GB2375591A

GB2375591A - Electric shower with automatic control

Info

Publication number: GB2375591A
Application number: GB0211303A
Authority: GB
Inventors: Colin Graham
Original assignee: NewTeam Ltd
Current assignee: NewTeam Ltd
Priority date: 2001-05-18
Filing date: 2002-05-17
Publication date: 2002-11-20
Also published as: GB0211306D0; GB0211303D0; GB2375592A; GB0112097D0; GB2375593A; GB0211305D0

Abstract

An electric shower has a water heater (10) with a water inlet (14), a water outlet (16) and plurality of electrical heating elements (24-30) for heating water flowing through the heater from the inlet to the outlet during use of the shower. The heater further has a sensor (42) for sensing the inlet water temperature and a sensor (46) for sensing the flow rate of the water passing through the heater. An automatic control means (38) adjusts the flow rate of the water passing through the heater and activates the heating elements in different combinations in order to provide and maintain substantially a predetermined outlet water temperature.

Description

Electric Shower The present invention relates to an electric shower and in

particular to an electric shower having a water heater with a plurality of heating elements.

Electric showers are known which have a water heater with an electric heating element. To 5 heat the water, an electric current is passed through the heating element and the heat thus generated is transferred to the water as it passes through the water heater. The temperature of the water leaving the shower is dependent on a number of factors including the temperature of the water entering the shower, the flow rate of the water passing through the water heater and the power rating of the heating element.

10 It is also known to provide an electric shower having a water heater with two heating elements. A manual control on the shower allows a user to selectively activate either of the elements on their own or both of the elements together to ensure that a desired water temperature is achieved. Typically, the elements each have a different power rating so that the user is able to select from three available power ratings - high, medium and low.

1 5 In order to provide for a shower which is capable of automatically compensating for changing conditions, such as sudden changes in inlet water temperature or varying flow conditions, it is known to provide a heater having a plurality of heating elements and an automatic control system for switching the elements on and off to maintain a desired or predetermined outlet water temperature. US 4, 713, 525, for example, discloses a microcomputer controlled 20 electric water heater for a shower, in which the microcomputer operates in response to a user selected desired outlet water temperature to compare the inlet water temperature with the actual outlet water temperature and activates the required number of heater elements to achieve the desired outlet water temperature selected by the user.

Such automatically controlled shower heaters work well but their ability to accurately deliver 25 and maintain a desired outlet water temperature is limited. Often the smallest difference in heating element power which can be achieved by varying the combination of elements which

are switched on is too large to cope with small variations in the flow rate or the inlet water temperature without over compensating. As a result the shower may not be able to provide and maintain precisely the outlet water temperature desired by the user.

An object of the present invention is to provide an improved electric shower which 5 overcomes or at least mitigates the problems of the known electric showers.

In accordance with the invention, there is provided an electric shower comprising a water heater having a water inlet, a water outlet and a plurality of electrical heating elements for heating water flowing through the heater from the inlet to the outlet during use ofthe shower, 10 the heater further comprising means for sensing the inlet water temperature, means for sensing the flow rate of the water passing through the heater, and automatic control means adapted, in use, to adjust the flow rate of the water passing through the heater and to activate the heating elements in different combinations in order to provide and maintain substantially a predetermined outlet water temperature.

15 By adjusting both the flow rate of the water and the combination of elements which are activated, the inventive shower is able to more accurately deliver and maintain the predetermined outlet water temperature than is the case with the prior art showers which rely

on adjusting only the amount of heat provided by the heating elements.

Preferably, the automatic control means is adapted, in use, to monitor the inlet water 20 temperature and to determine an optimum flow rate and combination of elements required to provide and maintain substantially the predetermined outlet water temperature and to adjust the flow rate and activate the heating elements accordingly.

Preferably, the control means is adapted to select an optimum combination of heating elements and flow rate which maximises the flow rate of water whilst providing and 25 maintaining substantially the predetermined outlet water temperature.

Preferably, the heater further comprises means for sensing the outlet water temperature and

the automatic control means is further adapted, in use, to monitor the actual outlet water temperature achieved and, if the actual water temperature differs from the predetermined outlet water temperature, to recalculate the optimum flow rate and combination of elements required in order to bring the outlet water temperature to the predetermined value and to 5 adjust the flow rate and activate the heater elements accordingly.

Advantageously, the automatic control means comprises microprocessor circuitry including a memory into which are stored algorithms for use in determining the optimum flow rate and combination of heating elements required.

Preferably, the automatic control means is adapted, in use, to monitor the maximum flow rate 10 of the water passing through the shower and to store maximum flow rate to the memory for subsequent use in determining an optimum flow rate and combination of elements required to provide and maintain substantially the predetermined outlet water temperature.

Preferably, the automatic control means comprises a solenoid controlled valve for varying the flow rate of the water passing through the heater in use.

15 Preferably, each heating element has a different power rating.

Preferably, there are four heating elements.

Preferably, means are provided to selectively limit the maximum power consumption of the heater to a pre-determined value which is less than the power consumption of the heater when all the heater elements are activated.

20 The means to selectively limit the maximum power consumption ofthe heatermay comprise means which inhibits the activation of combinations of heater elements having a combined power consumption in excess of the predeterrnined value.

Preferably, the shower further comprises a user interface by means of which a user can select

the predetermined outlet water temperature. In which case, the user interface may be adapted to input to the control means a signal indicative of the predetermined outlet water temperature selected by the user.

An embodiment of the invention will now be described, by way of example only, with 5 reference to the accompanying drawings in which: Figure 1 is a schematic drawing showing the water heater of an electric shower in accordance with the invention; and Figure 2 is a perspective view of part of the control means of the water heater of Figure 1.

water heater 10 for an electric shower comprises a heater tube 12 having an inlet 14 and 10 an outlet 16. The tube 12 has an inner tube member 18 and an outer tube member 20. When in use, the tube 12 is arranged so as to be aligned substantially vertically.

Water at ambient temperature from a suitable water supply (not shown) enters the heater tube 12 through the inlet 14 from where it flows, via a solenoid controlled valve 22, down through the inner tube member 18. When the water reaches the bottom of the inner tube 15 member, it flows back upwards between the inner tube member and the outer tube member 20 towards the outlet 16. From the outlet, the water is delivered to a shower head (not shown) by means of suitable pipe work (also not shown).

Four electrical heating elements 24, 26, 28, 3 0 are affixed to the external surface of the outer tube member 20. Each heating element is selectively and independently connectable to an 20 electrical power supply 32 by means of a respective relay 34.

Each element when connected to the power supply generates heat which is transferred across the outer tube member 20 to the water as is flows up the tube 12 between the inner tube member 1 g and the outer tube member 20.

Each of the elements has a different power rating and so generates a different amount of heat when connected to the power supply. In the present embodiment, a first of the elements 24 has a power rating of 1542W, a second element 26 has a power rating of 2313W, a third element a power rating of 3084NN, whilst a fourth element has a power rating of 3855W. This 5 arrangement gives a minimum power rating of 1542W if only the first element 24 is activated and a maximum combined power rating for all elements of approximately 10.8kW.

It will be noted that the power ratings of the elements are based on a step value of 771W.

Thus the first element 24 has a power rating of 2 x 771 W. the second element 26 has a power rating of 3 x 771W, the third element 28 has a power rating of 4 x 771W arid the fourth 10 element 30 has a power rating of 5 x 771W.

As indicated above, each of the elements can be activated independently of the others by closing its respective relay 34 to connect the element to the power supply. By activating the elements either singly or together in various combinations, 12 different power ratings are possible as shown in the table below.

15 Elements activated Power rating First 1542W Second 2313W Third 3084W Fourth 3855W 20 First & Third 4626W First & Fourth or Second & Third 5397W Second & Fourth 6168W Third & Fourth or First & Second & Third 6939W First & Second & Fourth 7710W 25 First & Third & Fourth 8481W Second, Third & Fourth 9255W First & Second & Third & Fourth 10794W For the avoidance of doubt, it should be noted that throughout this specification, including

the clarions, terms such as "combination", or "a combination of elements", when used in 30 reference to the heating elements are to be understood as including a single heating element.

The water heater also comprises a control means, indicated generally at 36, which is operative to control the outlet water temperature of the shower and the rate of flow of water through the shower. The control means comprises a Central Processing Unit (CPU) 38 which has microprocessor circuitry including a memory and which is operatively connected to relay 5 drivers 40 for selectively opening and closing the relays 34 connecting tile heating elements to the power supply. The CPU is also operatively connected at 35 to the solenoid valve 22 to control the flow of water through the heater tube 12.

Input data for the control means is provided by an inlet water temperature sensor 42 for sensing the temperature of the water entering the heater, otherwise known as the inlet water 10 temperature; an outlet water temperature sensor 44 for sensing the temperature of the water leaving the heater, otherwise letdown as the outlet water temperature' and a flow meter 46 for measuring the flow rate of the water. The temperature sensors 42, 44 and the flow meter 46 are all connected to the CPU by suitable cables 43, 45, 47 and the CPU may also have the necessary signal processing circuitry to convert the signals from the sensors into a suitable 15 fonn for the microprocessor. Such signal processing circuitry may include an analog to digital converter for example.

A user interface 48 is also provided. The user interface 48 has various displays for the user and input devises, such as push buttons, through which the user can select a desired mode of operation for the shower. In particular, the interface provides an input device through which 20 the user can select a desired or predetermined outlet water temperature for the shower. The user interface is connected to the CPU as indicated at 50, so that a signal from the user interface indicative of the predetermined outlet water temperature selected by the user can be input to the CPU.

Operation of the shower will now be described.

25 On first use of the shower, the control means checks the systems ability to supply water by opening the solenoid valve 22 and monitoring the flow rate of the water as sensed by the flow meter 46. The maximum flow rate, or flow capacity, of the system is retained in the memory of the control means and will be updated each time the shower is operated. This ensures that any changes in flow capacity, due for instance to a build up of deposits in the pipe work 30 supplying the shower, can be taken into account by the control means when selecting the

optimum flow rate and heater element combination to provide and maintain the desired outlet water temperature.

Typically, but not exclusively, an electric shower in accordance with the invention is designed to operate with a maximum flow rate of up to approximately 10 L/m. If the flow 5 capacity of the system exceeds this value, the solenoid valve 22 is operated to limit the maximum flow rate through the heater accordingly.

Subsequently, when a user wishes to take a shower, the user operates the appropriate controls on the user interface. This may include activating a switch to turn the shower on and selecting a desired outlet water temperature.

10 Once the shower has been turned on, the control means checks the inlet water temperature as sensed by the inlet water temperature sensor 42 and calculates the optimum combination of water flow rate (up to the maximum flow rate for the shower), and heater element power to achieve the desired water temperature. The required combination of elements is then activated by closing the appropriate relay or relays 34 and the flow rate of the water is 15 controlled by means of the solenoid valve 22.

During the shower, the control means will continue to monitor the inlet water temperature and the flow rate of the water. If there are any changes, such as a drop in the temperature of the water entering the shower, then the optimum flow rate and element combination are automatically re-calculated and adjusted to maintain the desired outlet water temperature.

20 The control means will also monitor the actual outlet water temperature as sensed by the outlet water sensor 44, to ensure that the desired outlet water temperature has been achieved.

If the actual outlet water temperature is different from the desired temperature, then the control means will vary the flow rate and/or the element combination until the actual outlet water temperature matches the desired outlet water temperature as selected by the user.

25 In calculating the optimum combination of flow rate arid heater element power, the control means is programmed to maximise the flow rate of water through the shower for the selected temperature, up to the maximum flow rate of the heater. The control means will thus detennine whether a desired outlet water temperature can be achieved at the maximum flow rate by selecting a particular combination of heating elements. If not, the control means

determines the combination of heater elements which it predicts will achieve an outlet water temperature that is closest to, but less than, the desired temperature and will then calculate the amount by which the flow rate needs to be reduced in order to achieve the desired outlet temperature with that combination of elements. The control means then activates the selected 5 combination of elements and adjusts the flow rate accordingly. In effect, the control means uses the selection of heater element combinations as a course temperature control with adjustment of the flow rate being used to fine tune the outlet water temperature.

At all times the control means will seek to provide the predetermined outlet water temperature at the highest possible flow rate up to the maximum flow rate of the shower. As 10 indicated above, the control means monitors the flow capacity of the shower during use. In the event that the maximum possible flow rate drops, for example due to a build up of deposits in the supply pipe work, the control means uses the new lower maximum flow rate when calculating the optimum combination of flow rate and heater element power.

Where a change in the inlet water temperature is detected during use of the shower, the 15 control means will assess whether the change needs to be compensated for by changing the combination of heater elements which are activated, the flow rate of the water through the heater, or a combination of both. If the change in inlet water temperature is small and a change in the heater element combination would over compensate, the control means may vary the flow rate only. However, the control means will change both the element 20 combination and the flow rate if this enables the desired outlet water temperature to be delivered at a higher flow rate.

Changes in the flow rate of the water through the heater, due for example to a sudden drop in the pressure of the water supply, will be compensated for by adjusting the solenoid valve 22 alone whenever possible. Where the flow rate of the water entering the heater drops, the 25 solenoid valve 22 will be opened to compensate. If, however, the solenoid valve is already hilly open or if opening the valve is not sufficient to fillly compensate for the drop in flow rate, the control means will recalculate the required combination of heater elements and flow rate to produce the desired outlet water temperature at the highest possible flow rate. If the flow rate should subsequently increase, the control means will again recalculate the required 30 combination of heater elements and flow rate required to deliver the desired outlet water temperature whilst maximising the flow rate of the water within the limits of the heaters capacity.

In certain circumstances, the shower may have an input to allow the user to select a reduced flow rate. For example, the shower may have a low flow rate mode which can be selected by the user when they wish to apply shampoo. Where a user has selected a reduced flow rate mode in this way, the control means will treat the reduced flow rate as if it were the 5 maximum flow rate when controlling the outlet water temperature.

In calculating the optimum combination of heating elements and flow rate to achieve the desired outlet temperature, the microprocessor uses preprogrammed algorithms which are based on the nominal power ratings ofthe heating elements 24, 26, 28, 30. However, due to manufacturing tolerances, the actual power output of the elements in any particular shower 10 may vary from these nominal values. Thus, any particular element may generate more or less heat than expected. Furthermore, the performance of the elements may vary during the life of the heater.

In order that the control means can more accurately predict and select the optimum combination of elements and flow rate, the microprocessor has a self-calibration facility.

15 During use of the shower, the microprocessor monitors the actual outlet water temperature achieved for any given combination of activated heating elements, flow rate and inlet water temperature and compares this with an expected outlet temperature for those conditions.

Where differences between the values ofthe actual and expected outlet water temperature is detected, this information is used to generate a correction factor or weighting for each 20 element. The correction factors are stored to memory for subsequent use by the control means when calculating the required combination of elements and flow rate. This allows for a progressively more accurate predictive setting of the element and flow rate combinations available. As was discussed earlier, in the embodiment shown, the maximum combined power rating 25 of all the elements is approximately 1 0.8kW. This value has been selected because it utilizes the maximum capability of currently available terminal blocks which is 45A at a voltage of 240V. However, there may be occasions when it is desired to fit the shower as a replacement for a previously fitted shower which had a lower power rating and where the existing cabling cannot be used safely with this load. In order that the shower can be used safely in these 30 circumstances, the shower 10 is provided with a jumper link 52 which can be positioned between any one of a number of pairs of terminals 54, 56, 58, 60, 62, 64 to selectively limit the maximum power consumption ofthe shower. Positioning the jumper link on a particular

pair of links will cause the control means to disallow any combination of elements having a power consumption above the maximum power consumption selected.

In the present embodiment there are six pairs of the links, the first pair 54 is provided as a shipping position and with the link connected across this pair no heating elements can be 5 activated. The remaining five pairs of links allow for maximum power settings of 6.94kW, 7.711cW, 8.48kW, 9.25kW, and 10.8kWrespectively. These values allowing for replacement of existing showers with wiring from 4mm2 to 1 Omm2.

It will be understood that other methods could be adopted for selecting the maximum permitted power consumption for the shower. For example a multi-position switch could be 10 used rather than the link arrangement. Alternatively the maximum power consumption could be selected by programming the microprocessor.

The ability to limit the maximum power consumption of the shower means that a manufacturer need supply only one shower to meet all the normal power ratings currently in use, rather than having to supply a range of showers each having a different maximum power 15 rating. This considerably reduces manufacturing and marketing costs.

Although the present embodiment has been described as having four heating elements, it should be understood that the invention encompasses a shower having a heater with any number of heating elements from two upwards. Furthermore, the actual power ratings ofthe elements can be varied as appropriate to the application.

Claims

1. An electric shower comprising a water heater having a water inlet, a water outlet and a plurality of electrical heating elements for heating water flowing through the heater 5 from the inlet to the outlet during use of the shower, the heater further comprising means for sensing the inlet water temperature, means for sensing the flow rate of the water passing through the heater, and automatic control means adapted, in use, to adjust the flow rate of the water passing through the heater and to activate the heating elements in different combinations in order to provide and maintain substantially a 10 predetermined outlet water temperature.

2. An electric shower in accordance with claim 1, in which the automatic control means is adapted, in use, to monitor the inlet water temperature and to determine an optimum flow rate and combination of elements required to provide and maintain substantially the predetermined outlet water temperature and to adjust the flow rate 1 S and activate the heating elements accordingly.

3. An electric shower as claimed in claim 1 or claim 2, in which the control means is adapted to select an optimum combination of heating elements and flow rate which maximises the flow rate of water whilst providing and maintaining substantially the predetermined outlet water temperature.

20

4. An electric shower in accordance with any one of claims 2 to 3, in which the heater further comprises means for sensing the outlet water temperature and the automatic control means is further adapted, in use, to monitor the actual outlet water temperature achieved and, if the actual water temperature differs from the predetermined outlet water temperature, to recalculate the optimum flow rate and 25 combination of heater elements required in order to bring the outlet water temperature to the predetermined value and to adjust the flow rate and activate the heating elements accordingly.

5. An electric shower in accordance with any one of claims 2 to 4, in which the automatic control means comprises microprocessor circuitry including a memory into 30 which are stored algorithms for use in determining the optimum flow rate and combination of heating elements required.

6. An electric shower as claimed in claim 5, in which the automatic conko1 means is adapted, in use' to monitor the maximum flow capacity of the heater and to store maximum flow capacity to the memory for subsequent use in determining an optimum flow rate and combination of elements required to provide and maintain 5 substantially the predetermined outlet water temperature.

7. An electric shower in accordance with any previous claim, in which the automatic control means comprises a solenoid controlled valve for varying the flow rate of the water passing through the heater in use.

8. An electric shower in accordance with any previous claim, in which each heating 10 element has a different power rating.

9. An electric shower in accordance with any previous claim, in which there are four heating elements.

10. An electric shower in accordance with any previous claim, in which means are provided to selectively limit the maximum power consumption of the heater to a pre 15 determined value which is less than the combined power consumption of all the elements in the heater.

11. An electric shower in accordance with claim 10, in which the means to selectively limit the maximum power consumption ofthe heater comprises means which inhibits the activation of combinations of heater elements having a combined power 20 consumption in excess of the pre-determined value.

12. An electric shower in accordance with any previous claim, in which the shower further comprises a user interface by means of which a user can select the predetermined outlet water temperature.

13. An electric shower as claimed in claim 12, in which the user interface is adapted to 25 input to the control means a signal indicative of the predetermined outlet water temperature selected by the user.

14. An electric shower substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.