AU2007203198B2 - Improvements in Water Heating Systems - Google Patents

Description

C07102 1 Improvements In Water Heating Systems Field of the invention [001] This invention relates to a method and arrangement for conserving water in a water heating system. The invention also provides a method and arrangement for conserving energy. [002] The invention is applicable to water heating systems and can be applied advantageously in instantaneous water heaters. Background of the invention [003] Instantaneous water heaters are expected to deliver water at a given temperature. These systems detect a demand for hot water by the initiation of water flow through the system. However, because such heaters are normally quiescent until there is a demand for hot water, the water which is in the system before the demand commences, leaves the heater unheated or only partially heated. This incompletely heated water is usually permitted to run down the drain because it is not at the temperature required by the user. This can amount to a few litres of water wasted each time the system is used. [004] The term "incompletely heated water" as used herein means water which is delivered from the water heater at a temperature which is below threshold temperature. This threshold temperature can be below the nominal operating temperature of the water heating system. Summary of the invention [005] The present invention provides a water heating system including a water conserving arrangement, the system including: a main water heater adapted to heat mains water; an auxiliary tank; temperature sensing means adapted to sense the temperature of the water from the main heater; a diverter; wherein, when there is a demand for hot water, the diverter directs water from the main heater to the auxiliary tank when the temperature of the water from the main heater is below a first threshold temperature, and the diverter directs water from the main heater to an outlet when the temperature of the water from the main heater exceeds the first threshold temperature, 07102 2 and wherein water from the auxiliary tank is directed to the outlet when the temperature of the water from the main heater is below the first threshold temperature. [006] The system can include an auxiliary heater adapted to heat water in the auxiliary tank. [007] The auxiliary heater can be adapted to heat the water in the auxiliary tank to a second threshold temperature. [008] The main water heater can be an instantaneous water heater. [009] The main water heater can be one of a first gas heater or a first electric heater. [010] The auxiliary heater can be either a second gas heater or a second electric heater. [011] The main heater can be a first gas heater, wherein the first gas heater can include a pilot flame for the main heater adapted to provide heat for the auxiliary tank. [012] The system can include a pump controllable to pump water from the main water heater to the auxiliary tank to replace the water in the auxiliary tank with water at a higher temperature from the main heater. [013] The pump can be connected to circulate water between the main heater and the tank. [014] The main heater can be controllable to heat water passing through the main heater to within an operating temperature range having an upper and a lower operating temperature threshold. [015] The present invention also provides a water conserving arrangement adapted for retro-fitting to an installed water heating system having a main water heater, the arrangement including: an auxiliary tank; and a flow diverter; the flow diverted being connectable to receive an initial flow of water from the main water heater; the diverter being adapted, in response to a demand for hot water, to divert water from the main heater to the auxiliary tank when the temperature of the water from the main tank is below a first threshold temperature, and to direct the water from C07102 3 the main heater to an outlet when the temperature of the water from the main heater exceeds the first threshold temperature, wherein water from the auxiliary tank is directed to the outlet when the temperature of the water from the main heater is below the first threshold temperature.. [016] The arrangement can include an auxiliary heater arranged to heat water in the tank. [017] The invention also provides a method and arrangement in which incompletely heated water from a water heater is collected in a water storage means and is made available for use. [018] The "dead" water can be stored in a tank and heated to maintain it at a temperature suitable for use. [019] According to another embodiment of the invention there is also provided a method of conserving water in a water heating system including a water heater and an auxiliary tank, the method including the steps of detecting the commencement of water flow, initiating heating of water in the water heater, monitoring the temperature of the water from the water heater; diverting water from the water heater to the auxiliary tank while the temperature of the heated water is below a first threshold temperature; switching the flow from the water heater to the system output when the water temperature from the water heater reaches a first threshold temperature; wherein water from the auxiliary tank is directed to the outlet when the temperature of the water from the main heater is below the first threshold temperature.. [020] The method can further include the steps of heating the water in the auxiliary tank to above an auxiliary threshold temperature; maintaining the water in the auxiliary tank above the auxiliary threshold temperature; and in response to a demand for hot water, delivering water from the tank to the system output until the temperature of the water from the main water heater exceeds the first temperature threshold. [021] The water in the auxiliary tank can be exchanged with the water in the water heater at the end of a water usage.

C07102 4 [022] The method can include the steps of measuring the temperature of the water in the tank; measuring the temperature of the water in the heater. The exchange of water can be stopped when the temperature of the water in the tank is greater than the temperature of the water in the heater. [023] The method can include the step of measuring the volume of water pumped. The exchange of water can be stopped when the volume popped reaches a predetermined volume. [024] According to another embodiment of the invention there is provided a three-way valve having a flow control sensor adapted to control the flow of fluid through the valve, the valve including an auxiliary signal means adapted to provide an indication of the status of the sensor. Brief description of the drawings [025] 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: [026] Figure 1 is a schematic illustration of a first arrangement embodying the invention. [027] Figure 2 is a schematic illustration of a second arrangement embodying the invention. [028] Figure 3 illustrates a modification of the arrangement of figure 2 in which a tempering valve is adapted for use as the diverter. [029] Figure 4 illustrates a first arrangement using gas to heat the auxiliary tank. [030] Figure 5 illustrates a second arrangement using gas to heat the auxiliary tank. [031] Figure 6 illustrates the flow paths of a system according to an embodiment of the invention. [032] Figure 7 shows a tempering valve which has been modified to provide an external auxiliary signal.

C07102 5 [033] Figure 8 illustrates an arrangement using a piston and cylinder arrangement to replace the pump. [034] Figure 9 is an equivalent electrical circuit for use in explaining the operation of the arrangement of Figure 8. [035] Figure 10 shows a further arrangement embodying the invention. Detailed description of the embodiment or embodiments [036] The invention will be described with reference to the drawings. [037] The devices illustrated in the drawings have apertures which, in normal operation may serve as inlets or outlets. However, in some embodiments of the invention, some of the apertures may serve as inlets at one stage and as outlets at another stage of operation. Thus the term "ports" will be used to refer to the apertures interchangeably with the terms 'inlet' or "outlet". [038] Figure 1 illustrates a water heating system of the type referred to as an instantaneous hot water system which embodies the invention. [039] An instantaneous gas water heater 102 has two ports, namely a water inlet 104, and a heated water outlet 106. Heating energy is provided via a gas inlet 108. Such a system includes control means, including a demand detector such as a water flow detector 123 to determine when there is a demand for hot water when water is drawn off via system outlet 122. When a demand is detected, the gas flow to the main gas heater is turned on, and the gas is ignited to heat the heat exchanger within the heater 102. The gas can be ignited by a pilot flame or by other suitable means such as an electronic spark generator. [040] A water conservation system includes a storage tank 116 and a flow diverter 112. The tank has four ports 117, 119, 121, 122. The flow diverter has three ports, 111, 113, 115. The volume of the tank 116 can be approximately the same volume as the "dead" water in the system on the input side of the tank 116, i.e., from heater input 104 to tank input 121. The dead volume is the water which has cooled below the operating temperature since the last time the heater was used and will not be heated to the operating temperature before exiting the system via outlet 122. This 07102 6 can include water in the instantaneous heater which will not reach the operating temperature before it leaves the instantaneous heater. [041] The flow diverter 112 has an input 115 and is controlled in response to suitably located temperature sensor means and control means to direct the water from the heater 102 either to the storage tank 116 via outlet 111, or via outlet 113 to the system outlet 122. [042] One-way valves, such as valve 136 can be provided to prevent undesired flows in the system. [043] The storage tank 116 includes a first inlet 121 and a second inlet 119, a first outlet 117, and a second outlet 122. The first inlet 121 and second outlet 122 are preferably located proximate the lower end of the tank 116, and the second inlet 119 and the first outlet 117 are preferably located proximate the upper end of the tank 116. [044] The first inlet 121 is connected to the outlet I 11 of the diverter valve 112. [045] The first outlet 117 connects to the system outlet 122 via junction 120. [046] The second inlet 119 is connected to outlet 113 of diverter 112 via non return valve 118. [047] A flow detector 123 can be used to detect when flow commences. Alternative methods of detecting flow can also be used. For example, a rapid temperature drop proximate the inlet 121 of tank 116 can be used to determine that flow has commenced. [048] Optionally, the first outlet 117 of tank 116 connects to the outlet 113 of diverter 112 via junction 125, and the second outlet 122 of tank 116 connects to inlet 104 of heater 102. A non-return valve 137 prevents water entering tank 116 from the junction 134 and port 122. [049] Preferably, auxiliary heating means 128 are provided to heat the water in the tank 116. The heating means shown is a heating tape 128 wound around the tank 116. However, other heating means can be provided within the scope of the invention. For example, a heating element can be provided within the tank 116. In a further alternative, the tank 116 can be heated by gas.

C07102 7 [050] In the embodiment of Figure 1, an electric switch 130 is provided to control the supply of power 132 to the heating element 128. [051] A control means 140 is show illustratively connected to sensors and controlled elements of the system. [052] Sensor connexions 142, 146, 150 provide sensor information for the control means 140. For example, sensor connexion 142 is connected to a temperature sensor measuring the temperature of the heated water from the heater 102, sensor connexion 150 is connected to a sensor which measures the temperature of the water flowing into the diverter 112, and sensor connexion 146 is connected to a sensor which measures the temperature of the water near the upper portion of the tank 116. In a suitably insulated system, the outlet temperature from the heater 102 may be practically the same as the temperature of the water at the input 115 of diverter 112 when the water is flowing. [053] Control connexions 144, 148, 152, 154 enable control of the gas heater 102, the electric switch 130, the diverter valve 112, and pump 126 respectively. [054] While a single controller 140 is illustrated, some or all of the controlled elements, such as the heater 102, the diverter 112, pump 126, and the element switch 130 can alternatively have individual control means associated therewith. For example, switch 130 can be thermostatically controlled by a thermostat which senses the temperature of the water in tank 116. Similarly, the operation of the diverter valve 112 can be controlled by a sensor within the diverter valve itself. [055] The operation of the auxiliary heating system will now be described. [056] The heater 102 is assumed to have a design output operating temperature range of Tmin to Tmax. In operation, when the system has not been used for some time, the water in the heater 102 will cool to a temperature which may be significantly below the minimum specified operating temperature Tmin of the heater 102. [057] A temperature sensor (not shown) associated with the control of the auxiliary heater 128 senses the temperature of the water in the tank 116 and the switch 130 is controlled to maintain the temperature of the water in the tank above an 07102 8 auxiliary threshold temperature T 1 . For example, the temperature sensor can be connected via connexion 146 to controller 140 which operates switch 130 to maintain the water in tank 16 within a predetermined temperature range. [058] As mentioned previously, in an alternative arrangement, switch 130 can be controlled by an independent thermostat associated with tank 116. [059] The temperature of the water in tank 116 can be maintained at a level to inhibit growth of harmful bacteria such as Legionella. Preferably, the water in tank 116 is maintained at approximately 60*C. [060] When a demand for water is detected, the cool "dead" water in the heater 102 is diverted by the diverter 112 to input 121 of tank 116, and the heated water from the tank 116 is supplied to output 122 via port 117. At the same time, the heater 102 is ignited and commences to heat the water which flows into the heater 102. [061] The diverter 112 has a temperature sensor associated with it and operates by diverting water from inlet 115 to output I ll when the temperature of the water is below a threshold value, referred to herein as the diversion threshold temperature, and when the temperature of the water exceeds the diversion threshold temperature, the diverter switches the flow to the output 113. Thus, when the water from the heater 102 is above the diversion threshold temperature, the diverter 112 bypasses the tank 116 input 121 and diverts the flow to port 119, and then out port 117. The pressure drop through the heater and diverter prevent the water from flowing out port 122 and back to the junction 134, i.e., junction 134 is at a higher pressure than port 122 when flow occurs. [062] Consequently, when the temperature of water which has been heated reaches the diverter 112 at a temperature equal to or above the diversion threshold temperature, the diverter directs the water to output 113, and thence to port 119 via non-return valve 118. In this way, the temperature of the output water at 122 is maintained at a satisfactory level for use and the initial cold water output is minimized. Alternative configurations are possible. For example, the non-return valve 118 can alternatively connect to the input side of the flow meter 123 as shown in dotted line at 118'.

C07102 9 [063] A person skilled in the art, having read this description will understand that the diverter can alternatively be operated by a timer which in a system in which the control is adapted to switch the diverter to connect the heater output to the system water outlet when a predetermined time period has elapsed. The predetermined time can be the time it takes for the water passing through the heater to reach the operating temperature range. Similarly, the operation of the diverter can be based on the flow, so that the diverter is switched when a predetermined volume has passed, such as the volume of the tank. [064] A further feature of the invention is illustrated in dashed line in Figure 1. This involves the "scavenging" of the remnant hot water in the heater when the outlet tap is turned off by exchanging that water with the cold water stored in the tank. In this arrangement, when the demand for hot water ceases, water in the main heater 102 is exchanged with water in the tank 116. This is done in the case where the temperature of the water in the tank is higher than the temperature of the water in the tank. [065] The outlet 119 of tank 116 is connected to input 117 of tank 116 via junction 120 and pump 126, and a second outlet 122 of tank 116 is connected to input 104 of heater 102. A one way valve 136 serves to prevent counter-flow in cold water inlet pipe 138. [066] When the demand ceases, the heater 102 is turned off. The water in the heater 102 and its associated plumbing is now at about the maximum operating temperature Tmax, which will normally be greater than the temperature of water in the tank. Thus pump 126 is operated to replace the water in the tank 116 with the hotter water from the heater 102. The water in the heater 102 is pumped to the tank via diverter 112 and inlet 117. One way valve 118 blocks the path from outlet 113 of diverter 112 to port 119 of the tank 116. [067] When the diverter detects that the temperature of the water from the tank 116 has dropped below the diverter threshold temperature, the diverter 112 closes the port 113 and opens port 111. This effectively blocks the pump circulation path. The pump can be controlled to switch off due to the back pressure or in response to a 07102 10 temperature signal indicating that the temperature of the water has fallen to the diverter threshold temperature. [068] Because the hotter water from heater 102 has replaced the "dead" water in the tank 116, the auxiliary heater 128 will not be required to heat the water in tank 116 until the water cools to the threshold temperature from the hotter temperature Tmax. Thus the auxiliary heater 128 is turned off for a longer time interval after hot water has been drawn from the system. [069] The operation of the pump can be controlled via a temperature sensor measuring the outlet temperature from 106 of heater 102, so that, when the heated water has been pumped out of the heater 102, the pump is turned off. [070] The pump operation can be controlled in a number of ways. A first way is to measure the volume of water pumped and turn the pump off when the volume of water in the heater has been pumped. A second way is to use temperature of the water in the heater and the tank, and to turn the pump off when the temperature of the water in the heater is lower than the temperature of the water in the tank. [071] The heater 102 can have a flow control mechanism which trips or initiates its burner when the flow through the heater 102 exceeds a first threshold flow rate. The pump 126 can be adapted to have a flow rate less than the first threshold flow rate so that the circulation between the tank 116 and the heater 102 via the pump does not trip the heater burner. The flow threshold for the pump 126 of the embodiment of Figure 1 can be of the order of 3 to 6 L/min, and the pump has a flow rate of the order of 2 L/min. A flow restrictor (c.f. 894 in Figure 8) can be included in the scavenging path in series with the pump 126 to limit the flow rate. [072] A person skilled in the art will understand that the invention encompasses both a "snap action" or "toggle" operation of the change-over valve 112, 212, and a more gradual transitional change-over in the region of the threshold temperature. [073] The embodiment of Figure 2 is similar to that of Figure 1, but has a different scavenging flow path.

C07102 11 [074] Figure 2 illustrates an alternative configuration of a system embodying the invention. An instantaneous gas water heater 202 has two ports, namely a water inlet 204, and a heated water outlet 206. Heating energy is provided via a gas inlet 208. Such a system includes control means, including a demand detector such as a water flow detector 223 to determine when there is a demand for hot water when water is drawn off via system outlet 222. When a demand is detected, the gas flow to the main gas heater is turned on, and the gas is ignited to heat the heat exchanger within the heater 202. The gas can be ignited by a pilot flame or by other suitable means such as an electronic spark generator. [075] In Figure 2, the water conservation system includes a storage tank 216 and a flow diverter 212. The tank has four ports 217, 219, 221, 222. The flow diverter has three ports, 211, 213, 215. The volume of the tank 216 can be approximately the same volume as the "dead" water in the system on the input side of the tank 216, i.e., from heater input 204 to tank input 221. The dead volume is the water which has cooled below the operating temperature since the last time the heater was used and will not be heated to the operating temperature before exiting the system via outlet 222. [076] The flow diverter 212 has an input 215 and is controlled in response to suitably located temperature sensor means and control means to direct the water from the heater 102 either to the storage tank 216 via outlet 211, or via outlet 213 to the system outlet 222. [077] One-way valves, such as 236 can be provided to prevent undesired flows in the system. [078] The storage tank includes a first inlet 221 and a second inlet 217, a first outlet 219, an a second outlet 222. The first inlet 221 and second outlet 222 are preferably located proximate the lower end of the tank 216, and the second inlet 219 and the first outlet 219 are preferably located proximate the upper end of the tank 216. [079] The first inlet 221 is connected to the outlet 211 of the diverter valve 112. [080] The first outlet 217 connects to the system outlet 222 via junction 220.

C07102 12 [081] The second inlet 219 is connected to outlet 213 of diverter 212 via non return valve 218. [082] A flow detector 223 can be used to detect when flow commences. [083] Optionally, the first outlet 219 of tank 216 connects to the inlet 217 of tank 216 via junction 225 and pump 226, and the second outlet 222 of tank 216 connects to inlet 204 of heater 202. A non-return valve 240 prevents water entering tank 216 from the junction 234. [084] The operation of the auxiliary heating system of Figure 2 will now be described. [085] The heater 202 is assumed to have a design output operating temperature range of Tmin to Tmax. In operation, when the system has not been used for some time, the water in the heater 202 will cool to a temperature which may be significantly below the minimum specified operating temperature Tmin of the heater 202. [086] The temperature of the water in tank 216 can be maintained at a level to inhibit growth of harmful bacteria such as Legionella as described with reference to Figure 1. [087] When a demand for water is detected, the cool "dead" water in the heater 202 is diverted by the diverter 212 to input 221 of tank 216, and the heated water from the tank 216 is supplied to output 222. At the same time, the heater 202 is ignited and commences to heat the water which flows into the heater 202. [088] The diverter 212 has a temperature sensor associated with it and operates by diverting water from inlet 215 to output 211 when the temperature of the water is below a threshold value, referred to herein as the diversion threshold temperature, and when the temperature of the water exceeds the diversion threshold temperature, the diverter switches the flow to the output 213. Thus, when the water from the heater 202 is above the diversion threshold temperature, the diverter 212 bypasses the tank 216. [089] When the temperature of water which has been heated reaches the diverter 212 at a temperature equal to or above the diversion threshold temperature, C07102 13 the diverter directs the water to output 213, and thence to output 222 via junction 220. In this way, the temperature of the output water at 222 is maintained at a satisfactory level for use and the initial cold water output is minimized. [090] Figure 3 is an arrangement similar to that of Figure 2, in which a tempering valve 312 has been used as the diverter 212, and in which a different flow path arrangement is used. [091] The advantage of using a tempering valve in this novel manner is that the tempering valve has its own temperature sensing control for the flow diversion. Thus can be in the form of a wax driven piston/cylinder arrangement which trips when the wax melts. The melting point of the wax can be chosen by blending selected additives, such as an oil, to the wax. A standard tempering valve has a hot water inlet, marked "H", a cold water inlet marked "C" and a mixed outlet marked "M". However, the tempering valve is used in this embodiment in a manner different from its normal operating mode. In normal operation, the port 311 is the hot inlet "H", the port 313 is the cold inlet "C", and the port 315 is the tempered water outlet "M". The temperature sensor measures the temperature of the water in the M port 315. In this embodiment, the port 315 is used as the inlet, the port 311 (the normal hot inlet) is the default outlet when the valve is below its trigger temperature, and the port 313 is used as the outlet when the temperature of the water exceeds the threshold value. Thus, when the initial demand commences, the water is diverted through tank 316 until the temperature of the water from outlet 306 of heater 302 exceeds the operating temperature f the tempering valve. The trigger temperature of the tempering valve can be selected. In one embodiment, the trigger temperature can be in the range of 40'C to 60*C. The trigger temperature can be 50'C. [092] The system can be retrofitted to existing instantaneous water heaters. [093] The system can also be integrated into new instantaneous water heaters. [094] The heat for the auxiliary water tank can be supplied by the gas supply or other suitable heat source. [095] Figure 4 illustrates an arrangement 402 including a heat exchanger 412 and gas burner 414, in which the pilot light 416 of the burner 414, 414 is used to Z07102 14 provide heating for the tank 412. This arrangement requires a pilot light having sufficient heat output to heat the tank 412 to the required temperature. [096] Figure 5 shows a modification of the arrangement of Figure 4 having a pair of pilot lights 516, 518 connected to the gas supply via valves 520, 522. Thus pilot 516 can be used both as a pilot light and to heat the tank 512, while pilot 518 is used to only to light the burner 514. Control means (not shown) operate the valves 520, 522 so that, when the water in tank 512 is at the required temperature, the pilot 516 is turned off. The valve 522 can be optional so that 522 is opened shortly before valve 520 is closed. [097] A blow back pipe 524 used to ignite the burner 514 from pilot 516. The pipe 524 ducts gas from the burner 514 to the pilot 516 where it is ignited and the flame is drawn down the pipe. This permits the pilot and tank 512 to be located away from the main burner 514. A blow-back pipe operates on the principle which causes a Bunsen burner to blow back to the air intake when the gas/air mixture is not correctly adjusted. [098] Electronic ignition can be provided to ignite the pilot lights. Alternatively, a "blow-back" pipe can be used to ignite one pilot from the other. [099] Figure 6 illustrates the flow paths of a system according to an embodiment of the invention. The heating means for the tank have been omitted for clarity. [0100] Figure 6 shows a heat exchanger 102 having its output connected to the M port of three way valve 112. The valve has its H port connected to the tank inlet, while the C port bypasses the tank 116 and connects to the outlet 122. The tank outlet 119 also connects to outlet 122 via junction 120. [0101] When water is drawn off and the heater 102 is cold, the valve 112 causes the cold water from the heater 102 to be diverted to the tank 116 and the warm water in the tank is supplied to the outlet 122. [0102] When the water from the heater 102 reaches the operating temperature, the valve 112 operates to switch the flow to port C and bypass the tank 116. At this C07102 15 stage, the cold water from the heater 102 has been transferred to the tank 116 and hot water is supplied directly to the outlet 122 from heater 102. [0103] When the flow through outlet 122 is shut off, the pump 126 is started. The pump draws water from tank 116 and through heater 102 to valve 112 where it is diverted to port C because it is still above the operating threshold temperature. Because the outlet 122 is closed, the water enters the tank 116 via junction 120 and tank "outlet" 119. A controller 510 monitors the temperature of the water and stops the pump 126 when the water temperature falls below a predetermined temperature. [0104] The pump operation can alternatively be controlled by the valve 112 as discussed with reference to Figure 7. [0105] Figure 7 shows a tempering valve which has been modified to provide an external auxiliary signal. In its normal mode of operation, the tempering valve is a three port device with a hot inlet 704 (H), a cold inlet 706 (C), and a mixed outlet 702 (M). A temperature sensor 708 is located proximate the mixed outlet port 702 and regulates the relative volumes of hot and cold water supplied to the outlet 702. A valve 722 is shown as the means of regulating the flow. The sensor 708 can be designed to have an abrupt switch action at the melting point of the wax. [0106] However, in the embodiment described above the valve is used as a diverter valve, port 702 is used as the inlet, and the sensor measures the temperature of the water entering the valve. By default, when the water commences flowing after a period of non-use, the water is diverted out port 704 (which is the hot inlet in normal operation) because the sensor 708 detects cold water. Thus port 704 is connected to the inlet of the tank in this embodiment of the invention. This causes the water in the tank to be delivered to the outlet 122 of the system. When the water reaches the operating temperature threshold, the sensor switches the valve so water flows out port 706. [0107] The valve of Figure 7 has been modified by the inclusion of an auxiliary signal means 716. In this embodiment, the auxiliary signal means is a toggle switch having an operating arm 714 which is arranged to cooperate with a sliding member 710. Sliding member 710 is arranged to operate the arm 714 when the wax in sensor 708 melts or solidifies. Thus the toggle switch can provide an indication of the C07102 16 state of the sensor 708. The toggle switch 718 can be used to control the pump to stop it when the temperature of the water from the heat exchanger 102 falls below the operating temperature range. Thus the pump 126 in Figure 6 can be controlled from the valve rather than from the control means such as 610 of Figure 6. [0108] Figure 7 illustrates a tempering valve modified to provide an external status indication. The valve in normal use has hot and cold inlet ports 704, 706, and a mixed outlet 702. A cylinder 708 contains wax and triggers the operation of valve 722. An additional status sensor 716 has been added. The sensor includes a position detector in the form of a lever 714 which engages with a sliding member 710 operated by the wax cylinder. In this embodiment, the sensor 716 is a toggle switch which is arranged to trip when the wax melts. Thus this arrangement can provide an external status indication at 716. [0109] Figure 8 illustrates a further arrangement embodying the invention, in which a spring loaded piston and cylinder arrangement 880 replaces the pump as a source of energy for the scavenging operation at the end of a water demand period when the outlet tap is turned off. [0110] A cylinder 882 contains a piston 884 which is biased towards the port 887 by spring 886. [0111] The heat exchanger 802 connects to the cylinder 882 via the H port of the diverter 812, and to the outlet via the C port. [0112] When the outlet tap is opened, the "dead" water flows via the H port of the diverter to the port 887 of cylinder 882, compressing the piston and spring and forcing the water above the piston out port 888 to the system outlet via flow sensor 823. [0113] When hot water is detected at the port M of the diverter, the path through the H port closes and the path through the C port opens, bypassing the cylinder and connecting the outlet of the heater 802 to the system outlet. [0114] When the outlet tap is turned off, the flow from the mains via the heater ceases. The flow detector 823 thus indicates that the flow has ceased. This indication is used to close normally open inlet tap 890. For example, the flow sensor C07102 17 outlet is connected to controller 892. The removal of the mains pressure source from the system leaves the spring loaded piston 884 as the source of motive force in the fluid circuit of the system. The piston is forced down the cylinder by the spring 886 and forces the cold water from the cylinder through the cold inlet of heater 802 via junction 885. The remnant hot water in the heater is pushed through the diverter C outlet to the port 888 of cylinder 882 above the piston. The inlet tap 890 is opened when cold water exits the heater 802. A choke 894 can be used to control the rate of flow from the cylinder to the heater. [0115] Figure 9 is an "equivalent" electrical circuit for use in illustrating the operation of the arrangement of Figure 8. Note that "closed" in relation to an electrical switch means that the contacts are in a condition to permit current to flow. [0116] The battery 902 represents the source of mains pressure. The switch 904 represents an inlet tap. Diode 906 represents a one-way valve. The impedance 908 represents the flow resistance of the heater. The change-over switch 910 represents the diverter having a first output contact 912 equivalent to the H port and a second output contact 914 equivalent to the C port. The capacitor 916 represents the spring loaded cylinder/piston combination. Switch 918 represents an outlet tap. Current sensor 920 represents the flow detector having an output serving as a first input for controller 932. Diode 924 represents an optional second one-way valve. Detector 930 measures an input characteristic of switch 910 and produces an output signal to control the switch 910 and to serve as a second input for controller 932. Of course, detector 932 cannot measure the temperature of the current, but it can detect another characteristic of the current, such as duration, time/current integral, etc. [0117] The switch 902 is normally closed. Initially the contact of switch 910 is connected to output 912. When outlet switch 918 is closed, current flows from the battery 902 via switch 904, diode 906, impedance 908 switch 910 capacitor 916 switch 918 and flow detector 920. The flow is self limiting in that, when the capacitor is charged to the same voltage as the battery voltage, current ceases to flow via this path. This is the equivalent of the piston being pushed to the top of the cylinder in Figure 8. The detector 930 can be set to detect this condition or to measure a time -07102 18 lapse, or to measure the time flow integral or other suitable characteristic and to cause the switch 910 to change to the bypass contact 914. [0118] Current flow continues until switch 918 is opened. When switch 918 is opened, the current flow ceases and this is detected by detector 920. This condition is signalled to controller 932 which causes switch 904 to open temporarily. This removes the battery voltage from the rest of the circuit. Because the capacitor 916 is now the only source of voltage in the circuit, it will commence to discharge via all available circuit paths. Because switch 910 is connected via terminal 914, the discharge path is via junction 926, optional diode 922, junction 914, heater impedance 908 switch 910 terminal 914, junction 928, and back to the capacitor 916. [0119] Detector 930 determines when the reverse flow is complete and signals to the controller 932 to close switch 904 in readiness for the next operation of switch 918. Optionally, a choke impedance, such as an inductor 934, can be included in series with or instead of diode 922. [0120] Figure 10 shows a further arrangement embodying the invention and having an alternative scavenging path. [0121] In Figure 10, the operation while water is being drawn off via the system outlet is as for the other embodiment of Figure 2. [0122] When the outlet tap is closed, this is sensed by the flow sensor 1023, and the pump 1026 is turned on, drawing water from the tank 1016 via port 1022 and into heater 1002 via port 1004. This forces the hot water from heater 1002 out port 1006 and into diverter 1012. The hot water exits the diverter via port 1013 and enters tank 1016 via port 1019. this continues until the remnant hot water is emptied from heater 1002 and is replaced by cold water from tank 1016. This can be detected in any suitable manner, for example, either by a temperature sensor associated with the heater 1002, or by the operation of diverter 1012 in switching to close port 1013 and open port 10 11. Alternatively a timer may be used based on the time the pump tales to circulate the "dead" water. A further option is illustrated in Figure 10, in which a flow sensor 1050 detects that the circulation via port 1013 has stopped. This flow sensor can be used to send a status signal to the pump to cause the pump to stop. The status 07102 19 signal can be sent to a central controller 1040, and the central controller can send a stop signal to the pump. [0123] The auxiliary heating tank or cylinder can be incorporated with a heater, or installed adjacent to the heater, or installed at a remote location such as near a shower outlet. In the case where the auxiliary heater tank is remote from the heater, the cold water supply pipes can be used as the return path. [0124] In this specification, reference to a document, disclosure, or other publication or use is not an admission that the document, disclosure, publication or use forms part of the common general knowledge of the skilled worker in the field of this invention at the priority date of this specification, unless otherwise stated. [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. [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 (20)

1. A water heating system including a water conserving arrangement, the system including: a main water heater adapted to heat mains water; an auxiliary tank; temperature sensing means adapted to sense the temperature of the water from the main heater; a diverter; wherein, when there is a demand for hot water, the diverter directs water from the main heater to the auxiliary tank when the temperature of the water from the main heater is below a first threshold temperature, and the diverter directs water from the main heater to an outlet when the temperature of the water from the main heater exceeds the first threshold temperature; and wherein water from the auxiliary tank is directed to the outlet when the temperature of the water from the main heater is below the first threshold temperature.

2. A water heating system as claimed in claim 1, including an auxiliary heater adapted to heat water in the auxiliary tank.

3. A water heating system as claimed in claim I or claim 2, wherein the auxiliary heater is adapted to heat the water in the auxiliary tank to a second threshold temperature.

4. A system as claimed in any one of the preceding claims, wherein the main water heater is an instantaneous water heater.

5. A system as claimed in any one of the preceding claims, wherein the main water heater is one of a first gas heater or a first electric heater.

6. A system as claimed in claim 2 or any one of claims 3 to 5 as appended to claim 2, wherein the auxiliary heater is either a second gas heater or a second electric heater. -07102 21

7. A system as claimed in any one of the preceding claims, wherein the main heater is a first gas heater, wherein the first gas heater includes a pilot flame for the main heater adapted to provide heat for the auxiliary tank.

8. A system as claimed in any one of the preceding claims, including a pump controllable to pump water from the main water heater to the auxiliary tank to replace the water in the auxiliary tank with water at a higher temperature from the main heater.

9. A system as claimed in claim 8, wherein the pump is connected to circulate water between the main heater and the tank.

10. A system as claimed in claim 8 or claim 9, wherein the main heater is controllable to heat water passing through the main heater to within an operating temperature range having an upper and a lower operating temperature threshold.

11. A water conserving arrangement adapted for retro-fitting to an installed water heating system having a main water heater, the arrangement including: an auxiliary tank; and a flow diverter; the flow diverted being connectable to receive an initial flow of water from the main water heater; the diverter being adapted, in response to a demand for hot water, to divert water from the main heater to the auxiliary tank when the temperature of the water from the main tank is below a first threshold temperature, and to direct the water from the main heater to an outlet when the temperature of the water from the main heater exceeds the first threshold temperature; and wherein water from the auxiliary tank is directed to the outlet when the temperature of the water from the main heater is below the first threshold temperature.

12. An arrangement as claimed in claim 11, including an auxiliary heater arranged to heat water in the tank. C07102 22

13. A method of conserving water in a water heating system including a main water heater, diverter means, a system outlet, and an auxiliary tank, the method including the steps of: detecting the commencement of water flow; initiating heating of water in the water heater; monitoring the temperature of the water from the water heater; diverting water from the water heater to the auxiliary tank while the temperature of the heated water is below a first threshold temperature; switching the flow from the water heater to the system output when the water temperature from the water heater reaches the first threshold temperature; and wherein water from the auxiliary tank is directed to the outlet when the temperature of the water from the main heater is below the first threshold temperature.

14. A method as claimed in claim 13, including the steps of: heating the water in the auxiliary tank to above an auxiliary threshold temperature; maintaining the water in the auxiliary tank above the auxiliary threshold temperature; and, in response to a demand for hot water, delivering water from the tank to the system output until the temperature of the water from the main water heater exceeds the first temperature threshold.

15. A method as claimed in claim 13 or claim 14 including the step of: exchanging the water in the auxiliary tank with the water in the water heater at the end of a water usage.

16. A method as claimed in claim 15, including the steps of: measuring the temperature of the water in the tank; measuring the temperature of the water in the heater; and stopping the exchange of water when the temperature of the water in the tank is greater than the temperature of the water in the heater. 07102 23

17. A method as claimed in claim 14, including the steps of: measuring the volume of water pumped; and stopping the exchange of water when the volume pumped reaches a predetermined volume.

18. A system in any one of claims I to 10 or an arrangement in claim 1 or claim 11, wherein the diverter is a three-way valve and includes a flow control sensor adapted to control the flow of fluid through the diverter, and an auxiliary signal means adapted to provide an indication of the status of the sensor.

19. A water heating system substantially as herein described with reference to the accompanying drawings.

20. A method of delivering heated water substantially as herein described with reference to the accompanying drawings.