"DUAL CHAMBER WATER HEATER"

BACKGROUND OF THE INVENTION Field of Invention This invention relates to hot water heaters of the type used to provide hot water on demand. Description of the Prior Art

Heaters to provide hot water on demand to a user are well-known in the art. Heaters that provide hot water for domestic or workplace uses are of two general types; storage/reservoir units, and instant heat units. Storage units are more commonly found in domestic dwellings than in offices, and generally work as follows, large reservoir tank in the heater is filled with water from a mains circuit at room or atmospheric temperature. The contents of the heater is then heated by a heating unit, for example an element in the tank, to a set temperature. The contents are then maintained at this temperature. The heating unit is used to re-heat the contents of the storage tank to the required temperature if this drops below a certain level. The pre-heated water in the tank is used as a reservoir to provide hot water to a user on demand, e.g. for baths, washing etc. If the contents is kept at a high temperature (e.g. greater than 90 ⁰ C), then the amount of energy required to keep the contents of a tank at higher temperatures is correspondingly greater, due to the increased thermal gradient between the tank contents and atmosphere. For this reason, the water in storage tanks is not usually kept at a high temperature, and instead is kept at a lower temperature — e.g. 60 ⁰ C — so that the amount of energy used to maintain the contents at this temperature is not prohibitive.

As the water is usually stored at a lower temperature, it is normally too cool to be suitable for beverage or foodstuff preparation. Instant heat units are becoming more commonly used in both domestic and office situations. Heaters of this type provide water of the required temperature only when this is 'demanded' by a user, by heating the water as it is demanded or drawn off by a user. The operation of instant heat units can generally be described as follows: when water is demanded by a user (e.g. by turning on or activating a tap), water at a temperature significantly below boiling point (e.g. room temperature) is supplied to the heater, either from a storage reservoir or from a mains supply. This water passes into the heating unit and is heated to the required temperature, usually by using a gas burner. The heated water is then supplied directly from the heating unit to a user, immediately after it has been heated. Larger, domestic instant heat units tend to be designed to have a greater flow, as they are intended to provide a large volume of hot water at a

temperature suitable for washing,-baths etc. However, the water provided by these larger units is usually too cool for cooking, beverage preparation, etc.

Smaller 'instant hot water' units are becoming increasingly popular for use in situations where a smaller volume of hot water is required each time the heater is used, but where water at a higher temperature is required, and where the unit will be used more frequently. For example, in office kitchens a heating or boiling unit will be used at frequent intervals throughout the course of a working day for beverage preparation or similar. Water at a temperature close to boiling is required every time water is drawn off.

Office-type units are generally smaller than domestic instant heat units. As they are intended to provide lower volumes of water for any one use or at any one time, it is cost-effective to use units of this type to supply water at a high temperature. In units of this type, water is either supplied to the heater directly from the main circuit (at room temperature), or a small amount of water is heated and stored at an intermediate temperature. This water is then heated to a higher temperature and provided to a user when it is demanded. One problem with all of the heater types described above is that of heating efficiency.

Considerable power is required to heat (and then store) hot water at temperatures significantly above room temperature. Most heater designs are a compromise between storage volume, storage temperature, instant heating efficiency, and overall volume (the overall volume including insulation or other external accessories). Design improvements have generally been driven by consumers demanding greater efficiency (that is, lower power bills). Other considerations that are becoming more important include ecological issues, with fuel (heating) efficiency becoming more important. Also, health and safety issues are becoming increasingly important. If water is being provided at high temperatures, it is important that the possibility of a user being accidentally scalded or burnt is minimised. In order to improve efficiency, it is known in the art to construct tanks that are divided by internal partitions or similar into two distinct sub-chambers or sub-tanks. One of these sub- chambers receives mains water and heats it to an intermediate temperature — below boiling but above room temperature. This heated water is then passed through to the second sub-chamber where it is heated to a higher temperature (e.g. close to boiling) for delivery to a user. The second, higher temperature sub-tank is replenished with water from the first sub-tank as water is drawn off. Usually, the first sub-tank has a greater volume than the second, higher temperature, sub-tank. This dual tank design has the advantage that the lower temperature body of water will not lose heat energy as rapidly as water heated to close to boiling, as the thermal gradient between the lower temperature water in the first sub-tank and atmosphere is shallower. However, when higher temperature water is required, less energy and time is needed to heat the

water in the second chambet firoin the intermediate temperature to a high temperature. This arrangement allows high temperature water to be provided at irregular intervals e.g. to prepare beverages throughout a working day in an office, but increases the overall efficiency of the system. Examples of this type of design are shown in US 3,383,495, US 4,575,615 and US

4,757,182.

Another type of design uses a nested tank configuration to increase efficiency. In this configuration, the smaller (high temperature) tank is nested inside a larger (intermediate temperature) outer tank. The water in the outer tank is heated to an intermediate temperature, for example 60 ⁰ C, and the water in the inner tank is heated to a higher temperature (close to boiling) for dispensing to a user. This configuration has the advantage that the outer tank and its contents act at least partially as an insulating jacket around the higher temperature chamber. In a similar manner to that outlined above, high temperature water at indeterminate or irregular intervals can be provided, with increased system efficiency. Examples of this type of design are shown in US 2,386,949 and US 3,617,700.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a hot water heater that goes some way towards overcoming the disadvantages described above, or which will at least provide users with a useful choice.

Accordingly in a first aspect, the invention may broadly be said to consist in a water heater for providing hot water to a user, comprising: a storage unit adapted to hold a first volume of water, and having a mains conduit adapted for connection to a mains water supply so that said storage unit can receive water from said mains water supply, said storage unit also having a storage heating element adapted to heat and maintain said first volume of water at an intermediate temperature between room temperature and boiling point in use, a boiling unit, adjoining said storage unit and adapted to hold a second volume of water and having a boiling heating element adapted to heat and maintain said second volume of water

at a high temperature in use, said boiling unit also having a dispensing mechanism adapted to allow a user to draw off water from said boiling unit, a connection conduit, running between said storage unit and said boiling unit, so that in use said boiling unit can receive water from said storage unit, said boiling unit and said storage unit separated by an airgap.

Preferably when assembled ready for use said storage unit is located above said boiling unit.

Preferably the base of said storage unit is a convex surface, and the top of said boiling unit is a concave surface. Preferably the curvature of said convex surface substantially matches the curvature of said concave surface so that the size of said airgap is the same size between a substantial portion of said concave and convex surfaces.

Preferably said dispensing mechanism comprises a pump, in fluid communication with said boiling unit. Preferably said dispensing mechanism also comprises a dispensing conduit, one end of said dispensing conduit fluidically connected to said pump to receive said water from said boiling unit via said pump, the other end of said conduit adapted for connection to a user-operated tap.

Preferably the relative capacity and dimensions of said storage unit and said boiling unit, the relative curvatures of said concave and convex surfaces, and the size of said airgap, are calculated so that heat transfer to the storage unit from the boiling unit compensates for heat losses from the storage unit to the surrounding environment.

Preferably the relative capacity and dimensions of said storage unit and said boiling unit, the relative curvatures of said concave and convex surfaces, and the size of said airgap, are calculated so that heat transfer to the storage unit from the boiling unit compensates for heat losses from die storage unit to the surrounding environment and the energy input required to said boiling unit element to compensate for said heat losses is minimised.

Preferably said airgap is between 6mm and 15mm.

Even more preferably sad airgap is 9mm.

Preferably the capacity of said storage unit is between 10 and 14 litres, and the capacity of said boiling unit is between 1.5 and 3.5 litres.

Even more preferably, the capacity of said storage unit is 12 litres, and the capacity of said boiling unit is 2.5 litres.

Preferably said intermediate storage temperature is between 70-90 ⁰ C.

Even more preferably said intermediate storage temperature is a set point temperature of substantially 80 ⁰ C.

Preferably said boiling unit farther comprises a rim, aligned substantially vertically and running around the top edge of said boiling unit, said storage unit resting on said rim in use.

Preferably said storage unit and said boiling unit are circular in plan view, each having a diameter in the region of 27cm. Preferably when said storage unit and said boiling unit are assembled to form part of said water heater, the height of said water heater from the base of said boiling unit to the top of said storage unit is in the region of 40cm.

Preferably said water heater further comprises a casing, said storage unit and said boiling unit located within said casing in use. Preferably said water heater further comprises insulating material, the space between said water heater and said casing filled with said insulating material, so that said insulating material surrounds and fully encloses said storage unit and said boiling unit. any space between said water heater and said casing is filled with an insulating material, filling said casing, and surrounding and fully enclosing said storage unit and said boiling unit. Preferably said insulating material is formed as two separate expanded polystyrene pieces that together form an insulating shell that encloses said water heater.

Preferably the contents of said boiling unit is heated and maintained at a temperature between 92°C and 99°C by said boiling element.

Even more preferably, the contents of said boiling unit is heated and maintained at a temperature of 3°C below boiling point by said boiling element.

Preferably said boiling element has a power output in the region of 1.8 kW.

Preferably said storage element has a power output in the region of 1.8 kW.

Preferably at least part of the length of said connection conduit is located in said storage unit, submerged in the upper third of the contents of said storage unit. Preferably that end of said connection conduit that is located in the storage unit faces upwards.

Preferably when said storage unit is filled to the required level, said end is just below the surface of said contents.

Preferably said storage unit further comprises a dispensing conduit adapted for connection to a tap to enable a user to draw off water from said storage unit, said storage unit having an outlet, said dispensing conduit connected at said outlet, said storage unit also having a balance valve located at said outlet, said balance valve adapted to cool water exiting said storage unit to a maximum temperature of 70 ⁰ C.

Preferably said water heater further comprises a control mechanism,

said storage unit also having a pressure switch adapted to send a storage unit full signal to said control mechanism when the storage unit is filled to the required pressure, and a storage unit depleted signal to said control mechanism when said storage unit is not filled to said required pressure, said boiling unit also having a boiling level probe adapted to send a boiling unit full signal to said control mechanism when said boiling unit is filled to the required boiling level, and a boiling unit depleted signal to said control mechanism when said boiling unit is not filled to said required boiling level, said mains conduit also having a mains supply tap, said mains supply tap controlled by said control mechanism, said connection conduit also having a connection tap, said connection tap controlled by said control mechanism, said boiling level probe sending said boiling unit depleted signal to said control mechanism when water is drawn off from, said boiling unit via said dispensing mechanism, said control mechanism instructing said connection tap and said mains supply tap to open in response to receiving said boiling unit depleted signal, said storage unit receiving additional water from said mains conduit, said additional water displacing at least part of the contents of said storage unit and causing said contents to pass into said boiling unit via said connection conduit, said boiling level probe sending said boiling unit full signal to said control unit when said boiling unit has been refilled, said control unit instructing said connection tap to close in response to receiving said boiling unit full signal, said storage pressure sensor sending said storage unit full signal to said control unit when said storage tank has been refilled, said control unit instructing said mains supply tap to close in response to receiving said storage unit full signal.

Preferably said storage unit further comprises a thermostat, said thermostat activating said storage element when the temperature of the contents of said storage unit drops below

Alternatively said thermostat sends a signal relating to the temperature of the contents of said storage unit to said control unit, said control unit activating said storage element when the temperature of the contents of said storage unit drops below said set storage unit temperature.

Preferably said set storage unit temperature is 80 ⁰ C. Preferably said boiling unit further comprises a thermistor, said thermistor activating said boiling heating element when the temperature of the contents of said boiling unit drops below a set boiling unit temperature.

Alternatively said thermistor sends a signal relating to the temperature of the contents of said boiling unit to said controller to activate said boiling heating element when the temperature of the contents of said boiling unit drops below said set boiling unit temperature.

Preferably said set boiling unit temperature is 95°C.

In a second aspect, the invention may broadly be said to consist in a user-operated tap for use with a water source, comprising: a tap body, said body having a nozzle adapted for dispensing water, said tap body adapted for connection to a surface in use, a tap conduit located inside said tap body, one end of said tap conduit fluidically connected to said nozzle, the other end of said tap conduit adapted for fluid connection to said water source, at least one user-operable lever, connected to and movable relative to said tap body, said lever having a plurality of positions including a first position where said tap is turned off, a first part of said lever located outside said tap body and manipulable by a user, a second part of said lever located inside said tap body, a sensor assembly located inside said tap body and adapted to sense the position of said second part, at least one spring, connected to said at least one lever and said tap body in such a manner that said lever is biased towards said off position, said sensor assembly generating a variable signal that is dependent on the position of said second part.

Preferably said at least one lever is pivoted about an axis inside said tap body, said second part describing an arc inside said tap body as said lever is pivoted.

Preferably said spring is a leaf spring.

Preferably said first position is said off position.

Preferably when said lever is in said first position, said variable signal is turned off.

Preferably said sensor mechanism also has at least one pair of sensors, located inside said tap body at opposite ends of said arc, the number of said pairs of sensors corresponding to the number of said at least one levers.

Preferably said pair of sensors are magnetically sensitive, the inner end of said second part of said lever further comprising a magnet, said tap further comprising a sensor board to which said pair of sensors are connected, said variable signal dependent on the position of said magnet relative to each of said sensors.

Preferably the inner end of said spring further comprises an inner hook, and the outer end of said spring further comprises an outer hook, said lever having a lever recess into which said inner hook connects in use, said tap body having a body recess into which said outer hook connects in use, in use said lever moving relative to said tap body when manipulated downwards by a user, from said first position where said spring is substantially undeformed, to a position

where said spring is deformed and exerts a reaction force on said lever directed to returning said lever to said first position.

Preferably said inner hook is a 180° bend, and said outer hook is a 90° bend. Preferably said outer hook further comprises a kink, and said tap body further comprises a tab over which said kink engages when said lever is in said first position.

Preferably said outer hook, said kink and said tab are adapted such that when a user rotates said lever upwards, said kink detents over said tab to remain in position until downwards force is exerted by said user.

Preferably said tap further comprises a first user operable lever and a second user operable lever, said first parts of said first and second levers coloured to indicate to a user what temperature water will be dispensed.

Preferably said tap further comprises a safety button, said button operable by a user to activate or deactivate said tap.

Preferably said safety button further comprises at least one LED, said LED indicating to a user whether said tap is activated or deactivated.

Preferably said safety button operates an override circuit, which turns said variable signal off when said override circuit is activated.

Preferably said variable signal is sent to a controller, which is adapted to control and vary the flow of fluid from said water source based on said variable signal, said controller ensuring that there is no flow from said water source when said lever is in said off position.

Preferably said water source is a water heater as described in any one of the statements above relating to said water heater.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

The term "comprising" as used in this specification means "consisting at least in part of. When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present.

Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

The invention consists in the foregoing and also envisages constructions of which the following gives examples.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred forms of the present invention will now be described with reference to the

accompanying drawings in which;

Figure 1 shows a preferred embodiment of a hot water heater, with an outer casing shown in outline, and a control unit shown located in a recess on the casing.

Figure 2 shows an exploded view of the water heater of Figure 1, with a heater unit, conduits, surrounding insulation shown, all located within the outer casing in use.

Figure 3 shows the exploded view of Figure 2, with the heater unit also shown separated or exploded in order to show an upper storage unit and a lower boiling unit of the heater unit.

Figure 4 shows a cutaway view of the heater unit of Figures 2 and 3, with internal detail of the storage unit, the boiling unit and the conduits that run between the units shown.

Figure 5 shows a view of the storage unit and the boiling unit assembled with the control unit connected, and detail of the conduits that run between and which feed the units also shown.

Figure 6 shows a perspective view of a tap that can be used with the hot water heater. Figure 7 shows the tap of Figure 6 mounted on a benchtop.

Figure 8 shows an exploded view of the tap of Figure 6, with the main sub- components and sub-assemblies shown, including a user operated lever sub-assembly.

Figure 9 shows a detailed exploded view of the lever sub-assembly shown in Figure 8. Figure 10 shows the lever sub-assembly of Figures 8 and 9 assembled. Figures Ua-c show cutaway side views of part of the tap of Figure 6, with detail of the lever sub-assembly of Figures 9 and 10 in three positions; Figure 11a showing the lever in a first or off position, Figure lib showing the lever in a position where a user has pressed downwards and Figure lie showing the lever in a position where a user has pulled upwards. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS While the invention is susceptible to embodiment in different forms, a specific preferred embodiment is shown in the drawings, and described in detail. The present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein. The preferred embodiment is described below in relation to a hot water heater or hot water unit of the type used to provide water for beverage preparation in an office or similar. It will be appreciated, however, that the present invention can be used in any application where it is beneficial to provide hot water on demand.

Figure 1 shows a view of a preferred embodiment of a hot water heater 101 or hot water unit enclosed by an external ot outer casing 100, shown in outline, the water heater 101, the casing 100, and the other secondary items forming a heater unit. The main components of the hot water heater 101 are located inside the external casing 100 in use. In the preferred

embodiment, the casing 100 forms part of the hot water heater. However, the internal hot water heater 101 is referred to as a separate item from the casing 100. Where 'water heater' is referred to in this specification, this should be taken as either including or excluding the casing 100, as appropriate. Where 'heater unit' is used in this specification, this refers to the casing 100, the hot water heater 101, and all the secondary items such as a control unit 123, insulation 102, etc. In use, the heater unit is intended to be located in a storage space such as a cupboard under a kitchen sink or similar. The external casing 100 can be removed or opened to allow settings to be adjusted, maintenance to be carried out, etc. The casing 100 acts to protect the internal components from accidental damage, and also helps to protect users from inadvertent contact with hot surfaces, etc. In the preferred form, the space between the casing 100 and the outer skin of the hot water heater 101 can be filled with insulative material 102, such as expanded polystyrene foam.

A number of external ports pass through the casing 100, so that conduits 104 and similar apparatus can pass through the casing 100 to connect with the water heater 101. The casing includes recesses for the location of external control panels, power points, or similar. These power points and external control panels are shown generally as panels 103 in Figure 1.

Figures 2 and 3 show exploded views of the preferred, form of the heater unit. The heater unit has a casing 100, water heater 101, insulation 102, control panels 103 and conduits 104. The preferred shape of the water heater 101 is cylindrical, with two rounded end caps. It should be noted that a water heater with flat ends could also be used. When the water heater 101 is located in the casing 100, there is a space between the generally rectangular or cuboid casing 100 and the water heater 101. This space between the casing 100 and the external skin of the water heater 101 is filled with the insulating material 102.

As shown in Figures 2 and 3, the preferred form of the insulating material 102 is two separate pieces of expanded polystyrene, brought together to enclose the water heater 101. These two insulating halves are in turn enclosed by the casing 100.

As shown in Figure 3, the water heater 101 is comprised of two separate units, an upper- storage chamber or storage unit 110, and a lower boiling chamber or boiling unit 111. The two units 110 and 111 'nest' in use, the units directly adjacent or adjoining one another, with the curve of the concave top 107 of the boiling unit 111 matching the curve of the convex base 106 of the storage unit 110, the convex base 106 adjacent to the concave top 107. The preferred form of the storage unit has a convex curved base 106 (and a curved top) as this form allows the contents to be stored under pressure, whilst keeping the walls reasonably thin. The boiling unit 111 has a rim 130 standing proud of, and running around the circumference of the concave top 107. The concave top 107 follows the curve of the convex base 106 of storage unit 110 as this

allows the akgap between the two to be kept substantially constant. The rim 130 is a continuation of the wall of the boiling unit 111 in the preferred embodiment, and is substantially vertical. The outer part of the base 106 of the storage unit 110 rests against this rim 130, so that there is no direct contact between the base 106 and the top 107. It should also be noted that when the water heater 101 is assembled and ready for use, the two units 110, 111 are not physically connected (i.e. they are not attached together by welding, gluing, clamping etc). Instead, the units 110 and 111 are kept in position relative to one another by their mutually interlocking or nested shapes, and the surrounding insulation material 102. It should also be noted that the rim 130 as described above follows the circumferential perimeter of the boiling unit 111. However, the rim 130 does not have to be at the outer circumferential edge — it could be located slightly radially inwards of the circumferential edge. Also, although it is preferred that the rim 130 is a continuous loop, the rim 130 could be discontinuous in other embodiments.

Both the storage unit 110 and the boiling unit 111 are formed from copper in the preferred embodiment. The preferred capacity of the storage unit 110 is approximately 12 litres, and the preferred capacity of the boiling unit 111 is approximately 2Y2 litres. Each of the units

110, 111 has a diameter of approximately 30cm, and the total overall height of the water heater 101 once assembled is approximately 40cm.

The operation of the heater unit, the internal structure of the two units 110 and 111, and the external connections between each of the units 110, 111 and other elements of the system will now be described with particular reference to Figure 4.

Figure 4 shows the storage unit 110 nested into the concave top part of the boiling unit

111, as has been described above. The surrounding insulation 102 and casing 101 are not shown. Each of the units 110, 111 contains a heater element to heat the water that is stored in the units 110, 111 to the required temperature. The storage unit element (storage element 121) passes into the side of the storage unit 110 at approximately mid-height of the unit 110, and is preferably aligned substantially horizontally. The boiling unit element (boiling element 122) passes in through the side of the boiling unit 111, also preferably aligned substantially horizontally.

When the two units 110, 111 are brought together, with the (upper) storage unit 110 resting on the rim 130, an air gap 105 is created between the convex base 106 of the storage unit 110 and the concave top 107 of the (lower) boiling unit 111. In the preferred embodiment, the curvature of the base 106 and the top 107 substantially match, so that the air gap 105 is a substantially constant 9mm gap at all points between the base 106 and the top 107. It should be noted that the curvature matching does not have to be identical at all points between the two surfaces. However, it is preferred that the air gap is constant across a substantial portion of the two surfaces. In the preferred embodiment, the substantial portion amounts to 80% or more.

No further support is necessary to keep the units 110, 111 in place relative to one another. However, the insulation material 102 in the preferred form provides additional support to the two water tanks 110, 111.

As described above, the capacity of the storage unit 110 is approximately 12 litres. The storage unit 110 is kept topped up to this capacity by a connection to a mains water supply via mains conduit 112, which passes into the side of the tank 110 close to the base 106. The mains supply water entering the tank 110 is at or close to room temperature, and as it enters the storage unit 110 it sinks to the bottom, below the heated water already present in the storage unit 110. When water is drawn off from the storage unit 110, the storage unit 110 is topped up to its 12 litre capacity from the mains conduit 112. The storage unit 110 operates as a normal mains pressure water heater by allowing the room temperature pressurised mains water entering via mains conduit 112 to push out the hot water within storage unit 110 when water is drawn off from the water heater 101.

The storage element 121 heats and. maintains the contents of the storage unit 110 at an intermediate set point temperature of substantially 80 ⁰ C. It is preferred that the water in the storage tank 110 is maintained at a set point temperature of 80 ⁰ C. However, it is preferred that the temperature of the contents of storage unit 110 does not significantly .exceed this temperature. The storage element 121 is constructed as a standard heating element of the type that is well-known in the art, rated at approximately 1.8 kW in the preferred embodiment. Storage element 121 is powered by a connection to a mains electricity supply that is controlled by a control unit 123, located on or recessed into the outer casing so that it can be accessed by a user. The storage unit 110 also contains a temperature sensor such as a thermostat (not shown). If the temperature of the contents of the storage unit 110 falls below a lower temperature level — e.g. just below 80 ⁰ C, the thermostat activates the storage element 121 to raise the temperature back to the set point temperature of 80 ⁰ C. Once the contents of the storage unit 110 has been raised to the reqtαired temperature, the thermostat deactivates the storage element 121. This can be done either by having the thermostat send a signal relating to the temperature of the contents of said storage unit to the control unit 123 which then activates the element 121, or the thermostat can be partially or fully independent of the control unit 123. The control unit can also act as a programmable timer, shutting down the heater unit and allowing the water in the storage unit and boiling unit to cool during periods of non-use (e.g. at night). The timer can be programmed to activate the heater unit at a specified time. For example, if the heater unit is used in an office environment, the timer can be programmed to activate the heater unit at a specified time before the office is due to open, so that the hot water is available as soon as workers arrive. In the preferred embodiment, the timer settings can be

adjusted via an auxiliary control system and timer (not shown), that are mounted on the casing 100. This allows a user to adjust the settings without opening or removing the casing 100.

A connection conduit 113 connects the upper storage unit 110 and the boiling unit 111. The conduit 113 passes through the side wall of the upper storage unit 110, close to the top of the storage unit 110. As shown in figure 10, in the preferred form the connection conduit 113 is bent or shaped so that the end 114, located inside the storage unit 110, faces upwards. That part of the length of connection conduit 113 inside the storage unit 110 is located towards the top of the storage unit 110, in approximately the top third. End 114 is the uppermost part of the connection conduit 113. This arrangement has a dual advantage: firstly, locating the end 114 of the conduit 113 at the top of the storage unit 110 facing upwards ensures that only the hottest water (at the top of the storage unit 110) enters the conduit 113. Secondly, locating the conduit 113 at the top of the storage unit 110 ensures that heat transfer away from the water in the conduit 113 is minimised, as the conduit 113 will be in contact with the higher temperature water at the top of the storage unit 110. As described above, conduit 113 runs between the storage tank 110 and the boiling unit

111. Water from the storage unit 110 enters the boiling unit 111 via the conduit 113, and is therefore pre-heated to between 75-80 ⁰ C. Due to the construction described above, there is minimal heat loss from the water in transit through the conduit 113. The water from storage unit 110 arriving in the boiling unit 111 is heated quickly and efficiently from the 75-80 ⁰ C at which it arrives, to the required higher set point temperature of 3°C below boiling point — i.e. 97-98°C in preferred operating conditions (preferred embodiment temperature). This process is controlled by the control unit 123 on the outer casing 100, which receives signals from a boiling unit level probe (not shown) inside the boiling unit 111. The preferred form of boiling level probe sends three signals to the control unit: a first signal, or boiling unit depleted signal, which is sent when the level of the contents of the boiling unit 111 drops below 2.5 litres, a second signal, or boiling unit empty signal, which indicates an unsafe water level to activate the boiling element 122, and a third signal, which indicates that the boiling unit 111 is full, or that the content is at the required level. When the control unit 123 receives the boiling unit depleted signal from the boiling level probe indicating that the level has dropped below 2.5 litres, the control unit sends instructions to a connection tap (such as a solenoid controlled tap or similar (not shown)) on conduit 113 to open. Simultaneously, the control unit 123 sends a signal to a mains supply tap (not shown) on the mains conduit 112 instructing the mains supply tap to open. The control unit 123 controls the operation of both the connection tap and the mains supply tap. Opening the mains supply tap causes additional water from the mains connection to enter the storage unit 110. This causes the contents of the storage unit 110 to overtop the end 114 of the conduit 113. As end 114 is

located at the top of the storage unit 110, only the hottest water in the storage unit HO enters the conduit 113 and passes through the connection conduit 113 into the boiling unit 111. When the boiling unit 111 is filled to its 2.5 litre capacity, the boiling level probe sends the boiling unit full signal to the control unit 123, indicating that the tank 111 is filled to the required level. The control unit 123 instructs the connection tap to shut in response to this signal. Water continues to flow through the mains supply tap into the storage unit 110 until the water pressure in the tank equals the inlet water pressure. The storage unit 110 contains a pressurestat or pressure switch (not shown) which operates by sending a signal to the control unit to close die main supply tap when the tank pressure exceeds the inlet pressure by 10%, and to open the main supply tap when the storage unit 110 water pressure drops below the inlet pressure.

The control unit 123 also controls the operation of the heater elements 121, 122. The control unit 123 receives signals relating to the temperature of the contents of the units 110, 111 and cycles the heater elements 121, 122 on and off as required to raise or maintain the temperature of the contents of the units 110, 111. Water in the boiling unit 111 is stored at 3°C below boiling point until use — that is, at 97-

98°C under normal operating conditions - until use. The contents of the boiling unit is maintained at this higher temperature by way of the heating element 122. Element 122 has the same power rating as element 121 used in the storage tank 110, and in the preferred embodiment is rated at 1.8 kW. The smaller size of the boiling unit 111 ensures that the contents can be heated to the required temperature very quickly. Heat losses from the boiling unit 111 are also minimised by use of the insulation 102, and the airgap 105. Boiling unit 111 includes a thermistor that monitors the temperature of the contents of the boiling unit and sends a signal to the controller to activate the boiling element 122 when the temperature "of the contents falls below a temperature close to boiling. A user or users draw off hot water as it is required, from the boiling unit 111 via a dispensing mechanism connected to the boiling unit 111. In the preferred embodiment at least part of the dispensing mechanism is a pump 120 in the side of the boiling unit 111. As the preferred embodiment of the water heater is intended to be located under a sink or similar, the pump 120 provides water via a dispensing conduit or similar to a user-activated tap or similar at bench top height, above the water heater. In the preferred form, the pump 120 is an electrically- controlled pump, of the type that are well-known in the art. When water is drawn off, the contents of the boiling unit 111 is immediately replenished by water from the storage unit 110, as described above. Usually, amounts of approximately Vz litre at a time are drawn off from the boiling unit 111 for e.g. tea and coffee preparation. This accounts for roughly 20% of the total contents of the boiling unit 111. When this is replenished with Vz litre of water at approximately

80 ⁰ C, the reduction in the temper ature of the contents of the boiling unit 111 is not significant. It has been found that the replenished contents can be brought back up to the required temperature of 3°C below boiling temperature (that is, between 97-98°C under normal operating conditions) very quickly. In terms of the operation of the water heater 101, bringing the contents of the boiling unit 111 back up to the required temperature is effectively instantaneous.

In the most preferred embodiment, water can also be drawn off from the storage unit 110 at the lower temperature of 60-70 ⁰ C, if required for washing or similar. This water is drawn off via a dispensing conduit or a standard sink faucet, or similar. The drawn off water is reduced from 80°C to 60-70°C via a balance valve 131 in the outlet of the storage unit 110 so as to prevent damage to seals, pipes and the such in the hot water lines immediately exiting the storage unit 110.

As described above, when storing water at a temperature above atmospheric (e.g. atmospheric temperature assumed to be approximately 30 ⁰ C), there will always be some heat losses. There are two main heat loss paths in the system described: firstly, heat is lost from the main storage unit 110 through the insulation 102 and through the paths formed through the insulation 102 to allow the conduits 104 and control circuitry access to the heater unit 101. Secondly, heat is lost from the boiling unit 111 via the insulation 102 and also via conduction and convection to the storage unit 110. As there will always be some heat loss from both the storage unit 110 and the boiling unit 111, the configuration of the heater 101 is arranged to take advantage of this inevitable heat loss and minimise the associated problems. Firstly, the base 106 of the storage unit 110 rests on the rim 130 of the boiling unit 111. There is no direct contact between the base of the storage unit 110 and the top of the boiling unit 111, except through the rim 130. This arrangement minimises the surface area available for heat conduction from the boiling unit 111 to the storage unit 110. Secondly, the boiling unit 111, which operates at a higher temperature than the storage unit 110, is located below the storage unit 110. THs ensures that heat lost from the boiling unit 111 via convection in the airgap 105 is transferred upwards to the storage unit 110, as primary energy loss via convection is upwards. By configuring the heater units 110 and 111 in this way, at least part of the energy losses from the boiling unit 111 are transferred as energy gains to the storage unit 110. By creating a system close to the design parameters outlined above (tank capacities and dimensions, a preferred upper temperature of water in the storage tank 110 of 80 ⁰ C, an airgap size of approximately 10mm), the energy losses from the boiler unit 111 can be closely matched to the energy losses from the storage unit 110 (occurring via the insulation and the paths as described above), and can be used to compensate for the majority (e.g. 90%) of these losses. With the temperature of the water in the storage unit 110 at the preferred temperature of 80 ⁰ C ₃

the energy losses from the storage unit 110 are almost completely compensated for by the heat transfer from the boiling unit 111 with the contents stored at 3°C below boiling point. The boiling element 122 only needs to be cycled on and off approximately twice a minute to maintain the system 101 at this state. Any energy losses from the storage unit 110 that are not compensated for by convection and conduction effects are compensated for by cycling the storage element 121. This design and layout has been found to significantly increase system efficiency.

It can be seen that the size of the airgap 105 (controlling convection) and the nesting arrangement (controlling surface contact area and therefore conduction) are carefully tuned so that heat losses from the boiling unit are not critical, but that the inevitable heat losses are converted to benefit the overall system. It should also be noted that it is possible to vary these parameters to tune the overall system to achieve the same result. For example, the convex and concave surfaces could be manufactured with different curvatures, so that the size of the airgap varies from point to point across the two surfaces. Alternatively, the relative temperatures of the contents of the two units, or their relative dimensions, could be varied. This variation of the parameters is tuning the system to achieve energy efficiency and reduce the necessity of cycling the heating elements to maintain the contents of the units at the desired level.

TAP

The user-operated tap referred to above, suitable for use with the heater unit described above, shall now be described in more detail with reference to Figures 6-11.

The overall form of the preferred embodiment of the user-operated tap is shown in Figure 6 as a single tap body or tap 200. The body of tap 200 has three main parts: a hollow vertical stem 201 that in use is mounted to a surface such as a bench top or similar as shown in Figure 7, and two branches that split from the top of the stem 201 and which are angled slightly upwards so that the tap body has the overall form of a T- ot Y-shape. The branches of the preferred form are angled slightly upwards from the horizontal. It should be noted that the tap 200 could be adapted for mounting to any suitable surface or point, such as a wall, pillar or similar. One branch of the Y-piece (the lever arm 220) includes a pair of user operated lever bodies 202, 203 that form the end of the lever arm 220. A user can manipulate the lever bodies 202, 203 by pulling them up or pushing them downwards. Pressing one of the lever bodies downwards activates the tap and causes water to be dispensed e.g. from the boiling unit 111 , or from another source such as a water chiller (not shown), depending on which body is depressed. The second branch of the Y-piece (main body 221) has a dispensing nozzle: 204, located at the end and on the underside of main body 221, facing downwards.

An exploded view of the tap 200, showing the main sub-parts, is shown in Figure 8. A set of silicon tubes 205 is located inside the vertical stem 201 to carry water from the boiling unit 111, and the water chiller (not shown). The inner ends of the silicon tubes 205 are connected to the inner ends of a complimentary set of copper pipes 206, which run from the junction of the Y-piece to the nozzle 204, inside the main body 221. The silicon tubes 205 and the copper pipes 206 together form a tap conduit, with the free end of the silicon tubes 205 connected to the end(s) of the dispensing conduit running from the boiling unit 111. In the preferred embodiment a conduit runs from the storage unit 110 also, and is connected to one of the silicon tubes 205. A base flange 207 is included in the preferred embodiment to aid mounting of the tap 200 to a mounting surface such as a bench top. The lever bodies 202, 203 are included as part of a lever subassembly 210 that connects to the tap 200, the subassembly 210 forming part of both the stem 201 and the lever arm 220. A safety button 218 is included in the structure of the tap 200. The safety button 218 acts as an electrical, switch. When it is activated, it stops inadvertent operation of the lever bodies 202, 203, thereby preventing accidental spillage of boiling water. The preferred form of the lever subassembly 210, and the operation of the lever bodies

202, 203 is described in more detail below, with reference to Figures 9-11.

An exploded view of the lever subassembly 210 is shown in Figure 9. In the preferred embodiment, the lever subassembly 210 includes the following main parts: a rear cap 211, two lever bodies 202, 203, two lever arms 212, two lever springs 213, and a sensor board 214. The lever bodies 202, 203 include a set of end caps 208, 209 that are pressed into recesses in the tops of the bodies 202, 203 during assembly. These ends caps 208, 209 can be differently coloured as required by a user — e.g. one end cap can be coloured red to show that activating that lever body causes the tap 200 to produce hot water at a temperature close to boiling point (water from the boiling unit 111). The rear cap 211 is generally L-shaped (the ϊ/ is inverted in use). When assembled, the rear cap 211 attaches to, and forms part of, the tap 200, with the outer surfaces of the rear cap 211 lying flush with the main body of the stem 201 and the lower part or underside of the lever arm 220. The rear cap 211 includes pivot recesses 216 on its upper surface, the upper surface being located inside the body of the tap 200 in use. When the tap 200 is fully assembled, pivot projections 217 on the lever arms 212 locate into these pivot recesses 216, allowing each of the lever arms 212 to pivot around the pivot recesses 216, independent of each other and also independent of the rear cap 211. On the outer side of the pivot projections 217 (that side furthest away from the Y-junction), the body of each of the lever arms 212 extends outwards to form a projection 219. Each of the lever bodies 202, 203 includes a complimentary recess so that the lever bodies 202, 203 can locate onto these projections 219 in use. The lever arms 212 and

the lever bodies 202, 203 move as one unit when assembled. These parts do not move relative to one another. Where reference is made in this specification to a 'first part', this should be understood as referring to a part of the assembly that includes at least that part of the lever arm 212 on the outer side of the pivot projections 217, and which preferably also includes the attached lever body (either 202 or 203).

On the inner side of the pivot projections 217, the body 223 of each of the lever arms 212 extends outwards and curves downwards so that when the tap 200 is assembled, the body 223 angles downwards into the stem 201. Where reference is made in this specification to a 'second part', this should be understood as referring to at least that part of the lever arm 212 on the inner side of the pivot projections. When the lever arms 212 are rotated around the pivot recesses 216, the inner ends 224 of the lever arms 212 describe a short arc inside the stem 201. A magnet 225 is attached to each of the ends 224.

Sensor board 214 is a PCB board which is located inside the stem 201 in use, and forms at least part of a sensor assembly. The sensor board 214 is oriented so that it runs across the width of the stem 201, in the same orientation or plane as the υ of the tap 200. One edge of the board 214 locates into a slot 229 in the rear cap 211 to hold the board 214 in position. A pair of sensors is located on each side of the board (four sensors in all, two on each side). The board, sensors and the lever arms 212 are sized and located so that when the tap 200 is assembled, each pair of sensors is located at opposite ends of the short arcs described by the ends 224 of each of the lever arms 212. One pair of sensors - 226, 227, located on one side of the board 214, is shown in Figure 9 and Figure 11.

The sensors 226, 227 are magnetically sensitive. As the corresponding magnet 225 describes the short arc in response to movement of the lever arm 212, as outlined above, the sensors 226, 227 respond. It can be seen that the location of the magnet 225 directly corresponds to how far the lever body 203 has been depressed. As the magnet 225 moves, the sensors 226, 227 send a variable signal to the control unit 123, the signal varying depending on the position of the lever arm 212, and corresponding to the position of the magnet 225. The control unit 123 activates and cycles pump 120 depending on the signal. For example, if a user requires hot water from the boiling unit 111, they depress the appropriate lever body — e.g. lever body 203. When lever body 203 is depressed, this moves magnet 225 away from the off position, close to sensor 226, and towards sensor 227. The movement of the magnet causes the sensors 226, 227 to send the variable signal to the control unit 123, indicating that lever body 203 has been depressed. The signal will vary depending on how far the magnet 225 has been moved. When the control unit 123 receives this signal, the control unit 123 activates the pump 120, which pumps water from the boiling unit 111 through the tap 200 to the nozzle 204. The

variable signal allows the control unit to vary the activation of the pump 120, and therefore the volume of the flow through the pump 120 and the tap 200 can be varied depending on how far a user has depressed the lever body 203. It should be noted that although one sensing mechanism has been described above, any appropriate sensing mechanism could be used if required. When the tap 200 is not in use, and the lever bodies 202, 203 are not depressed, or immediately after use when the lever bodies 202, 203 are returned to a position where they are not depressed, the corresponding sensors are either inactive (or they are deactivated as the lever body returns to this position). Alternatively, the sensors can send a signal to the control unit 123 indicating that the lever body or bodies (and therefore the magnets) are in an 'off position. The control unit 123 responds by deactivating the corresponding pump or pumps ,(i.e. if lever body 203 is depressed, signals are sent to control unit 123 from sensors 226, 227, and the control unit activates pump 120. When lever body 203 returns to a non-depressed state, the control unit deactivates pump 120). A similar arrangement can be used if chilled water has been requested from the water chiller (not shown). In the preferred embodiment, the lever bodies 202, 203 are spring-loaded so that when they are not actively depressed by a user, they automatically return to the default, non-depressed position. The preferred form of spring loading shall now be described.

The lever subassembly 210 includes a pair of lever springs 213, one for each of the arms 212. The lever springs 213 generally have the form of leaf springs or flat springs, with a flat central body portion, a 180° hook or bend 232 at the inner end and a 90° hook or bend 233 that includes a kink 235 at the outer end. Each of the lever arms 212 has a central portion 230 shaped so that the 180° hooked end 232 can hook onto or slide over the central portion 230. The shaped central portion 230 is located so that when the springs 213 are in position, the centrepoint of the hook 232 corresponds to the centre of rotation of the lever arm 212. The outer end 233 of each of the springs 213 is shaped to engage with tabs or projections 234 on the rear cap 211, the kink 235 'clicking' over the projections so that the spring 213 is held in place.

When either of the lever bodies 202, 203 is depressed, the corresponding attached lever arm 212 will rotate. The rear cap 211 is connected to the tap 200 and remains stationary, so the central body portion and the outer end 233 of the corresponding spring 213 will also remain stationary. However, as the lever arm 212 rotates downwards, it presses against the underside of the 180° bend 232 and rotates this portion of the spring 213 downwards and inwards towards the body of the tap 200. The spring 213 will deform as the outer end 233 is held in position. As the spring 213 is bent in this manner, it exerts a reaction force on the lever arm 212. When the user removes pressure from the lever body, the reaction force from the spring 213 causes the lever arm 212 and the lever body to return to the non-depressed position.

When either of the lever bodies 202, 203 is pulled or rotated upwards from the first or off position, the corresponding attached lever arm 212 will rotate. The rear cap 211 is connected to the tap 200 and remains stationary, but the central body portion and the end 233 of the corresponding spring 213 are attached to the lever arm 212 and rotate freely with it. As the lever arm 212 rotates upwards, end 233 and the kink 235 deform over the tab or projection 234 allowing the lever arm 212 to detent and remain in the up position. The user must then push the lever back down to re-set it into the first or off position. The tap will therefore remain on until the user pushes the cap back to the central rest position.

The lever subassembly 210 also includes a safety board 215. In the preferred embodiment, this is connected to the safety button 218. The safety button 218 is used to activate or deactivate the tap 200 (by activating or deactivating the pump 120). LED's on the safety board protrude through the top surface of the safety button 218. These LED's indicate the status of the switch (locked or unlocked) to a user, and also indicate the readiness of the dual chamber water heater, and the performance of any other items in use with the system, such as a water filter.

It should also be noted that the tap 200 described above could be used, or can be adapted for use with, other types of hot water heater other than the one described in the preferred embodiment. The tap 200 could also be used independently with other water sources if required, for example by connecting it to a mains conduit. Preferred Features

1. A user-operated tap for use with a water source, comprising: a tap body, said body having a nozzle adapted for dispensing water, said tap body adapted for connection to a surface in use, a tap conduit located inside said tap body, one end of said tap conduit fluidically connected to said nozzle, the other end of said tap conduit adapted for fluid connection to said water source, at least one user-operable lever, connected to and movable relative to said tap body, said lever having a plurality of positions including a first position where said tap is turned off, a first part of said lever located outside said tap body and manipulable by a user, a second part of said lever located inside said tap body, a sensor assembly located inside said tap body and adapted to sense the position of said second part, at least one spring, connected to said at least one lever and said tap body in such a manner that said lever is biased towards said off position,

said sensor assembly generating a variable signal that is dependent on the position of said second part.

2. A user-operated tap as outlined in paragraph 1 above wherein said at least one lever is pivoted about an axis inside said tap body, said second part describing an arc inside said tap body as said lever is pivoted.

3. A user-operated tap as outlined in paragraph 1 or paragraph 2 above wherein said spring is a leaf spring.

4. A user-operated tap as outlined in any one of paragraphs 1 to 3 above wherein said first position is said off position.

5. A user-operated tap as outlined in paragraph 4 above wherein when said lever is in said first position, said variable signal is turned off.

6. A user-operated tap as outlined in any one of paragraphs .1 to 5 above wherein said sensor assembly comprises at least a pair of sensors, located inside said tap body at opposite ends of said arc, the number of said pairs of sensors corresponding to the number of said at least one levers.

7. A user-operated tap as outlined in paragraph 6 above wherein said pair of sensors are magnetically sensitive, the inner end of said second part of said lever including a magnet, said tap further comprising a sensor board to which said pair of sensors are connected, said variable signal dependent on the position of said magnet relative to each of said sensors.

8. A user-operated tap as outlined in any one of paragraphs 1 to 7 above wherein the inner end of said spring includes an inner hook, and the outer end of said spring includes an outer hook, said lever including a lever recess into which said inner hook connects in use, said tap body including a body recess into which said outer hook connects in use, in use said lever moving relative to said tap body when manipulated downwards by a user, from said first position where said spring is substantially undeformed, to a position where said spring is deformed and exerts a reaction force on said lever directed to returning said lever to said first position.

9. A user-operated tap as outlined in paragraph 8 above wherein said inner hook is a 180° bend, and said outer hook is a 90° bend.

10. A user-operated tap as outlined in any paragraph 8 or paragraph 9 above wherein said outer hook includes a kink, and said tap body includes a tab over which said kink engages when said lever is in said first position.

11. A user-operated tap as outlined in paragraph 10 above wherein said outer hook, said kink and said tab are adapted such that when a user rotates said lever upwards, said kink detents over said tab to remain in position until downwards force is exerted by said user.

12. A user-operated tap as outlined in any one of paragraphs 1 to 11 above wherein said tap includes a first user operable lever and a second user operable lever, said first parts of said first and second levers coloured to indicate to a user what temperature water will be dispensed.

13. A user-operated tap as outlined in any one of paragraphs 1 to 12 above wherein said tap includes a safety button, said button operable by a user to activate or deactivate said tap.

14. A user-operated tap as outlined in paragraph 13 above wherein said safety button includes at least one LED, said LED indicating to a user whether said tap is activated or deactivated.

15. A user-operated tap as outlined in paragraph 13 or paragraph 14 above wherein said safety button operates an override circuit, which turns said variable signal off when said override circuit is activated.

16. A user-operated tap as outlined in any one of paragraphs 1 to 15 above wherein said variable signal is sent to a controller, which is adapted to control and vary the flow of fluid from said water source based on said variable signal, said controller ensuring that there is no flow from said water source when said lever is in said off position.

17. A user-operated tap as outlined in any one of paragraphs 1 to 16 above wherein said water source is a water heater as described in any one of the statements above in the 'summary of the invention' section which relate to a water heater.