GB2115912A - Instantaneous water heater for shower unit - Google Patents

Abstract

An instantaneous water heater for a shower unit incorporates a temperature-sensitive device (13) disposed so as to monitor the temperature of the water downstream of the heating means (7A, 7B), an electrically operated valve (9) for controlling the flow of water through the heater and control means (11, 12) operative both to close the valve (9) and de-energise the heating means (7A, 7B) should the detected temperature of the water exceed a predetermined safe value. Scalding due to thermal lag in the water temperature control system is thereby avoided. Preferably the heater is controlled by a microprocessor from a low voltage manual control panel separate from the main body of the heater. <IMAGE>

Description

SPECIFICATION Water heaters This invention relates to so-called instantaneous electric water heaters, that is to say heaters ofthe kind incorporating electric heating means, commonly in the form of one or more sheathed or open coil wire electric heating elements, designed to heat the water as it is flowing through.the heater, and is primarily, though not exclusively, concerned with such water heaters designed for use as shower units.

One difficulty which is often experienced with electrically heated shower units as constructed hitherto is that the temperature of the water emerging from the heater may rise to an undesirably high level.

This may occur, for example, if the flow of water is restricted, or alternatively if it is stopped and then restarted afteronlya shorttime interval beforethe heating means has cooled down, the residual heat in the heating means being transferred to the temporarily static water, so when the flow is restarted it could emergefromthe heaterata dangerously high temperature. This is clearly undesirable, and an object of the present invention is to provide a form of instantaneous water heater, especially for a shower unit, which is designed to avoid this problem.

According to the present invention an instantaneous electric water heater incorporates a tempera turesensitive device disposed so as to monitor the temperature of water downstream ofthe heating means, an electrically operated valve for controlling theflowofwaterthrough the heater and control means responsive to the temperature sensitive device and operative to close the valve and de-energise the electric heating means should the sensed temperature of the water exceed a predetermined value.

Byshutting off the flow of water, as well as de-energising the heating means, when the sensed water temperature attains a value considered to be unsafe, for example 56"C, the danger of a user being accidentally scalded is effectively avoided.

Preferablythe power supplied to the valve and the electric heating means is controlled by one or more controlled semiconductor devices, such as triacs, the heater also being provided with a microprocessor for controlling the operation ofthe or each semiconductor device and a separate low-voltage manual control panelforfeeding control signals to the micropprocessor.

The control means may be operable normally to open the valve and initiate the operation of the heater by actuation of a manual control, and preferably includes an inhibiter circuit which becomes effective to prevent opening of the valve in the event of the valve having been closed in response to the water from the heater reaching an excessively high temperature, unless a second manual control is also actuated.

This will prevent inadvertent starting of the heater buy a user once the valve has closed under such conditions, at least until the temperature of the heating means has fallen to a suitably low value.

Preferably the heater also includes an audible and/or visual warning device, which becomes operative when the temperature of the water approaches a predetermined unsafe value.

The or each controlled semiconductor device is conveniently mounted on a thermally conductive member in close thermal contact with a pipe through which cold water is introduced into the heater, this serving to cool the device in use of the heater.

Preferably the heater incorporates two separately controllable heating elements, each associated with a respective controlled semiconductor device, the control means being arranged to control the phase of trigger pulses applied to the devices so as to vary the periods of conduction of the devices in each half cycle of the supply voltage, and hence the power supplied to the elements.

The two heating elements are preferably arranged to be switched on or off at different instants to avoid excessive power surges.

On switching off the heaterthewateris preferably arranged to continue flowing, either until the monitored temperature ofthe water reaches a sufficiently low value, or alternatively for a predetermined time interval sufficient to enable the water to cool to a safe temperature.

Means are preferably provided for adjusting the temperature of the water leaving the heater a desired value, for example by applying appropriate signalsto the micro-processor.

Means may also be provided for adjusting the rate of flow of the water, the micro-processor, in such a case, being arranged to maintain the outputtempera to rue of the water atthe set value, at least within normal flow rate limits.

Preferably the instantaneous electric water heater of the present invention is incorporated into a shower unitwith its main bodyoutsidetheshowerarea and is provided with a separate low voltage manual control panel accessible from within the shower area. The control panel may be arranged to control both the flow rate and the temperature of the water, the microprocessor being arranged to maintain the temperature of the water atthe set value for different flow rate settings.

The heater may include a visual display device which gives an indication ofthetemperature ofthe water leaving the heater. The display device may, for example, incorporate a series of LED's arranged to light up in sequence, underthe control of the microprocessor, as the water temperature increases.

The LED's are conveniently disposed in line and arranged to be progressively illuminated from one end, giving a readily understandable indication ofthe water temperature.

The invention will now be described byway of example with reference to Figures 1 and 2 of the accompanying schematic drawings of which: Figure 1 shows a shower unit incorporating a water heater in accordance with the invention; and Figure 2 shows a water heater in accordance with the invention.

Figure 1 shows a shower unit incorporating an instantaneous electric water heater having a main body 1 mounted on a wall outside the shower cubicle 2, and connected to an inlet water pipe 3 and to an electric mairs supply cable 4. An cutlet pipeS 5extends through the wall of the shower enclosure to a spray head 6. Although the latter s shown as fixed, it could be connected to the outlet pipe 5 of the heater by a flexible pipe in known manner.

The heater comprises, as shown in diagrammatic form and not to scale in Figure 2,two 4kW electric heating elements 7A, 7B (Fig. 2) arranged, either individually or together, to heat the water passing through the heater. The rate of flow of water is controlled by a manual control 8 within the shower cubicle 2.

A solenoid on-offvalve 9 controls the passage of waterthrough the heater, and operation ofthe valve 9 and the heating elements 7A, 7B is control led by a micro-processor 10 through triacs 11. The triacs controlling the heating elements are mounted on a metal plate 12 in closethermal contact with the inlet pipe 3. Atemperatu re sensor 13, in thermal contact with the outlet pipe 5, provides one of the inputs to the microprocessor 10.

Acontrol panel C is separate from the main body 1 ofthe heater and is mounted on a wall, within the shower area itself. The control panel C which may be in the form of a small flat box similar in size, for example to a bathroom tile, is wired to the body 1 of the heater unit by means of a thin ribbon type cable 24, and has a series of touch button controls 16 to 19 which providefurther inputs to the microprocessor 10forstarting the flow of waterthrough the heater and energising the heating elements 7A, 78, for stopping the operation of the heater, and for increas ing or decreasing the watertemperature respectively.

Also on the control panel C is an indicator 14, comprising a series of, for example ten, LED's 15 connected to outputs ofthe microprocessor, to provide a visual indication ofthe temperature of water leaving the heater.

On first switching on, the sixth LED, which represents a presettemperature, will light up to indicate that the heater is operative and as the temperature of the water rises the sequence of LED's will commence to light up progressivelyfrom oneend in the manner of a thermometer until the water reaches the temperature selected, therefore giving the user a ready indication ofthe watertemperature at any moment.

The microprocessor controls the heatertriacs through interface circuits 22 and 23 maintaining the temperature of water leaving the water heater at the setvaluewithin normal flow rate limits, butshould the flow rate be set at a value which is too lowto enable the microprocessorto provide the required temperature control, such that the temperature ofthe water rises, the solenoid valve is actuated to cut-off the flow of water and the heating elements are switched off when a predetermined maximum 'safe' temperature is attained, for example 56"C.

Ifthis should occurthe heater cannot be restarted simply by depressing the "start" button 16, but requires the simultaneous depression of both buttons 16 and 19. This prevents the inadvertent re-starting ofthe heater by a userwhile the water temperature is above an unsafe value.

When switching-offthe heater by depressing the "stop" button 17, the water will continue to flow until the monitored temperature has fallen sufficiently to carry away excess, residual heat ofthe heating elements. so as to ensure that the temperate re of the water emerging from the heaterwhen it is next switched on is belowthe "safe" value.

The microprocessor is designed to ensure that, when the shower unit is switched on, the water is heated to a preset comfortable temperature, thereby avoiding the need to re-set the watertemperature each time the unit is used.

The present invention, by enabling the body of the heaterto be mounted outside the shower area avoids the need for mains electrical supplies to enterthe area and thus provides an additional safety feature.

In a modification ofthe heater described, the water flow-rate could be set at a value say of 3 litres per minute, or alternateively it could be controlled electrically bythe addition of one or more further touch buttons on the control panel in association with a suitable flow valve with electrical activation.

Claims (13)

1. An instantaneous electric water heater incorporating a temperature-sensitive device disposed so asto monitorthe temperature of the water downstream ofthe heating means, an electrically operated valve for controlling the flow ofwaterthrough the heater and control means responsivetothetempera- ture-sensitive device and operative to close the valve and de-energisetheheating means should the temperature ofthe water exceed a predetermined value.

2. Awater heater as claimed in Claim 1 wherein said value is approximately 56"C.

3. Awaterheaterasclaimed in Claim 1 or Claim 2 incorporating one or more controlled semiconductor devices for controlling the heating means, the heater also being provided with a microprocessorfor controlling the operation of the or each said semiconductordevice and a low-voltage manual control panel separate from the main body ofthe heater for feeding control signals to the microprocessor.

4. Awater heater as claimed in Claim 3 additionally including first and second manual controls and an inhibiter circuit,whereinthe control means is operable normally to open the valve and initiate operation ofthe heater by actuation of the first manual control, the inhibiter circuit is effective to prevent opening of the valve in the event of the valve having been closed in response to the waterfrom the heater reaching an excessively high temperature and the second manual control is effective to disable the inhibiter circuit.

5. Awater heater as claimed in Claim 3 or Claim 4 wherein the microprocessor is incorporated in the main body ofthe heater.

6. A shower unit incorporating a water heater as claimed in any of Claims 3 to 5, wherein the main body ofthe heater is located outside the shower area and the low-voltage manual control panel is accessible fromwithin the shower area.

7. A shower unit as claimed in Claim 6 wherein said control panel is provided with an audible or visual warning device which becomes operative when the temperature ofthe water from the shower approaches a predetermined unsafe value.

8. Ashower unit according to Claim 7 wherein said control panel is provided with a series of LED's arranged to light up in series, underthe control of the microprocessor, as the temperature ofthe water from the shower increases.

9. A shower unit as claimed in any of Claims 6to 8 wherein the or each controlled semiconductor device is mounted on a thermally conductive member in close thermal contactwith a cold water supply pipe to the heater.

10. A shower unit as claimed in Claim 6 wherein on switching offthe water is arranged to continue flowing, either until the monitored temperature of the water reaches a sufficiently low value, orfor a predetermined time interval sufficient to allow the water to cool to a safe temperature.

11. A shower unit as claimed in any of Claims 6to 10 wherein the microprocessor is arranged to adjust the rate of flow of water so as to maintain the temperature ofthewaterfrom the showerat a set value.

12. A shower unit substantially as described hereinabove with reference to Figure 1 of the accompanying drawings.

13. A water heater substantially as described hereinabove with reference to Figure 2 of the accompanying drawings.