GB2140990A

GB2140990A - Water heaters

Info

Publication number: GB2140990A
Application number: GB08411865A
Authority: GB
Inventors: Robert Lewis
Original assignee: R L & D Ltd
Current assignee: R L & D Ltd
Priority date: 1983-05-12
Filing date: 1984-05-09
Publication date: 1984-12-05
Also published as: GB8411865D0; GB2140990B

Abstract

A water heater of the kind in which flowing water is heated by electric heating elements has a first heating element 7 and a second heating element 8 which are in series. When a triac switch 16 is conductive electricity from a mains supply L, N passes through them and heat is generated by the elements. When another triac switch 12 is also conductive electricity from the supply passes through the first heating element 7 but not through the second 8 so that the total resistance is less and the heat output is increased. Additional heating elements 9, 10 with an associated triac switch 13 may act in a similar manner. The heating elements may be bare wire coils extending along a water passageway and some may be subdivided into portions spaced apart to reduce any tendency to momentary temperature variations in the heated water when switching occurs (Fig. 4). The resistances of elements 7 to 11 may be arranged so that by operating various combinations of triacs 12, 13, 14, 16 the heat output may be increased from a base level to a maximum level in seven equal increments. The triacs may be under manual or thermostatic control. Alternatively, a microprocessor (21), (Figure 5), may control the triacs, a solenoid water flow valve (24) and an indicator (31) in response to inputs from manual selectors (27 to 30), or temperature sensor (25), and a switch (26) responsive to absence of water flow. <IMAGE>

Description

SPECIFICATION Water heaters This invention relates to water heaters, and in particular to water heaters of the kind (hereinafter referred to as the kind specified) comprising electric heating means operative in use to raise the temperature of water flowing through the heater.

It has been proposed in heaters of the kind specified to provide heating means in the form of a plurality of heating elements and also to provide selector switch means capable of being switched to each of a plurality of different heating settings, the arrangement being such that in use each different heating setting of the selector switch means results in electricity being supplied to a different heating element orto a different electrical combination of heating elements so that the heating means yields heat energy at different rates for heating the water.

A heater of the type described in the last preceding paragraph may include heating means which, under the control of the selector switch means, is capable of yielding heat energy, for heating the water, at each of a relatively large number of different rates, each rate of heat output differing from the next by a relatively small increment. The use of such heating means makes it possible to provide a water heater such that in use a stream of water flowing through it at a constant speed and at a constant starting temperature can be heated to any of a range of temperatures each of which differs from the next by a temperature step so small that the user normally has no need or desire for the water to be heated to other, intermediate temperatures.

Alternatively (or in addition) the use of such heating means makes it possible to provide a water heater such that a stream of water flowing through it can be heated to a temperature which is equal to a predetermined temperature or is sufficiently close to that predetermined temperature for a user not to desire any closer approximation to the predetermined temperature, irrespective of any variation in the temperature of the incoming water within a relatively wide range of temperatures and/or irrespective of any variation in the rate of flow of water within a relatively wide range of flow rates.

In order to enable the heating means to be switched so as to yield heat energy at a relatively large number of different rates, while it incorporates only a relatively small number of individual heating elements, it has been proposed to provide heating means comprising a set of heating elements each successive one of which is arranged to yield energy at a rate twice that at which the immediately preceding member of the set yields energy. By the appropriate selection of individual heating elements or different groups of heating elements within the set it is possible to cause such heating means to yield energy at different rates which are the successive integral multiples from 1 to 2"-1 1 (where n is the number of electric heaters) of the rate at which energy is yielded by the least powerful heater of the set.

Other arrangements to achieve comparable effects are of course possible but in general require the use of a larger number of heating elements.

While it is often desirable to provide a water heater capable of heating water to substantially any temperature within a given range of temperatures, it is usually unnecessary for that range to extend downwards to the temperature of the unheated, incoming water. For this reason it has been proposed to include in the heating means a base heater operative in use to yield heat at a certain minimum rate and to operate continuously (or substantially continuously) while the water heater is in operation. Where the heating means comprises a plurality of heating elements and selector switch means of the kind described above, the arrangement is such that, whichever heating setting the selector switch means is in, the base heater remains operative.

An aim of the present invention is to provide an improved arrangement of heating elements which enables any of several advantages to be obtained, as described in more detail below.

According to the present invention there is provided a water heater of the kind specified in which the electric heating means comprises a first heating element and a second heating element and selector switching means which in a first setting enables electricity to pass through said first and second heating elements in series and a second setting enables electricity to pass through said first element but enables no electricity or substantially no electricity to pass through said second element so that in use said first and second heating elements, considered together, yield less heat energy when the switching means is in its first setting than they do when the switching means is in its second setting.

In a preferred arrangement the applied voltage remains unaltered or substantially unaltered when the switching means is switched from either of its settings to the other setting. With that arrangement the ratio of the heat output from the combined first and second elements, when the switch means is in its first setting, to the heat output from the first element, when the switch means is in its second setting, is equal or substantially equal to the ratio of the resistance of the first element to the sum of the resistances of the first and second elements.

Hitherto it has been the usual practice in water heaters of the kind specified to provide primary and secondary heating elements individually connectable to the electricity supply through switch means such that in a primary position of the switch means the primary element alone is connected to the electricity supply while in a secondary position of the switch means either the secondary element alone is connected to the electricity supply or both elements are connected to the electricity supply in parallel with each other.

Each of those arrangements has it disadvantages.

Where the arrangement is such that the supply is switched from the primary element to the secondary element it is necessary to provide two relatively large elements; the primary element may be considered to be the equivalent of said first and second elements in series, while the secondary element may be considered to be the equivalent of said first element alone. Use of the present invention can thus enable the bulk of the resistance elements to be reduced. In cases where the elements extend along one or more passageways through which the water flows, there are further advantages. First the total length of passageway occupied by the elements can be reduced.Secondly there is a reduced likelihood of significant temperature variations occurring in the heated water; these can arise when the electricity supply is switched from the primary element to the secondary element, for water heated by one element can be subsequently heated to a higher temperature by the other, orwaterthat has passed one element while it is unheated may subsequently pass the other element after it has been switched off, so that that particular portion of water remains substantially unheated. This disadvantage is reduced in using the present invention as the first element is heated both when the switch means is in its first position and when the switch means is in its second position so that none of the water can escape being at least partially heated as it passes over the first element.

Where the arrangement is such that the electricity supply is switched from the primary element alone to the primary and secondary elements in parallel, the primary element is again the equivalent of said first and second elements in series, so that the secondary element (provided to enable the heat output to be increased) is an additional element which increases the bully of the resistance elements used.

It is within the scope of the present invention for the heating elements to be disposed in a tank or similar vessel in which the water is heated in bulk. In a preferred form of heater, however, the heating elements extend along one or more passageways through which the water is caused to pass when the heater is in use.

Moreover, while it is within the scope of the present invention for the elements to be electrically insulated from the water, the elements are preferably not electrically insulated from the water. In particular the elements are preferably in the form of bare resistance wires. The thickness of the resistance wire of the second element is preferably less than the thickness of the resistance wire of the first element as the second element does not have to carry a current as high as that carried by the first element. This use of resistance wire of a reduced gauge for the second element also leads to a reduction of the overall length of resistance wire used and to an increase in safety, as the gauge of each element can be so chosen that in the event of overloading or overheating the wire from which it is formed can act as a fuse.On the other hand it would be within the scope of the invention for the first and second elements to be constituted by different parts of a unitary length of resistance wire, a tapping being provided at the place where they meet. Moreover either one of the two elements or each of the two elements may be constituted by two or more separate resistors.

The separate resistors constituting the element or each element, or at least some of those resistors, may be disposed in different passageways and/or may be disposed at spaced locations in the same passageway.

Such arrangements can help in avoiding still further any tendencies there may be for significant temperature variations in the heated water to occur following a change in setting of the switch means. IF desired, two or more of such resistors may constitute spaced portions of a unitary length of resistance wire.

It will, of course, be understood that this principle of subdividing one or more of the heaping elements is of general application. Therefore, from another aspect the present invention consists in a water heater of the kind specified in which the electric heating means comprises two or more heating elements extending along a passageway or passageways through which the water is caused to pass when the heater is in use, and selector switching means enabling electricity to be passed through the elements, different settings of the switching means enabling electricity to be passed through different ones of the elements or different combinations of elements so as to yield different heat outputs, at least one of the elements being constituted by two or more separate resistors, those resistors, or at least some of those resistors, being disposed in different passageways and/or being disposed at spaced locations in the same passageway.

The water heater preferably includes at least one additional heating element, capable of being brought into and out of use by the switching means. In particular, additional heating elements with associated selector switching means may be arranged in a manner similar to said first and second elements and selector switching means.

The water heater is preferably of the kind in which there is base heating means operative in use to yield heat at a certain minimum rate and to operate continuously (or substantially continuously) while the water heater is in operation. While continuous operation is preferred, it would for example be possible for the base heating means to be momentarily switched off during changes in the switch settings. In a preferred arrangement said first heating element constitutes at least a part of the base heating means. Nevertheless the base heating means need not be constituted by the same heating element or group of elements when the selector switching means is in different settings, the sole characteristics of the base heater means being that it yields heat at a certain minimum rate, and that it is constituted by at least one invariable heating element.

The heater may have a control system operative to control the selector switch means so as in use to maintain the temperature of the heated water at a substantially constant value, the control system including manually operable switch means such that operation of the switch means leads to a progressive rise or fall in said value. This kind of control system is of application not only to water heaters of the type outlined above but is of general application to other, similar, types of water heaters as well.Therefore, from another aspect the present invention consists in a water heater of the kind specified in which there is control means operative in use to cause the temperature of the water heated by the heater two be maintained at our substantially at a selected temperature, the control means also including automatic adjustment means operative in use to cause progressive variation of the selected temperature, within predetermined limits of possible variation, and switch means operable by a user to enable the adjustment means to be operated at will, and thus to enable the selected temperature to be varied at will.

The switch means is preferably such as to require continuous use by the operator to cause operation of the adjustment means, release of the switch means causing operation of the adjustment means to cease. Thus the switch means may comprise one or more push-buttons or the like spring-loaded switches. Preferably the switch means is such as to enable the user to cause operation of the adjustment means in either of two different ways, at will, one way leading to an increase in the selected temperature and the other way leading to a decrease in the selected temperature (provided that the selected temperature is not already at the appropriate end of the range of possible selected temperatures). Thus there may be two push-buttons or like spring-loaded switches.

Preferably there is display means which in use provides a visual indication of the selected temperature.

The indication may be of any desired kind and/or on any appropriate scale its function being to enable the user to distinguish one selected temperature from another.

Embodiments of the present invention are illustrated diagrammatically in the accompanying drawings, in which Figure 1 is a circuit diagram of a simple form of heating means and switch means for use in a water heater embodying the present invention, Figure 2 is a circuit diagram of a more complicated form of heating means and switch means for use in a water heater embodying the present invention, Figure 3 is a diagrammatic layout of one practical embodiment of the heating means shown in Figure 2, Figure 4 is a diagrammatic layout of another practical embodiment of the heating means shown in Figure 2, and Figure 5 is a diagram illustrating the principal components of a control system, for heating means embodying the present invention, when the heating means is used for heating water for a shower.

The heating means shown in each of the accompanying drawings is preferably constituted by one or more lengths of bare resistance wire extending along a passageway through which water flows when the heater is in use. The or each length of wire is preferably in the form of an open helical coil or spiral co-axial with the passageway. The passageway may be of non-rectilinear shape. In one particularly convenient arrangement the passageway comprises a body formed with two parallel, vertical bores interconnected by a short horizontal bore at the bottom. There is a water inlet a little below the top of one of the vertical bores and a water outlet adjacent to the top of the other of the vertical bores. The resistance wires extend along the bores from a point adjacent to the inlet to a point adjacent to the outlet.At least one electrical lead extends through the body and into a part of the passageway spaced away from the inlet and from the outlet. As will become apparent from the following description, some leads may be connected as tappings to heating wires, part way along their lengths, while others may be connected to the ends of heating wires.

In each instance the supply of electricity to the heating means is controlled by switch means. This may include one or more safety switches of the kind operative to cut off the supply of electricity if the flow of water through the heater ceases. In addition the switch means includes selector switch means enabling the heating wires to be connected to a source of electricity in each of two or more different arrangements so that the heat output can be varied. The selector switch means may be manually operable or otherwise under the direct control of the user. Alternatively the selector switch means may be controlled thermostatically to enable a predetermined or selected water temperature to be maintained.

The heating means shown in Figure 1 comprises a resistance wire 1, which constitutes a first heating element, and a resistance wire 2, which constitutes a second heating element. The wires 1 and 2 are connected in series and conveniently comprise successive portions of a unitary piece of resistance wire. The first element 1 is connected to the neutral line N of a source of mains electricity. The point of connection between the elements 1 and 2 is connected to one contact 3 of a three-way switch 4, while the other end of the element 2 is connected to another contact, 5, of the switch. The pole 6 of the switch is connected to the live line L of the source of electricity. When the pole 6 of the switch is in contact with the contact 5 the switch is in its first setting and electricity passes through the elements 1 and 2 in series.When the switch is in the position illustrated, which is its second setting, electricity passes through the first element 1 but not through the second element 2. If the mains voltage is V and the resistance of the first and second elements is R1 and R2 respectively, the heat output in the first switch setting is proportional to V2/(R1 + R2) while the heat outout in the second switch setting is proportional to V2/(R1). The heat output in the first switch setting is therefore less than that in the second switch setting.

The principle illustrated in Figure 1 is incorporated twice in the heating means shown in Figure 2. In this heating means there are five heating wires, 7,8,9, 10 and 11. One end of each of wires 7, 10 and 11 is connected to the neutral line N of the main supply. The other ends of those wires are connected to the live line Lthrough triacs 12, 13 and 14 respectively. Those ends of wires 7 and 10 connected to triacs 12 and 13 are connected to heating wires 8 and 9 respectively. At their ends remote from wires 7 and 10 the heating wires 8 and 9 are interconnected by a line 15 which is in turn is connected to the live line L through a triac 16.

In place of the triacs, other forms of semiconductor switches may be used, if desired.

The values of the resistances are so chosen that when a current flows through triac 16, the series-connected wires 8 and 7 and the series-connected wires 9 and 10 (which are in parallel with wires 8 and 7) the power output represents a base value which is the minimum power output required when the heater is in use. If both triacs 12 and 16 are rendered conductive no current flows through wire 8, but the power output of resistor 7 increases, so that its value is greater than that of the combined wires 8 and 7 previously referred to. The increase in overall power output is a relatively small value. Similarly, if triacs 13 and 16 are rendered conductive no current flows through wire 9, but the overall power output increases. The arrangement is in fact such that the increase in the power output is twice the increase that resulted from malting triac 12 conductive.Finally, if triac 14 is rendered conductive a current passes through wire 11. This is arranged to have a power output equal to twice the increase that resulted from making triac 13 conductive.

The power output of the base heating means, that is the heat generated when triac 16 alone is conductive, is preferably between about 5 kw and 6 kw. The increase in power output that occurs when triac 12 is rendered conductive is preferably between about 0.4 kw and about 0.6 kw, a value of about 0.6 lw often being particularly convenient.

It will be appreciated that resistance wires 7 and 8 constitute respectively first and second heating elements of the aforementioned kind, and that resistance wires 10 and 9 likewise constitute respectively first and second heating elements of the aforementioned kind. The wires 7 and 8 constitute one branch of an electric circuit, while the wires 10 and 9 constitute another branch of said electric circuit, the two branches being in parallel.

Switch means (not shown) is provided to control the triacs 12, 13, 14 and 16. The switch means may have eight settings. In setting No. 0 all the triacs are non-conductive. In each of the other settings one or more of them is conductive, the arrangement being indicated in the following table in which a dash (- ) indicates non-conductivity and a cross (X) conductivity. The resultant total power output is given in the last column, B representing the power output of the base heating means and A the least increase in power output that can be obtained with this arrangement.It will be observed that after setting No. 1 each successive setting results in the power being increased by the amount A Setting Triacs conductive Total power 16 14 13 12 output 0 O 1 X - - - B 2 X - - X B+A 3 X - X - B+2A 4 X - X )( B + 3A 5 X X - - B+4A 6 X X - X B+5A 7 X )( X - B + 6A 8 X X X X B+7A If desired two or more of the resistance wires may constitute portions of a unitary length of wire. Indeed, all the resistance wires may constitute successive portions of a unitary length of wire. Nevertheless, as explained above, it is preferred to arrange for each resistance to be of a gauge of wire appropriate to the particular power output of that resistance.Figure 3 shows an arrangement in which the resistances are connected end to end; they may either form part of a unitary length of wire or be constituted by separate lengths of wire joined together to form a single heater. Tappings 17, 18 and 19 from the heater are connected respectively to triacs 12, 16 and 13, while the lower end 20 of the heater is connected to triac 14. The neutral line N is connected to the upper end of the heater and to another tapping. A single heater of this kind may be mounted so that it extends lengthwise along a passageway through which the water flows. The water preferably flows in a direction such that passes first over the resistance wire 7.In practice it is found, however, that when the setting of the switch means is altered from one number to an adjacent one (neither being zero 0) there may sometimes be a momentary fluctuation in water temperature that is noticeable. As explained above, this may for example occur when a short portion of water in the passageway passes over each of the numbered heating wires in turn and by chance remains largely unheated or is over-heated.

In order to reduce that problem the resistance wires may be subdivided and rearranged in the passageway. One preferred arrangement is shown in Figure 4 where there are five successive lengths of resistance wire, with connections and tappings as illustrated. If the heating elements 7, 8, 9, 10 and 11 have resistance values A, B, C, D and E respectively, then the successive heating wires and portions of heating wires in the passageway, from top to bottom of Figure 4, have the values; A/3, C/2, B, 2A/3, E/3, 2D/3, C/2, 2E/3 and D/3. Unlike the arrangement with the heater shown in Figure 3, the water would successively pass over the resistance wires from the bottom of Figure 4 to the top thereof.

Numerous other arrangements are of course possible. In another type of heater the resistance wires are disposed in parallel passageways so that the incoming water is sub-divided into separate streams each of which flows through only one passageway, the streams subsequently being recombined.

Figure 5 illustrates diagrammatically a control system for the heater and suitable for use when the heater is used for heating water for a shower. The system incorporates a microprocessor 21 which in to err incorporates the major part of the switch means and is connected to a control unit 22 having four output leads 23 for providing signals for switching the fourtriacs 12, 13, 14 and 16 on and off. The unit 22 is also connected to a solenoid valve 24 which, when open, allows water to flow through the heater. Connected to the microprocessor are a temperature sensor 25, which in use supplies a signal corresponding to the actual temperature of the heated water, and a safety switch 26, which causes the heater elements to be de-energised if it senses no flow ofwater.

An operator unit 27 is also connected to the microprocessor 21 and has three push-buttons 28 or similar manually operable controls. One, when depressed, switches the heater on in such a manner that water flows through it without being heated at all; another, when depressed, switches the heater on in such a manner that the water is heated by the heater wires as described above; and the third, when depressed switches the entire heater off, and among other things causes the solenoid valve 24 to close, thus stopping the flow of water.

In addition there is a second operator unit, 29, connected to the microprocessor. This is connected to switch means comprising two push-buttons 30.

The arrangement is such that when the heater is first swiched on using the appropriate one of the buttons 28, control means comprising the microprocessor and the temperature sensor 25 operates as a thermostat to maintain the temperature of the heated water at or substantially at a predetermined starting temperature, which is of a temperate value. This predetermined starting temperature is indicated on display means comprising an indicator 31 connected to the microprocessor 21. If the user requires water at a higher temperature he or she presses an appropriate one of the push-buttons 30. This causes operation of automatic adjustment means which causes a gradual and progressive increase in the thermostat setting until the button is released. The value of the thermostat setting is displayed on the indicator 31.If the user wishes to reduce the thermostat setting he or she depresses the other one of the push-buttons 30. This causes operation of the automatic adjustment means so that there is a gradual and progressive decrease in the thermostat setting until the button is released, and as before the value of the setting is displayed on the indicator 31. The automatic adjustment means is in fact afforded by the microprocessor, but it could equally well be constituted by an electro-mechanical device.

The heater incorporates a valve which controls the flow rate of the water so that it is substantially constant and independent of the pressure of the water supply. The flow rate is so selected that when the incoming water is at a constant temperature an adjustment in the setting of the switch means from any setting to the next neighbouring setting (neither setting being zero) the resultant change in the temperature of the heated water is not more than 5'F (2.78"C) and preferably not more than 4"F (2.22"C). Such temperature steps can readily be tolerated by the users of showers, who do not normally want or require smaller steps.

In a modified form of heater the control system for the electric heating means is of the kind that is the subject of patent application No.8329917 of R L & D Limited.

Claims

1. A water heater of the kind specified in which the electric heating means comprises a first heating element and a second heating element and selector switching means which in a first setting enables electricity to pass through said first and second heating elements in series and a second setting enables electricity to pass through said first element but enables no electricity or substantially no electricity to pass through said second element so that in use said first and second heating elements, considered together, yield less heat energy when the switching means is in its first setting than they do when the switching means is in its second setting.

2. A water heater according to claim 1 in which the applied voltage remains unaltered or substantially unaltered when the switching means is switched from either of its settings to the other setting.

3. A water heater according to either of claims 1 and 2 in which the heating elements are disposed in a tank or similar vessel in which the water is heated in bulk.

4. A water heater according to claim 3 in which the elements are electrically insulated from the water.

5. A water heater according to either of claims 1 and 2 in which the heating elements extend along one or more passageways through which the water is caused to pass when the heater is in use.

6. A water heater according to claim 5 inwhich the elements comprise bare resistance wires.

7. A water heater according to either of claims Sand 6 in which the elements or at least portions of the elements are constituted by a unitary length of resistance wire.

8. A water heater according to any one of claims 5 to 7 in which at least one of the elements is constituted by two or more separate resistors.

9. A water heater according to claim 8 in which the separate resistors constituting the element or each element, or at least some of those resistors, are disposed in different passageways and/or are disposed at spaced locations in the same passageway.

10. A water heater according to any one of the preceding claims in which there is at least one additional heating element, capable of being brought into and out of use by the switching means.

11. A water heater according to claim 10 in which there are additional heating elements with associated selector switching means arranged in a manner similar to said first and second elements and selector switching means as claimed in any one of claims 1 to 9.

12. A water heater according to any one of the preceding claims in which there is base heating means operative in use to yield heat at a certain minimum rate and to operate continuously (or substantially continuously) while the water heater is in operation.

13. A water heater according to claim 12 in which said first heating element constitutes at least a part of the base heating means.

14. A water heater according to claim 12 in which the base heating means comprises two branches of an electric circuit in parallel, one of said branches comprising said first and second heating elements in series and the other of said branches comprising third and fourth heating elements in series, the third and fourth elements being arranged in a manner similar to said first and second elements as claimed in any one of claims 1 to 9.

15. A water heater according to any one of the preceding claims in which said selector switching means comprises one or more triacs or similar semiconductor switches.

16. A water heater of the kind specified and substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

17. A water heater of the kind specified and substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

18. Awater heater according to claim 17 in which the heating means is substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

19. A water heater according to claim 17 in which the heating means is substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

20. A water heater according to any one of the preceding claims incorporating a control system substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.