AU2007332141A1

AU2007332141A1 - A controllable water heater

Info

Publication number: AU2007332141A1
Application number: AU2007332141A
Authority: AU
Inventors: Brendan Vincent Bourke
Original assignee: Rheem Australia Pty Ltd
Current assignee: Rheem Australia Pty Ltd
Priority date: 2006-12-12
Filing date: 2007-12-11
Publication date: 2008-06-19
Anticipated expiration: 2027-12-11
Also published as: NZ577168A; NZ583763A; AU2007332141B2; AU2010200835B2; AU2010200835A1; WO2008070906A1

Description

WO 2008/070906 PCT/AU2007/001906 1 A Controllable Water Heater Field of the invention [001] This invention relates to a controllable water heater. Background of the invention [002] The characteristics of an instantaneous gas water heater are that the incoming water is heated to a preset temperature by the gas. The gas is only turned on and ignited when the tap is opened by a user to draw water. In some systems, the flow rate of the water is regulated to a maximum rate matched to the heating capacity of the gas heater, so that the outlet water will be in an outlet range about the preset temperature. Where the flow is below this maximum rate, the gas can be regulated to ensure that the temperature does not exceed the preset maximum temperature. [003] One form of instantaneous gas water heater comprises a finned tube construction with a pipe formed into a plurality of horizontal sections in a zig-zag manner, the pipe sections having heat exchanger fins attached. The fins are usually copper. A gas burner located below the heat exchanger arrangement provides heat to the heat exchanger. When the gas is ignited by a controller on detection of water being drawn off, there is a lapse of more than 20 seconds, typically 30 seconds before the outlet water reaches the operating temperature. The user usually allows this water to flow down the drain until the required temperature is reached. Thus several litres of water can be wasted on start up of the system. [004] In known systems using such an arrangement, the outlet temperature is usually fixed. [005] It is desirable to provide a system and method for providing the user with an option to select an outlet water temperature. [006] In some cases, the hot water tap can be located at some distance from the water heater, at the end of a "dead leg". Any changeover arrangement located at the end of a dead leg between an auxiliary heater and a main heater may require sensing and control links to the main controller of the system.

WO 2008/070906 PCT/AU2007/001906 2 Summary of the invention [007] Accordingly, the invention provides an instantaneous gas water heater system having a main gas heater and an auxiliary storage heater tank connected to provide pre-heated water to the system outlet during the start-up period of the main heater. [008] A first embodiment of the invention provides, in a water heating system including a main water heater, a method of reducing the delivery of water at a temperature below a predetermined temperature range, the method including the steps of: maintaining a store of stand-by hot water at a temperature above a minimum outlet temperature threshold; connecting the stand-by hot water to the outlet directly or via the main heater. [009] The method can include detecting the commencement of flow of water to an outlet. [010] The method can include the step of mixing the stand-by hot water with the water inlet supply before delivery to the system outlet. [011] The main water heater can be an instantaneous gas water heater, the method including the step of turning the instantaneous gas water heater on when the flow is detected. [012] The method can include the step of mixing stand-by hot water with water from the instantaneous gas water heater before delivering the mixed water to the outlet. [013] The method can include the step of monitoring the temperature of the water from the main heater and monitoring the temperature of the stand-by hot water, and calculating a mixing ratio to achieve the required outlet temperature. [014] The method can include controlling the flow of water from the main heater and the stand-by hot water to obtain the required outlet temperature. [015] The method can include the step of reducing the flow of the stand-by hot water as the temperature of the water from the main heater increases.

WO 2008/070906 PCT/AU2007/001906 3 [016] A mixed flow of water from the water supply and the stand-by hot water can be connected to the input of the main heater. [017] The stand-by flow can be mixed with the output of the main heater. [018] The method can include the steps of mixing the stand-by water with the water supply to form a first mixed flow, supplying the first mixed supply to the input of the main heater, and mixing the first mixed supply with water from the outlet of the main heater to provide an outlet flow. [019] The invention also provides a hot water supply system including a main water heater and an auxiliary water heater, wherein: the auxiliary heater is a storage water heater; the output of the auxiliary heater is connected to a system outlet by one or more of the following: directly; or via the main heater; or after mixing with the inlet water supply. [020] A controllable throttle valve can be configured to mix the output from the auxiliary heater with either the incoming water or the outlet of the main heater, or both, for supply to a system outlet. [021] A first controllable diverter valve can be adapted to control the outlet from the auxiliary heater. [022] The output of the auxiliary heater can be combined with the water supply inlet and connected to the inlet of the main heater. [023] The outlet of the auxiliary heater can be combined with the inlet water supply and connected to the output of the main heater. [024] The main heater can be an instantaneous gas water heater. [025] A first temperature sensor can be provided to sense the temperature of the inlet water, a second temperature sensor to sense the temperature of the stored water.

WO 2008/070906 PCT/AU2007/001906 4 [026] A third temperature sensor can be adapted to sense the temperature of the outlet water. [027] A fourth temperature sensor can be adapted to sense the temperature of the hot water in the main heater. [028] A controller can be adapted to control the flow regulator. [029] The invention also provides a hot water supply system having an on demand main heater and a booster heater, wherein the outlet of the main and the outlet of the booster heater are connected as inputs to a tempering valve which is adapted to produce an outlet flow within a predetermined temperature range. [030] The arrangement can include control means responsive to the temperature of the water supplied from the main heater to switch off the booster heater or to close off the flow of from the booster heater to the tempering valve when the main heater outlet temperature reaches a predetermined value. [031] The main heater can be connected to a first inlet of the tempering valve, and the outlet of the booster heater is connected to a second inlet of the tempering valve. [032] The outlet of the main heater can connected to the inlet of the booster heater, the outlet of the booster heater is connected to a first inlet of the tempering valve, and the clod water supply is connected to a second input of the tempering valve. [033] The invention also provides a water heater having first and second heaters and first and second tempering valves, the outlets from the first and second heaters being connected as inputs to the first tempering valve, and the outlet of the first tempering valve and the cold water inlet being connected as inputs to the second tempering valve. [034] The invention also provides a water heating system including a water conserving arrangement, the system including: a main water heater having an inlet and an outlet and being adapted to heat mains water; WO 2008/070906 PCT/AU2007/001906 5 an auxiliary heater having an inlet and an outlet; a mixer having first and second inlets and an outlet; the outlet of the main heater being connected to the input of the auxiliary heater; the outlet of the auxiliary heater being connected to the first inlet of the mixer; the outlet of the main heater being connected to the second input of the mixer; temperature sensing means adapted to sense the temperature of the water from the outlet of the mixer; a mixer control adapted to control the flows via the first and second inlets of the mixer in accordance with the outlet temperature of the mixer; the main water heater being an on-demand heater; the auxiliary heater being adapted to heat water to a first temperature threshold; the mixer being adapted to increase the flow of water via the first inlet of the mixer and decrease flow via the second inlet of the mixer when the outlet temperature of the mixer is below a second temperature threshold, and to decrease flow via the first inlet of the mixer and increase flow via the second inlet of the mixer when the temperature is above the second threshold temperature. [035] A further embodiment of the invention provides a controllable three port valve having a common port and first and second variable ports, and an adjustable flow control member adapted to control the relative apertures of the adjustable ports, and a controllable drive means adapted to operate the control member. [036) Another embodiment of the invention provides a flow control arrangement including a valve, the valve including temperature sensing means, the arrangement including a controller adapted to control the drive means to position the flow control member in response to the temperature sensor. [037] A flow control arrangement including a valve, including first and second temperature sensing means to sense the temperature at corresponding ones of WO 2008/070906 PCT/AU2007/001906 6 the variable ports, and a controller adapted to control the position of the flow control member in response to the first and second temperature sensing means. Brief description of the drawings [038] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [039] Figure 1 illustrates an arrangement adapted to reduce corrosion from condensation on the gas heater heat exchange copper plates. [040] Figure 2 shows an arrangement embodying the invention adapted to provide pre-heated water from an auxiliary heater to the main water heater; [041] Figure 3 shows a further arrangement embodying the invention adapted to provide pre-heated water to the water heater; [042] Figure 4 shows a further arrangement embodying the invention adapted to provide pre-heated water to the water heater. [043] Figure 5 illustrates a further water heater system embodying the invention. [044] Figure 6 illustrates another water heater according to an embodiment of the invention. [045] Figure 7 shows a modification of the arrangement of Figure 6. [046] Figure 8 shows a further embodiment of the invention. [047] Figure 9 shows an alternative arrangement embodying the invention using autonomous control of the tempering valves and auxiliary heater. [048] Figure 10 shows a further arrangement embodying the invention; [049] Figure 11 shows another arrangement embodying the invention; [050] Figure 12 shows an additional arrangement embodying the invention. [051] Figure 13 is a schematic illustration of a controllable valve.

WO 2008/070906 PCT/AU2007/001906 7 Detailed description of the embodiment or embodiments The invention will be described with reference to the accompanying drawings. In the drawings, sensor lines connexion lines are shown in dot-dash form, while control lines are dotted. To avoid clutter in some drawings, some sensor and control lines are shown only in part with arrows pointing to the controller. [052] Available tempering valves can be three-port devices having two inputs (hot and cold) and one outlet port which has a proportion of the two inlet port flows to provide a required temperature output. [053] Various embodiments of the invention make use of three port devices. A first type of three port device can have two inlets and one outlet, and this will be referred to as a single outlet device. These devices can have autonomous control of which inlet is connected to the outlet, or of the relative proportion of flow from each inlet to the outlet. For example, a tempering valve can selectively balance a hot and a cold inlet to produce an outlet art a desired temperature. [054] A second type of three port device used in embodiments of the invention has one inlet and two outlets, and this will be referred to as a single inlet three port device. Such a device can be used to direct the input to either a first or a second outlet. For example, a diverter single inlet device can determine which outlet is to be selected based on the temperature of the water at the inlet. The device can be designed so that the changeover is fairly abrupt as the temperature of the inlet water crosses a temperature threshold. [055] Both the single inlet device and the single outlet device can be autonomously controlled, for example by expansion and contraction of a wax in a cylinder in response to temperature variations. A piston can be displaced by the wax in response to its thermal coefficient of expansion. The transition temperature of the wax can be used to produce a substantial physical displacement of a piston. [056] The invention also contemplates the use of controllable three port devices which can be regulated by an external controller and servo-motors such as stepper motors.

WO 2008/070906 PCT/AU2007/001906 8 [057] Instead of having a controller and a regulated gas flow or water flow to produce the required outlet temperature, the instantaneous gas heater can be free running, having a predetermined water flow rate and a predetermined gas flow rate, so the amount of heat added to the water is constant, and the temperature differential from the inlet water temperature is determined by these factors. [058] A temperature and pressure relief valve can be provided to ensure the heater is not subject to excessive pressure loads. [059] The arrangement of Figure 1 shows an instantaneous gas heater 130 controlled by a controller 104, which includes a programmable processor. A governor, including a flow sensor such as a venturi with associated transducer or turbine 122, and stepper motor controlled throttle 158 combines with bypass valve 120 under the control of the processor 104 to control the proportion of water which passes through the heater 130 and the proportion which is diverted directly to the outlet 150. One or more temperature sensors such as 142 (hot water), 144 (heater inlet), 146 (governor inlet), 148 (mixed outlet) can be located as required to provide temperature data to the controller 104 to produce the required water temperature. [060] The controllable water heater 130 can have a controller 104, which can include a processor and user input means such as a keypad or dial, and display. The heater also includes an auxiliary warm water store (102) having an inlet 112 connected to a cold water supply 116, and warm water outlet 114. Cold water enters the heater 130 via inlet 134, and heated water exits via outlet 136. Alternatively, the main heater 130 can be designed to be free running with fixed water inlet flow rate and fixed gas flow rate. Overtemperature protection, such as temperature and pressure relief valve or overtemperature gas shut-off can also be provided. [061] A bypass arrangement includes a bypass valve 120 which is controllable to divert a controlled proportion of cold water from the water supply directly to the outlet 150. An instantaneous gas heater 130 receives the water provided by the bypass arrangement. The bypass valve can be adapted to be responsive to the outlet temperature sensor 148 or the water flow rate to increase or decrease the amount of cold water diverted to the outlet depending on whether the outlet temperature is above or below a selected temperature.

WO 2008/070906 PCT/AU2007/001906 9 [062] The diverter valve can be controlled via a controller, such as main controller 104, or by a local controller located proximate the outlet. Alternatively, the diverter valve 120 can be mechanically linked with the temperature sensor 148. In some arrangements, a bypass valve can be used to allow the heat exchanger of the gas heater to operate at higher temperature that that required if there is a possibility that condensate may occur due to burner operation. Copper heat exchangers can be attacked by the corrosive condensate. On start-up a percentage of the stored hot water would be bypassed directly to the hot water outlet of the heater. This water would be mixed with the cold/warm water exiting the heat exchanger at a flow rate, controlled by the flow governor, to give the desired mixed temperature. [063] As shown in Figure 1, a governor can include a flow detector 122, such as a turbine driven signal generator, a stepper motor controlled throttle valve 158, and a temperature sensor 146. This arrangement is particularly suitable for regulating the outlet temperature from the main heater 132 when the gas flow is unregulated. The flow signal generator 122 notifies the controller 104 when flow starts. It can also be adapted to report the magnitude of the flow. The processor 104 can use this flow information to initiate the gas burner of the main heater 130 and also to control the throttle valve by sending control signals to the stepper motor to control the aperture of the throttle valve. The controller can be programmed to determine the necessary water flow rate based on the heating capacity of the gas burner of the main heater to produce the selected outlet temperature. Thus the controller matches the flow rate to the heating capacity of the gas heater 130. [064] However, it can take over 20 seconds, typically 30 seconds for the water to reach the required operating temperature. Thus, in the example of a bathroom shower, the water which is below the required temperature is usually allowed to flow to a drain unused. An embodiment of the invention is illustrated in Figure 2. [065] The system of Figure 2 includes an instantaneous gas water heater 230, an auxiliary heater 202, a governor including turbine 222, and stepper motor controlled throttle valve 258, and controller 204. Preferably, the auxiliary heater is a storage heater with a small capacity.

WO 2008/070906 PCT/AU2007/001906 10 [066] A preferred range of capacities for the auxiliary heater is between 2 L and 5 L. However, the size of the auxiliary tank is not critical to the invention, the only requirement being that the capacity is sufficient to provide heated water during the warm up period of the instantaneous gas water heater. [067] Preferably, the auxiliary heater is operated at a temperature sufficiently high to inhibit growth of Legionella bacteria. In a preferred embodiment, the temperature of the auxiliary heater is set within 65'C to 70*C. [068] The auxiliary heater 202 has a controllable heating element 209 controlled by controller 204, for example via a switch 210 connecting the heating element 209 to the power supply 208. Other means of heating the auxiliary heater are within the scope of the invention. For example, a flexible electric heater strip can be wound on the outside of the tank 202. [069] Temperature sensors 242, 244, 246, 248 can be provided to provide temperature data to the controller. [070] The instantaneous gas water heater 230 has an input 234 which is fed from the water supply line 216 via a governor and/or with heated water from an auxiliary heater 202 via a diverter valve 220 under control of the processor 204. [071] The diverter valve can be a two-state valve (open/closed) or a continuously variable valve. The diverter valve 220 can be a solenoid operated valve controllable by the controller 204. [072] When the system has not been used for some time, the water in the instantaneous gas heater 230 will have cooled towards the ambient temperature. Thus, when the heater is turned on, the turbine 222 will inform the controller that water flow has commenced, and the controller will ignite the gas burner 232. However, because the temperature of the water from the instantaneous gas water heater has not reached the required operating temperature, the controller will operate the throttle valve 258 to block or reduce the amount of cold water from the water supply 216 entering the instantaneous gas water heater 230, while opening the diverter valve 220 to permit water from the auxiliary heater to flow into the inlet 234 of the instantaneous gas water heater 230. Thus the water is supplied at the temperature of the auxiliary heater WO 2008/070906 PCT/AU2007/001906 11 or at a temperature determined by the blending of the water from the auxiliary heater with the supply water via throttle valve 258. After the cold water has been purged from the main heater 230, the instantaneous gas water heater 230 will begin to produce heated water so that the outlet temperature detected by sensor 248 will begin to rise above the required outlet temperature. In response to this, the controller begins to open the throttle valve 258 using the associated stepper motor. Hence the controller maintains the outlet water temperature within a predetermined temperature range. [073] The auxiliary temperature sensor 206 can also control the closing of the diverter valve 220, so that, when the temperature of the water from the auxiliary heater falls below that of the main heater, the flow from the auxiliary heater is stopped. [074] Where there are additional temperature sensors for example 246 measuring the water supply temperature and 206 measuring the temperature of the water in the auxiliary tank 202, the processor can be programmed to calculate the flow rates of the cold and pre-heated water to maintain the outlet temperature within a required range. [075] In know instantaneous water heater arrangements, the outlet temperature can be fixed. In an embodiment of the invention, the user can select the required outlet temperature so that the outlet temperature need not be fixed. That is, the user can select T4 in equation 1 below. [076] The relative amounts of water drawn from the governor and the auxiliary heater on start-up can be calculate from the formula: X = (T4 - T2)/(T1-T2) [equation 1] where: T1 is the inlet water temperature (246); T2 is the temperature of the water in the auxiliary heater (206); T4 is the required outlet temperature programmed into the controller; and X is the normalized proportion of water drawn through the governor, ie, the proportion of bypass water drawn from the auxiliary tank is 1-X.

WO 2008/070906 PCT/AU2007/001906 12 [077] Thus, the initial outlet temperature T4 can be achieved by the controller controlling the throttle 258 to produce the relative flow of X : (1 -X) for the cold water supply to the auxiliary heater water flow. As the instantaneous gas water heater approaches operating temperature, the proportion of water from the supply is increased and the proportion from the auxiliary heater decreased.. When the instantaneous gas water heater reaches full operating temperature, the diverter valve 220 is closed. [078] The instantaneous gas water heater has a maximum flow for any required outlet temperature determined by the maximum heat transfer via the heat exchanger of the gas heater 232. Preferably, the heat transfer capacity of the heat exchanger and the maximum flow rate are chosen so that, for the maximum flow, there is an upper limit to the outlet temperature. [079] However, if the instantaneous gas water heater is generating maximum heat transfer, and the flow is below this maximum rate, the temperature of the outlet water will rise above the required outlet temperature. Thus, in a further embodiment, the controller 204 can control the amount of gas supplied to the instantaneous gas water heater via a gas flow control valve (not shown) to maintain the outlet temperature in the required range. Alternatively, a mechanically controlled valve using, eg, a bi-metal temperature sensing element or a wax expansion/phase change piston arrangement sensing the outlet water temperature, can be used to regulate the amount of gas supplied to the burner. [080] While the controller can be programmed to close the diverter valve when the main heater has reached operating temperature, alternative modes of operation can be implemented without departing from the scope of the invention. In an alternative embodiment, the diverter valve 220 can be left open until the user turns off the water flow, so that the auxiliary heater acts as a booster for part of the water flowing into the main heater 230. The controller can thus control the burner 232 to take account of the additional thermal input from the auxiliary heater. When the main heater has reached its operating temperature, the throttle 258 can be opened to permit the flow via both paths to equate to the maximum flow for which the instantaneous gas water heater is designed. Alternatively, the controller can turn the auxiliary heater WO 2008/070906 PCT/AU2007/001906 13 element of when the main heater has reached its design operating temperature. A choke may be used in the auxiliary heater path to ensued the combined flow does not exceed the maximum flow rate. [081] The system illustrated in relation to Figure 2 is suitable for compensating for the warm up period of the instantaneous gas water heater, but does not compensate for the cold water already present in the instantaneous gas water heater. [082] Figure 3 illustrates an embodiment of the invention which compensates for the cold water in the instantaneous gas water heater on start up. [083] In Figure 3, the outlet 314 from the auxiliary heater 302 can be connected to the inlet 334 of the instantaneous heater 330, or to the system outlet 350, or it can be shut off. [084] The arrangement is similar to that of Figure 2, except that the plumbing is arranged to connect the outlet from the auxiliary heater 302 to the system outlet 350. A further controllable valve 360 is used to prevent bypass of the inlet water from the governor to the outlet 350 when the instantaneous gas water heater has attained its required operating temperature. [085] The instantaneous gas water heater 330 can receive its input at 334 from the supply via the governor and also can receive input from the auxiliary heater 302. This arrangement has two mixing points 352, 354. At 352, unheated water from the governor throttle 358 mixes with water from the auxiliary heater 302 and is divided between the input to the instantaneous gas water heater 334, and the second mixing point 354 via valve 360. If the flow resistance on the two paths (via the instantaneous gas water heater and via valve 360) between 352 and 354 are equal, the flows will divide equally between the paths. A choke can be added to one of the paths to adjust the flow resistances to achieve a desired distribution between the two flow paths. [086] The temperature sensor 348 can be used to regulate the throttle 358 to control the outlet temperature at 350 during the warm up phase of the instantaneous gas water heater.

WO 2008/070906 PCT/AU2007/001906 14 [087] Figure 4 illustrates a further embodiment of the invention in which the outlet from the auxiliary heater is fed to the system outlet 450, but not to the inlet 434 of the instantaneous gas water heater 430. In this arrangement, only the outlet from the governor throttle 458 is fed to the instantaneous gas water heater inlet 434. The outlet from the auxiliary heater 402 mixes with the outlet of the instantaneous gas water heater at junction 454. The governor regulates the flow through the instantaneous gas water heater 430 to obtain the required outlet temperature at 450. Again, the valve 420 is operated to control the flow of heated water from the auxiliary heater 402. [088] In a further embodiment illustrated in Figure 5, the diverter valve 220 of Figure 2 can be omitted. This arrangement can operate in a number of different modes. [089] In one mode, the throttle 558 can be used to close the governor path until the main heater reaches full operating temperature, and all the flow can be via the auxiliary heater 202. The controller 504 turns the auxiliary heater element off when the main heater reaches its operating temperature. The auxiliary heater element is turned on once the flow stops. In this mode, the flow sensor can be located before (upstream of) the junction 518 so it registers the flow through the system. [090] Alternatively flow can be via both the governor path and the auxiliary path. This can be done to cool the water from the auxiliary heater 502 to the required outlet temperature. [091] In another embodiment, the auxiliary heater element can remain on during the flow, and the controller can control the burner 532 to take account of the additional thermal input from the auxiliary heater. [092] Figure 6 illustrates a gas heater 630, 632 having a cold water inlet 636 and gas inlet 638. A flow regulator 658 controls the flow of cold water from cold water supply 616. A controller 604 receives inputs from temperature sensors 606, 642, 662. An electric heater 602 is connected to mains power 608 via switch 610 which is controlled by a thermostat or by controller 604. Flow sensor 622 detects demand for hot water at outlet 650.

WO 2008/070906 PCT/AU2007/001906 15 [093] Figure 6 illustrates an embodiment of the invention in which the outlet 634 of the instantaneous gas heater 620 and the outlet of the electric booster heater 602 are connected as inlets of temperature adjusting valve such as a tempering or mixing valve 680. [094] A tempering valve has a first and a second inlet, and a common outlet. A temperature sensing element in the outlet adjusts the proportion of water from the first and second inlets to adjust the outlet temperature towards a desired outlet temperature. Normally, the first inlet is a hot water inlet, and the second inlet is a cold water inlet. In normal use, the tempering valve initially has the first inlet fully open and the second inlet fully closed, and adjusts the proportion of cold to hot as the sensor detects an overtemperature at the outlet. [095] In this embodiment of the invention, the booster heater is connected to the first or "hot" inlet, and the gas heater is connected to the second or "cold" inlet. Thus, when the user turns the tap on, water is first drawn from the booster heater, and the tempering valve admits water from the gas heater to cool the outlet temperature to the selected operating temperature. Thus the "dead" water (water below the operating temperature) is utilized while the gas heater comes up to its designed temperature. [096] In more detail, when demand is detected at outlet 650 by flow sensor 622, the gas heater is ignited by the controller 604, while the auxiliary heater is maintained above the required outlet temperature, at least during periods of normal use. In the case where one of the inlet flows is above or equal to a target temperature, eg, 3 8'C to 40*C, and the other is below or equal to the target temperature, the tempering valve can adjust the proportion of these inlet flows to produce a desired output temperature flow at outlet 650. The tempering valve can have internal adjustment mechanisms to achieve the target temperature. [097] The electric booster heater 602 can store water at a temperature sufficiently above the user requirements, so that, when an initial demand for water commences, the tempering valve 680 draws water from the electric booster 602 and the dead water from the gas heater 630 and mixes the flows to produce water at a temperature within the desired outlet temperature range at outlet 650.

WO 2008/070906 PCT/AU2007/001906 16 [098] When the outlet from the gas heater 630 reaches the target outlet temperature, as detected, for example, by the temperature sensor 642 or by the tempering valve's internal temperature control means, the tempering valve closes off the flow from the electric booster 602, and passes the controlled flow from the gas heater 630 unmixed. When the water in the electric booster reaches its upper temperature limit, eg, 70*C, the controller 604 turns the electric booster heater 602 off until the temperature falls to its lower temperature threshold, eg, 604C. [099] The tempering valve 680 can be a standard self-regulating device. This can include manual adjustment to select a preferred outlet temperature. In an alternative embodiment, the tempering valve can include an adjustable valve arrangement controlled by the controller 604 to enable electronic selection and adjustment of the output temperature. [0100] In Figure 7, similar numbers represent the corresponding feature in Figure 6, except that the initial digit is "7" instead of "6". In a modification of the arrangement of Figure 6 shown in Figure 7, the outlet 734 from the gas heater 730 can be connected to the input of the electric booster 702, and the cold water inlet can connect to the tempering valve 780 in place of the gas heater connexion. Thus, when the gas heater reaches the required temperature, as detected, for example, by temperature sensor 742, the heating element of the electric booster is switched off, and the water from the gas heater flows via the booster heater to the tempering valve. In this arrangement, it is not necessary to regulate the gas heater to the required outlet temperature because this function can be implemented by the tempering valve 780. [0101] The arrangements of Figures 6 & 7 overcome the start-up water wastage associated with gas fired instantaneous heaters without losing the remote temperature control capability. In addition, the water in the auxiliary heater when the water demand ceases is at the outlet temperature of the main heater and has been heated by gas rather than electricity. Thus electrical heating is used in the auxiliary heater to maintain the water in the auxiliary heater at the auxiliary heater temperature. [0102] On start-up, the tempering valve is supplied with hot water from the electrically boosted vessel & cold water either from the cold water line or the outlet from the gas heater. When the gas heater hits operating the temperature controlled WO 2008/070906 PCT/AU2007/001906 17 water will pass directly through the tempering valve without any mixing. However, if the main heater exceeds the desired outlet temperature, the tempering valve operates to reduce the temperature to the required value. [0103] In Figure 8, similar numbers represent the corresponding feature in Figure 6, except that the initial digit is "8" instead of "6". Figure 8 illustrates a further embodiment of the invention having first and second tempering valves 880 and 882. The first tempering valve 880 combines the flows from the gas heater 830 and the electric heater 802, while the second tempering valve 882 combines the output of first tempering valve 880 and the cold water inlet 816. The first tempering valve acts in the same manner as the tempering valve 680 in Figure 6. The auxiliary heater is connected to the hot inlet of the tempering valve, and the main heater is connected to the cold inlet of the tempering valve 880. The second tempering valve can reduce the requirement to regulate the gas flow for gas heater 830, so the temperature of the water from the gas heater 880 can rise above the required user temperature, and the second tempering valve 882 will temper the outlet water temperature to the required value. [0104] Figure 9 shows an instantaneous gas heater 902 (the main heater) with cold water inlet 934, outlet 906, and gas supply 908 operated by controller 904 in response to flow detector 922, which can be a venturi flow detector with suitable transducer to transmit a flow signal to controller 904. Main heater outlet 934 feeds into auxiliary heater 902 via input 921, and also feeds into the cold inlet 983 of tempering valve 980. The outlet 914 of auxiliary heater 902 feeds into the hot inlet 981 of tempering valve 980. The tempering valve 980 has a mixed outlet 985 (M) which is intended to deliver water at the set temperature To. To can be set by suitable choice of the internal temperature control of the mixing valve 980. For example, where the internal controller is a wax piston, the wax composition can be chosen to operate at a required outlet temperature. [0105] The operation of the tempering valve 980 is as follows. When the outlet temperature from the tempering valve is below To, the internal temperature controller will operate to increase flow from the hot inlet 981 (H) and to reduce the flow from the cold inlet 983 (C), and when the temperature reaches the required WO 2008/070906 PCT/AU2007/001906 18 temperature, the mixing valve controller will maintain the current settings of its hot and cold inlets. If the temperature exceeds the set temperature, the mixing valve control will increase the proportion of water entering the cold inlet and reduce the proportion entering the hot inlet. [0106] When the system has not been used for some time, the water in the main heater will have cooled towards ambient temperature. The water in the auxiliary heater is kept at a set temperature TA by electrical heating element 909 and temperature control means (not shown). [0107] When a flow of water is detected by the flow detector 922, the controller 904 will ignite the gas heater of main heater 930. However, in the initial heating phase, the water from the main heater outlet will be at a temperature below the required outlet temperature set by the mixing valve. Thus the flow from the main heater via the cold inlet will be shut off and water will be drawn from the auxiliary heater 902 via the hot inlet 981 of the tempering valve. Thus the under-temperature water in the main heater 930 will be diverted to the auxiliary heater 902. [0108] The following table indicates the operation of the tempering valve 980: TEMPERING VALVE [980] OPERATION MAIN HEATER AUX HEATER TEMP VALVE TM TA <To < To H < To > To H+C >To > To C > To > < To C [0109] As long as the water entering the cold inlet is below the operating temperature To, and the outlet temperature is below the operating temperature, the tempering valve control will open the hot inlet and draw water from the auxiliary WO 2008/070906 PCT/AU2007/001906 19 heater. If the outlet temperature exceeds the operating temperature, the tempering valve will open the cold inlet. The tempering valve control is sensitive to the outlet temperature, so if the outlet temperature exceeds the set temperature, it will increase flow from the cold inlet and reduce flow from the hot inlet, whether the excess temperature is from the water entering via the hot or cold inlet. [0110] If the auxiliary hater temperature TA is set below the operating temperature To, then, as long as the output from the main heater is below the operating temperature, the hot inlet will be open and the cold inlet will be closed. Thus the cooled water in the pipe from the outlet of the main heater to the cold inlet of the tempering valve will be locked in the pipe. Once the hot water from the auxiliary heater has been used, the cold water from the main heater will flow through the auxiliary heater, and the tempering valve control will sense the under-temperature and maintain the hot inlet open and the cold inlet closed. Thus a cold outlet flow from the tempering valve will occur. Hence, the auxiliary heater temperature is preferably maintained above the operating temperature, as the tempering valve can reduce this to the operating temperature by drawing water via the cold inlet to temper the water from the hot inlet. In this mode, the cold water from the main heater can be mixed with the hot water from the auxiliary heater. Preferably, the volume and temperature of the auxiliary heater are chosen to ensure that the cold water from the main heater is exhausted before the hot water from the auxiliary heater is used up. [0111] In some countries, health regulations may require that the auxiliary heater be maintained above the bacterial growth temperature, nominally 60'C. In one embodiment, the auxiliary heater is maintained at 70 C. [0112] The arrangement of Figure 9 is suitable for use where the main heater is set to produce water at the required outlet temperature, i.e., where Tm ~ To . [0113] The arrangement of Figure 9 can also be used in conjunction with a cold tap outlet controlled by the user to provide water at a temperature required by the user where Tm > To. [0114] In an alternative embodiment, the operating temperature of the mixing valve 980 can be controlled by a controller, such as controller 904.

WO 2008/070906 PCT/AU2007/001906 20 [0115] Figure 10 shows an alternative embodiment in which the water from the main heater 1030 passes through the auxiliary heater 1002. The outlet from the auxiliary heater is connected to the hot inlet 1081 of mixing valve 1080. The cold inlet of the mixing valve 1080 is connected to the cold water supply 1016. The flow sensor 1022 detects the commencement of water flow and signals this to the controller 1004 which turns on the main gas heater 1030. As the main heater and the auxiliary heater are in series, the flow from the auxiliary heater, which is above the required outlet temperature, is mixed with cold water in mixing valve 1080 to produce the required outlet temperature. However, when the pre-heated water from the auxiliary heater 1002 is used up, the cold water from the main heater enters the auxiliary heater. Thus, in this arrangement, the auxiliary heater should be capable of heating the outlet flow to the required temperature in a similar manner to an instantaneous water heater. Thus, in this arrangement, the auxiliary heater needs to have a high power capacity to ensure that there is not a cold surge during use. [0116] Figure 11 shows an arrangement which combines the arrangements of Figures 9 and 10. The arrangement of Figure 1 uses two three-port devices 1180, 1190. The main heater outlet 1134 is connected to the inlet of the auxiliary heater 1102 and to the cold inlet 1183 of mixing valve 1180. The outlet 1114 of the auxiliary heater connects to the hot inlet 1181 of the mixing valve 1180. The outlet 1185 of the mixing valve 1180 is connected to the hot inlet 1191 of mixing valve 1190, and the cold water supply 1116 is connected to cold inlet 1193 of the mixing valve 1190. [0117] The arrangement of Figure 11 operates as follows. When the main heater has cooled below the required outlet temperature, and there is a demand for hot water, the flow detector 1222 triggers the main heater 1230 via controller 1204. Flow is initially via the auxiliary heater as the default condition of the mixing valve is H open, C closed. Because the auxiliary heater temperature is above the required system temperature, mixing valve 1180 partially opens cold inlet 1183 to reduce the temperature to the required temperature. As the outlet 1185 of mixing valve 1180 is connected to the hot inlet 1191 of mixing valve 1190, this passes directly to the outlet 1195 of mixing valve 1190. The main heater 1130 is adapted to reach its operating temperature before the hot water from the auxiliary heater 1102 is used up. The WO 2008/070906 PCT/AU2007/001906 21 operating temperature of the main heater is set above the required outlet temperature of the system. Thus, as the water from the main heater exceeds the required outlet temperature, the cold valve opens further, increasing the flow from the main heater and decreasing the flow from the auxiliary heater. This results in the outlet temperature from the first mixing valve 1180 exceeding the required outlet temperature. At this point, the second mixing valve 1190 operates to admit cold water from the clod inlet 1193 and produce output water at the required temperature. [0118] The mixing valves 1180 and 1190 can be set to the same operating temperature, or the mixing valve 1180 can be set to a higher operating temperature than that of 1190. [0119] Figure 12 illustrates a further arrangement in which the outlet 1234 of the main heater 1230 is connected to a diverter valve 1270. The diverter valve can be a tempering valve installed back-to-front, with its normal outlet 1275 as its inlet, and its hot inlet 1271 and its cold inlet 1273 used as outlets. Accordingly the term inlet port will be used to refer to the port 1275, and hot port will be used to refer to port 1271, and cold port will be used to refer to port 1273. The sensing element is in the inlet port 1275 so an overtemperature will cause an increase in outlet flow via cold port 1273, and an undertemperature will cause an increased flow via hot port 1271. [0120] Thus, on cold startup, the flow from the main heater will be to the hot port 1271 which is into the auxiliary heater 1202, and the outlet from the auxiliary heater will flow into the hot inlet 1281 of mixing valve 1280. As the auxiliary heater is maintained above the required operating temperature, mixing valve 1280 will admit cold water via port 1283 to achieve the required outlet temperature. [0121] When the main heater reaches the set point for the diverter 1270, the diverter 1270 will begin to open port 1273 while beginning to close port 1271. As the operating temperature of the main heater is above the required outlet temperature set by mixing valve 1280 for outlet 1250, the diverter 1270 will close off flow to the auxiliary heater 1202 and all flow will be via port 1273. Again mixing valve 1280 will temper the water supplied to outlet 1250 to the preset operating temperature.

WO 2008/070906 PCT/AU2007/001906 22 [0122] Figure 13 is a schematic illustration of a controllable valve adapted to be operated by a stepper motor 1388. The valve is a three port device having a common port 1385 and two variably selectable ports 1381, 1383. A diverting closure member such as vane 1387 is adapted to control the proportions of the two variable ports 1381, 1383 which is in communication with the common port 1385. The vane can provide total exclusion of one port, as for example when it is in the position shown in dotted line 1384, in which it rests on seal surface 1386 and closes port 1385. Similarly, port 1381 can be closed when the vane is in the position shown by dotted line 1389. Stepper motor 1388 is connected to the vane 1387 and can be controlled by a control means to adjust the position of vane 1387 between the end positions 1384, 1389. A temperature sensor 1398 can be provided to detect the temperature of the water in the port 1385 and notify a controller. [0123] A valve as shown in Figure 13 can be used to provide the end user with the option of controlling the outlet temperature of the system by programming a controller to operate the vane to adjust the flows to achieve the required output temperature. The control of the vane can be by a feedback mechanism, in which the controller continually adjusts the vane until the required temperature is achieved. Alternatively, where the controller also has the temperatures of the water at the ports 1381 and 1383, and details of the relative apertures for each position of the vane, the processor can calculate a setting for the vane from these temperatures. [0124] The applicant does not concede that the background technology discussed herein is part of the common knowledge in the field. [0125] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of". A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear. [0126] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

WO 2008/070906 PCT/AU2007/001906 23 [0127] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims

1. In a water heating system including a main water heater and a hot water store, a method delivering water within a first predetermined temperature range, the method including the steps of: maintaining the hot water store at a temperature above a minimum outlet temperature threshold; connecting the stand-by hot water to the outlet directly or via the main heater.

2. A method as claimed in claim 1, including the step of mixing the stand-by hot water with the water inlet supply before delivery to the system outlet.

3. A method as claimed in claim 1 or claim 2, wherein the main water heater is an instantaneous gas water heater, the method including the step of turning the instantaneous gas water heater on when the flow is detected.

4. A method as claimed in claim 3, including the step of mixing stand-by hot water with water from the instantaneous gas water heater before delivering the mixed water to the outlet.

5. A method as claimed in any one of the preceding claims, including the step of monitoring the temperature of the water from the main heater and monitoring the temperature of the stand-by hot water, and calculating a mixing ratio to achieve the required outlet temperature.

6. A method as claimed in any one of the preceding claims, including controlling the flow of water from the main heater and the stand-by hot water to obtain the required outlet temperature.

7. A method as claimed in any one of the preceding claims, including the step of reducing the flow of the stand-by hot water as the temperature of the water from the main heater increases.

8. A method as claimed in any one of the preceding claims, wherein a mixed flow of water from the water supply and the stand-by hot water is connected to the input of the main heater. WO 2008/070906 PCT/AU2007/001906 25

9. A method as claimed in any one of the preceding claims, including the steps of mixing the stand-by water with the water supply to form a first mixed flow, supplying the first mixed supply to the input of the main heater, and mixing the first mixed supply with water from the outlet of the main heater to provide an outlet flow.

10. A method as claimed in claim 1, wherein the stand-by flow is replaced by the output of the main heater when the temperature of the water from the main heater reaches the first predetermined temperature range.

11. A hot water supply system including a main water heater and an auxiliary water heater, wherein: the auxiliary heater is a storage water heater; the output of the auxiliary heater is connected to a system outlet by one or more of the following: directly; or via the main heater; or after mixing with the inlet water supply.

12. A system as claimed in claim 11, including a controllable throttle valve and configured to mix the output from the auxiliary heater with either the incoming water or the outlet of the main heater, or both, for supply to a system outlet.

13. A system as claimed in claim 12, including a first controllable diverter valve adapted to control the outlet from the auxiliary heater.

14. A system as claimed in any one of claims 11 to 13, wherein the output of the auxiliary heater is combined with the water supply inlet and connected to the inlet of the main heater.

15. A system as claimed in any one of claims 11 to 14, wherein the outlet of the auxiliary heater is combined with the inlet water supply and connected to the output of the main heater. WO 2008/070906 PCT/AU2007/001906 26

16. A system as claimed in any one of claims 11 to 15, wherein the main heater is an instantaneous gas water heater.

17. A system as claimed in any one of the preceding claims including a first temperature sensor to sense the temperature of the inlet water, a second temperature sensor to sense the temperature of the stored water.

18. A system as claimed in claim 17 including a third temperature sensor adapted to sense the temperature of the outlet water.

19. A system as claimed in claim 17 or claim 18, including a fourth temperature sensor adapted to sense the temperature of the hot water in the main heater.

20. A system as claimed in any one of claims 11 to 19, including a controller adapted to control the flow regulator.

21. A hot water supply system having an on-demand main heater and a booster heater, wherein the outlet of the main heater and the outlet of the booster heater are connected as inputs to a tempering valve which is adapted to produce an outlet flow within a predetermined temperature range.

22. A system as claimed in claim 21, including control means responsive to the temperature of the water supplied from the main heater to switch off the booster heater or to close off the flow of from the booster heater to the tempering valve when the main heater outlet temperature reaches a predetermined value. 22. A system as claimed in claim 21, wherein the main heater is connected to a first inlet of the tempering valve, and the outlet of the booster heater is connected to a second inlet of the tempering valve.

23. A system as claimed in claim 21, wherein the outlet of the main heater is connected to the inlet of the booster heater, the outlet of the booster heater is connected to a first inlet of the tempering valve, and the clod water supply is connected to a second input of the tempering valve.

24. A water heater having first and second heaters and first and second tempering valves, the outlets from the first and second heaters being connected as WO 2008/070906 PCT/AU2007/001906 27 inputs to the first tempering valve, and the outlet of the first tempering valve and the cold water inlet being connected as inputs to the second tempering valve.

25. A water heating system including a water conserving arrangement, the system including: a main water heater having an inlet and an outlet and being adapted to heat mains water; an auxiliary heater having an inlet and an outlet; a mixer having first and second inlets and an outlet; the outlet of the main heater being connected to the input of the auxiliary heater; the outlet of the auxiliary heater being connected to the first inlet of the mixer; the outlet of the main heater being connected to the second input of the mixer; temperature sensing means adapted to sense the temperature of the water from the outlet of the mixer; a mixer control adapted to control the flows via the first and second inlets of the mixer in accordance with the outlet temperature of the mixer; the main water heater being an on-demand heater; the auxiliary heater being adapted to heat water to a first temperature threshold; the mixer being adapted to increase the flow of water via the first inlet of the mixer and decrease flow via the second inlet of the mixer when the outlet temperature of the mixer is below a second temperature threshold, and to decrease flow via the first inlet of the mixer and increase flow via the second inlet of the mixer when the temperature is above the second threshold temperature.

26. A controllable three port valve having a common port and first and second variable ports, and an adjustable flow control member adapted to control the relative apertures of the adjustable ports, and a controllable drive means adapted to operate the control member.

27. A flow control arrangement including a valve as claimed in claim 26, the valve including temperature sensing means, the arrangement including a controller WO 2008/070906 PCT/AU2007/001906 28 adapted to control the drive means to position the flow control member in response to the temperature sensor.

28. A flow control arrangement including a valve as claimed in claim 26, including first and second temperature sensing means to sense the temperature at corresponding ones of the variable ports, and a controller adapted to control the position of the flow control member in response to the first and second temperature sensing means.

29. A method of operating a water heater system substantially as herein described with reference to the accompanying drawings.

30. A hot water supply system substantially as herein described with reference to Figures 2 to 7 of the accompanying drawings.