AU642445B2

AU642445B2 - Heater for liquid

Info

Publication number: AU642445B2
Application number: AU67151/90A
Authority: AU
Inventors: Brian William Hammond
Original assignee: Heatrae Sadia Heating Ltd
Current assignee: Baxi Heating UK Ltd
Priority date: 1989-11-09
Filing date: 1990-11-08
Publication date: 1993-10-21
Anticipated expiration: 2010-11-08
Also published as: GB2248103A; NZ236016A; WO1991007624A1; GB9121751D0; GB2248103B; AU6715190A; GB8925326D0

Description

Title: Heater for liquid.

Description of Invention

This invention relates to a heater for liquid and more particularly, but not exclusively, to a water heater for use in providing hot water, for example, for the making of hot drinks or other uses.

It is preferred for such a heater to be ready to supply hot water at a generally constant temperature all the time, notwithstanding that hot water may be drawn off irregularly and more cold water needs to be introduced to replenish the supply.

Swiss specification 302463 discloses a water heater but the control circuit which controls operation of the heater is unnecessarily complex and is inefficient in that to finely control the temperature of the water within the heater so that a supply of hot water at a generally constant temperature is always available, sophisticated temperature sensing devices are required.

According to the present invention we provide a heater for liquid comprising a vessel having an inlet for cold liquid and an outlet for hot liquid, and an outlet through which vapour given off from the heated liquid passes into a chamber, a first sensor means at a first level, a second sensor means at a second, higher, level, and a third sensor means, the first sensor means being sensitive to the temperature of the liquid in the vessel, the second sensor means being sensitive to the presence of liquid at the second level and the third sensor means being sensitive to the temperature within the chamber, the first, second and third sensor means each being connected in a control circuit which is arranged to supply power to a heating means to heat the liquid in the vessel until the third sensor means senses a first threshold temperature, and then to cut off the power to the heating means, and the control circuit being arranged to supply power to an electrically operated valve means to open the valve means to permit cold liquid to enter the vessel through the inlet when both the first sensor means senses that the temperature of the liquid in the vessel has risen to a second threshold temperature and the second sensor means senses no liquid at the second level.

A heater in accordance with the invention provides for simple and efficient operation.

The invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is an schematic front sectional view of a water heater in accordance with the invention,

FIGURE 2 is a schematic side sectional view of the water heater of Figure 1,

FIGURE 3 is a circuit diagram of a control circuit for the water heater of Figures 1 and 2, and,

FIGURE 4 is a circuit diagram of an alternative control circuit for the water heater of Figure 1.

FIGURE 5 is a circuit diagram of another alternative control circuit for the water heater of figure 1.

Referring to the drawings, there is shown a water heater 10 comprising a water storage vessel 11 which has in its lower region, a heating means comprising an electrical heating element 12. The vessel 11 is generally cylindrical with end walls 13,14. The upper end wall 13 is connected to a condensing chamber 15 via a connecting duct N whereas the lower end wall 14 has an opening which receives a plate 16 on which the heating element 12 is provided.

A first opening 18 from the vessel 11 provides an outlet for hot water, the opening 18 having provided in it a tap T which has connected to it a conduit c which extends downwardly. The tap T may be opened or closed by a user to draw off hot water. The outlet opening 18 is spaced upwardly from the lower end wall 14 of the vessel at a level generally corresponding with the heating element 12, so that in use, the vessel 11 cannot be emptied so far as to entirely expose the heating element 12 to the air, which could lead to damage of the heating element 12.

A second opening 20 is provided below the heating element 12 for the inlet of cold water, the inlet opening 20 being connected to an inlet conduit 21 via a solenoid operated valve 22, to a water source.

Attached to the side wall of the vessel 11 is a first sensor means comprising an electro mechanical sensing device 26 such as a bi-metallic switch, at a level slightly above the inlet opening 20 and slightly below the level of the heating element 12, and outlet opening 18.

A further opening 27 is provided in the side wall of the vessel 11 in which a tube 23 is received, the tube 23 being filled with water as the vessel 11 fills so that the level of water in the tube is always generally the same as the level of the water in the vessel 11. Secured to a wall of the tube 23 is a second sensor means again comprising an electro mechanical sensing device 28 such as a bi-metallic switch.

The tube 23 extends upwardly from the opening 27 where it opens into the condensing chamber 15.

The condensing chamber 15 has a third sensor means comprising, in this example, a single electro mechanical temperature sensing device 29 (e.g. a bi-metallic switch) extending through a top wall thereof so as to be responsive to sense the temperature of vapour within the condensing chamber. The chamber 15 also has an opening 30 which receives a pressure relief device such as a frangible member which bursts if excess pressure occurs in the condensing chamber 15. However, a vent pipe 31 is provided which extends from the chamber 15 downwardly through the bottom B of the casing C of the heater 10 normally to vent the chamber 15 and maintain atmospheric pressure in the vessel 11.

The vessel 11 is provided with insulation I at least in the region where hot water is stored, but such insulation is cut away at least in the regions of sensor 26, the outlet opening 18, the inlet opening 20 and the opening 27.

The tube 23 is provided with insulation 12 except in the region of sensing device 28, and a further sensing device 24 to be described, and adjacent the top of the tube 23.

The condensing chamber 15 is however uninsulated so that steam produced as the water in the vessel 11 is heated, can condense onto the relatively cold surfaces thereof.

The plate 16 secured in the opening 15 in the lower end wall 14 of the vessel 11, includes a drain boss 32 to enable the vessel 11 to be completely drained if desired, and the plate 16 is arranged to be easily removable for maintenance purposes.

Within the vessel 11 is a baffle 25 to prevent water splashing into the condensing chamber 15 and hence to influence sensor 29, during heating of the water near to boiling point. The duct N from the chamber 15 into the vessel 11 is cranked to assist.

The casing C of the heater has a pair of brackets L for affixing the heater 10 to a support.

The heating element 12 and the sensing devices 26,28 and 29, and the solenoid operated valve 22, are all components in an electrical control circuit, one example of which is illustrated in figure 3, and alternative examples of which are illustrated in figures 4 and 5.

Referring first to figure 3, initially to fill the vessel, a main switch S is manually moved to a "fill" position where it is manually held. This completes a circuit to the solenoid valve 22 so that power is supplied to the valve 22 in response to which a valve member thereof moves to allow water to flow through the inlet 20 into the vessel 11. When the water level reaches that of the outlet 18, i.e. where it at least partially covers the element 12, the switch S can be released and hence the valve member of the solenoid valve 22 will move towards the closed position to stem the flow of further water into the vessel 11.

When it is desired to use the heater for heating water, the main switch S is moved to an "on" position where it is arranged automatically to latch. The temperature sensing device 29 in the condensing chamber 15 will sense the temperature in the chamber 15 and because no water has been heated, and no hot vapour has been given off from the heated water, the device 29 will sense a temperature below a first threshold temperature i.e. "cold" and consequently power which is supplied to the device 29 will be directed to the heating element 12.

Heating of the water in the vessel 11 will thus occur until the device 29 senses a temperature in the condensing chamber 15 has risen to the first threshold temperature i.e. the device 29 will sense "hot " and the power supply to the heating element 12 will be cut off. The temperature in the condensing chamber 15 will increase due to vapour being given off from the heated liquid in the vessel 11 passing upwardly through duct N into the chamber.

When the main switch is "on" device 29 will thus control the heating element 12 and heating will occur whenever the device 29 senses "cold" which in general will always be when the temperature of the water in the vessel 11 is below a maximum temperature.

Sensing devices 26 and 28 will control filling of the vessel 11 as follows. As the temperature of the water in the vessel 11 will initially be below a second threshold temperature, the device 26 will sense "cold" and hence no power will be supplied to the solenoid operated valve 22 so that no water will enter the vessel through the inlet 20. However, when the water has been heated by the heating element 12 to the second threshold temperature, the device 26 will sense "hot" and hence power will be supplied to the device 28.

When device 28 senses the temperature below a third threshold temperature i.e. "cold" which will denote that the hot water level is below the level of device 28, power will be supplied to the solenoid valve 22 to cause the valve 22 to open and allow more cold water into the vessel 11. However, soon after cold water enters the vessel 11, the temperature of the liquid within the vessel 11 will again fall below the second threshold temperature and so device 26 will again sense "cold" so that power to the solenoid 22 will be cut off.

When the temperature of the water in the vessel again reaches the second threshold temperature, device 26 will again sense "hot" and provided device 28 still senses "cold" valve 22 will again be opened to allow yet more cold water into the vessel 11.

Thus the water is heated in cycles as the water level rises so that however much water is in the vessel (above the minimum) in use, the water temperature is maintained near to the second threshold temperature at which device 26 switches, so that hot water at a generally constant temperature is always available to a user.

When the (hot) water level reaches the level L2 of device 28, device 28 will sense "hot" i.e. a temperature above the third threshold temperature and so device 26 will cut off the power supply to the solenoid valve 22 so that no more water can enter the vessel. The control means then relies solely on the device 29 of the condensing chamber 15 to sense temperature which will change as steam from the heated water impinges upon the device 29 in the chamber 15. Whenever the device 29 senses "cold" i.e. a temperature below the first threshold temperature, the circuit to the heating element 12 will be completed whereas if device 29 senses "hot" i.e. a temperature above the first threshold temperature, the circuit to the heating element 12 is broken.

When the vessel 11 is full to the level L2 of device 28, device 29 will maintain the temperature of the water near to boiling point by cycling the element 12 "on" and "off" until water is drawn off through the outlet 18 when sensor 28 will again sense "cold" as the (hot) water level falls below the level 12 of device 28. In this instance, more water will be allowed into the vessel 11 as the solenoid valve 22 will be opened, provided that device 26 senses "hot".

An advantage of the present invention is that the devices 26,28 and 29 need not be expensive accurate temperature sensors to enable fine control of the temperature of the water within the vessel 11 to be achieved but may for example comprise simple bi-metallic switches.

The first threshold temperature sensed by device 29 may for example be arranged to switch off i.e. sense "hot" at a relatively low calibration setting of about 80°C. so that device 29 reacts quickly to the presence of steam and switches off the heating element 12.

Because the condensing chamber 15 is uninsulated, when the heating element 12 is switched off, the temperature within the chamber 15 will drop quickly compared with the temperature of the water in the insulated vessel 11. When the temperature of the chamber 15 has dropped to, say 70°, device 29 may be arranged to again sense "cold" but in this time, because vessel 11 is well insulated the temperature of the water within the vessel 11 will have dropped by a much lesser amount say 1° or 2° C.

The further temperature sensing device 24 which is in contact with the wall of the tube 23 is not part of the control circuit of figure 3 but is connected with a neon or other light, to indicate when the (hot) water level in the vessel 11 has reached a mid level LI. Any other suitable water level indicator could instead be provided.

Preferably sensing device 28 is also connected to a neon or other light to indicate when (hot) water has reached the maximum level in the vessel indicated by a level L2.

It will be appreciated that the control circuit of figure 3 is thus able to supply and maintain power to the heating element 12 until sensing device 29 cuts off the supply, regardless of the sensing states of devices 26 and 28.

Referring now to figure 4, an alternative control circuit for the heater 10 of figure 1 is shown.

The vessel 11 may initially be filled in exactly the same manner as described above with reference to figure 3.

When the main switch S is moved to an "on" position, the temperature sensing device 26 then senses the temperature of the water in the vessel 11. Water which has not yet been heated will be below a threshold temperature and so the device 26 will sense "cold" and consequently the circuit will be completed to the electrical heating element 12 via an auxiliary current path indicated at P.

Heating of water in the vessel 11 will occur until device 26 senses that the temperature of the water in the vessel 11 has risen to the threshold temperature at which device 26 is arranged to sense "hot" when the power supply to the heating element 12 will be cut off. As the water level in the vessel is below level LI of the device 28 initially, the device 28 will sense "cold" and so a circuit to the solenoid valve 22 is completed and water will again enter the vessel 11 through the inlet 20 until device 26 again senses "cold" which will occur soon after cold water begins to enter the vessel 11 when the circuit to the solenoid 22 will again be broken and the circuit to the heating element 12 will again be heated.

When the temperature of the water in the vessel 11 again reaches the threshold temperature at which device 26 is arranged to sense "hot" and device 28 senses "cold", further water will enter the vessel and so on until the water level has risen to the level 12 of device 28.

Thus again the water is heated in cycles as the water level rises so that however much water is in the vessel in use, the water temperature is maintained near to the threshold temperature of device 26 so that hot water of a generally constant temperature is always available to a user.

When the hot water level reaches the level L2 of the device 28 and device 28 senses a temperature above the threshold value at which the device 28 is arranged to sense "hot", the device 28 provides power to the device 29 provided in the chamber 15 and the control means then relies on the device 29 in the condensing chamber 15 to sense temperature which will change as steam from the heated water passes upwardly through the duct N into the chamber 15 and impinges upon the device 29.

Whenever the device 29 senses a temperature below a threshold temperature at which device 29 is arranged to sense "cold" the circuit to the heating element 12 will be completed whereas when device 29 senses "hot" the circuit to the heating element 12 will be broken.

Device 29 will thus again maintain the temperature of the water near to boiling point by cycling the element 12 "on" and "off" until water is drawn off through the outlet 18 when device 28 will again sense "cold" as the (hot) water level falls below the level of device 28. In this instance, more water will be allowed into the vessel as the solenoid valve 22 will be opened provided that sensor 26 senses "hot".

Again, at least when device 26 senses "hot" and device 28 "hot", the control circuit will maintain the power to heating element 12 until the sensing device 29 senses "hot" when power to the element will be cut off.

Figure 5 shows a modification to the circuit of figure , in which the third sensor means includes a further temperature sensing device 35 . The further temperature sensing device 35, is like device 29, and senses the temperature within the condensing chamber 15, but the device 35 is arranged to sense "hot" at a higher temperature than device 29, so that in ordinary operation, the device 35 senses "cold". The device 35 may be mounted alongside device 29 so as to extend through the top wall of the condensing chamber 15.

It has been found with the arrangement of figure 4, that particularly when the valve 22 is open and water is entering the vessel through inlet 20, hot vapour in the vessel 11 is displaced upwardly into the chamber 15, and the movement of this hot vapour can trigger the device 29 to sense "hot", even when the temperature of the water in the vessel is well below the first threshold temperature.

Accordingly, during filling of the vessel 11, when valve 22 is activated, the coil of a relay 36 is energised and hence contacts 37 are closed, so that power is supplied to the heating element 12 via a second current path P2, unless the device 35 senses "hot". Suitable means would need to be provided to ensure that element 12 is not actuated during initial filling when switch S is moved to the "fill" position. Thus when the valve 22 is inoperative, power to the heating element 12 is controlled by sensing device 29 which switches to cut off the power to the element 12 at a threshold temperature, which in this case is the first threshold temperature.

During filling, when valve 22 is operative, power to the heating element 12 is controlled by sensing device 35 which switches to cut off the power to the element 12 at a higher, threshold temperature, which in this case is the first threshold temperature (assuming device 29 is also properly sensing "hot") .

Various other modifications are possible to the heater and control circuit described without departing from the scope of the invention.

For example, if desired, the main switch S need not have a "fill" position as described, but rather the vessel 11 may actually be filled via an auxiliary "fill" pipe until the level of the water in the vessel is at least the level of the outlet 18.

Means may be provided to enable a substance which inhibits scaling, to be introduced to the vessel 11.

The heater 10 may be used for heating liquids other than water, in which case, the temperatures at which the sensing devices 26 and 29 (and 35 where provided) , at least are arranged to switch, may need to be altered.

Although the temperature sensing devices 26,28,29 (and 35 where provided) are described as being electro mechanical devices such as bi-metallic switches, if desired any other suitable type of temperature sensing device may be provided. The devices 26,28,29, need not be provided in the exact positions shown and may be in direct thermal contact with the water or other liquid rather than with the vessel wall, the tube 23 wall or the condensing chamber 27 wall as desired.

The second sensing means 28 need not be a temperature sensing device as described but could be any other type of device which senses when the level of liquid in the vessel has reached the level L2 of the second sensor means 28. Thus in the circuit of figures 3 and 4 and 5, instead of having "hot" and "cold" contacts, the device may have contacts to indicate that the liquid level in the vessel 11 has reached sensor 28 or has not, respectively.

The heating vessel 11 may be of other configurations to that shown, as may the condensing chamber 15, although preferably the condensing chamber 15 is situate above the vessel 11 so that the vapour given off from liquid being heated in the vessel can pass upwardly into the condensing chamber 15.

The heating element 12 although preferably arranged in a horizontal orientation as shown, may be arranged in an upright orientation as desired. Instead of providing a heating element 12, any other heating means controlled by either of the control circuits described may be used.

The configuration of the casing C may be changed as desired.

The features disclosed in the foregoing description or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A heater for liquid comprising a vessel having an inlet for cold liquid and an outlet for hot liquid, and an outlet through which vapour given off from the heated liquid passes into a chamber, a first sensor means at a first level, a second sensor means at a second, higher, level, and a third sensor means, the first sensor means being sensitive to the temperature of the liquid in the vessel, the second sensor means being sensitive to the presence of liquid at the second level and the third sensor means being sensitive to the temperature within the chamber, the first, second and third sensor means each being connected in a control circuit which is arranged to supply power to a heating means to heat the liquid in the vessel until the third sensor means senses a first threshold temperature and then to cut off the power to the heating means, and the control circuit being arranged to supply power to an electrically operated valve means to open the valve means to permit liquid to enter the vessel through the inlet when both the first sensor means senses that the temperature of the liquid in the vessel has risen to a second threshold temperature and the second sensor means senses no liquid at the second level.

2. A heater according to claim 1 wherein the first and third temperature sensor means comprise electro mechanical devices.

3. A heater according to claim 2 wherein the first temperature sensor means is in thermal communication with a wall of the vessel. to be responsive to the temperature of vapour within the chamber.

5. A heater according to any one of claims 1 to 4 wherein the second sensor means is a temperature sensor which senses the presence of liquid at the second level by sensing a temperature above a third threshold temperature.

6. A heater according to claim 5 wherein the second temperature sensor means is in thermal communication with a tube connected to the vessel such that the liquid level in the tube is generally the same as the liquid level in the region of the second temperature sensor.

7. A heater according to any one of the preceding claims wherein the third temperature sensor means comprises a single sensing device, the control circuit being arranged to cut off the power to the heating means in response to the third sensor means regardless of the sensing conditions of the first and second sensor means whereby the heating element is controlled by only the third of the sensor means.

8. A heater according to any one of claims l to 6 wherein the third sensor means comprises a pair of temperature sensing devices arranged to be sensitive to respective different temperatures within the chamber, the control circuit being responsive to one of the devices of the third sensor means to cut off the power supply to the heating means from a first circuit path, when a temperature above an associated threshold temperature is sensed, and the control circuit providing power to the heating means via an alternative circuit path when both the electrically operated valve means is operated and the other of the temperature sensing devices of the third sensor means senses a temperature below an associated, higher, threshold temperature, the first threshold temperature being the respective associated temperature of the pair of temperature sensors depending upon the current path by which power is supplied to the heating means.

9. A heater according to any one of claims 1 to 6 wherein the third sensor means comprises a single sensing device, the control circuit providing power to the heating means when the first sensor means senses a temperature above the second threshold temperature and the second sensor means senses the presence of liquid at the second level, until the single sensing device of the third sensor means senses a temperature above the first threshold temperature.

10. A heater according to any one of claims l to 9 wherein the electrically operated valve is a solenoid valve and the heating means is an electrical heating element.

11. A heater according to any one of claims 1 to 10 wherein the outlet for hot water has an associated tap to enable a user manually to control the supply of hot water drawn from the heater.

12. A heater according to any one of claims l to 11 wherein the outlet to the chamber is provided at a level above the second level.

13. A heater according to any one of the preceding claims wherein the chamber is separated from and located above the vessel and is connected to the outlet of the vessel by a connecting duct through which the liquid vapour may pass upwardly from the vessel into the chamber. 14. A heater according to claim 13 wherein means are provided to deter liquid from the vessel splashing into the chamber.

15. A heater according to claim 13 or claim 14 wherein the third temperature sensor is provided on a top wall of the chamber.

16. A heater according to any one of claims 1 to 15 wherein the vessel is insulated and the chamber is not.

17. A heater according to any one of claims l to 16 wherein a vent is provided from the chamber to atmosphere.

18. A heater for liquid substantially as hereinbefore described with reference to and as shown in the accompanying drawings.