WO1988008658A1

WO1988008658A1 - An electric hot water heater

Info

Publication number: WO1988008658A1
Application number: PCT/AU1988/000118
Authority: WO
Inventors: Anthony Edward Kent; Gianfranco John Montagner
Original assignee: Friends Of The University Of Wollongong Limited
Priority date: 1987-04-21
Filing date: 1988-04-21
Publication date: 1988-11-03

Abstract

An electric hot water heater has a water storage vessel (1) with a cold water inlet (3) adjacent the bottom and a hot water outlet (4) adjacent the top. The heater includes an off-peak heating circuit which has a first heating element (5) disposed in a lower portion of said vessel (1) and an associated first thermostat switch (6) to control flow of current therethrough during the off-peak supply period. An auxiliary heating circuit is connected to a continuous mains supply and includes an ON/OFF switch (12) to control supply of current to the auxiliary heating circuit, an auxiliary heating element (7), and an associated second thermostat switch (8) to control flow of current through the auxiliary heating element (7) when the ON/OFF switch (12) is in the ON condition. Circuit means operable in response to the auxiliary thermostat switch (8) when the ON/OFF switch (12) is in the ON condition permit supply of current to the off-peak heating circuit only when the second thermostat switch (8) senses a temperature above a selected value and interrupts the supply of current to the auxiliary heating element (7). The circuit means further permits supply of current to the off-peak heating circuit irrespective of the water temperature sensed by the auxiliary thermostat switch (8) when the ON/OFF switch (12) is in the OFF condition.

Description

TITLE: AN ELECTRIC HOT WATER HEATER TECHNICAL FIELD

This invention relates to electric hot water heaters and more particularly to electric water heaters utilizing ah off-peak-supply and having an auxiliary heating capacity.

BACKGROUND ART

Water heaters utilizing lower cost off-peak electricity supply are widely used and generally rely upon the generation of a relatively large volume of hot water which is stored in an insulated vessel for use during periods when off-peak supply is not available. A difficulty often arises with such devices when consumption of hot water exceeds the available supply since hot water is then not available until the next off-peak supply period. This problem has been addressed by the provision of an auxiliary heating circuit which is manually operable to provide supplemental heating in non-off-peak periods should this become necessary. Off-peak water heaters with supplementary heating have hitherto suffered some disadvantages. Firstly, practical difficulty has been encountered in providing a satisfactory arrangement which will reliably prevent simultaneous operation of the auxiliary heating function and off-peak heating function whilst maximising the amount of heating performed by the off-peak supply.

Another problem encountered with the hitherto available water heaters is that the consumer is not aware when the supply of hot water is about to be exhausted and thus are unable to activate the auxiliary supply in sufficient time to ensure that a continuous supply is available.

DISCLOSURE OF INVENTION

It is an object of this invention to provide an improved hot water heater which will overcome or ameliorate at least one of the abovementioned disadvantages.

Accordingly, this invention consists in an electric hot water heater comprising a water storage vessel having a coldr ater inlet adjacent the bottom thereof and a hot water outlet adjacent the top thereof; a first (off-peak) heating circuit for connection to an off-peak mains supply including a first heating element disposed within a lower portion of said vessel and an associated first thermostat switch to sense the temperature of water in said vessel at or below the level of said first heating ^"element and provide a flow of current therethrough during the off-peak supply period when water temperature is below a first selected value; a second (auxiliary) heating circuit for connection to a continuous mains supply including a selectively operable ON/OFF switch means to control supply of current to said second circuit from said continuous supply, a second (auxiliary) heating element disposed within an upper portion of said vessel and an associated second thermostat switch to sense the temperature of water in said vessel below the level of said second heating element and above the water sensed by said first thermostat switch, said second thermostat switch providing a flow current through said second heating element when -it senses temperature is below a second selected value and said ON/OFF switch means is in the ON condition; and circuit means operable in response to said second thermostat switch when said ON/OFF switch is in the ON condition to permit supply of current to said first heating circuit from said off-peak supply only when said second thermostat switch senses a temperature above said second selected value and interrupts supply of current to said second heating element, said circuit means operable when said ON/OFF switch means is in the OFF condition to permit supply of current to said first heating circuit from said off-peak supply irrespective of the water -temperature sensed by said second thermostat switch. It will be apparent that when the ON/OFF switch means is in the OFF condition the off-peak heating circuit functions substantially in the known manner when supply is made available and under the control of the associated first thermostat switch.

When the ON/OFF switch means assumes the ON condition the auxiliary heating circuit will not be energised unless the associated second thermostat switch senses tha^'t the water temperature is below the second selected temperature. If the water is below this temperature the auxiliary heating circuit is energised by the thermostat switch to heat the water in the vessel until the water at the level sensed by the second thermostat switch attains the selected temperature. Since the temperature of the water is sensed at a level below auxiliary heating element the operation of the auxiliary heating circuit Is effective in heating water in the portion of the vessel above the level at which the second thermostat senses water temperature as will^* be further described below.

- Once the water in the upper portion of the vessel has attained the selected temperature and the supply of current to the auxiliary heating element is interrupted by the associated thermostat switch the supply of current to the off-peak heating circuit is permitted. Thus should the ON/OFF switch means be in an ON condition and the auxiliary heating circuit energised when the normal off-peak supply period commences the supply of current to the off-peak heating circuit will be inhibited until the auxiliary heating circuit sufficiently heats the water for the second thermostat to sense that the water temperature is above the selected temperature. Once this condition is assumed the supply of current to the auxiliary heating circuit is interrupted and the supply to the off-peak heating circuit is enabled thus allowing normal off-peak operation. Since the water temperature sensed by the second thermostat is above the off-peak heating element it will during normal off-peak operation continually sense that the water is above the selected temperature since the first thermostat located lower in the vessel will have previously detected a drop in temperature and have activated the off-peak heating circuit. This operation is ensured if the first selected temperature is substantially the same or higher than the second selected temperature. This operation will be further described in connection with the preferred embodiment of the invention.

Preferably, the circuit means provide a common neutral connection for the off-peak heating circuit and the auxiliary heating circuit which is selectively connected to complete one or other of the circuits. This can be done by way of a suitable diverting switch.

In one embodiment the ON/OFF switch means and the diverting switch comprise a single throw double pole switch connected so that in one position or "throw" the off-peak circuit is completed and the auxiliary circuit is open and In the other position or throw (corresponding to the ON condition of the switch means) the auxiliary heating circuit is completed and the off-peak circuit can only be completed via the second thermostat switch.

The ON/OFF switch means can in one embodiment include a relay which upon operation of the switch latches the switch in an ON condition until the flow of current in the second heating circuit is interrupted by the associated thermostat switch. This provides for a "one shot" heating since the auxiliary heating circuit is switched to the OFF condition when the second thermostat senses that the water temperature has risen to above the selected value.

Preferably the first selected temperature sensed by the first thermostat is substantially equal to the second selected temperature sensed by"the second thermostat switch. This ensures that the temperature to which the water is heated is the same irrespective of whic heating circuit is utilized.

It is also preferred that the auxiliary heating circuit includes an indicator which indicates when a current is flowing in the auxiliary heating element. ^"The indicator preferably takes the form of a light which is visibly located on the heater or elsewhere so that the consumer is aware that auxiliary heating is taking place. A second indicator is also preferably included- in the auxiliary heating circuit and associated with the second thermostat so as to give an indication that the water at the level sensed has fallen below the selected temperature. This light thus provides an indication of when auxiliary heating is necessary. This second indicator can also take the form of a light suitably located on the heater or elsewhere.

It is also preferred that the water temperature sensed by the second thermostat switch associated with the auxiliary heating circuit is at a level above which about 20% of the water capacity of the vessel is disposed. In this way the auxiliary heating only heats the top 20% of the contents of the vessel which is adequate in most instances. The second indicator light will thus become illuminated when approximately 20% of the vessel's hot water capacity remains as will be described in further detail below.

It will thus be apparent that the present invention provides a particularly simple and reliable arrangement for the control of the heating elements in a hot water heater which ensures that both elements are not activated simultaneously and prevents subsequent heating of the water by the auxiliary heating circuit once the off-peak heating comes into operation. In this regard it will be noted that there can be a slight delay in the utilization of off-peak supply if the auxiliary heating is actually underway at the commencement of the off-peak supply period but the frequency of occurence and the period involved does not result in a substantial reduction in the amount of off-peak heating achieved.

In addition, provision of indicator lights described above provides a ready indication of when auxiliary heating is required and when continuous supply electricity is being utilized for auxiliary heating.

The heater of the present invention also only requires the addition of the necessary circuitry and thus can be substantially based on existing heater configurations.

BRIEF DESCRIPTION OF DRAWINGS

Two embodiments of this invention will now be described by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic cross-sectional representation of a water heater according to this invention;

Figure 2 is a schematic circuit diagram of a first embodiment of the circuitry used in the heater of figure 1; and

Figure 3- is a schematic circuit diagram of a modification to the circuitry of figure 2.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring to figure 1 a hot water heater according to this invention comprises a generally cylinderical water storage vessel 1 which includes a conventional form of insulation 2. A cold water inlet 3 is disposed adjacent the bottom of a vessel and a hot water outlet 4 is disposed adjacent the top of the vessel. A first off-peak heating element 5 is disposed in a lower portion of the vessel and an associated thermostat switch 6 is positioned slightly below, the level of element 5.

An auxiliary heating element 7 is disposed in the upper portion of the vessel above an associated thermostat switch 8. The thermostat switch 8 is arranged to sense water temperature at a level about one fifth of the way down the vessel so that approximately 20% of the water capacity of the vessel is disposed above the thermostat switch 8. Auxiliary heating element 7 is disposed immediately -above the thermostat switch 8 so as to heat that upper 20% of the water in the tank. If the water in the vessel is hot (the -heating process will be described with reference to the circuit diagram below) the hot water for use is withdrawn via outlet 4 while cold water is admitted simultaneously via inlet 3 near the bottom of the vessel. If there is no heating during withdrawal of the water then the cold water entering the bottom of the vessel remains cold and at the bottom and is separated from the hot water above by a distinct interface. The interface is preserved by reason of the density difference between the hot and cold water and the avoidance of turbulent mixing of the water due to the location of the inlet and outlet. The hot water layer normally therefore moves upwardly in a tank as each withdrawal is made assuming there is no heating of the water in the meantime. Thus when the level of cold water reaches thermostat switch 8 only approximately 20% of the tank capacity of hot water remains.

Operation of auxiliary heating element 7 is under the control of the associated thermostat 8 which discontinues the supply of current to element 7 as soon as the water at . the level of the thermostat reaches a selected temperature so that the auxiliary heating ciruit will serve only to heat the top 20% of the tank.

The physical heating by the off-peak element 5 and associated thermostat 6 is substantially the same as in a conventional water heater in that the element 5 heats the water, when off-peak supply is available, to a temperature determined by thermostat 6.

Referring to Figure 2 the circuit diagram for an electric hot water heater according to this invention is shown in schematic form. The circuit comprises an active terminal 9 for connection to a continuous main supply (not i shown) a neutral terminal 10 for connection to the same continuous main supply and an off-peak active terminal 11 for connection to an off-peak electricity supply (not shown) . The off-peak element 5 and associated thermostat switch 6 of Figure 1 are shown as are auxiliary heating element 7 and associated thermostat switch 8. A single pole^"double throw switch 12 includes two switching contacts 13 and 14. The off-peak circuit is formed by contact 13, which is closed when contact 14 is open and vice versa, thermostat switch 6, and off-peak element 5.

An auxiliary heating circuit comprises switch 14, thermostat switch 8 and auxiliary heating element 7. A first indicating light, in the form of a light emitting diode 15 is-connected in series with a diode 16 between the continuous active terminal 9 and thermostat switch 8 so as to be illuminated when the thermostat switch 8 is in the "cold" position in which a connection is made between terminals 17 and 18 for supply of current to auxiliary element 7. However, because the light emitting diode 15 is connected directly to the active terminal it will be illuminated simply by the thermostat being in the "cold" position and it does not require a flow of current through element 7. The indicating light 15 can be located in any visible position on the heater or at some remote location. In the "hot" position thermostat switch 8 establishes a connection between terminals 17 and 19, terminal 19 being connected to the neutral side of off-peak element 5 so that when thermostat switch 8 is in the "hot" position a circuit is established from neutral terminal 10 through off-peak element 5 and associated thermostat switch 6 to off-peak active terminal 11.

A second indicating light in the form of light emitting diode 20 is connected in series with a diode 21 and in parallel with a resistor 22. The resistor is provided to prevent flickering of the diode 20. As will be apparent diode 20 is illuminated when both contact 14 is closed and thermostat 8 is in the "cold" position thus indicating that there is a current flowing in auxiliary heating element 7. The second light 20 can be located in any suitable visible location on the heater or some remote location.

The operation of the circuit shown in figure 2 is as follows. In the illustrated configuration single pole double throw switch 12 which comprises an ON/OFF switch means is in the OFF condition and contact 14 is open. In this switch position contact 13 is closed so that a off-peak heating circuit is established from neutral terminal 10 via switch 13, off-peak heating element 5 and thermostat switch 6. Thus the off-peak circuit is in a condition to commence normal operation when the off-peak supply is made available.

Diode 15 which in use is usually coloured differently to diode 20 will only be illuminated if thermostat switch 8 is in the illustrated "cold" position. This indicates that the water at the level sensed by thermostat switch 8 is below the selected temperature, usually about 65°C, and that therefore less than 20% of the capacity of the storage vessel contains hot water. The consumer is thus made aware of the depleted state of the hot water supply and if desired can opt to activate the auxiliary heating circuit. This is done by operating the switch 12 so as to close contact 14 and open contact 13. The ON/OFF switch is then in the ON condition and whilst thermostat switch 8 remains in a cold position current flows through auxiliary element 7 and heats the water in contact therewith. As described above the element 7 is disposed in the upper portion of the tank along with associated thermostat switch 8 so that only the upper 20% of the tank is heated to the temperature determined by switch 8. While current flows through the element 7 light emitting diode 20 is illuminated to remind the consumer that electricity from the continuous supply, which usually involves a high tariff, is being consumed.

When the water in the upper portion of the tank reaches a selected temperature switch 8 reverts to the "hot" position and a connection is made between terminals 17 and 19. This interrupts the supply of current to heating element 7 and completes the off-peak heating circuit. Thus if off-peak supply subsequently becomes available the off-peak circuit can operate in the usual manner. If the off-peak supply has become available whilst current is flowing in the auxiliary heating circuit the off-peak heating circuit will assume normal operation as soon as switch 8 changes to the "hot" condition. During the period of off-peak supply the switch 8 will remain in the "hot" condition because it is disposed above the switch 6 used to control the off-peak heating element. In this regard it will be apparent that because the lower thermostat will detect a drop in water temperature as the cold water enters from the bottom it will result in the off-peak element heating the water prior to the cold water level reaching upper thermostat switch 8.

It will be apparent that the circuit of figure 2 provides a common neutral connection for the off-peak and auxiliary heating circuits which is selectively connected to complete one or other of the circuits. When the auxiliary heating circuit is in the OFF condition contact 13 is closed and thus constitutes a diverting switch so that the operation of the off-peak heating circuit is independent of the temperature sensed by auxiliary thermostat switch 8.

When the auxiliary heating circuit is in the ON condition the neutral connection is made to one or other of the auxiliary heating circuit or the off-peak heating circuit via thermostat switch 8.

This comparatively simple arrangement which for its operation relies upon the physical positioning of the thermostat switch 8 above the level of the thermostat switch 6 associated with the off-peak heating circuit provides a particularly reliable means of preventing simultaneous operation of the auxiliary and off-peak heating circuits whilst maximising the amount of heating performed by the off-peak supply. It will be appreciated that there can be a slight delay in the utilization of off-peak supply if the auxiliary heating is underway at the commencement of the off-peak period but the frequency of occurrence and the time involved does not result in a • substantial reduction in the amount of off-peak heating achieved.

Figure 3 shows a modification to the circuit shown in Figure 2. The same reference numerals have been used to indicate the components common to the circuit of Figure 2. The modification involves the substitution of a dual contact relay control switch 12A for the single throw double pole switch 12. A relay coil 23 for control of switch 12A in series with a push button switch 24 are connected between the continuous active terminal 9 and terminal 18 of thermostat switch 8. Connection is also made between a point intermediate the push button switch and coil 23 and the terminal of contact 14A remote from the continous active terminal 9. When the thermostat switch 8 is in the cold position as shown, push button 24 can be activated to close the relay switch 12A as current flows through coil 23 and through the circuit completed by the relay switch 8. This closes contact 14A and opens contact 13A so that the auxiliary heating circuit assumes the ON condition described above. Once contact 14 closes current is maintained in the coil 23 by the connection between the terminal of contact 14A and the point intermediate switch 24 and coil 23. The relay switch thus latches the auxiliary heating circuit in an ON condition until the circuit is broken by thermostat switch 8 assuming the "hot" condition. The. operation of the circuit shown in figure 3 is otherwise identical to that described above in figure 2. The difference in operation however, is that the auxiliary heating is "one shot" operation in that once the upper portion of a tank is heated to the selected temperature and switch 8 assumes the hot condition auxiliary heating circuit is turned OFF and will not resume the ON condition until push button 24 is again activated. This circuit has the advantage of alleviating the consumer of the need to remember to turn off the auxiliary heating circuit.

Claims

CLAIMS : -

1. An electric hot water heater comprising a water storage vessel having a cold water inlet adjacent the bottom thereof and a hot water outlet adjacent the top thereof; a first (off-peak) heating circuit for connection to an off-peak mains supply including a first heating element disposed within a lower portion of said vessel and an associated first thermostat switch to sense the temperature of water in said vessel at or below the level of said first heating element and provide a flow of current therethrough during the off-peak supply period when water temperature is below a first selected value; a second (auxiliary) heating circuit for connection to a continuous mains supply including a selectively operable ON/OFF switch means to control supply of current to said second circuit from said continuous supply, a second (auxiliary) heating element disposed within an upper portion of said vessel and an associated second thermostat switch to sense the temperature of water in said vessel below the level of said second heating- element and above the water sensed by said first thermostat switch, said second thermostat switch providing a flow current through said second heating element when it senses temperature is below a second selected value and said ON/OFF switch means is in the ON condition; and circuit means operable in response to said second thermostat switch when said ON/OFF switch is in the ON condition to permit supply of current to said first heating circuit from said off-peak supply only when said second thermostat switch senses a temperature above said second selected value and interrupts supply of current to said second heating element, said circuit means operable when said ON/OFF switch means is in the OFF condition to permit .supply of current to said first heating circuit from said off-peak supply irrespective of the water temperature sensed by said second thermostat switch.

2. An electric hot water heater as claimed in claim 1 wherein said circuit means provides a common neutral connection for said first circuit and said second circuit which is selectively connected to complete said first circuit or said second circuit.

3. An electric hot water heater as claimed in claim 2 wherein said circuit means includes a diverting switch to provide a direct neutral connection to said first circuit when said ON/OFF switch means is in the OFF condition and to break that connection when said ON/OFF switch means is in the ON condition so that said common neutral connection can be-selectively connected to complete said first circuit or said second circuit via said second thermostat switch.

4. An electric hot water heater as claimed in claim 3 wherein said ON/OFF switch means and said diverting switch comprise a single throw double pole switch.

5. An electric hot water heater as claimed in any one of claims 1 to 4 wherein said ON/OFF switch means is disposed in the active connection to said second circuit.

6. An electric hot water heater as claimed in claim 3 wherein said diverting switch comprises a relay controlled switch.

7. An electric hot water heater as claimed in claim 6 wherein said relay controlled switch operates in dependence upon current flow in said second heating circuit.

8. An electric hot water heater as claimed in any one of claims 1 to 3 wherein said ON/OFF switch means includes a relay which upon operation of the switch latches the switch in an ON condition until the flow of current in the second heating circuit is interrupted by said second thermostat switch.

9. An electric hot water heater as claimed in claim 6 or claim 7 wherein said relay controlled switch and said ON/OFF switch means comprise a dual pole relay switch.

10. An electric hot water heater as claimed in any one of claims 1 to 9 wherein said second circuit includes first indicator means to indicate the supply of current to said second heating element.

11. An electric hot water heater as claimed in any one of claims 1 to 10 wherein said second circuit includes second indicator means to which indicates when said second thermostat switch senses a temperature below said second selected temperature.

12. An electric hot water heater as claimed in any one of claims 1 to 11 wherein the water temperature sensed by said second thermostat switch is at a level above which about 20% of the water capacity of the vessel is disposed.

13. An electric hot water heater as claimed in any one of claims 1 to 12 when said first selected temperature is substantially equal to said second selected temperature.

14. An electric hot water heater substantially as herein described with reference to Figure 1 and Figure 2 or Figure 1 and Figure 3 of the accompanying drawings.