GB2150716A

GB2150716A - Electric water heaters

Info

Publication number: GB2150716A
Application number: GB08428287A
Authority: GB
Inventors: Robert Lewis
Original assignee: Rl & D Ltd
Current assignee: Rl & D Ltd
Priority date: 1983-11-09
Filing date: 1984-11-08
Publication date: 1985-07-03
Also published as: GB2151050A; GB2150716B; GB8428287D0; GB8428286D0; GB8329917D0

Abstract

An electric water heater has electrical heating means (8) for heating water flowing through it to a shower rose (15). The temperature of the heated water is sensed by temperature sensor (13) which causes a controller (9) to vary the power output of the heating means to cause or attempt to cause the temperature of the heated water to remain at a predetermined constant value. If the power output of the heating means rises to or above an upper limit the controller causes a motor (6) to alter the setting of a constant-flow valve (4) so as to reduce the rate of flow of the water. This enables the user to have a hot shower even on a very cold day, though with a somewhat reduced flow of water. If the power output then falls to or below a lower limit the motor re-opens the valve. The predetermined water temperature may be varied by the user. <IMAGE>

Description

SPECIFICATION Electric water heaters This invention relates to electric water heaters and in particular to electric water heaters of the kind (hereinafter referred to as the kind specified) which incorporates electrical heating means operative to heat water flowing through the heater.

Water heaters of the kind specified are often employed for heating water for use in showers, and are generally powered from the domestic mains electricity supply. When a water heater is used for this purpose it is normally necessary for the power output of the heating means to be variable to enable a variety of different circumstances to be accommodated. For example, on a hot day, when the temperature of the incoming water is already quite high and the user requires the temperature of the heated water to be only moderate, it may well be necessary to employ only a limited amount of power to heat the water, even though the water may be flowing at its maximum possible rate of flow.On a cold day, however, when the temperature of the incoming water may be only a little above O"C and the user may require the water to be heated to a relatively high temperature the heating means may have to be operated at a much higher power output. Now it can happen that in such circumstances the maximum available power output is insufficient to raise the temperature of the water to the desired temperature unless the normal rate of flow of water is somewhat reduced. It has therefore been proposed to provide a heater with a warning device which generates a visual signal to the user when the heater is operating at maximum power output but is unable to heat the water to the desired temperature, so as to warn the user that he or she should take appropriate steps to reduce the rate of water flow through the heater.

An object of the present invention is to provide an improved arrangement.

According to the present invention there is provided an electric water heater of the kind specified and which is intended in normal use to raise the temperature of the water to or substantially to a predetermined, required temperature, temperature sensing means responsive to the actual temperature of the water heated by the heating means, control means responsive to the temperature sensing means and operative in normal use to vary the power output of the heating means in such a manner as to cause or attempt to cause the actual temperature to equal or substantially equal the required temperature, adjustable valve means operative to control the rate of flow of water through the heater in such a manner that at any adjustment setting of the valve means the rate of water flow remains substantially constant, provided that the pressure of the incoming water is within a certain pressure range, but that the rate of water flow is different at different adjustment settings of the valve means, and adjustment means operative in normal use to cause adjustment of the valve means in such a manner as to reduce the rate of water flow when or if the power output of the heating means rises to or above a predetermined upper limit.

The predetermined upper limit of the power output is preferably the maximum available power output of the heating means.

It would be possible for the adjustable valve means to have only two possible settings and for the heater to operate, in normal use, in such a manner that there is one rate of water flow for as long as the power output remains below the predetermined upper limit but there is a reduced rate of water flow when the power output reaches or exceeds the predetermined upper limit.

Alternatively the valve means might have three possible settings or some other small number of possible settings. In a preferred form of heater, however, the valve means has a continuous range of possible settings.

The adjustment means is preferably electrically actuated. In the case of valve means having only two possible settings or some other small number of possible settings the adjustment means may comprise one or more solenoids; where the valve means has a continuous range of possible settings, however, the adjustment means preferably comprises an electric motor.

Preferably the adjustment means is also operative in normal use to cause adjustment of the valve means in such a manner as to increase the rate of water flow when or if the power output of the heating means falls to or below a predetermined lower limit. Moreover the arrangement is preferably such that the heating means is capable of operating at any of a plurality of different power outputs, or at any power output within a range of different power outputs, between said predetermined upper limit and said predetermined lower limit. With that arrangement it is normally possible for the control means to vary the heat output of the heating means to compensate for minor fluctuations in demand, such as may for example arise from fluctuations in the temperature of the incoming water, without the adjustment means coming into operation.

Reference has been made above to the way in which the heater operates in normal use, and that phrase 'normal use' is intended to refer herein to situations that occur when the heater has been operating for sufficiently long for it to be unaffected by the circumstances that arose when operation of the heater was initiated, and that occur when steps are taken to cause the heater to cease operation.

When the heater is initially put into operation or is switched off, different considerations apply for a short period so that the heater is usually required during that period to operate in a manner different from the manner adopted when it is in normal use.

When the heater is initially put into operation the actual temperature of the water is likely to be considerably less than the required temperature; the control means is therefore preferably operative to cause the heating means to yield a relatively high power output so that the actual temperature of the water is raised as rapidly as possible. If, as is likely, the power output were to rise to or above said upper limit at this time, then in normal use this would result in a reduction in the rate of water flow. Such a reduction is not required, however, during the initial stages of operation of the heater, and the arrangement is therefore preferably such as to prevent a reduction in water flow during the initial stages of operation.In fact the arrangement is preferably such that after the heater has been turned on the adjustment means cannot start to come into operation to start reducing the water flow until the valve means has reached a predetermined open state permitting water to flow at a rate greater than that at which it flows when the adjustment means is at another setting or settings.

When the heater is turned off the power output of the heating means falls to zero. As this occurs it necessarily falls below the lower limit referred to above with the results that this might lead to the adjustment of the valve means to increase the rate of flow of water. In a preferred arrangement, however, the turning off of the heater leads to adjustment of the valve means to a closed position so that the the water flow ceases. Nevertheless, if the reduction in power output of the heating means takes place only gradually after the heater is turned off, and this may for example be necessary to avoid problems with network disturbance, the closure of the valve means may have to be delayed somewhat to ensure that there is not temporary overheating of the water.Where the adjustment means comprises an electric motor, however, and closure is relatively slow, there may well be no need to arrange for further delay.

While the heater may be such that the required temperature is unalterable by a user, the heater preferably includes temperature setting means which can be adjusted by a user to vary the required temperature.

The heating means may be of any suitable kind. The heating means preferably comprises one or more bare, uninsulated heating elements with which the water comes into contact when the heater is in use. Alternatively the heating means may comprise one or more electrically insulated heating elements.

An electric water heater of the kind specified and in accordance with the present invention will now be described in more detail, by way of example, with reference to the accompanying drawing, of which the single figure is a diagram illustrating the layout of the heater.

The heater is intended for use in heating water for use in a shower. The heater has a water inlet pipe 1 which is connected to the domestic mains water supply by way of a manually closable stop-cock 2. A pipe 3 leads from the stop-cock to a constant flow valve 4 which constitutes the adjustable valve means referred to above. The constant flow valve 4 is of a kind such that at any given setting it permits water to flow through the heater at a constant or substantially constant rate which is largely or wholly independent of the pressure of the water supplied to it through the pipe 3, provided of course that the pressure of the incoming water does not rise to an excessive value or fall below a certain minimum value. The valve 4 is adjustable, by rotation of a spindle 5, to any setting within a range of settings.At one end of the range the valve is closed and prevents any flow of water; as the spindle is rotated from the position in which the valve is closed it permits a progressively increased rate of water flow until the valve is fully open and a maximum flow rate is achieved. At any given setting the flow rate remains constant or substantially constant, provided that the pressure of the water in the pipe 3 is not unduly high or unduly low. The valve 4 may be of the kind described and illustrated in the complete specification of British patent No. 1 601 375 of Reinhard Carl Mannesmann and Wolf-Dieter Keppell trading as Mannesmann 8 Keppel Electronics. Rotation of the spindle 5 in either direction can be effected by a reversible electric motor 6 which incorporates reduction gearing, this constituting adjustment means for the valve.The period required for the valve to be adjusted from its closed state to its fully open state or vice versa is several seconds in duration, for example eight seconds.

A pipe 7 leads from the valve 4 to a heating unit 8 which may comprise a labyrinthine duct containing coils of bare, uninsulated, electrical heating wire. The physical construction of the heating unit has no bearing on the present invention, and as several types of suitable heating unit are known, the construction will not be described herein. The coils in the heating unit are so connected as to constitute four heating elements: a base element and three additional elements I, II and Ill. The additional elements are such that No. I is rated at a minimum power A, No. II is rated at twice that minimum power, 2A, and No. III is rated at four times that minimum power, 4A.In normal use of the heater the base element is operated continuously to give a power output B but one or more of the three additional elements may be powered as may be required to provide any one of seven different principal power outputs (i) to (vii) each of which differs from the next adjacent power output by said minimum power. The principal power output (i) also differs from the base power output B, which may also be considered as principal power output (o), by said minimum power. This is illustrated in the following table in which the base output and principal power outputs are shown sequentially, a cross (x) indicating that an element is powered and a dash (-) indicating that it is not powered.

Principal Heating Elements Total Power Power Output Output B I II III (o) x - - - B (i) x x - - B + A (ii) x - x - B + 2A (iii) x x x - B + 3A (iv) x - - x B + 4A (v) x x - x B + 5A (vi) x - x x B + 6A (vii) x x x x B + 7A The switching on and off of each of the heating elements is effected by an associated triac, or similar solid-state switching device, operated by a controller 9 which constitutes control means.

The controller incorporates a microprocessor and responds to signals fed to it in the manner described below. The controller also generates signals for the operation of the electric motor 6.

The connection between the controller and the heating unit is indicated by the line 10 and that between the controller and the electric motor by the line 11.

In order to avoid the network disturbance that would occur if the heating unit were switched from one principal power output to the next, and to provide for fine variation in the heat output, the controller can operate to provide any of nine intermediate power outputs between each adjacent pair of principal heat outputs. This is carried out in the following manner. During each successive sequence of ten cycles of the a.c. mains supply used to operate the heater the controller can operate to switch the triacs or other switches so that the heating unit dissipates power at one principal rate during one or more of the cycles and then dissipates power at an adjacent principal rate during the remaining cycles. Thus there are in all seventy uniformly spaced rates at which the heating unit can heat the water flowing through the unit, from the base rate (o) to a maximum rate (vii).In the microprocessor these rates are numbered sequentially from 0 to 70. Strictly speaking each intermediate power output is only an average output over successive periods of ten cycles each, but in practice the heat intake by the water is effectively uniform.

Water from the heating unit 8 passes by way of a pipe 1 2 to a temperature sensor 13, which constitutes temperature sensing means, and thence by way of a pipe 1 4 to a rose 15; part of the pipe 1 4 may of course be flexible. The temperature sensor 1 3 is connected to the controller 9 by a line 16, and within a range of working temperatures the controller recognises some 32 different temperatures, sensed by the sensor 13, substantially uniformly spaced apart.

The controller is also connected to a numerical display 1 7 and a plurality of user-operable buttons 18, 19, 20, 21 and 22. When button 18 (bearing the legend COLD) is depressed, the controller causes the motor 6 to open the valve 4 to the maximum extent but does not cause the heating unit 8 to be energised. If the button 1 9 (bearing the legend OFF) is then depressed the controller causes the motor to close the valve and then to switch the entire heater off. If the button 20 (bearing the legend HOT) is depressed, however, the controller causes the motor to open the valve and causes the heating unit 8 to dissipate heat at a progressively increasing rate.

At the same time the number "16" is displayed by the numerical display, this indicating a required water temperature considered suitable for a person taking a shower. That temperature may typically be 106"F (41.1on). If the button 21 (bearing the legend UP) is depressed the number displayed progressively increases to a maximum possible value of "28", the increase continuing only while the button is held depressed. Conversely, if the button 22 (bearing the legend DOWN) is depressed the number displayed progressively decreases to a minimum possible value of "01", the decrease continuing only while the button is held depressed. By suitable manipulation of the buttons 21 and 22 the user is thus able to set the display at any desired number between "01" and "28".Each of these numbers corresponds to a different required temperature between about 94"F (34.4"C) and 125"F (51.7"C), the different required temperatures being approximately uniformly spaced apart.

If the user initially depresses the button 20 but does not depress either of the buttons 21 and 22 the motor 6 opens the valve 4 until it is fully open, and the controller 9 progressively increases the power output of the heating unit 8 in such a manner as to avoid network disturbance but at the same time to reduce as far as possible the time taken for the actual temperature, as sensed by the sensor 1 3, to equal or substantially equal the required temperature corresponding to the displayed number "1 6". The heater would normally be so designed that even if the temperature of the incoming water was only slightly above 0 C the heating unit was sufficiently powerful to enable the water to be heated to that required temperature.The heater can be considered as in normal operation as soon as the valve 4 is fully open.

Should the user require water at a higher temperature and therefore depress the button 21 to raise the value of the number displayed, and the value of the required temperature, the controller 9 acts so as to try to increase the actual water temperature so that it is equal to or substantially equal to the required temperature. In many circumstances that can be achieved but if the required temperature is relatively high and the temperature of the incoming water is relatively low, the maximum power of the heating unit may be insufficient to enable the actual water temperature to rise sufficiently high This becomes apparent if the principal power rate reaches the value 70. When that occurs the controller operates to start the motor 6 adjusting the valve 4 to reduce the water flow.While the rate of water flow decreases, the water temperature consequently rises until the desired water temperature is reached. After that, as the water flow continues to decrease, the controller automatically reduces the power output of the heating unit. As soon as the power output falls below 70 the motor 6 is automatically stopped by the controller. In fact, owing to inevitable time lags, the power output rate is likely to fall to a value in the mid-sixties or even lower. Should the power output fall below 60 the controller operates the motor in the reverse direction so as to increase the water flow again. As soon as the power output rises to 60 or exceeds 60 the controller stops the motor.In this way the power output can be retained in the sixties, that is close to the maximum possible power output, with the consequence that the extent to which the water flow is reduced is as small as is reasonably practicable.

When ever a state such as this is reached, slight variations in the temperature of the incoming water, or any other minor fluctuations in operation, can normally be overcome by slight variations in the power output of the heating unit, without the motor 6 being cause to operate.

Should the user select a required temperature corresponding to a displayed number lower than "1 6" it is most unlikely that the power output of the heating unit would ever reach its maximum value, corresponding to the rating 70. Nevertheless there is nothing positively to prevent the heater operating in the manner described.

When the user depresses the button 1 9 while the heating unit is in operation the controller operates to reduce the power output of the heating unit as rapidly as possible, subject to the avoidance of network disturbance. At the same time the motor 6 is caused to adjust the valve 4 to its fully closed state. Closure of the valve takes several seconds, for example eight seconds, that period being considerably longer than the period required for reducing the power output of the heating unit to zero. Therefore the reducing flow of water that occurs while the heater is being turned off does not become overheated. Finally, when the valve 4 is fully closed the electric supply to the heater is automatically cut off.

If, while the heater is in normal operation, the user tries to turn off the heater by means other than depression of the button 19, as for example by operation of a circuit breaker in the power supply, the power output of the heating unit is immedidately reduced to zero, with the likelihood of consequent network disturbance. At the same time the motor ceases to operate, so that cold water remains flowing. The inconvenience of the latter occurrence would be likely to deter the user from repeating the action on another occasion. The stop-cock 2 is preferably positioned so as to be relatively inaccessible by the user. Nevertheless, in the event of a fault or a powerfailure it would be possible to cut off the water flow by closure of the stop-cock.

Claims

1. An electric water heater of the kind specified and which is intended in normal use to raise the temperature of the water to or substantially to a predetermined, required temperature, temperature sensing means responsive to the actual temperature of the water heated by the heating means, control means responsive to the temperature sensing means and operative in normal use to vary the power output of the heating means in such a manner as to cause or attempt to cause the actual temperature to equal or substantially equal the required temperature, adjustable valve means operative to control the rate of flow of water through the heater in such a manner that at any adjustment setting of the valve means the rate of water flow remains substantially constant, provided that the pressure of the incoming water is within a certain pressure range, but that the rate of water flow is different at different adjustment settings of the valve means, and adjustment means operative in normal use to cause adjustment of the valve means in such a manner as to reduce the rate of water flow when or if the power output of the heating means rises to or above a predetermined upper limit.

2. An electric water heater according to claim 1 in which said predetermined upper limit of the power output is the maximum available power output of the heating means.

3. An electric water heater according to either one of claims 1 and 2 in which the valve means has a continuous range of possible settings.

4. An electric water heater according to any one of the preceding claims in which the adjustment means is also operative in normal use to cause adjustment of the valve means in such a manner as to increase the rate of water flow when or if the power output of the heating means falls to or below a predetermined lower limit.

5. An electric water heater according to claim 4 in which the arrangement is such that the heating means is capable of operating at any of a plurality of different power outputs, or at any power output within a range of different power outputs, between said predetermined upper limit and said predetermined lower limit.

6. An electric water heater according to any one of the preceding claims in which there is means for causing the heater to cease operation, and when that means is put into operation it causes adjustment of the valve means to a closed position so that water flow ceases, and brings about a reduction to zero of the power output of the heating means.

7. An electric water heater according to any one of the preceding claims in which there is temperature setting means which can be adjusted by a user to vary the required temperature.

8. An electric water heater substantially as herein described with reference to the accompanying drawing.