GB2154813A

GB2154813A - Electric water heaters

Info

Publication number: GB2154813A
Application number: GB08505219A
Authority: GB
Inventors: Robert Lewis
Original assignee: DOLPHIN SHOWERS Ltd
Current assignee: DOLPHIN SHOWERS Ltd
Priority date: 1984-02-28
Filing date: 1985-02-28
Publication date: 1985-09-11
Also published as: GB8505219D0

Abstract

Water flowing through the heater is heated to a predetermined temperature and booster means 8,9 are operable to increase the heater power output and increase the water flow rate without causing a significant variation in said temperature. A control circuit which prevents unlimited operation of the booster may have timing means which terminates operation of the booster after a predetermined time and then inhibits a further operation of the booster for a predetermined non-operational period. In normal operation, the heater may operate at a current equal to or less than the maximum continuous current which the supply circuit is designed to carry, whereas that design current is exceeded when the booster is in operation. The control may then keep a running total of the extent to which the energy used by the heater exceeds, or is less than, the energy that would be dissipated if it ran at the design current, booster operation being terminated if the running total exceeds a predetermined value. A main heater 7 in a water duct 3 is controlled by a temperature sensor 10 and operates in normal use. When a boost button is pressed, a solenoid valve 8 opens and a booster heater 9 in a water duct 4 is operated at a fixed power level, the sensor 10 continuing to control the heater 7 so that the water temperature in a common outlet duct 6 remains at the set level. Alternatively the rate of flow of water may be adjusted by thermostatic means. <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) comprising electric heating means operative in use to raise the temperature of water flowing through the heater.

The standard mains electricity supply to dwellings in the U.K. consists of a singlephase a.c. supply at 240 volts. Many domestic circuits are designed to operate at a maximum continuous operating current of 30 amps, so that the maximum power output of any appliance is 7.2 kw. In the operation of a well-known and widely used form of shower unit embodying an electric water heater of the kind specified, cold water flows from the mains supply and passes through an electrically powered water heater which heats the water to the desired temperature. If the required rise in water temperature is relatively large, as may well happen in winter when the temperature of the incoming cold water is only little above 0 C, only a restricted quantity of water per unit time can be raised to the desired temperature when using the maximum power output of 7.2 kw.While the rate of flow of water may be adequate for a person taking a shower, it is believed that it would be advantageous if it were possible to make some provision for the rate of flow of water to be increased.

An aim of the present invention is to provide a system enabling this to be achieved.

According to the present invention there is provided an electric water heater of the kind specified which in normal operation is capable of heating water flowing through it to a predetermined or selected temperature and which includes booster means operative to bring about an increase in the power output of the heating means and an increase in the rate of flow of water through the heater, while not causing a significant variation in said temperature, and monitor means operative to prevent unlimited operation of the booster means.

The monitor means is preferably such that it operates to cause operation of the booster means to cease after a predetermined booster period has elapsed, provided that operation of the booster means has not already been caused to cease by some other agency. While it might be possible to arrange for the booster period to be adjustable, that period is preferably such as not to be adjustable (at least in normal use of the heater). The booster period is preferably within the range of from 1 5 seconds to two minutes. Generally it is preferred to provide a booster period of not more than one minute. A particularly preferred booster period is about 20 seconds.

The heater may be such that the booster means is brought into operation automatically, either when operation of the heating means as a whole is started or at a predetermined time after normal operation of the heating means is started. Preferably, however, the arrangement is such that the booster means can be brought into operation by the user at any moment convenient to the user provided that the operation of the booster means is not, at that moment, prevented by the monitor means. In particular the arrangement is preferably such that unless its use is otherwise inhibited the booster means can be brought into operation as soon as the heating means is brought into operation.Initiation of the operation of the booster means can preferably be effected by the operation of a switch or the like by the user, the arrangement preferably being such that once the switch or the like has been operated the booster means can remain in operation without the need for the user to maintain operation of the switch or the like.

The heater is preferably so arranged that after the booster means has been put into operation it remains in operation until it is automatically caused to cease operation either in response to a signal from the monitor means at the end of the booster period or when the heating means as a whole is switched off.

The heater may be provided with indicating means operative to indicate to the user when the booster means is available for use. The indicating means may, for example, comprise a signal which is illuminated when the booster means is available for use or which is illuminated when the heating means is on but use of the booster means is prevented by the monitor means.

As explained in more detail below, the heater may be such that when the heater is in normal operation it takes an electric current equal to or less than the maximum continuous operating current (or design current) which the supply circuit is designed or intended to carry, but when the booster means is in operation the current taken by the heater is greater than the design current. In order to avoid the supply circuit being damaged by the temporary overloading that occurs when the booster means is in operation, the arrangement is preferably such as to make it impossible or at least difficult for the user to reinitiate operation of the booster means, following discontinuance of the booster means by the monitor, without the intervention of a nonoperational period during which the booster means is not in operation and cannot be put into operation by the user.One method of ensuring that there is a non-operational period is to provide latch means such that during any one operation of the heating means the booster means can be operated no more than once; in consequence, after causing operation of the booster means the user can bring the booster means into operation again only after switching the entire heater off and switching it on again. Another method of ensuring that there is a non-operational period is to arrange for the monitor means to prevent reinitiation of the operation of the booster means until at least a predetermined nonoperational period has elapsed. Both methods may be employed in the same heater if desired.

Timing means is preferably provided, this being operative to prevent reinitiation of the operation of the booster means until at least a predetermined nonoperational period has elapsed. The timing means may be brought into operation on each occasion that the booster means ceases to operate but is preferably brought into operation on each occasion the booster means is brought into operation, the timing means measuring out both the operational and non-operational periods. The timing means is preferably such that it can continue to operate after the supply of electricity to the heater has been cut off. This prevents the timing means being overridden by a user temporarily switching off the electricity supply to the heater.Another method of preventing a user overriding the timing means is to cause the timing means first to measure out a full non-operational period each time the heater is switched on. The problem then, however, is that when the heater is switched on after an extended off period it is not possible to initiate use of the booster straight away. Where, as is preferred, the timing means is such that it can continue to operate without a supply of electricity, the timing means preferably includes energy-storage means which acts as a source of energy for the timing means when the mains supply ceases. The energy-storage means may comprise an electric cell or battery, this preferably being automatically recharged when the heater is on.Alternatively the energy-storage means may comprise an electric capacitor or it may be such as to store energy mechanically, for example by loading a spring or raising a weight.

In order that the temperature of the heated water should remain substantially unaltered when the booster means is operated, it is necessary for the rate of flow of water and the power output of the heating means to be increased substantially proportionately to each other. It may be sufficient for the rate of flow and the power output to be increased simultaneously by predetermined amounts, but preferably the amount by which one of them is increased is predetermined while the amount by which the other of them is increased is determined by thermostat means operative to maintain substantially unaltered the temperature of the heated water.Thus in a preferred arrangement operation of the booster means causes the flow rate of the water to be increased by a predetermined amount, the necessary increase in the power output of the heating means being effected by thermostat means operative to adjust the power output of the heating means so as to maintain substantially unaltered the temperature of the heated water. Nevertheless it would be possible to arrange for operation of the booster means to increase the heat output of the heating means by a predetermined amount and for the rate of flow of water to be adjusted appropriately by thermostat means. In either case the arrangement is preferably such that both during normal operation and during operation of the booster means the rate of flow of water is substantially independant of the pressure of the incoming water (within a predetermined range of pressures).This can be effected by means of one or more constant-flow devices.

It would be possible for the arrangement to be such that the heater as a whole automatically ceased to operate at the end of a booster period. In general, however, such an arrangement is considered to be unsuitable as it would result in the hot-water supply being cut off at a moment not directly chosen by the user. It is therefore much preferred to provide an arrangement in which the heater reverts automatically to normal operation at the end of a booster period, provided, of course, that its operation has not been caused to cease before that, as for example by the user turning the heater off or by some safety device responding to a fault and operating to turnthe heater off.Where, as is preferred, the heater can revert to normal operation at the end of a booster period, it is necessary to arrange for there to be a linked, proportional reduction in both the power output of the heating means and the rate of flow of water.

This can be effected by an arrangement which is the converse of any of those outlined above and which are effective to bring about linked, proportional increases in the power output and the rate of flow of water. In particular either of the arrangements incorporating thermostat means could well be used. Variations of the rate of water flow when the booster means is put into operation and when it ceases operation may be effected in any one of a number of different ways. For example there may be valve means for controlling the rate of flow of water through a duct and capable of assuming two or more different on settings or there may be two or more ducts through which water can flow in parallel when the booster means is in operation, one or more of the ducts being closed by valve means when the booster is not in operation.

The valve means may in either case be operated directly by the user or it may be operated by electrically-powered control means or electro-hydraulic or other control means.

In one preferred arrangement the heater incorporates a first pathway for water and a second pathway for water in parallel with the first pathway. Each pathway contains a con stant-flow device and, each pathway has a heating element constituting part of the heating means and operative in use to raise the temperature of water flowing through it.

Downstream of the heating means the pathways join to provide a common outlet. Temperature-sensing means in the outlet constitutes part of a thermostat which includes control means for varying the power output of the first heating means (i.e. the heating means for the first pathway). An on/off valve is provided in the second pathway. In normal use of the heater the on/off valve is closed so that water passes through only the first pathway; as it does so it is heated by the first heating means, under the control of the temperature-sensing means. When the booster means is put into operation the on/off valve opens, permitting an additional flow of water through the second pathway. The water flowing through the second pathway is heated by the second heating means, which has a constant power output.Streams of heated water from the two pathways flow into the common outlet where they blend and quickly reach a temperature intermediate the temperatures of the individual streams. The temperature-sensing means responds to this intermediate temperature and causes the control means to vary the power output of only the first heating means so as to bring the intermediate temperature to the predetermined thermostat temperature. When operation of the booster ceases the on/off valve is closed again and the second heating means is switched off. The heater is thus able to revert to its normal operation.

As explained above, it is possible for the heater to operate for a limited period with a current greater than that for which the electric supply circuit was designed. The fact that it is possible for the heater to be used in this way is based on an appreciation of the fact that electric supply circuits are generally designed to permit relatively small overloading for a moderate length of time before dangerous or unwanted effects occur and before the fuses blow or cut-outs operate. It is also based on the appreciation that provided the average current of the heater over a prolonged period does not exceed that for which the circuit was designed, or exceeds it only a little, no problems should arise. The principal problems that do tend to arise when circuits are overloaded for long periods result from excessive rises in temperature of the wiring or other parts of the circuits.When the overloading is such that the increase in current above the design current is relatively small -for example less than half the design current-any resulting temperature rises tend to be relatively small and tend to build up slowly over a prolonged periods period considerably greater than the full booster period. Similarly, many fuses are designed to accept overloading for a relatively long period before they blow.Thus, in general, the lengths of the periods of time during which problems tend to arise as the result of overloading are considerably greater than the maximum periods of overloading that occur when using the present invention, so that provided the average current or power output of the heater over a prolonged or extended period is no greater, or is only little greater, than that for which the electric supply circuit was designed, no problems should arise.

In heaters of the kind outlined above the booster period can continue for a given length of time, determined by the monitor means, the monitor means incorporating timing means to determine that length of time. Likewise, timing means may be used to prevent the booster means being operated too frequently. The timing means may, for example, be operative to prevent the heater being turned on again, after being turned off, until a predetermined down period has elapsed. Alternatively it may be operative to prevent the booster means being operated until a predetermined normal period has elapsed since the end of the last preceding booster period.

It is to be understood that the term nonoperational period is used herein to denote a period during which the booster means is not in operation, the term down period is used herein to denote a period during which the heating means as a whole is not in operation, and the term normal period is used herein to denote a period during which the heating means is in operation but the booster means is not in operation. Thus a nonoperational period may be constituted by a down period or by a normal period or by a combination of down and normal periods.

In an alternative arrangement to those outlined above the duration of the booster period and/or any down period and/or any normal period can be caused to vary in accordance with the power used by the heater in such a manner as to ensure that over an extended period of time the average current used or the average power output of the heating means or the total of energy expended does not exceed that for which the supply circuit was designed or exceeds it only by a predetermined, limited amount.

In normal circumstances the voltage of the supply to the water heater will remain substantially constant so that the power dissipated by the heating means and the power required to operate the monitor means and any other ancilliary equipment forming part of the heater will in each case be directly proportional to the current. For convenience, therefore, it is assumed in this description that the power and current are in direct proportion to each other.

Further, it will generally be the case that the maximum power dissipated by the heating means will be very much greater than the power required to operate the monitor means and any ancillary equipment, such as illuminated displays, forming part of the heater. In this description, therefore, it will for convenience be assumed that all the power taken by the heater is in fact dissipated by the heating means.

Moreover, current passed through the heating means for the purpose of generating heat to raise the temperature of the water will hereinafter be referred to as the main current.

It is envisaged that the maximum current or power supplied to the heater during a booster period would not exceed twice the predetermined design value. Preferably the maximum current or power supplied to the heater during a booster period would not exceed one and a half times the predetermined design value.

When the heater is such that there is thermostat means to vary the heat output of the heating means, while the rate of flow of water, during normal operation, is constant, it will often happen that the heater is not using the full design current. In such circumstances, when the booster means is then operated to increase the rate of flow of water to a higher level, the current used by the heater during the booster period may well exceed the design current by only a relatively smali amount. It may therefore be possible to increase the duration of the booster period without giving rise to problems in the supply circuit. In addition, or alternatively, any down period and/or normal period may be reduced.

One criterion that may be used in controlling the variation of any of those periods is the energy used in operating the heater. If an electric supply circuit is operated at the current for which it is designed (the design current) then during any given period a certain amount of energy is employed in the supply circuit, this energy being dissipated largely or wholly as heat energy.

In operating an electric water heater in the manner outlined above, the current employed during a booster period is normally greater than the design current. In consequence, during a booster period, the amount of energy dissipated in the supply circuit exceeds by a known amount the energy (the design energy) that would be dissipated in the supply circuit if the current were equal to the design current. During any down period, when the heater is not in use, no power or substantially no power is dissipated in the supply circuit.

Further, during normal operation of the heater, the energy dissipated in the supply circuit may be lower than the design energy.

The heater is preferably such that over an extended period the average power dissipated in the supply circuit will be equal to or less than the power that would have been dissipated in the supply circuit if the current supplied had been the design current throughout that total period.

Nevertheless, if the heater is first turned on and the booster means is immediately brought into operation it is likely that there is an amount of excess energy dissipated in the supply circuit. Provided that the amount of excess energy is limited to a predetermined value and is balanced by one or more subsequent reductions in energy dissipation, no problems should arise in the supply circuit.

That excess amount of energy dissipated in the supply circuit is, of course, proportional to an amount of energy used by the water heater.

Therefore, a preferred form of monitor means is one which is capable of operating in the following manner or in a manner equivalent to the following manner, namely to register a running total of energy variation, that is the amount by which the energy used by the heater varies from a predetermined set energy value, during each successive time increment, (the values of the variations being positive if exceeding the set energy value and negative if below the set energy value) and to prevent the heater operating in such a manner as to allow that running total of energy variation to exceed a predetermined excess energy value.

Electric water heaters incorporating monitor means of the kind outlined in the last preceding paragraph are the subject of patent application No. 8412713 of R L 8 D Limited.

In practice it is intended that the set energy value should be equal to the design energy so that if the heater were to operate continuously at the design current or power the running total of energy variation would remain at zero.

In one form of heater the arrangement is such that if the running total of energy variation exceeds the excess energy value, the booster period is terminated and no further booster period can be initiated until or unless running total of energy variation is reduced to zero or below zero.

In a preferred form of heater, however, the arrangement is such that the booster period remains constant and the monitor means serves to vary the non-operational period in such a manner that the running total of energy variation does not exceed the excess energy value.

The monitor means preferably incorporates a microprocessor.

While the nature of the invention has been outlined above with particular reference to water heaters for showers, the invention is of broader scope and may be applied to electric water heaters for supplying heated water to devices other than showers.

An embodiment of the present invention will now be described in more detail by way of example, and with reference to the accompanying drawing which is a diagrammatic representation of part of an electric water heater embodying the present invention.

In this embodiment the invention is applied to a water heater for supplying hot water to a shower (not shown). The water heater may incorporate an arrangement of the well-known kind comprising an insulating body formed internally with labyrinthine water ducts containing heating means in the form of heating elements shaped as coils of bare, non-insulated wire co-axial with the ducts.

The heater is intended for use with a singlephase a.c. mains supply of 240 volts, designed to provide a continuous current of up to 30 amps. The supply is therefore intended and designed to produce a maximum power output of 7.2 kw. The water heater, however, is such that when it is in operation at maximum power it operates at about 43 amps, that is at 10.3 kw. It will be noted that the increase in maximum power above the design power (3.1 kw) is a little less than half the value of the design power (7.2 kw). The supply circuitry incorporates a cartridge fuse rated at 30 amps but designed to continue conducting electricity at 43 amps for a relatively long period, such as at least 45 minutes, before burning out. The fuse may be made in accordance with BS 1361.

The heater has a water inlet duct 1 with a main on/off valve 2 which may be solenoidoperated or manually operated. Downstream of the valve 2 the inlet duct divides to provide two parallel water passages 3 and 4. Each passage contains, near its inlet end, a constant-flow device 5 operative to enable water to flow through that passage at a rate substantially independent of the water pressure at the inlet. At their outlet ends the two passages join a common outlet duct 6. Downstream of the associated constant-flow device 5 the first passage 3 contains heating elements 7 constituting a main heating means. A solenoid-operated on/off valve 8 is provided in the second passage 4 near the inlet end thereof and is operative to open and close the passage.Downstream of the valve 8 and the associated constant4low device 5 the second passage 4 contains a heating element 9 constituting booster heating means. In the common outlet duct 6 there is a temperatureresponsive device 10 which responds to changes in the temperature of the water in the common outlet duct and forming part of a thermostat.

In normal use, when the heater is switched on the valve 2 opens and the solenoid valve 8 is closed and water passes only through the first passage 3. The power dissipated by the main heating means 7 is automatically controlled so as to maintain constant the temperature of the water in the common outlet duct 6. The maximum power output of the main heating means is 7.2 kw, but the actual power output at any moment may well be rather less than this.

The heater has an electric switch (not shown) operable by a boost button which can be depressed by the user and at once released. When the heater is in operation and the button has been depressed the solenoid valve 8 opens, allowing water to flow through the second passage 4, and the booster heating means 9 operates at a fixed power output of 3.1 kw. The arrangement is such that if the temperature of the water in the common outlet duct 6 before the booster button was depressed was a typical, mean temperature then depression of the booster button results in the thermostat causing little or no variation in the heat output of the main heating means 7. Any such variation in heat output that does occur is of course in response to a signal from the temperature-responsive device 10 and is such as to maintain constant the temperature of the water in the common outlet duct 6.

Timing means (not shown) is provided and is operative to permit the booster period to continue for only about 20 seconds. At the end of that booster period (provided the heater as a whole was not previously switched off) the solenoid valve 8 closes again and the electricity supply to the booster heating means 9 is cut off. The timing means is also operative to measure out a period of about 2 minutes 20 seconds starting from the beginning of the booster period. Energy-storage means is provided to enable the timing means to continue its operation in measuring out that period even in the event of the heater being switched off before the period has expired.

The period measured out constitutes a booster period and an additional 2 minute non-operational period. The arrangement is such that the booster means cannot be brought into operation again until or unless that non-operational period has expired. It will be appreciated therefore that even if the heater is used at maximum power output and with the booster means operated as frequently as possible the average power output is only (20/(20 + (2 x 60))) x 3.1 kw = 0.44 kw above the design power of the 7.2 kw. This can be tolerated for quite an extended period, though in practice it is unlikely that the heater would be used for more than about 1 5 minutes without its being switched off. It is in fact usual for a person taking a shower to have the heater in operation for no more than about 5 minutes.

The heater is also provided with indicating means in the form of a lamp (not shown) which is illuminated during the period measured out by the timing means, so that the user is made aware of the fact that he or she cannot start using the booster means as long as the lamp remains lit.

Particular mention has been made above of water heaters embodying the present invention and designed for use with an a.c. mains supply of 240 volts operative at a design current of 30 amps. The heaters, however, have booster means such that when they are in operation the current taken exceeds the design current and may, for example, rise to 43 amps. It must, of course, be understood that these figures are given merely to illustrate the invention and that the invention is equally applicable to water heaters designed to operate with circuits operative at other design currents such as 35 amps or 40 amps. For example a water heater embodying the present invention may dissipate about 9 kw in normal use (the current thus being 37.5 amps) and may dissipate 1 3 kw when the booster means is in operation (the current then being about 54 amps).

Claims

1. An electric water heater of the kind specified which in normal operation is capable of heating water flowing through it to a predetermined or selected temperature and which includes booster means operative to bring about an increase in the power output of the heating means and an increase in the rate of flow of water through the heater, while not causing a significant variation in said temperature, and monitor means operative to prevent unlimited operation of the booster means.

2. An electric water heater according to claim 1 in which the monitor means is such that it operates to cause operation of the booster means to cease after a predetermined booster period has elapsed, provided that operation of the booster means has not already been caused to cease by some other agency.

3. An electric water heater according to claim 2 in which the booster period is within the range of from 1 5 seconds to two minutes.

4. An electric water heater according to any one of the preceding claims in which the arrangement is such that the booster means can be brought into operation by the user at any moment convenient to the user provided that the operation of the booster means is not, at that moment, prevented by the monitor means.

5. An electric water heater according to claim 4 in which initiation of the operation of the booster means can be effected by the operation of a switch or the like by the user, the arrangement being such that once the switch or the like has been operated the booster means can remain in operation without the need for the user to maintain operation of the switch or the like.

6. An electric water heater according to any one of the preceding claims and which is provided with indicating means operative to indicate to the user when the booster means is available for use.

7. An electric heater according to any one of the preceding claims in which the arrangement is such as to make it impossible for the user to reinitiate operation of the booster means, following discontinuance of the booster means by the monitor, without the intervention of a non-operational period during which the booster means is not in operation and cannot be put into operation by the user.

8. An electric water heater according to claim 7 in which there is timing means operative to prevent reinitiation of the operation of the booster means until at least a predetermined non-operational period has elapsed.

9. An electric water heater according to any one of the preceding claims which is such that operation of the booster means causes the flow rate of the water to be increased by a predetermined amount, the necessary increase in the power output of the heating means being effected by thermostat means operative to adjust the power output of the heating means so as to maintain substantially unaltered the temperature of the heated water.

10. An electric water heater according to any one of the preceding claims in which the arrangement is such that the heater reverts automatically to normal operation at the end of a booster period, provided that operation of the heater has not been caused by other means to cease before that.

11. An electric water heater of the kind specified and substantially as hereinbefore described with reference to the accompanying drawing.