GB2254678A

GB2254678A - Instantaneous electric water heater

Info

Publication number: GB2254678A
Application number: GB9107624A
Authority: GB
Inventors: Robin Edward Brash
Original assignee: Triton PLC
Current assignee: Triton PLC
Priority date: 1991-04-10
Filing date: 1991-04-10
Publication date: 1992-10-14
Anticipated expiration: 2011-04-10
Also published as: GB2254678B; GB9107624D0

Abstract

An instantaneous electric water heater, especially suitable for use in a shower unit, comprises two heating elements 4 and 5 for heating water flowing from an inlet pipe 1 to an outlet pipe 3, a bi-metallic switch 11 for sensing the outlet water temperature and operable when both of the heating elements 4 and 5 are energised and when the outlet water temperature exceeds a predetermined limit, for causing one of the heating elements 4 to be de-energised, the other 5 of the heating elements being maintained energised. <IMAGE>

Description

Water Heaters This invention relates to water heaters and more particularly to so-called instantaneous electric water heaters, especially for electric showers.

In U.K. Patent No. 2115912B there is disclosed an instantaneous electric water heater for a shower comprising a pair of heating elements which are adapted to heat water as it flows through the heater and which is provided with a temperature sensor for monitoring the outlet water temperature and which causes the flow of water through the heater to be terminated and the heating elements to be de-energised should a predetermined "safe" outlet water temperature be exceeded. A manual reset operation is required to restart the heater. Such a heater suffers from the problem that hot water supplied from such a heater to a shower head can be terminated abruptly which can be inconvenient to a person using the shower.

In U.K. Patent No. 2194317B there is disclosed a similar form of instantaneous water heater for a shower in which the outlet water temperature is again monitored but it is envisaged that should the predetermined "safe" outlet water temperature be exceeded the heating elements are de-energised, but the flow of water through the heater is possibly maintained. Such a heater suffers from the problem of so-called hot-cold cycling in which the heater would be operating normally providing hot water to a shower head, and when the safe" temperature is exceeded the heating elements are de-energised so that cold water is supplied to the shower head, which again is inconvenient to a person using the shower.

It is an object of the present invention to provide an improved instantaneous electric water heater especially suitable for use in showers, in which the above described problems are alleviated.

According to the present invention there is provided an instantaneous electric water heater comprising at least two heating elements adapted to heat water flowing through said heater, temperature sensing means for sensing the outlet water temperature of said heater and operable when said two heating elements are energised and when said outlet water temperature exceeds a predetermined limit for causing one of said two heating elements to be de-energised, the other of said two heating elements being maintained energised.

In this way, when the outlet water temperature exceeds said predetermined limit, only one of the heating elements is de-energised so that water flowing through the heater is still heated but to a lower temperature by the other heating element which is still energised, whereby the hot-cold cycling described previously is replaced by hot-cool cycling which is much more acceptable to a user of a shower which is supplied by such a heater.

In carrying out the invention it may be arranged that said temperature sensing means is operable for causing said one of said heating elements to be re-energised when said outlet water temperature falls below a further predetermined limit.

In a preferred arrangement according to the invention it may be arranged that said two heating elements have different watts density ratings, and the heating element having the higher watts density rating is de-energised when said predetermined limit is exceeded.

It may be arranged that said temperature sensing means comprises a bi-metallic switch, which is conveniently connected in series with said one of said heating elements.

It may also be arranged that said temperature sensing means comprises two bi-metallic switches which operate at different temperatures, the bi-metallic switch having the lower operating temperature being connected in series with said one of said heating elements, and the bi-metallic switch having the higher operating temperature being connected in series with said other of said heating elements.

Advantageously, a further temperature sensing means may be provided associated with said heating elements and operable for causing said heating elements to be de-energised when another predetermined temperature limit is exceeded.

The instantaneous electric water heater may have general application but it is especially envisaged for use in a shower unit.

An exemplary embodiment of the invention will now be described reference being made to the accompanying single figure drawing which is a diagrammatic representation of an instantaneous electric water heater in accordance with the present invention.

The instantaneous water heater shown in the accompanying drawing comprises a water inlet pipe 1 coupled to a heating unit or can 2 from which extends a water outlet pipe 3. The heating can 2 comprises two heating elements 4 and 5 which, when energised, cause water flowing from the water inlet pipe 1 through the heating can 2 and to the water outlet pipe 3 to be heated.

Power to the heating elements 4 and 5 is derived from the electrical mains which is connected to a terminal block 6. The neutral line N of the electrical mains is connected from the terminal block 6 directly to one side of each of the heating elements 4 and 5.

The live line L of the electrical mains is connected from the terminal block 6 to temperature responsive cut-out switch 7 which is arranged in thermal contact with the heating can 2 and which is normally closed but which opens should the temperature of the heating can 2 exceed a predetermined temperature.

The temperature responsive cut-out switch 7 is connected in series to two further switches 8 and 9 which form part of selector mechanism 10 which controls the individual energisation of the heating elements 4 and 5. Switch 8 is connected directly to the free end of heating element 5 and switch 9 is connected to- the free end of heating element 4 via a further temperature sensing device 11, conveniently in the form of a normally closed bi-metallic switch, which is mounted on the water outlet pipe 3 and which senses the temperature of the water therein.

The heater thus far described operates as follows: Assume that the selector mechanism 10 is activated to close both of the switches 8 and 9 and also that a water flow control valve (not shown) has been actuated to allow cold water to flow into water inlet pipe 1.

The heating can 2 will initially be cold so that the temperature responsive cut-out switch 7 will be closed. The bi-metallic switch 11 mounted on the water outlet pipe 3 will also be closed.

In this condition both of the heating elements 4 and 5 will be energised and will cause the water flowing from the water inlet pipe 1 through the heating can 2 and to the water outlet pipe 3 to be heated.

Should the water temperature in the outlet pipe 3 exceed a predetermined temperature, e.g. 570C, the bimetallic switch 11 is caused to open circuit, so causing the heating element 4 to be de-energised. The heating element 5 remains energised and continues to heat the water flowing through the heating can 2, albeit to a lower temperature than is the case when both of the heating elements were energised.

As the temperature in the water outlet pipe 3 cools, this is sensed by the bi-metallic switch 11 which, when a predetermined lower temperature limit is reached, is again caused to close, to re-energise the heating element 4. In this way the outlet water temperature is maintained within a set temperature band determined by the bi-metallic switch 11 in accordance with a hot-cool cycling mode. Should, for any reason, the temperature of the heating can 2 exceed the operating temperature of the temperature responsive cut-out switch 7, this will be caused to open-circuit to cause both of the heating elements 4 and 5 to be de-energised.

It may be arranged that the temperature sensing device 11 could take the form of two bi-metallic switches, one for each of the heating elements 4 and 5, the switches being designed to operate at different temperatures whereby, for example, heating element 4 is de-energised at say 52 0C and heating element 5 is de-energised at say 560C.

Although the heating elements 4 and 5 may take any convenient form, it is envisaged that they may be provided with different, so-called, watts density ratings. Typically heating element 4 may be of 3.8 KW with a high watts density rating e.g. 0.3W/mm2 and heating element 5 may be of 3.8 KW with a low watts density rating e.g. 0.2W/mm2. In such a situation it has been found advantageous to switch the high watts density rating heating element 4 rather than the low watts density rating heating element 5.

Although in the embodiment which has been described only two heating elements 4 and 5 have been included, it should be appreciated that more than two heating elements, and typically three heating elements may be used under the control of the selector mechanism 10. Typically the heating elements may comprise: element 1 - 3.8 KW high watts density rating element 2 - 3.8 KW low watts density rating element 3 - 1.9 KW low watts density rating enabling the following combinations to be achieved, heating element 1 being switched by the bi-metallic switch 11 in each case:: elements 1 + 2 + 3 = 9.5 KW elements 1 + 2 = 7.6 KW elements 1 + 3 = 5.7 KW In such an arrangement, it may be arranged, for example, that the bi-metallic switch 11 is connected in circuit with elements 1 and 3 above, and that both of these elements are de-energised when the bi-metallic switch 11 becomes open circuit, element 2 being maintained energised.

In the arrangement which has been described, a temperature sensing device 11 in the form of a bimetallic switch has been used. It will be appreciated that if this is used directly to switch one or more heating elements, it could be required to have a high current rating which would result in it being prohibitively expensive. In order to obviate the need for a high current switch it is envisaged that a low current switch, or some other form of temperature sensing device, such as a thermistor, could be used in conjunction with some electronic circuitry in order to switch the heating element or elements via suitable switching devices e.g. relays, triacs, etc.

Although the instantaneous water heater which has been described has wide general application, it is especially envisaged for use in a shower unit, in which case the water outlet pipe 3 would provide water to a shower head (not shown) and the selector mechanism 10 would form part of the control system of the shower unit.

Claims

1. An instantaneous electric water heater comprising at least two heating elements adapted to heat water flowing through said heater, temperature sensing means for sensing the outlet water temperature of said heater and operable when said two heating elements are energised and when said outlet water temperature exceeds a predetermined limit for causing one of said two heating elements to be de-energised, the other of said two heating elements being maintained energised.

2. A heater as claimed in claim 1, in which said temperature sensing means is operable for causing said one of said heating elements to be re-energised when said outlet water temperature falls below a further predetermined limit.

3. A heater as claimed in claim 1 or claim 2, in which said two heating elements have different watts density ratings, and the heating element having the higher watts density rating is de-energised when said predetermined limit is exceeded.

4. A heater as claimed in any preceding claim in which said temperature sensing means comprises a bi-metallic switch.

5. A heater as claimed in claim 4, in which said bi-metallic switch is connected in series with said one of said heating elements.

6. A heater as claimed in claim 4 or claim 5, in which said temperature sensing means comprises two bi-metallic switches which operate at different temperatures, the bi-metallic switch having the lower operating temperature being connected in series with said one of said heating elements, and the bi-metallic switch having the higher operating temperature being connected in series with said other of said heating elements.

7. A heater as claimed in any preceding claim, comprising a further temperature sensing means associated with said heating elements and operable for causing said heating elements to be de-energised when another predetermined temperature limit is exceeded.

8. A heater as claimed in any preceding claim, comprising three heating elements and in which said temperature sensing means is operable when said three heating elements are energised and when said outlet water temperature exceeds a predetermined limit for causing two of said heating elements to be de-energised, the other of said heating elements being maintained energised.

9. An instantaneous electric water heater substantially as hereinbefore described with reference to the accompanying drawing.

10. A shower unit incorporating an instantaneous electric water heater as claimed in any preceding claim.