GB2269466A

GB2269466A - Improvements in or relating to instantaneous water heaters

Info

Publication number: GB2269466A
Application number: GB9216898A
Authority: GB
Inventors: Geoffrey Hawke Whale; Terence Leslie Winnington; Robert Meadows; Nicholas John Beck
Original assignee: Kohler Mira Ltd
Current assignee: Kohler Mira Ltd
Priority date: 1992-08-08
Filing date: 1992-08-08
Publication date: 1994-02-09
Anticipated expiration: 2012-08-08
Also published as: GB2269466B; GB9216898D0; IE930541A1

Abstract

An instantaneous water heater has a flow control valve 2, a heat exchanger 3 and an electronic control unit 4. The control unit 4 is responsive to the water inlet temperature detected by a sensor 16 to control flow rate and/or power input to provide a source of water having a selected temperature. The valve and the heat exchanger are arranged to be closed/switched off at a predetermined temperature in order to prevent scalding. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO INSTANTANEOUS WATER HEATERS This invention concerns improvements in or relating to instantaneous water heaters, in particular, though not exclusively, for ablutionary appliances, especially showers.

A conventional instantaneous electric shower consists of a heat exchanger with electric heating elements and control valves to regulate the water flowing through the heat exchanger. Cold water from the mains water services is passed through the heat exchanger and then to a shower spray.

The water is heated in the heat exchanger to a comfortable temperature for showering. The control of the temperature is achieved initially by switching on an appropriate number of heating elements and is fine tuned by adjusting the flow rate of water.

The user controls usually consist of an on/off water and power selection control and a separate water flow rate control. The water outlet temperature is affected by changes either in the power input or in the flow rate and this can lead to confusion on the part of the user.

Another problem with instantaneous electric showers is that adjusting the water flow rate to vary the temperature can adversely affect the spray obtained. The spray must form a neat, well-defined pattern at the lowest flow rate and not be too forceful at the highest flow rate. The efficiency of the spray mechanism can have an effect in this respect. Thus, at low flow rate, the spray mechanism may not function properly preventing a hot shower being obtained with an acceptable spray using an economy power setting and, at high flow rate, the spray mechanism may limit the flow rate relative to the available water pressure preventing a cool shower being obtained using a high power setting.

There are other behaviour characteristics of instantaneous electric showers which are not user friendly. When the shower is turned on, even though the settings will ultimately result in the required shower temperature, it takes time for the shower temperature to reach a steady value. This time delay is caused by the heat exchanger progressively reaching its steady running conditions. Similarly, there is a time delay in the setting of the heat exchanger each time a shower user adjusts the control settings. Typically, even on the best showers, this time delay can be 10 or 15 seconds so it takes time to get the shower adjusted to user preference.

If the shower is turned off and then, after a minute or so delay, turned on again, the water remaining in the heat exchanger can get very hot due to the residual heat in the elements being dispersed to the water. The initial flush of water on re-starting causes a hot-shot which can be uncomfortable.

There are mechanisms to reduce this effect, usually by delaying the water turn-off after the electrical power turn-o. This then cools the heat exchanger so it partially suffers a start up lag again.

The present invention has been devised from a consideration of the problems known instantaneous water heaters for showers and similar ablutionary appliances.

According to the present invention there is provided an instantaneous water heater for ablutionary appliances such as showers comprising a heat exchanger, a flow control valve and electronic control means responsive to the water inlet temperature for controlling the flow control valve and/or heat exchanger to provide a selected water outlet temperature.

The electronic control means uses the difference between the sensed water inlet temperature and the selected water outlet temperature to compute either the flow rate required to obtain the selected water outlet temperature for a given power input or the power input required to obtain the selected water outlet temperature for a given flow rate and controls the flow control valve or heat exchanger accordingly.

Advantageously, the electronic control means is adapted to maintain the selected water outlet temperature constant.

Conveniently, the electronic control means is arranged to adjust the flow control valve to maintain the selected water temperature constant in response to change in the water inlet temperature and/or pressure affecting the temperature differential and flow rate respectively.

Additionally, the electronic control means may be arranged to adjust the flow control valve to maintain the selected water temperature constant in response to change in the electricity supply voltage affecting the power output of the heat exchanger.

Preferably, the electronic control means is adapted to vary progressively the flow rate to match changes in the power output of the heat exchanger.

Advantageously, the flow control valve is electrically operable and responsive to the electronic control means for controlling the flow rate.

Conveniently, user operable means is provided for selecting the water outlet temperature and power input or flow rate, and the electronic control means is responsive to actuation of the user operable means for controlling the flow control valve and heat exchanger.

Preferably, the electronic control means is adapted to store selected settings of outlet water temperature and:power input or flow rate for recall by actuation of the user operable means.

Conveniently, the electronic control means is responsive to actuation of the user operable means to control the power input to the heat exchanger in response to water flow.

Preferably, the electronic control means is responsive to the actual water outlet temperature to close the flow control valve and switch-off the heat exchanger at a pre-determined temperature above the normal temperature range for comfortable showering, for example in the event of a malfunction giving rise to an unsafe water outlet temperature.

Other features, benefits and advantages of the invented instantaneous water heater will be understood from the following description of exemplary embodiments given by way of example only with reference to the accompanying drawings wherein: FIGURE 1 is a front view of an instantaneous water heater according to the present invention; FIGURE 2 is a front view of the water heater shown in Figure 1 with the front cover and control panel removed; FIGURE 3 shows a schematic layout of the main electrical circuits of the electronic control unit; FIGURE 4 shows an alternative control panel for the water heater shown in Figures 1 to 3; and FIGURE 5 shows a schematic layout of the main electrical circuits of a modified electronic control unit.

The electronically controlled instantaneous water heater shown in Figures 1 to 3 of the accompanying drawings comprises an elongate rectangular casing 1 housing a flow control valve 2, a heat exchanger 3 and an electronic control unit 4 mounted on a back plate 5 for securing to a wall or like installation surface.

An inlet coupling 6 for connection to the water supply, for example mains cold water, and an outlet coupling 7 for connection to an ablutionary appliance, for example a shower head are provided. As shown in Figure 2, the inlet coupling 6 is arranged for bottom entry of the main supply but the coupling 6 can be rotated through 900 for rear entry of the mains supply.

The electronic control unit 4 is powered by a dc low voltage supply from a 12v transformer 8 connected to a terminal block 9 for the incoming mains electricity supply and is response to user actuation of a control panel 10 mounted on a front cover 11 of the casing 1 to operate the flow control valve 2 and heat exchanger 3 for delivery of water having a selected temperature to the ablutionary appliance.

The front cover 11 is releasably secured to the back plate 5 and a multiple wire connection (not shown) is provided between the control panel 10 and the electronic control unit 4 with a multipin connector or flexible lead sufficient to allow the front cover 11 to be removed for installation, servicing or repair of the water heater.

The electrical circuits of the electronic control unit 4 are contained in a printed circuit board and include a main control circuit having a central control processor 12 connected to a solenoid coil 13 of the flow control valve 2 and to respective switch relays 14 for each of three separate heating elements 15 of the heat exchanger 3.

The central control processor 12 is arranged to receive signals from a water inlet temperature sensor 16 and a flow sensor 17 positioned between the flow control valve 2 and the inlet to the heat exchanger 3, and from a water outlet temperature sensor 18 positioned at the outlet from the heat exchanger 3.

The user operable controls mounted on the control panel 10 include three start buttons 19 corresponding respectively to selection of one, two or three heating elements 15 of the heat exchanger 3 to provide three different power settings, a stop button 20 and a rotatable temperature control knob 21.

Associated with each start button 19 is an indicator light 22 that is illuminated on user actuation of the button to show the selected setting. An indicator light 23 associated with the stop button 20 is also illuminated on user actuation of the button 20 and also shows that the electrical power supply to the water heater is switched on, it being usual practice to fit isolation switches to allow the power supply to be switched off for installation, servicing or repair of the water heater.

In operation of the water heater, the user selects the required water outlet temperature by rotating the control knob 21 to the appropriate setting and the required power input to the heat exchanger 3 by pushing the appropriate start button 19. The central control processor 12 responds to actuation of the start button 19 by applying a voltage to the solenoid coil 13 and switch relays 14 to open the flow cohtrol valve 2 and to switch on the selected number of heating elements 15 when the signal from the flow sensor 17 indicates sufficient water flow relative to the power input for the selected water temperature. This arrangement provides a fail-safe mechanism ensuring that the heating elements 15 will not be switched on if there is insufficient flow or if there is sufficient flow but no signal from the flow sensor 17 for any reason.

The central control processor 12 computes the required flow rate to obtain the selected water outlet temperature for the selected power input to the heat exchanger 3 using the signal from the water inlet temperature sensor 16 and adjusts the voltage applied to the solenoid coil 13 of the flow control valve 2 to achieve the required flow rate using the signal from the flow sensor 17 to compare the actual flow rate with the computed flow rate.

Once switched on and running, the actual water flow rate and the inlet water temperature are continuously monitored and the required flow rate recomputed many times per second with appropriate adjustment made to the voltage applied to the solenoid coil 13 to maintain equal the actual and computed flow rates so that the water outlet temperature is maintained substantially constant for a given setting of the temperature control knob 21.

In this way, changes in the inlet water temperature affecting the temperature differential with the selected water outlet temperature andtor the water supply pressure affecting the flow rate which would cause the water outlet temperature to change are compensated by adjustment of the flow rate to maintain the outlet water temperature constant.

If the user actuates the temperature control knob 21 to change the outlet water temperature setting, the control processor 12 responds by recomputing the required flow rate and adjusting the voltage applied to the solenoid coil 13 to achieve the required flow rate for the new temperature setting.

Likewise, if the user actuates a different start button 19 to vary the power input to the heat exchanger 3, the control processor 12 responds by re-computing the required flow rate to maintain constant the selected water outlet temperature and adjusting the voltage applied to the solenoid coil 13 to achieve flow rate for the new power input.

As will be appreciated, varying the power input to the heat exchanger 3 causes the flow rate to change to maintain the outlet water temperature constant so that user actuation of the start buttons 19 has the effect of altering the spray force produced by the spray mechanism (not shown). As a result, the buttons 19 can be labelled as spray force selection control so that user understanding of the controls is facilitated by avoiding reference to heat or power selection implying temperature control which is provided solely by the control knob 21.

The electrical circuits of the electronic control unit 4 also include a separate back-up circuit in addition to the main control circuit. The back-up circuit has a central control processor 24 connected to a switch 25 connected in series with the solenoid coil 13 and to a pair of switch relays 26 connected in series with the switch relays 14 of the heating elements 15. The control processor 24 is arranged to receive signals from the water outlet temperature sensor 18 and to actuate the switches 25,26 to cut-off the electricity supply to the solenoid coil 13 and to the heating elements 15 if the sensed water outlet temperature is above usable showering temperatures.

The electronic control unit 4 for operating the flow control valve 2 and heat exchanger 3 can be further improved to enhance the performance of the water heater as now described.

Firstly, the manufacturing tolerances of the heating elements 15 is generally +5% to -10% of the nominal power rating. Hence, in order for the main control processor 12 to accurately compute the flow rate required to give a selected water temperature, the precise value of the power of the heating elements 15 is needed.

The main control processor 12 "learns" these values by monitoring the performance of the heat exchanger 3 by comparing the selected water outlet temperature with the actual water outlet temperature using the signal from the outlet temperature sensor 18 enabling precise adjustments to be made to the flow rate to maintain the water temperature constant for user selection of different power settings.

Also, by monitoring the outlet water temperature, failure of any one on the heating elements 15 can be detected. Such failures are usually a 100% open circuit failure caused by a break in the element resistance wire.

The main control processor 12 can then compensate for the lost heating element 15 by adjusting the flow rate and operating a service warning light 27 on the control panel 10 to indicate to the user that a repair is required.

The main control processor 12 may also be arranged to operate the flow control valve 2 to provide a progressive change of flow rate to correlate with the rate at which the power output of the heat exchanger 3 changes.

Thus, by progressively increasing the flow rate on start-up to match the rate of increase in power output of the heat exchanger 3, a selected outlet water temperature can be reached more quickly and, by progressively reducing the flow rate on shut-down to match the rate of decrease in power output of the heat exchanger 3, the water remaining in the heat exchanger can be left at the selected temperature avoiding a build-up of hot water if the water heater is re-started after a short delay of a minute or so.

Similarly, by progressively changing the flow rate to match the rate of change of power output of the heat exchanger 3 on user selection of a different power input, transient changes in the outlet water temperature that may be noticed by the user are significantly reduced or avoided altogether.

The main control processor 12 may also be arranged to monitor the electricity mains supply voltage by means of signals from a suitable sensor (not shown) and to compute -the required flow rate to compensate for the effect of change in the voltage on the power output of the heat exchanger 3 in addition to any adjustments made for change in the inlet water temperature and/or water flow rate as above-described.

Referring now to Figure 4, there is shown a control panel similar to that shown in Figure 1 but with an additional facility for storing settings of power input and water temperature in a memory of the electronic control unit for recall later. Like reference numerals are used to indicate parts corresponding to Figure 1.

The control panel 10 has a store button 28 and four memory buttons 29 for selectively storing particular combinations of power input and outlet water temperature by pressing in association with the store button 28.

Associated with each memory button 29 is an indicator light 30 that is illuminated on user actuation of the button 29.

The electronic control unit is responsive to user actuation of any of the memory buttons to compute and control the flow rate required to obtain the memory set outlet water temperature for the memory set power input and the sensed water inlet temperature irresptective of the position of the temperature control knob 21.

When operating in memory mode, the temperature control knob 21 is not effective until it has been rotated to the position corresponding to the memory set outlet water temperature. If, a new outlet water temperature is then selected, the light 30 associated with the memory button 29 will go out and the light 22 associated with the start button 19 corresponding to the power input will come on to show that the water heater is operating in "live mode". Similarly, when switching from "memory mode" to "live mode" by pressing one of the start buttons 19, the outlet water temperature remains at the memory setting until the control knob 21 has been rotated to the position corresponding to the memory set water outlet temperature. In this way, a sudden temperature change which the user may not expect is avoided.

As will be appreciated, when recalling stored combination of the power input and outlet water temperature by actuation of any of the memory buttons 29, the actual flow rate obtained will depend on the inlet water temperature which may change by 10 to 150C between summer and winter causing the flow rate to obtain the memory set outlet water temperature to vary significantly producing a noticeable change in the spray force.

Referring now to Figure 5, there is shown a modification to the electrical circuits shown in Figure 3 which enables this problem to be avoided. Like reference numerals are used to indicate corresponding parts.

The main control circuit of the electronic control unit 4 has four switch relays 14 connected to the central control processor 12 each controlling a respective heating element 15 of the heat exchanger (not shown). In this way, the combination of the heating elements 15 can be controlled to provide a wide range of power settings such that the power input to the heat exchanger can be varied progressively by selecting different combinations of heating elements 15.

The increased range of power settings available enables particular settings of flow rate and outlet water temperature to be stored in the memory of the control unit 4 such that, on recall, the control processor 12 computes the power input required to obtain the flow rate and water outlet temperature corresponding to the memory settings for the sensed water inlet temperature and switches on the combination of heating elements 15 to give the required power input. In this way, the effect of seasonal variations in the water inlet temperature are reduced so as not to benoticeable.

The "live mode" operation would be similar to that described above with reference to Figures 1 to 3 except that extra start buttons andlor flow increaseidecrease buttons may be provided on the control panel corresponding to the increased range of power settings available.

It will be understood that the invention is not limited to the embodiments above-described. For example, the user operable controls may be of any suitable type. Similarly, the electrical circuits and components of the electronic control unit may be of any suitable type. The same electronic control unit may conveniently be used for versions of the water heater with and without the memory facility with the memory being connected or disconnected as appropriate.

The flow control valve may be of any type allowing progressive control of the flow rate.

The number and power rating of the heating elements may be chosen to provide any desired power input or range of power inputs.

Claims

Claims:

1. An instantaneous water heater for ablutionary appliances such as showers comprises a heat exchanger, a flow control valve and electronic control means responsive to the water inlet temperature for controlling the flow control valve and/or heat exchanger to provide a selected water outlet temperature.

2. An instantaneous water heater according to Claim 1 wherein the electronic control means uses the difference between the sensed water inlet temperature and the selected water outlet temperature to compute the flow rate required to obtain the selected water outlet temperature for a given power input.

3. An instantaneous water heater according to Claim 1 wherein the electronic control means uses the difference between the sensed water inlet temperature and the selected water outlet temperature to compute the power input required to obtain the selected water outlet temperature for a given flow rate.

4. An instantaneous water heater according to any one of the preceding Claims wherein the electronic control means is adapted to maintain the selected water outlet temperature constant.

5. An instantaneous water heater according to Claim 4 wherein the electronic control means is arranged to adjust the flow control valve to maintain the selected water temperature constant in response to change in the water inlet temperature.

6. An instantaneous water heater according to Claim 4 or Claim 5 wherein the electronic control means is arranged to adjust the flow control valve to maintain the selected water temperature constant in response to change in water flow rate.

7. An instantaneous water heater according to any one of Claims 4 to 6 wherein the electronic control means is arranged to adjust the flow control valve to maintain the selected water temperature constant in response to change in the power output of the heat exchanger.

8. An instantaneous water heater according to any one of the preceding Claims wherein the electronic control means is adapted to vary progressively the flow rate to match changes in the power output of the heat exchanger.

9. An instantaneous water heater according to any one of the preceding Claims wherein the flow control valve is electrically operable and responsive to the electronic control means for controlling the flow rate.

10. An instantaneous water heater according to any one of the preceding Claims wherein user operable means is provided for selecting the water outlet temperature and power input or fibw rate, and the electronic control means is responsive to actuation of the user operable means for controlling the flow control valve and heat exchanger.

11. An instantaneous water heater according to Claim 10 wherein the electronic control means is adapted to store selected settings of outlet water temperature and power input or flow rate for recall by actuation of the user operable means.

12. An instantaneous water heater according to Claim 10 or Claim 11 wherein the electronic control means is responsive to actuation of the user operable means to control the power input to the heat exchanger in response to water flow.

13. An instantaneous water heater according to any one of the preceding Claims wherein the electronic control means is responsive to the actual water outlet temperature to close the flow control valve and switch-off the heat exchanger at a pre-determined temperature.

14. An instantaneous water heater for ablutionary appliances such as showers substantially as hereinbefore described with reference to the accompanying drawings.

15. An electric shower incorporating an instantaneous water heater according to any one of the preceding Claims.