GB2130693A

GB2130693A - Water heater

Info

Publication number: GB2130693A
Application number: GB08226652A
Authority: GB
Inventors: Michael J Spillard
Original assignee: PLAS TEC PRODUCTS Ltd
Current assignee: PLAS TEC PRODUCTS Ltd
Priority date: 1982-09-18
Filing date: 1982-09-18
Publication date: 1984-06-06

Abstract

A shower comprises a slug (24) located in the water passage and movable in response to the rate of flow of water through the passage, a wave emitter (25) and a wave detector (26) so arranged as to detect movement of the slug through the disturbance produced by the slug on the transmission of waves between the emitter and detector, and an electrical switch means responsive to the output of the wave detector and controlling the electrical supply to the heating element assembly. <IMAGE>

Description

SPECIFICATION Water heater This invention relates to a water heater particularly, but not exclusively, for a domestic shower, and of the kind in which an electrical heating element assembly is located in a water passage for heating the water which passes through the passage in use.

It is advisable to ensure that the electrical supply to the heater element assembly is reduced or cut-off in the event that the water flow rate through the passage is reduced to a low level, due to supply-fluctuations or because a manual control valve has been substantially shut off, in order to avoid over-heating of the water and of the element assembly.

It has previously been proposed for this purpose to incorporate a magnetic slug in the water flow passage and to detect movement of the slug in response to water flow by utilising its magnetic properties to operate a switch. Various problems can arise with that arrangement. The magnetic slug can be susceptible to corrosion, it may lose its magnetism, and it may pick up steel debris from pipes in countries where steel pipes are employed.

According to one aspect of the invention a shower heater of the kind set forth comprises a slug located in the water passage and movable in response to the rate of flow of water through the passage, a wave emitter and a wave detector so arranged as to detect movement of the slug through the disturbance produced by the slug on the transmission of waves between the emitter and detector, and an electrical switch means responsive to the output of the wave detector and controlling the electrical supply to the heating element assembly.

Such a slug can be made of a substantially noncorrosive material.

The disturbance may be produced by the slug in various ways.

Preferably the slug is substantially opaque to the waves and in use is caused by change in water flow rate to move from a position in which it substantially obstructs the wave path between the emitter and detector to a position in which it is substantially removed from said path.

Alternatively the slug might be arranged in suitable cases to act as a wave reflector and the emitter be arranged to detect waves reflected from the slug.

The portion of the water passage in which the slug is located is preferably arranged to be substantially vertical and the flow is in the upward direction in said passage portion whereby gravity provides a restoring force acting on the slug in opposition to the force of water flow, but in other cases a suitable restoring means may be employed.

The waves employed are preferably infra-red waves, but optical frequencies or ultra violet waves may be employed. Alternatively, sonic waves might be employed.

A disadvantage of using optical frequencies would be the need to provide suitable shielding against stray light.

One advantage of infra-red rays is that many plastics materials are substantially transparent to such rays, enabling the emitter and detector to be mounted externally of a plastics tube providing the fluid passage.

The emitter is conveniently an infra-red light emitting diode, and the detector is preferably an infra-red sensitive transistor.

Conveniently the diode and transistor are each mounted on bosses integrally provided on opposite sides of the plastics tube.

For use with infra-red rays the slug may conveniently be of brass or of a plastics material which is substantially opaque to infra-red rays.

A second aspect of the invention is concerned with the precise control of the temperature of the water issuing from the heater when the heater is in operation.

We have found that a shower which produces a succession of temperature 'pulses' of warmer and cooler water in a controlled manner can be most invigorating.

According to the second aspect of the invention a shower assembly comprises a water heater of the kind set forth and temperature control means connected to the electrical heating element assembly, the temperature control means being so arranged that the temperature of the water issuing from the heater in use is varied continuously in a pulsed manner.

The pulse frequency is preferably in the range 1-0.1 Hertz.

The temperature difference between the water and cooler pulses is preferably in the range 10-200C.

Although the temperature fluctuations may be produced in response to an electrically generated clock pulse signal, it is preferred that the control means comprises a temperature sensor which is responsive substantially to the temperature of the heated water and to arrange for natural oscillation of the control means and heating element assembly.

Natural oscillation is preferably achieved by suitable positioning of the temperature sensor in relation to the heating element assembly and by arranging for a suitable thermal inertia of the system. This is best arrived at by experimentation.

For this purpose the temperature sensor is preferably mounted adjacent to that end of the heating element assembly which the water reaches last.

The control means preferably comprises a thyristor means, preferably a TRIAC, connected in series with the heating element assembly and an A.C. mains voltage supply, a trigger signal for the thyristor means being produced in response to the output of the temperature sensor, conveniently by an integrated circuit unit.

A water heater for a domestic shower in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a front view of the water heater with the outer cover removed; Figure 2 is a front view of the water tube unit; Figure 3 is a rear view of the water tube unit; Figure 4 is a side view of the water tube unit looking from the left in Figure 2; Figure 5 is a scrap section on the line 5-5 of Figure 1 showing the infra-red emitter and detector; Figure 6 is a scrap section on the line 6-6 of Figure 1 showing the thermistor temperature sensor; and Figure 7 is a circuit diagram of the control circuit for the heating element assembly.

The water heater of Figure 1 comprises a moulded plastics back plate 1 for securing to a vertical wall of a shower enclosure and provided with a peripheral wall 2 for cooperation with the margin of a cover, not shown. A plastics water tube unit 3 is secured by screws 4 to the back plate 1 and comprises four principal tubular portions 5, 6, 7 and 8 arranged with their axes parallel and vertical, the tubular portions being positioned forwardly of an integral manifold assembly 9, Figures 3 and 4, comprising a pair of U-tubes 10 and 11. Two horizontal passages 12 respectively connect the upper ends of the tubular portions 5 and 6 to the upper ends of the limbs of the U-tube 9, and a further two passages 12 respectively connect the upper ends of the tubular portions 7 and 8 to the upper ends of the limbs of the other U-tube 11, thereby to define a tortuous flow passage for the water.The purpose of this arrangement, as is well known, is to provide a substantial water path between the heating elements and the inlet and outlet connections, 13, 14 respectively.

The metal water inlet connection 1 3 is sealingly secured to the open lower end of the tube portion 5, and the similar, outlet connection 14, for connection to a shower head, is connected at the lower end of tube portion 8. An electrical heating element assembly comprises a pair of helical heating coils 1 5, 1 6, indicated by dashes in Figure 1 located in the bores of tubular portions 6 and 7 respectively and extending for the full length of those bores. The heating coils 1 5, 1 6 are connected in parallel by bus bars 1 7, 1 8, the bus bar 17 being connected to a mains neutral lead 19, and the bus bar 18 being connected by a lead 20 to a TRIAC 40 the operation of which is controlled by signals on lead 22 from a control circuit 23.

With reference to Figures 1 and 5, the tubular portion 5 houses a brass slug 24 of square section in plan which acts in conjunction with an infra-red light emitter 25 and detector 26 as a flow sensor for detecting zero or inadequate water flow through the flow passage. A manual flow tap 27 is incorporated in the lower part of tubular portion 5 and is used to control the water flow rate to the shower head. When the tap 27 is turned off, the slug 24 is retained by gravity in the position shown in Figure 5, resting on a stop, not shown, in which position it obstructs the path of infra-red waves from emitter 25 to detector 26.

When tap 27 is turned on the slug 24 will be raised progressively by the water force, until with increasing flow it is lifted clear of the emitter and detector to allow infra-red waves to pass directly from the emitter 25 to the detector 26. The output from detector 26 is fed to control circuit 23 and the arrangement is such that in the absence of an output from detector 26 the TRIAC 40 is switched off, irrespective of other control signals. The dimensions of slug 24 are chosen such that a detector output is not produced until there is an adequate water flow through the heater to prevent scalding of the user, and to avoid burn-out of the elements 1 5, 16.

The emitter 25 is an infra-red emitting diode such as a TEXAS TIL 38, and the detector 26 is an infra-red sensitive transistor such as a TEXAS TIL 78, which, as shown in Figure 5, are conveniently secured in tubular bosses 28, 29 respectively provided integrally on tubular portion 5 and diametrically opposing each other. The tube unit 3 is formed of, for example, GRILAMID TR55 a polyamide plastics which is transparent to infrared light and thereby enables the emitter 25 and detector 26 to be mounted externally of the tubular portion 5.

A thermistor 30 is mounted in a tubular boss 31 provided integrally on tubular portion 7 adjacent to the upper end thereof, to detect the temperature of the water where it reaches the end of the heating element assembly, just prior to it entering the respective passage 12 leading to the upper end of U-tube 11. The close proximity of the thermistor 30 to the heater water in tube portion 7, and possibly the proximity to heater 16, assists in providing a temperature-pulsed water supply to the shower head.

A manually operable potentiometer 32 sets the average temperature of the outlet water, as will be explained in the following brief description of the circuit of Figure 7.

A transformer 33, rectifier bridge 34 and smoothing capacitor 35 provide a 12 volt D.C.

supply to the series circuit of a resistor 36 and infra-red emitting diode 25. The infra-red sensitive transistor 26 is rendered conducting by infra-red light from diode 25 when the slug 24 is raised by water flow to permit the infra-red rays to reach transistor 26, and the output of transistor 26 controls a transistor switch 37. The output of switch 37 is connected to the V+ terminal of an integrated circuit unit 38, via the relay R contact, to the integrated circuit TDA 1023, to provide an over-ride control of the unit 38, whereby when no infra-red light is received by transistor 26 switch 37 is in the off condition to inhibit operation of unit 38.

The output 39 of the integrated circuit unit 38 controls the operation of the TRIAC 40 through an opto-coupler 41. TRIAC 40 is connected in series with the heater element assembly H which consists of the elements 1 5 and 1 6, and the optocoupler enables the TRIAC 40 to control the live connection to the elements 1 5, 1 6 rather than the neutral connection, which adds to the safety of the heater.

The unit 38 is controlled by the output of thermistor 30 in conjunction with temperature setting potentiometer 32. Provided that switch 37 is on to remove the inhibit from the unit 38, the output 39 will vary in response to the difference between the temperature sensed by thermistor 30 and the temperature setting of potentiometer 32, whereby the power supplied to the heater H is increased by TRIAC 40 when the sensed temperature is less than the temperature set on potentiometer 32.

The positioning of the thermistor 30 closely adjacent to the upper end of the heating element 1 6 in conjunction with the thermal inertia of that part of the system in which the heating elements 1 5,1 6 are located gives rise to a controlled pulsing of the output 39 of the unit 38 for low and medium temperature settings of the potentiometer 32, resulting in a controlled temperature pulsing of the water leaving outlet 14. It will be appreciated that it is the temperature of the outlet water that is pulsing, and not the water flow rate. At high temperature settings of the potentiometer 32 pulsing does not occur and is not found desirable.

Claims

1. A shower heater of the kind set forth comprising a slug located in the water passage and movable in response to the rate of flow of water through the passage, a wave emitter and a wave detector so arranged as to detect movement of the slug through the disturbance produced by the slug on the transmission of waves between the emitter and detector, and an electrical switch means responsive to the output of the wave detector and controlling the electrical supply to the heating element assembly.

2. A shower assembly comprising a water heater of the kind set forth and temperature control means connected to the electrical heating element assembly, the temperature control means being so arranged that the temperature of the water issuing from the heater in use is varied continuously in a pulsed manner.