater.

[0072] An eighth aspect provides a whole building water heater comprising a heater tank according to the first aspect or an instantaneous water heater according to the second aspect.

[0073] A ninth aspect provides a bath fill comprising a heater tank according to the first aspect or an instantaneous water heater according to the second aspect.

[0074] The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied to any other aspect.

[0075] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings:

Figure 1 shows a sectional view of a portion of a heater tank;

Figure 2 shows a sectional view of the heater tank of Figure 1;

Figure3a and 3b show cross-sectional views through a first heater tube of the heater tank shown in Figure 2, at different points along its length;

Figure 4 shows a sectional view of part of the first heater tube in which the fluid flow path has a tapered portion;

Figures 5a and 5b illustrate the change in surface temperature of a heating element within the first heater tube provided by the tapered portion of the fluid flow path;

Figure 6 shows example electric heating power values for the electric heating elements in the heater tank shown in Figure 2;

Figure 7 shows a sectional view of another example of a heater tank for an instantaneous water heater;

Figure 8 shows a sectional view of a portion of the heater tank shown in Figure 7;

Figure 9 shows example power values for the electric heating elements of the heater shown in Figure 7; and

Figure 10 shows schematically an electric shower system.

[0076] Figure 2 shows a sectional view of a heater tank 1 for an instantaneous water heater. Figure 1 shows a sectional view of a portion of the heater tank 1.

[0077] Referring to Figures 1 and 2, the heater tank 1 has a heater tank inlet 12 and a heater tank outlet 14 and a fluid flow path 10 from the heater tank inlet 12 to the heater tank outlet 14.

[0078] The fluid flow path 10 passes through, in series, a first heater tube 2, a second heater tube 4, a third heater tube 6 and a fourth heater tube 8. The first heater tube 2, the second heater tube 4, the third heater tube 6 and the fourth heater tube 8 are integrally formed with each other, although they need not be. Each one of the first heater tube 2, the second heater tube 4, the third heater tube 6 and the fourth heater tube 8 extends from a first end 7 of the heater tank 1 to a second end 9 of the heater tank 1. The first heater tube 2, the second heater tube 4, the third heater tube 6 and the fourth heater tube 8 are arranged in parallel with each other.

[0079] At a point near the first end 7 of the heater tank 1, the first heater tube 2 is in fluid communication with the heater tank inlet 12. At a point near the second end 9 of the heater tank 1, the second heater tube 4 is in fluid communication with the first heater tube 2. At a point near the first end 7 of the heater tank 1, the third heater tube 6 is in fluid communication with the second heater tube 4. At a point near the second end 9 of the heater tank 1, the fourth heater tube 8 is in fluid communication with the third heater tube 6. At a point near the first end 7 of the heater tank 1, the heater tank outlet 14 is in fluid communication with the fourth heater tube 8.

[0080] As indicated schematically by a block arrow 10' (Figure 2), the fluid flow path 10 from the heater tank inlet 12 to the heater tank outlet 14 passes through, in series, the first heater tube 2, the second heater tube 4, the third heater tube 6 and the fourth heater tube 8. In use, fluid flows in a first direction from the first end 7 of the heater tank 1 towards the second end 9 of the heater tank 1 along the first heater tube 2 and the third heater tube 6. In use, fluid flows in a second direction opposite to the first direction (i.e. from the second end 9 of the heater tank 1 towards the first end 7 of the heater tank 1) along the second heater tube 4 and the fourth heater tube 8.

[0081] A first electric heating element 16 extends longitudinally within the first heater tube 2. The first electric heating element 16 extends from the first end 7 of the heater tank 1 to the second end 9 of the heater tank 1. The first electric heating element 16 has an electric heating element power and is operable to heat fluid, e.g. water, flowing, in use, within the first heater tube 2.

[0082] A second electric heating element 18 extends longitudinally within the second heater tube 4. The second electric heating element 18 extends from the first end 7 of the heater tank 1 to the second end 9 of the heater tank 1. The second electric heating element 18 has an electric heating element power and is operable to heat fluid, e.g. water, flowing, in use, within the second heater tube 4.

[0083] A third electric heating element 20 extends longitudinally within the third heater tube 6. The third electric heating element 20 extends from the first end 7 of the heater tank 1 to the second end 9 of the heater tank 1. The third electric heating element 20 has an electric heating element power and is operable to heat fluid, e.g. water, flowing, in use, within the third heater tube 6.

[0084] A fourth electric heating element 22 extends longitudinally within the fourth heater tube 8. The fourth electric heating element 22 extends from the first end 7 of the heater tank 1 to the second end 9 of the heater tank 1. The fourth electric heating element 22 has an electric heating element power and is operate to heat fluid, e.g. water, flowing, in use, within the fourth heater tube 8.

[0085] The heater tank 1 is adapted to be fixed to a mounting surface or a structure. The heater tank 1 comprises eight regularly-spaced mounting tabs 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h. Each mounting tab 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h comprises an aperture for receiving a mechanical fixing means such as a screw.

[0086] When installed as part of an instantaneous water heater, the heater tank 1 may be surrounded at least partially by a casing (not shown) along with further components of the instantaneous water heater, e.g. control circuitry configured to control operation of the heater tank 1. A user may be able to control the flow rate and temperature of water delivered by the instantaneous water heater to a fluid delivery device downstream of the instantaneous water heater. User control of the instantaneous water heater may be facilitated by any suitable user input means operably connected to the control circuitry configured to control operation of the heater tank 1.

[0087] The electrical heating of one or more of the first, second, third and fourth electric heating elements 16, 18, 20, 22 may be provided by an internal filament located within the electric heating element 16, 18, 20, 22. Each internal filament has a resistance and as such increases in temperature when an electric current passes through. Each internal filament may be arranged in a helical coil extending along a substantial portion of the length of each electric heating element 16, 18, 20, 22. In use, as a current passes through each internal filament and increases in temperature, thermal energy is transferred to the outer surface of each electric heating element 16, 18, 20, 22.

[0088] A cross-sectional view through the first heating tube 2 is shown at two points along its length in Figures 3a and 3b. The first second, third and fourth electric heating elements of the presently described embodiment are generally of the same shape, but that may not be the case in all embodiments. Each of the first, second, third and fourth electric heating elements 16, 18, 20, 22 comprises a substantially circular cross-section as can be seen for the first heating element 16 in Figures 3a and 3b. Each of the first, second, third and fourth electric heating elements 16, 18, 20, 22 is arranged substantially concentrically within its respective heater tube 2, 4, 6, 8 and has a smaller outer diameter than the inner diameter of its respective heater tube 2, 4, 6, 8. In this way, the fluid flow path 10 has an annular cross section along a substantial portion of each heater tube 2, 4, 6, 8 defined by the space between the inner surface of the heater tube 2, 4, 6, 8 and outer surface of the respective heating element 16, 18, 20, 22.

[0089] The fluid flow path within the first heater tube 2 comprises a tapered portion in which the separation (W₁ and W₂ marked in Figures 3a and 3b) between the outer surface 16a of the first heating element 16 and the inner surface 2a of the first heater tube 2 decreases along the length of the heater tube 2 in the direction of fluid flow. Part of the tapered portion is illustrated in the longitudinal cross-section through the first heater tube 2 shown in Figure 4. The tapered portion is illustrated in Figures 3a, 3b and 4, but is not visible in Figures 1 and 2.

[0090] The separation distance W₁ and W₂ is defined as the distance from an external surface 16a of the first electric heating element 16 to an internal surface 2a of the corresponding heater tube 2, in a direction perpendicular to a longitudinal axis of the fluid flow path 10 along said heater tube as illustrated in Figures 3a and 3b. Within the tapered portion the separation W decreases along the length of the first heater tube 16 in the direction of fluid flow. This can be seen in Figure 4 by the difference in separation distances W₁ and W₂ at different points along the length of the heater tube 2. The cross section shown in Figure 3a corresponds to a cross-section through the line A-A marked in Figure 4 and Figure 3b corresponds to the cross section through line B-B. The change in cross-sections is exaggerated for ease of illustration. The direction of fluid flow is shown by the block arrows in Figure 4.

[0091] The decrease in the separation distance within the tapered portion is arranged to cause the velocity of the fluid flow to increase so that the velocity along the heater tube is different at different positions along the heater tube. More specifically, the velocity is greater at a second position compared to a first position, where the second position is downstream of the first. By increasing the fluid flow velocity the volume of fluid flow per unit time is also increased.

[0092] By changing the geometry of the heater tube along the length of the heating element the rate at which heat is transferred from the surface of the heating element to the fluid flowing past it is changed. This effect is illustrated in Figures 5a and 5b. Each of these Figures shows the temperature of fluid within one of the heater tubes (the first heater tube in this example) in the left most panel, and the surface temperature of a respective heating element (the first heating element 16) is shown in the right most panel. Both the fluid flow and heating element temperature is shown in the centre panel of each of Figures 5a and 5b, with the direction of water flow indicated by the block arrows. The colour gradient shows variation in temperature with blue corresponding to a cold temperature and red a relatively hotter temperature.

[0093] Figure 5a shows the effect of the fluid velocity remaining constant along the length of the heater tube (i.e. the velocity is V1 at both the start and end of the heater tube shown in Figure Sa). As the water enters the heating tube at a relatively low temperature it is progressively heated as it flows along the length of the heating element. At the end of the heater tube where the water is coolest the heat transfer from the surface of the heating element is greater compared to at the opposite end where the water is hottest. This reduction in the rate of heat transfer from the surface of the heating element causes its temperature to increase along its length in the direction of water flow along it. This can be seen in the colour gradient in Figure 5a. As discussed above, the surface temperature of the heating element may become excessively high at downstream positions as it is not sufficiently cooled by the surrounding fluid, which can lead to limescale formation and increased risk of hot shots if the water flow is paused and quickly restarted.

[0094] Figure 5b shows a heating tube and heating element arrangement of the present invention. Here the heater tube comprises a tapered portion as described above in which the velocity of the water flow increases with increasing distance along the heating element in the direction of fluid flow. As can be seen in Figure 5b, the velocity is different between the start and end of the tapered portion (i.e. velocity V2 is greater than V1). By increasing the velocity of water flow the rate at which heat is transferred from the surface of the heating element increases with increasing distance along its length in the direction of fluid flow. This means that the heating element can be more effectively cooled further downstream along its length, giving a more uniform surface temperature as shown by the colour gradient of Figure 5b. This may reduce the maximum temperature of the heating element to reduce the risk of limescale formation and hot shots.

[0095] To reduce the risk of limescale formation the fluid velocity may be increased such that the maximum temperature of the surface of the heating element, during use, is less than 55°C. This has been found to be the threshold at which the production of limescale is promoted.

[0096] In the presently described embodiment the tapered portion of the heating tubes is tapered to an extent such that the surface temperature of the respective heating element is homogeneous (or at least approximately homogeneous). This may allow a constant surface temperature which reduces the risk of localised limescale formation and hot shots.

[0097] Despite the change in velocity of water within the tapered portion, the geometry of the space in which the water flows may be configured to maintain a laminar flow. Heat is therefore removed more effectively from the heating elements by the increase in flow volume per unit time, rather than by adding turbulence to the flow to increase the heat transfer rate.

[0098] Referring again to Figures 3a and 3b, the first electric heating element 16 and the interior of the first heater tube 2 have a circular cross section and are arranged concentrically such that the fluid flow path along the first heater tube 2 has an annular cross section. The width of the annular cross section (corresponding to the separation distance W described above) of the fluid flow path 10 may be up to or at least 1 mm, up to or at least 3 mm, up to or at least 5 mm or up to at least 1 cm. By having a relatively small width of the annular cross section, the flowing fluid, e.g. water, may be constrained such that it all remains in close proximity to a given electrical heating element as it flows along a given heater tube. Hence, heat transfer from the electrical heating element to the fluid, e.g. water, may be more efficient.

[0099] In the presently described embodiment, the inner surface 2a of the first heater tube 2 forming the tapered portion of the fluid path is tapered while the respective portion of the outer surface 16a of the heating element 16 has a constant cross-sectional size. The narrowing cross-section of the fluid flow path within the tapered portion is therefore formed by tapering only the inner surface of the heater tube. This may allow the heater tank to be more easily manufactured and assembled and help maintain a constant level of heating of the heating element.

[0100] In other embodiments the tapered portion may additionally or alternatively be formed by increasing the cross-sectional size of the heating element along its length to progressively reduce the size of the space in which fluid flows around it.

[0101] Although the heater tubes 2, 4, 6 8 and heating elements 16, 18, 20, 22 are shown as having a circular cross section to form an annular fluid flow path that may not be the case in all embodiments. In some embodiments, the heater tubes and heating elements may not be arranged concentrically and/or may not be circular such that other geometries are formed.

[0102] In the presently described embodiment, the tapered portion of the first heater tube 2 may extend substantially along all of its length in which the first heating element 16 is located. This may help to control the temperature of the heating element along all of its length to avoid limescale formation and hot shots. In other embodiments, the tapered portion may extend along a smaller part of the overall length of the heating element 16. For example, the tapered portion may be located only in a region extending from the most down stream end of the first heating element to increase the rate of heat transfer where the temperature of fluid flow is highest. In such an embodiment, a portion of the heater tube may have a constant cross-sectional size in a region not forming the tapered portion.

[0103] A similar tapered portion described above being provided for the first heater tube 2 may be provided for the second, third and fourth heater tubes 4, 6, 8. All of the first, second, third and fourth heater tubes 2, 4, 6, 8 may therefore have a tapered portion having any of the features described above. In other embodiments, only some of the heater tubes may be provided with a tapered portion.

[0104] In the embodiment shown in Figures 1 and 2 the first, second, third and fourth heating elements may have the same electric heating element power. As the heater tubes are connected in series, this results in the temperature of the fluid flowing through the heater tubes to progressively increase along the fluid flow path in the direction of flow until a maximum temperature is reached at the most downstream point on the heating elements. In this embodiment, each of the heater tubes is provided with a tapered portion such that the separation distance between the inner surface and respective outer surface of the heating element progressively decreases along the combined length of the first, second, third and fourth heating elements 16, 18, 20, 22.

[0105] For example, the tapered portion of the first heater tube 2 may have a first separation distance (i.e. parameter W defined above) at its upstream end which decreases to a second separation distance at its downstream end. The tapered portion of the second heater tube 4 may have a third separation distance at its upstream end, which is equal to the second separation distance. The separation distance may then decrease along the length of the second heating element 4 until it reaches a smaller fourth separation distance at its most downstream end. The same may be the case for a corresponding fifth, sixth, seventh and eighth separation distance of the third and fourth heater tubes. This may allow the fluid velocity to progressively increase along the full length of the heating elements and help to avoid any limescale production spots or hot shots.

[0106] The electric heating elements may have any suitable length and electrical power to provide suitable heating of the fluid. In the presently described embodiment, each of the first, second, third and fourth electric heating elements 16, 18, 20, 22 has an active heated length of 500 mm.

[0107] The shape of the fluid flow path within the heater tube may be tailored according to the input water temperature and/or the electrical heating power of the respective heating element to achieve the desired heating element surface temperature.

[0108] In one embodiment, the tapered portion of the fluid flow path in the first heater tube may have a separation distance of between 3.90 and 4.20 mm at an upstream end and a separation distance of between 3.10 and 3.40 mm at a downstream end. More preferably, the tapered portion of the fluid flow path in the first heater tube may have a separation distance of between 4.00 and 4.10 mm at an upstream end and a separation distance of between 3.20 and 3.30 mm at a downstream end. Even more preferably, the tapered portion of the fluid flow path in the first heater tube may have a separation distance of about 4.05 mm at an upstream end and a separation distance of about 3.25 mm at a downstream end. In each of these examples, the separation distance at the upstream end corresponds to distance W₁ in Figure 4 and the separation distance at the downstream end corresponds to the distance W₂ in Figure 4. In each of the examples in this paragraph the length of the tapered portion along the fluid flow path (labelled L in Figure 4) may be in the range 450 mm to 550 mm and more preferably in the range 490 mm to 510 mm and even more preferably about 500 mm.

[0109] In any of the examples in the previous paragraph, the diameter of the heating element 16 (labelled T in Figure 4) may be in the range 5.0 mm to 8.0 mm, and more preferably in the range between 6.0 mm and 7.0 mm and even more preferably about 6.4 mm.

[0110] More generally, in any of the embodiments disclosed herein, the separation distance may decrease by between 12% and 27% from the most upstream end of the tapered portion to the most downstream end of the tapered portion. Preferably, the separation distance may decrease by between 18% and 22% from the most upstream end of the tapered portion to the most downstream end of the tapered portion. Even more preferably, the separation distance may decrease by about 20% from the most upstream end of the tapered portion to the most downstream end of the tapered portion.

[0111] Further detail of the mounting of the heating elements within the heating tubes is described as follows. In the illustrated implementation, as can be seen in Figure 1 there is a first shared wall 24 between the first heater tube 2 and the second heater tube 4, a second shared wall 26 between the second heater tube 4 and the third heater tube 6 and a third shared wall 28 between the third heater tube 6 and the fourth heater tube 8. Fluid communication from the first heater tube 2 to the second heater tube 4 is provided by an aperture through the first shared wall 24, the aperture being located at a point near the second end 9 of the heater tank 1. Fluid communication from the second heater tube 4 to the third heater tube 6 is provided by an aperture 32 through the second shared wall 26, the aperture 32 being located at a point near the first end 7 of the heater tank 1. Fluid communication from the third heater tube 6 to the fourth heater tube 8 is provided by an aperture through the third shared wall 28, the aperture being located at a point near the second end 9 of the heater tank 1.

[0112] Each of the first, second, third and fourth electric heating elements 16, 18, 20, 22 comprises an electrical connector 36, 38, 40, 42 located near to the first end 7 of the heater tank 1. The electrical connectors 36, 38, 40, 42 are configured to be connected electrically to an electrical power supply such as, for example, a mains power supply. The electrical connectors 36, 38, 40, 42 may each form an electrical connection, in use, with an electrical power supply by any suitable means.

[0113] The electrical connectors 36, 38, 40, 42 are each located within a sealed portion 44, 46. 48, 50. Each sealed portion 44, 46. 48, 50 provides a watertight volume such that the electrical connectors 36, 38, 40, 42 are sealed away from fluid, e.g. water, ingress. A watertight seal for each sealed portions 44, 46. 48, 50 is provided by an O-ring seal 52, 54, 56, 58. The O-ring seals 52, 54, 56, 58 may comprise any suitable material such as a rubber or any suitable polymeric material. Other suitable sealing means may be employed instead of, or in addition to, one or more of the O-ring seals. There may be an electrical connector arranged in a similar sealed portion at the other end of each of the first, second, third and fourth electric heating elements 16, 18, 20, 22.

[0114] In the embodiments described above the electric heating power of each of the four heating elements is the same, and a uniform electrical heating power is provided along the length of each heating element. To further aid the provision of a homogeneous surface temperature of the heating elements or to avoid the most down-stream end have an excessively higher temperature the local electric heating element power may be varied.

[0115] Referring now to Figure 6, an embodiment is shown in which the heating elements 16, 18, 20, 22 are configured such that the fluid flowing, in use, along the fluid flow path experiences a reduction in a local electric heating element power as the fluid flows, in use, along the fluid flow path. The embodiment shown in Figure 6 includes features corresponding to those of Figures 1 and 2, including tapered portions of the flow path along each of the first, second, third and fourth heating elements 16, 18, 20, 22 as described above.

[0116] As illustrated in Figure 6, the first electric heating element 16 has an electric heating element power of 3.9kW, the second electric heating element 18 has an electric heating element power of 3.1kW, the third electric heating element 20 has an electric heating element power of 2.3kW, and the fourth electric heating element 22 has an electric heating element power of 1.5kW. In this way, the electric heating element power of successive electric heating elements reduces downstream. As such, as water flows along the flow path 10 the water is heated by electric heating elements having successively lower electric heating element powers. It should be understood that the electric heating elements may have any suitable electric heating element powers.

[0117] By reducing the electric heating element power successively in this way, a lower heating effect is achieved for heating elements further downstream along the fluid flow path. This means that where the fluid has already been heated to a higher temperature the heating elements are also heated to a lower temperature. This further reduces the amount of heat that must be transferred from the surface of the heating elements towards the end of the flow path, which may further reduce the maximum surface temperature reached and/or allow the surface temperature to be homogeneous over all of the heating elements.

[0118] The cross-sectional size of the fluid flow path within the first, second, third and fourth heater tubes 2, 4, 6, 8 may be determined according to the respective heating element power. This allows the velocity of fluid flow to be tailored to the electric heating element power to reduce the maximum surface temperature and/or improve the surface temperature homogeneity.

[0119] In one embodiment, the tapered portion of the fluid flow path provided within each heater tube may have the same geometry. The fluid velocity in each of the tapered portions may therefore be the same as each other. Although the water temperature will continue to increase along the flow path the reduction in heating element electrical power in successive heater tubes may balance out the need to further increase the flow velocity. This may allow the same tapered shape of the heater tube to be used for each of the first, second, third and fourth heater tubes while still providing a homogeneous or near homogenous heating element surface temperature. In terms of the first to eighth separations distances defined above, the first, third, fifth and seventh most upstream separation distances may be the same as each other. The second, fourth, sixth and eighth most downstream separation distances are also equal to each other.

[0120] In other embodiments, the tapered portions of each heater tube may have different geometries, or may be absent from some of the heater tubes, as required to provide the necessary fluid flow velocity.

[0121] As illustrated in Figure 6, The electric heating elements 16, 18, 20, 22 may be connected such that the first electric heating element 16 and the fourth electric heating element 22 form a first pair, and the second electric heating element 18 and third electric heating element 20 form a second pair. In this way, the first pair and the second pair each have a total power of 5.4 kW. Therefore, the total power of all four electric heating elements 16, 18, 20, 22 is 10.8 kW. A person skilled in the art will understand that the power values provided in the examples are only example values and that the power may be increased or decreased. By matching or nearly matching the total power of the first pair of electric heating elements and the second pair of electric heating elements, the electrical connections and electrical circuitry may be simplified.

[0122] The electrical power of each electric heating element 16, 18, 20, 22 may be determined by the conductive properties and configuration of the internal filament located within each electric heating element 16, 18, 20, 22. For internal filaments having the same conductive properties, an increase in helical pitch will provide a reduction in heating power provided. In some implementations, each electric heating element 16, 18, 20, 22 may comprise an internal filament having a greater helical pitch than any upstream electric heating elements.

[0123] In some embodiments, the electric heating elements may be connected electrically in two or more parallel circuits. For example, all of the positive connections may be connected to the electric heating elements 16, 18, 20, 22 at the first end 7 of the heater tank 1 and all of the neutral connections may be connected to the electric heating elements 16, 18, 20, 22 at the second end 9 of the heater tank 1. The control circuitry may comprise a printed circuit board, which may, for example, be located relatively close to the first end 7 of the heater tank 1. In such a configuration, a relatively large, thick cable may be required to connect the neutral connections to the printed circuit board.

[0124] Alternatively, the electric heating elements may be connected electrically in series. By connecting the electric heating elements in series, less additional electrical componentry may be required. For example, there may be no need to employ a relatively large, thick cable to connect the neutral connections at the second end of the heater tank 1 to the printed circuit board located relatively close to the first end 7 of the heater tank 1. Also, waste heat generation may be reduced.

[0125] Referring to Figures 7 and 8, another example embodiment of a heater tank 100 for an instantaneous water heater is shown. In this embodiment, the heater tank 100 has only two heater tubes 116, 118 and heating elements 116, 118. Corresponding reference numbers are used for components of the embodiment of Figures 7 and 8 that are the same as the embodiment of Figures 1 and 2. Anything described in connection with the embodiment of Figures 1 and 2 may therefore apply to the embodiment of Figures 7 and 8, and vice versa.

[0126] The heater tank 100 has a heater tank inlet 112 and a heater tank outlet 114 and a fluid flow path 110 from the heater tank inlet 112 to the heater tank outlet 114.

[0127] The fluid flow path 110 passes through, in series, a first heater tube 102 and a second heater tube 104. The first heater tube 102 and the second heater tube 104 are integrally formed with each other, although they need not be. Each one of the first heater tube 102 and the second heater tube 104 extends from a first end 107 of the heater tank 100 to a second end 109 of the heater tank 100. The first heater tube 102 and the second heater tube 104 are arranged in parallel with each other.

[0128] At a point near the first end 107 of the heater tank 100, the first heater tube 102 is in fluid communication with the heater tank inlet 112. At a point near the second end 109 of the heater tank 100, the second heater tube 104 is in fluid communication with the first heater tube 102. At a point near the first end 107 of the heater tank 100, the heater tank outlet 114 is in fluid communication with the second heater tube 104.

[0129] As indicated schematically by a block arrow 110' (Figure 7), the fluid flow path 110 from the heater tank inlet 112 to the heater tank outlet 114 passes through, in series, the first heater tube 102 and the second heater tube 104. In use, fluid, e.g. water, flows in a first direction from the first end 107 of the heater tank 100 towards the second end 109 of the heater tank 100 along the first heater tube 102. In use, fluid, e.g. water, flows in a second direction opposite to the first direction (i.e. from the second end 109 of the heater tank 100 towards the first end 107 of the heater tank 100) along the second heater tube 104.

[0130] A first electric heating element 116 extends longitudinally within the first heater tube 102. The first electric heating element 116 extends from the first end 107 of the heater tank 100 to the second end 109 of the heater tank 100. The first electric heating element 116 has an electric heating element power and is operable to heat fluid, e.g. water, flowing, in use, within the first heater tube 102.

[0131] A second electric heating element 118 extends longitudinally within the second heater tube 104. The second electric heating element 118 extends from the first end 107 of the heater tank 100 to the second end 109 of the heater tank 100.

[0132] The heater tank 100 has mounting tabs similar to the embodiment shown in Figures 1 and 2 and can similarly be surrounded at least partially by a casing. It may also be controlled by similar control circuitry. The features that are common with the embodiment of Figures 1 and 2 will not be described here. The skilled person will understand that they apply equally.

[0133] Although not visible in the Figures, the fluid flow path within each of the first and second heater tubes 102, 104 is provided with a tapered portion. These may be similar to those described above in connection with the embodiment of Figure 1. The tapered portions may have a geometry which is tailored to the heating element electric power to provide the desired control of the heating element surface temperature.

[0134] The embodiment of Figures 7 and 8 has a shared wall 124 between the first heater tube 102 and the second heater tube 104. Fluid communication from the first heater tube 102 to the second heater tube 1044 is provided by an aperture through the shared wall 124, the aperture being located at a point near the second end 109 of the heater tank 100.

[0135] Each of the first and second electric heating elements 116, 118 comprises an electrical connector 136, 138 similar to those of the embodiment of Figures 1 and 2. The electrical connectors 136, 138 are also each located within a sealed portion 144, 146, the detail of which will not be described again.

[0136] As illustrated in Figure 9, the first electric heating element 102 has an electric heating power of 6.6 kW and the second electric heating element 104 has an electric heating power of 4.2 kW. In this way, the electric heating element power of successive heating elements reduces downstream. As such, as fluid, e.g. water, flows along the fluid flow path 110 the fluid, e.g. water, is heating be electric heating elements having successively lower electric heating element powers. The total power of the first heating element 102 and the second heating element 104 is 10.8 kW. A person skilled in the art will understand that the power values provided in the examples are only example values and that the power may be increased or decreased.

[0137] In some embodiments, one or more of the electric heating elements may be configured to deliver a decreasing heating power in a downstream direction along its length. In this way, a single electric heating element may provide an electric heating element power that reduces along the fluid flow path. The deceasing heating power may be provided in combination with a tapered portion of the fluid flow path. The effect of both may be combined to allow the maximum temperature of the heating element be further reduced and/or the surface temperature homogeneity improved without impacted the heating of the fluid flow.

[0138] Figure 9 illustrates schematically a way in which heating power can be decreased along the heating elements. The first electric heating element 102 is made up of a series of twenty 20 electric heating element segments 105a-t. The twenty 20 electric heating element segments 105at each have an electric heating element segment power. The sum of the electric heating element segment powers equals the electric heating element power, i.e. 6.6 kW for the first electric heating element 102. The electric heating element segment powers decrease progressively in the downstream direction along the fluid flow path 110, as shown in Table 1 below. In this example, the first electric heating element 102 has an active heated length of 1000 mm. Each one of the 20 electric heating element segments 105a-t has a length of 50 mm.

Table 1 - Electric heating element segment powers for the first electric heating element 102 of the water heater 100 shown in Figures 7, 8 and 9. The sum of the electric heating element segment powers = an electric heating element power of 6.6 kW.

Electric heating element segment	Electric heating element segment power in kW
105a	0.39
105b	0.384
105c	0.378
105d	0.372
105e	0.365
105f	0.359
105g	0.353
105h	0.347
105i	0.341
105j	0.335
105k	0.328
105l	0.322
105m	0.316
105n	0.31
105o	0.304
105p	0.298
105q	0.292
105r	0.285
105s	0.279
105t	0.273

[0139] The second electric heating element 104 is made up of a series of twenty 20 electric heating element segments 107a-t each have an electric heating element segment power. The sum of the electric heating element segment powers equals the electric heating element power, i.e. 4.2 kW for the second electric heating element 104. The electric heating element segment powers decrease progressively in the downstream direction along the fluid flow path 110, as shown in Table 2 below. In this example, the second electric heating element 104 has an active heated length of 1000 mm. Each one of the 20 electric heating element segments 107a-t has a length of 50 mm.

Table 2 - Electric heating element segment powers for the second electric heating element 104 of the water heater 100 shown in Figures 7, 8 and 9. The sum of the electric heating element segment powers = an electric heating element power of 4.2 kW.

Electric heating element segment	Electric heating element segment power in kW
107a	0.267
107b	0.261
107c	0.255
107d	0.248
107e	0.242
107f	0.236
107g	0.23
107h	0.224
107i	0.218
107j	0.212
107k	0.205
107l	0.199
107m	0.193
107n	0.187
107o	0.181
107p	0.175
107q	0.168
107r	0.162
107s	0.156
107t	0.15

[0140] In the embodiment shown in Figure 7 and 8, the internal filament is arranged such that the helical pitch increases sequentially in a downstream direction along each segment. In this way, the internal filament extending along each segment has a helical pitch greater than the section of internal filament extending along the segment immediately upstream.

[0141] In some implementations, rather than or as well as comprising a series of electric heater element segments, one or more of the electric heater elements may be configured such that the local electric heating element power varies continuously along at least a portion of the length of the electric heater element(s).

[0142] In some implementations, one or more of the electric heating elements may comprise an internal filament in the form of a coil having a helical pitch. The local electric heating element power may vary, e.g. increase or decrease, along at least a portion of the length of the electric heating element, due to changes in the helical pitch of the internal filament.

[0143] Figure 10 shows schematically a plumbing system 350. An instantaneous water heater, illustrated as an electric shower unit 351 is mounted on a wall 352. The electric shower unit 351 comprises a casing 355 housing an instantaneous water heater comprising a heater tank such as the heater tank 1 or the heater tank 100 described above. The instantaneous water heater is connected to a water supply point (not shown) located within the wall 352. A hose 353 provides fluid communication from the instantaneous water heater to a spray head 354 located downstream thereof. A shower tray or bath tub (not shown) may be present to collect the water emitted from the spray head 354.

[0144] For convenience, the preceding examples have been discussed primarily in relation to electric showers. The skilled person will appreciate that other applications of the instantaneous water heater are possible. Similarly, the example embodiments are primarily discussed in terms of using water, but the skilled person will understand that the disclosure would equally apply to other fluids.

[0145] Employing a water heater tank or an instantaneous water heater according to the present disclosure may enable a wider range of designs and configurations of instantaneous water heaters. For example, it may be possible to manufacture instantaneous water heaters having a relatively flat form factor as compared with traditional instantaneous water heaters. An instantaneous water heater having a relatively flat form factor may provide for new design possibilities, for example, for electric shower units. An instantaneous water heater having a relatively flat form factor may allow for more efficient use of space. For instance, an instantaneous water heater having a relatively flat form factor may be suited for deployment in a cavity in or behind a wall or a ceiling, e.g. as part of a built-in electric shower system.

[0146] Some examples of applications for a heater tank or an instantaneous water heater according to the present disclosure will now be described.

[0147] An instantaneous water heater according to the present disclosure may be utilised in an electric shower system comprising a waste water heat recovery system and the instantaneous water heater. The waste water heat recovery system may be configured to transfer heat from a waste water stream to a stream of cold water, e.g. from a mains supply, being conveyed to the instantaneous water heater.

[0148] This may increase the temperature of the water entering the instantaneous water heater. Consequently, the instantaneous water heater may not need to operate to provide as great a temperature increase, in order to provide an output water stream having a user-desired temperature for showering. This may mitigate the decrease in flow rate that can be experienced by users of electric showers in winter when the temperature of the UK mains supply can be 15°C less than in summer (e.g. 5°C in winter and 20°C in summer). For example, in summer a 10.8 kW electric shower unit typically may provide a flow rate of around 8 litres per minute for a typical showering temperature of approximately 40°C, whereas, in the winter the flow rate can drop to around 4.5 litres per minute for a typical showering temperature of approximately 40°C. For example, in summer a 8.5 kW electric shower unit typically may provide a flow rate of around 6 litres per minute for a typical showering temperature of approximately 40°C, whereas, in the winter the flow rate can drop to around 3.5 litres per minute for a typical showering temperature of approximately 40°C. By utilising a waste water heat recovery system, the winter flow conditions can be improved by around 40%.

[0149] The relatively flat form factor of the heater tank disclosed herein may allow for a space efficient and/or convenient implementation of an electric shower system with an integrated waste water heat recovery system. For example, the heater tank shown in Figures 7, 8 and 9 may be relatively tall and suitable for use in a vertical orientation. Typically, the waste water heat recovery system is located at flow level. The electric shower system may be configured such that the heated stream of cold water may then enter the heater tank from floor level. The heater tank may be oriented vertically. Accordingly, the shower outlet and/or user controls may be present at a convenient and/or logical height.

[0150] Another example application for a heater tank according to the present disclosure is within a recirculating shower system. Generally, a recirculating shower uses stored hot water to provide the hot top up (HTU) energy to maintain showering temperature that compensates for the energy lost to the surrounding air. For instance, the HTU water temperature may be higher than the selected showering temperature by approximately 10°C and may be required to have a flow rate of around 2 litres per minute. An instantaneous water heater may be utilised to provide the HTU energy. A heater tank or an instantaneous water heater according to the present disclosure may be well suited to this purpose because the lower temperatures of the electric heating element(s) may reduce the build-up of limescale, as compared with conventional instantaneous water heater designs. Also, the relatively flat form factor of the heater tank disclosed herein may facilitate a relatively compact system design.

[0151] In another implementation of a recirculating shower system, a heater tank according to the present disclosure may be used to heat directly the recirculating flow.

[0152] Another example application for a heater tank according to the present disclosure is as part of an instantaneous water heater configured to supply a plurality of water delivery devices that utilise heated water. For instance, in a bathroom there may be a number of fluid delivery devices that utilise heated water such as a shower, wash basin taps and a bath fill. An instantaneous water heater comprising a heater tank according to the present disclosure may be configured to provide warm water to a wash basin tap and a shower. The low hot shot and low surface temperature characteristics of the heater tank may help to make it suitable for use in supplying hot water to a wash basin tap, even though the heater tank may be turned on and off repeatedly in such an application.

[0153] Another example application for a heater tank according to the present disclosure is to provide heated water to a wash basin tap, e.g. in a bathroom or a kitchen.

[0154] A kitchen tap may be configured such that it can deliver hotter water, e.g. water having a temperature of around 60°C, for pot washing, washing greasy utensils and hot water for floor cleaning etc. Higher temperature water dispensing can be achieved by controlling the water flow rate to the appropriate level.

[0155] The relatively flat form factor of the heater tank disclosed herein may allow, for example, the heater tank to be housed in a relatively small amount of space in an under-sink cupboard.

[0156] Another example application for a heater tank according to the present disclosure is to provide hot top up water heating for prolonged bathing, e.g. in a whirlpool bath. Water from the whirlpool bath may be conveyed to the heater tank inlet. The water from the whirlpool bath may typically have a temperature suitable for bathing such as from 35°C to 40°C. The water may be heated by a few degrees centigrade as it passes along the fluid flow path to provide a heated bath water stream. The heated bath water stream exits the heater tank outlet and is conveyed back into the bath. In this way, the water in the whirlpool bath may be maintained at a preferred bathing temperature for an extended period of time. In this application, the heater tank may have a total heating power of around 3 kW. The low surface temperature of the heating element(s) may help to reduce the likelihood of the build-up of limescale or other deposits. Also, the relatively flat form factor of the heater tank disclosed herein may mean that the heater tank can be conveniently incorporated within the overall form factor of the whirlpool bath.

[0157] Another example application for a heater tank according to the present disclosure is to provide water heating in a washing machine or a dishwasher. Typically, the washing machine or the dishwasher may have a cold water feed only. The heater tank may be utilised to heat the cold water to a desired wash temperature. Additionally or alternatively, a heater tank according to the present disclosure may be configured to heat a recirculated stream of water to provide hot top up water to maintain the desired wash temperature.

[0158] Another example application for a heater tank according to the present disclosure is a whole building water heater, e.g. a whole house water heater. For such an application, the water heater may have a total heating power of from 20 kW to 30 kW or higher.

[0159] Another example application for a heater tank according to the present application is a bath fill. For such an application, the water heater may have a total heating power of from 20 kW to 30 kW or higher.

[0160] The heater tank may be employed to provide a bath fill for a walk-in bath. Additionally or alternatively, the heater tank may be employed to provide hot top up water heating for prolonged bathing in the walk-in bath, in which case the heater tank may be configured similarly to the whirlpool bath example application described above.

[0161] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

1. A heater tank for an instantaneous water heater, comprising:

a heater tank having a heater tank inlet and a heater tank outlet and a fluid flow path from the heater tank inlet to the heater tank outlet; and

one or more electric heating elements operable to heat fluid flowing, in use, along the fluid flow path, wherein:

the one or more electric heating elements are each located within a respective heater tube through which the fluid flow path passes;

at least part of the fluid flow path is defined by a space between an outer surface of the heating elements and an inner surface of the heater tube in which each heating element is located; and

the fluid flow path comprises a tapered portion in which a separation distance between the outer surface of at least one of the heating elements and an inner surface of the respective heater tube decreases along at least a portion of the length of the heater tube in the direction of fluid flow whereby the velocity of fluid flow increases along the respective length of the heater tube in the direction of fluid flow.

2. A heater tank according to claim 1, wherein a laminar flow of fluid is maintained along the tapered portion of the fluid flow path.

3. A heater tank according claim 1 or claim 2, wherein the interior of the one or more electric heating elements and exterior of the respective heater tubes have a circular cross section and are arranged concentrically such that the fluid flow path along each heater tube has an annular cross section.

4. A heater tank according to any preceding claim, wherein the portion of the inner surface of the heater tube forming the tapered portion of the fluid path is tapered, and optionally wherein the portion of the outer surface of the heating element forming the tapered portion of the fluid path has a constant cross-sectional size.

5. A heater tank according to any preceding claim, wherein the one or more heating elements are configured such that the fluid flowing, in use, along the fluid flow path experiences a reduction in a local electric heating element power as the fluid flows, in use, along the fluid flow path.

6. A heater tank according to claim 5, wherein the fluid flow path is configured to bring fluid into contact with a series of two of more electric heating elements, in which a second one of the electric heating elements has an electric heating element power that is less than that of a first electric heating element immediately upstream thereof.

7. A heater tank according to claim 6, wherein the fluid flow path is provided with a first tapered portion along its length spanning at least part of the first electric heating element and a second tapered portion along its length spanning at least part of the second heating element, wherein the first and second tapered portions are arranged to provide the same reduction in fluid flow velocity as each other.

8. A heater tank according to any of claims 5 to 7, wherein one or more of the electric heating elements comprises a series of a plurality of electric heating element segments, wherein at least one of the electric heating element segments has an electric heating element segment power that is less than that of the electric heating element segment immediately upstream thereof.

9. A heater tank according to any of claims 5 to 8, wherein one or more of the electric heater elements is configured such that the local electric heating element power varies continuously along at least a portion of the length of the electric heater element(s).

10. A heater tank according to any preceding claim, wherein one or more of the electric heating elements comprises an internal filament in the form of a helical coil, and optionally wherein:
the local electric heating element power varies along at least a portion of the length of the electric heating element, due to changes in a helical pitch of the internal filament.

11. A heater tank according to any preceding claim, wherein the fluid flow path passes through a plurality of heater tubes and wherein two or more of the heater tubes are integrally formed with each other.

12. An instantaneous water heater comprising the heater tank of any one of claims 1 to 11.

13. An instantaneous water heater according to claim 12, wherein the heater tank is surrounded at least partially by a casing, and optionally wherein the casing surrounds at least partially further components of the instantaneous water heater.

14. An electric shower comprising a heater tank according to any of claims 1 to 11 or an instantaneous water heater according to claim 12 or claim 13.

15. A plumbing system, comprising a heater tank according to any of claims 1 to 11, an instantaneous water heater according to claim 12 or claim 13 and/or an electric shower according to claim 14.

Drawing