WATER HEATER

Abstract: Non-storage instantaneous water heater having a very small non-insulating tank (1) of a volume preferably less than 1 litre. An electric heating element (15) is located inside the tank (1) whilst a thermostat (20, 36) is mounted outside of, but in thermal contact with, the tank (1). A pressure transducer (25) switches the element (15) on when water flows out the outlet (14) thereby increasing the water pressure at the inlet (13) since the outlet (14) has an internal diameter less than that of the inlet (13) and the tank (1) is otherwise closed.

Description: "WATER HEATER" The present invention relates to water heaters and, in particular, to a non-storage instantaneous water heater which has a small uninsulated tank. This uninsulated tank does not store either a large quantity of water or water at an elevated temperature. BACKGROUND • ART Conventional water heaters include a large storage tank which is well insulated.. A large amount of water, of the order of several gallons or many tens of litres, is heated and maintained ready for use. Thus there are substantial heat losses since a relatively large mass of water radiates substantial heat, notwithstanding that the storage tank is always insulated. Such water heaters can be electrically heated by either off-peak power or be continuously connected to the mains and operated by a thermostat. It is also known to have relatively small water heaters which are so called "instantaneous" water heaters in that only a relatively small volume of water is stored in an insulated tank and as this water is drawn off, cold water is inserted into the tank and heated by a thermostatically controlled electric heating element. Again the volume of this tank, although much smaller than a conventional storage heater, still holds several litres of water. The above described arrangements are wasteful both in respect of the amount of material consumed in building the relatively large capacity water tanks, and also the waste of energy bought about by thermal losses which are inevitable where a volume of heated water is stored over time. It is the object of the present invention to. overcome, or substantially ameliorate, the above-mentioned disadvantages by provision of a water heater in which only a small, uninsulated tank is provided thereby saving in materials, and no effort is made to store a volume of heated water, thereby saving in heat losses. DISCLOSURE OF INVENTION According to one aspect of the present invention there is disclosed a non-storage instantaneous water heater comprising a small, uninsulated tank having an inlet and an outlet, a heating element in said tank, switch means connected in series with said heating element and sensing means responsive to flow of water in said outlet to close said switch means to activate said heating element only during said outlet water flow. BRIEF-DESCRIPTION OF DRAWINGS One embodiment of the present invention will now be described with reference to the drawings in which: Fig. 1 is a front elevation, partly in section, of the water heater of the preferred embodiment, Fig. 2 is a cross-sectional view along the line II-II of Fig. 1, Fig. 3 is a cross-sectional view taken along the line III-III of Fig. 1, Fig. 4 is a front elevation of the rear mounting plate forming a portion of the exterior housing of the heater of Fig. 1, and Fig. 5 is a circuit diagram showing the inter¬ connection of the various circuit elements of Fig. 2. BEST MODE OF CARRYING OUT THE INVENTION As seen in the drawings, the water heater of the preferred embodiment comprises a two part copper tank 1 which is approximately cylindrical in shape and formed by the joining about a mid-diameter of the tank 1 of two substantially identical halves. The tank 1 is mounted within a housing 2 having a front cover 3 and rear mounting plate 4. As seen in Fig. 3, the tank 1 is secured to the rear mounting plate 4 by means of a semcircular band 5 which has a U-shaped bend 6 at one end that is secured to the plate 4 at the other end by means of a fastener 7. The bend 6 engages a protrusion 8 to provide a convenient fixing arrangement. It will also be seen from Fig. 3 that the front cover 3 and rear mounting plate 4 overlap at 9 so as to provide a water tight seal between the front cover 3 and rear mounting plate 4. As seen in Fig. 4, the rear mounting plate 4 is also provided with an opening 10 through which an electric power cable (not illustrated) can enter the housing 2. As seen in Figs. 1 and 2, connectors 11 and 12 are provided for an inlet pipe 13 an outlet pipe 14 respectively The inlet pipe 13 has an internal diameter of approximately 6mm and terminates flush with the bottom of the tank 1. However, the outlet pipe 14 has an internal diameter of approximately 3mm (less than that of the inlet pipe 13) and is extended upwardly through the bottom of the tank 1 so as to terminate adjacent "the top of the tank 1) . A coiled heating element 15 (preferably 3kw) is located adjacent the top of the tank 1 with the heat generating coils 16 being located below the top 17 of the outlet pipe 14. This ensures that in use the coils 16 are always immersed in water. The heating element 15 is provided with terminals 18, 19 on the top of the tank 1. Also mounted on the top of the tank 1 is a metal body 20 having an annular centrally located peripheral flange 21. The body 20 contains a thermostat of conventional construction. The body 20 is mounted in thermal contact with the metal tank 1 by means of brass bolts 22 the heads of which are brazed or soldered to the copper tank 1. The bolts 22 pass through corresponding openings (not illustrated) in the flange 21 and the body 22 is secured in place by means of a pair of nuts 23 for each bolt 22l As seen in Fig. 2 in particular, the inlet pipe 13 is provided with a T-joint 24 which is externally threaded. A pressure transducer 25 having a plate like casing 26 is secured to the T-joint 24 by means of a tube 27 and nut 28 which when tightened provides a fluid tight seal between the tube 27 and T-joint 24. Located within the casing 26 is a rubber diaphram 29 which abuts one end of a .plunger 30 which passes through the casing 26. A recess 31 is provided in the other end of the plunger 30 and houses a helical spring 32. A microswitch 33 is mounted adjacent the pressure transducer 25 so ' that the spring 32 abuts the microswitch 33 thereby urging the plunger 30 away from the microswitch 33 and towards the diaphram 29. The microswitch 33 is normally open and closed by the plunger 30 depressing an operating button 34 of the microswitch 33. A neon lamp 35 is located in the front cover 3 just above the microswitch 33. The interconnection of the lamp 35 heating element 13, microswitch 33 and thermostat 36 is as illustrated in Fig. 5, the heating element being supplied from a main supply 37. When initially operated, the tank 1 is empty and the hot water tap (not illustrated) is operated so as to supply mains pressure cold water to the inlet pipe 13. In a fraction of a second, cold water flows through the inlet pipe 13 and commences to fill the tank 1 thereby expelling the air within the tank via the outlet pipe 14. When the tank is full, because the cross-sectional area of the interior of the outlet pipe 14 is less than that of the inlet pipe 13, the water in the inlet pipe 13 experiences an increase in pressure brought about by the constriction of flow. This increase of pressure is applied to the rubber diaphram 29 thereby moving the plunger 30 to the left as seen in Fig. 2 in order to activate microswitch 33. This completes the circuit for element 13 and lamp 35 which are . thereby respectively heated and illuminated. As cold water enters the tank 1 via the inlet pipe 13, the water is instantaneously heated by the element 15 and passes out the outlet pipe 17 as hot water. As soon as the hot water tap (not illustrated) is turned off, water ceases to flow through the inlet pipe 13 and also through the outlet pipe 14. In consequence, the pressure at the T-joint 24 in inlet pipe 13 is reduced thereby permitting spring 32 to move the plunger 30 away from the microswitch 34 which is thereby opened. In consequence, the element 15 is no longer energised. . In addition, the level of water within the tank drops to that of the top 17 of outlet 14 thereby maintaining the coil 16 of heating element 15 immersed. During subsequent operation of the heater, after water begins to flow in the inlet pipe 13, only a fraction of a second elapses before the tank 1 is entirely filled with water and water flows out the outlet pipe 14 in such a way as to restrict the flow of water through the tank 1 and thereby increase the pressure at T-joint 24. This again moves diaphram 29 so as to operate microswitch 23 and energise the heating element 15. It will be apparent that the thermostat 36 is in good thermal communication with the water in the tank 1 owing to the tank 1 being formed of copper and the body 20 of the thermostat 36 being also formed from metal. In consequence, the thermostat 36 senses the water temperature even through no portion of the thermostat 36 is actually immersed in the water within the tank 1. The thermostat 36 is set to open when the water in the tank 1 exceeds approximately 60-70°C. In addition, in the event of failure of the microswitch 33 then the thermostat 36 will prevent the heating element 15 from boiling the water in the tank 1 and thereby causing a possible explosion. Since the lamp 35 is operated in parallel with the heating element 15, if the lamp 35 is not illuminated, this indicates some defect if the hot water tap has been turned on at that time. INDUSTRIAL APPLICABILITY The apparatus pf the preferred embodiment has a number of very substantial operational and constructional features. Since the preferred size of the tank 1 is only of the order of 250-300ml the tank 1 can be manufactured at extremely low cost. Also no insulation is required and therefore the cost of this component of conventional water heaters is eliminated. Furthermore, because the thermostat 36 is not required to be immersed in the water within the tank, very low cost thermostats, such as normally used in small domestic electrical appliances, are suitable for use with the water heater of he present invention. A substantial operating advantage of the water - 6 - heater of the present invention is that no relatively large volume of hot water is stored and therefore energy losses caused by radiation of heat, are cut to an absolute minimum. After use, the very small volume of water which is 5 in the tank 1 is allowed to cool to room temperature. However, since the total volume is extremely small being only a fraction of a litre, the heat lost through this cooling is substantially negligible. In addition, since the hot water produced by the 10 heater of the present invention is not held in a heated state for a long period of time, that is the water is not "stewed", the hot water produced by the water heater of the present invention is suitable for use in making heated beverages such as tea and coffee. This is not the case with 15 conventional storage hot water systems and therefore an electric jug, or similar appliance, must be used to heat cold water in order not to impair the taste of the heated beverage. In temperate climates, the apparatus of the present 20 invention is most suitable as a point of use heater. That is to say, the heater is located adjacent the shower recess, bath, or sink where the hot water is intended to be used. However, in countries having a hot climate, because the difference in temperature between the incoming "cold" water 25 and the outgoing hot water is only very small, the apparatus of the preferred embodiment can be used to replace a domestic hot water service. In consequence, a very substantial saving in capital cost is achieved. The apparatus of the preferred embodiment has been 30 the subject of a cost analysis by the Department of Consumer Affairs of the Government of the State of New South Wales. The result of that analysis indicated that for the tariff of the Sydney County Council, 28 showers of 3 to 4 minutes duration for a conventional on line storage heater would 35 cost AS2.80. For a conventional off-peak storage heater the same showers can be obtained for approximately one half of that cost. However, the .apparatus of the preferred embodiment enables 56 showers of 5 minutes duration to be obtained at a cost of A$0.75. The foregoing describes only one embodiment of the present invention and modifications, obvious to those skilled in the art, may be made thereto without departing from the scope of the present invention. OMPI

Claims: CLAIMS 1. A non-storage instantaneous water heater comprising a small, uninsulated tank having an inlet and an outlet, a heating element in said tank, switch means connected in series with said heating element and sensing means responsive to flow of water in said outlet to close said switch means to activate said heating element only during said outlet water flow. 2. A heater as claimed in claim 1 wherein a thermostat is connected in series with said element, located outside said tank, and in thermal communication with water in said tank but not immersed in said water. 3. A heater as claimed in claim 2 wherein said tank is metal and said thermostat is mounted on an exterior surface of said tank and in thermal communication with said external surface. 4. A heater as claimed in claim 2 or 3 wherein said thermostat operates to prevent the water in said tank o being heated in excess of a temperature of from 60 C to 70°C. 5. A heater as claimed in any one of claims 1 to 4 wherein the internal cross-sectional area of said outlet is less than the internal cross-sectional area of said inlet, said tank is closed other than for said inlet and outlet, and said sensing means comprises a pressure transducer connected to said inlet and operable by the increase in water pressure in said inlet caused by filling of said tank with water and constriction of flow through said tank caused by the difference in cross-sectional areas of said inlet and outlet. 6. A heater as claimed in claim 5 wherein said pressure transducer comprises a diaphram, a plunger having one end abutting one side of said diaphram, water from said inlet being applied directly to the other side of said diaphram, said switch means comprises a microswitch which is mounted adjacent the other end of said plunger and operable thereby, and spring means are located between the other end of said plunger and the housing of said microswitch to urge said plunger away from said microswitch. 7. A heater as claimed in any one of claims 1 to wherein the volume of said tank is less than one litre. 8. A heater as claimed in claim 7 wherein the volume of said tank is approxiamtely 250ml. 9. A heater as claimed in any one of claims 1 to 8 wherein said outlet draws water from adjacent the top of said tank, said element is adjacent the top of said tank, and said inlet is located adjacent the bottom of said tank.

Inventors: WOODLEIGH RONALD JAMES
Applicants: WOODLEIGH RONALD JAMES
Application year: 1982
Main classification: F24H1
IPC codes: F24H1, F24H9