GB2375595A

GB2375595A - Water heater with temperature detector

Info

Publication number: GB2375595A
Application number: GB0217720A
Authority: GB
Inventors: John Edward Vallis
Original assignee: ZIP HEATERS
Current assignee: ZIP HEATERS
Priority date: 2000-07-18
Filing date: 2001-07-11
Publication date: 2002-11-20
Anticipated expiration: 2021-07-11
Also published as: GB0217720D0; GB2375594B; GB0217719D0; GB2375595B; GB2375594A

Abstract

A cold water reservoir 12 contains a sensor 48 to detect any increase in temperature and respond if a threshold level is exceeded. The response may be in the form of an audible or visual alarm or the activation of a valve to inhibit flow of water from a hot water reservoir 10. The hot water reservoir has a heating means 40 and is fed with water from the cold water reservoir by a feed pipe 14. The sensor may also control the operation of the heating means or a second sensor 46 may be used. A sleeve 18 of thermally-insulating material is in contact with an expansion pipe 16 that connects the hot water reservoir to the cold water reservoir. The sleeve extends to at least the depth of water in the cold water reservoir and thermally separates the water from the expansion pipe. The expansion pipe permits heated water forced out of the hot water reservoir by expansion to return to the cold water reservoir.

Description

Improvements relating to water heaters Field of invention

This invention concerns water heaters of the type in which cold water is stored in a reservoir above a second lower reservoir of heated water, for maintaining the level in the second reservoir.

Background to the invention

In water heaters of this type the heat from the lower reservoir has been found to raise the temperature of the volume of cold water to unacceptable levels and it is an object of the present invention to overcome this problem.

Summary of the invention

According to the present invention there is provided a water heater comprising upper and lower reservoirs in which cold water is stored in the upper reservoir for feeding the lower reservoir which contains water heating means, with an interconnecting passage for transferring cold water from the upper reservoir to the lower to maintain the level therein and an expansion pipe to permit heated water forced out of the lower reservoir by expansion to return to the upper reservoir, wherein means is provided to thermally separate the body of water in the upper reservoir from the expansion pipe to reduce the transfer of heat from the expansion pipe to the water in the upper reservoir, further comprising temperature sensing means for sensing the temperature of the water in the upper reservoir and adapted to produce a response if the temperature of the water therein rises above a predetermined level.

Since the reason for limiting the rise in temperature of the water in the upper reservoir is to reduce the risk of bacterial growth such as can cause legionnaires disease and organisms which can attack the gut, the invention provides for the actual sensing of the temperature

of the water in the upper reservoir in which cold water is stored for feeding the lower reservoir to detect if the temperature of the water in the upper reservoir exceeds a threshold (such as 39 C) above which microbiological growth can occur of harmful organisms which can promote disease.

The means to thermally separate the body of water in the upper reservoir from the expansion pipe comprises a sleeve which surrounds the expansion pipe to at least the depth of the water in the upper reservoir.

The sleeve may be spaced from the expansion pipe by an air gap, to form an annular chamber around the expansion pipe.

The annular chamber may be open at its upper end and closed at its lower end.

When closed, a drain may be provided to allow water collected in the annular space to drain away safely.

The sleeve may be formed from thermally insulating material and may be in contact with the expansion pipe.

At least that part of the expansion pipe which extends through the upper reservoir may be formed from a material having low thermal conductivity relative to that of copper so that whether thermally insulating material or an air gap exists between it and the sleeve, the transfer of heat from any hot water in the expansion pipe and the water in the upper reservoir is further restricted.

The expansion pipe may be formed from metal such as copper and the sleeve may be cylindrical and is also formed from metal such as copper and have an internal diameter which is substantially greater than the outside diameter of the expansion pipe and extends from the base of the upper reservoir to a height therein which is greater than the depth of water in the upper reservoir, the sleeve and the pipe being generally coaxially arranged so

that the sleeve is spaced from the pipe substantially by the same distance around the whole of its circumference, and the spacing is selected so as to ensure that under normal conditions, with the annular space between the pipe and the sleeve filled with air, the transfer of heat from the wall of the pipe to the wall of the sleeve is insufficient to cause any significant rise in temperature of the water in the upper reservoir which surrounds the sleeve. A collar of material having low thermal conductivity relative to copper (such as a suitable plastics material) may surround the expansion pipe where it passes through a wall of the upper reservoir so as to reduce the conduction of heat from the pipe to the upper reservoir.

A similar collar of low thermal conductivity material may surround the feed pipe (from the upper reservoir to the lower) where it passes through a wall of the upper reservoir to inhibit the transfer of heat from the feed pipe to the upper reservoir.

By wall is meant any wall of the reservoir including the base thereof.

Typically the upper end of the expansion pipe is bent to form an inverted U-bend so if that water is forced up the expansion tube due to excess temperature in the lower reservoir, it will be discharged in a generally downward direction.

Where an air gap exists between sleeve and expansion pipe the lateral separation of the discharge end of the inverted U-bend from the upstanding part of the expansion pipe is preferably greater than the radial spacing of the sleeve wall from the expansion pipe, so that if any discharge does occur it is directed at the water in the reservoir and not into the annular space between the expansion tube and the sleeve.

The level of cold water in the upper reservoir can be maintained at a predetermined level by water level responsive valve means which permits the inflow of cold water into the upper reservoir only if the level of water therein is below the said predetermined level.

Conveniently the valve means is a float operated valve such as is commonly employed in water cisterns and cold water storage tanks which have to be kept topped up by water from a water supply main.

The temperature sensing means provided by the invention may be adapted to activate an alarm and/or activate valve means inhibiting the flow of water from the lower reservoir.

The alarm may be visual or audible or both.

If the removal of water from the lower reservoir is inhibited, preferably means is provided for indicating to the user why the system will not allow hot water to flow therefrom.

According to a preferred feature the temperature sensing means may be adapted to control the operation of the heating means in the lower reservoir, to turn off the heating means if an overtemperature condition is sensed in the upper reservoir.

In a preferred arrangement means is provided for integrating any sensed temperature excess with time and the generation of an alarm and/or the inhibition of hot water flow from the lower reservoir or the turning off of the heating means in the lower reservoir, may be deferred until the integration reaches a predetermined value.

The temperature sensing means may comprise a device whose electrical characteristics vary with temperature and an electrical circuit is provided, adapted to respond to a change in the said electrical characteristics indicative of an excess of temperature above the said predetermined level, and to generate an electrical control signal in response to a sensed change. The control signal may be employed to drive a sounder or illuminate a lamp or both and/or turn off the energy supply to the heating means in the lower reservoir.

Where time integration is required the electrical circuit may include a timing device which is reset when the temperature condition is exceeded and if the temperature is still in excess

of the predetermined value after the timing device has timed out to a predetermined interval of time, the electrical control signal is generated.

The temperature sensing means may for example comprise a metal alloy junction or semi-

conductor device whose electrical characteristics vary with temperature.

The alarm may be generated proximate to the installation or at a remote location or both.

If at a remote location, an identifying signal is preferably transmitted with the signal generating the alarm, to indicate where the installation is located in which the upper reservoir water temperature has triggered the alarm.

If it is deemed sufficient to monitor whether the water temperature has exceeded the predetermined level during a period of time, as for example between service calls, a latching temperature sensing means may be used instead, which merely activates if the design temperature for the upper reservoir has been exceeded. This latching may be employed to indicate that the overtemperature condition has been sensed. This may serve merely to show why the heating element has been turned off, or as a warning for an engineer when making the next service call.

A latching temperature sensing device may include or comprise a visible chemical composition or a device which changes colour or changes from transparent to translucent, or becomes opaque, if its temperature rises beyond a given temperature. Such devices are employed in food storage containers which are to be stored in a frozen or chilled condition. The invention will now be described by way of example with reference to the accompanying drawings in which: Fig 1 is a side elevation partly in section of a dual reservoir arrangement to which the invention may be applied,

Fig 2 is a similar view of another dual reservoir arrangement to which the invention may be applied, Fig 3 is a similar view of a further dual reservoir arrangement having temperature sensing means in accordance with the invention, and Fig 4 is a schematic circuit diagram.

In Fig 1 a lower hot water reservoir 10 is supplied with water from an upper cold water reservoir 12 via a pipe 14. The reservoir 12 is kept topped up in a conventional manner from a cold water supply eg the cold water supply mains.

Heating means such as an electric powered immersion heater (not shown in Figs 1 & 2) heats the water in 10 and in the event of overheating and expansion occurring in 10, hot water is forced up vent pipe 16. A sleeve 18 surrounds the pipe 16 also spaced therefrom to create an annular air gap 20 to impede the transfer of heat from any hot water in 16 to the cold water in 12. Thermal insulation material 22 separates the two reservoirs. The lower end of the annular air gap 20 is closed off by the base wall of the upper reservoir 12. Although not shown, an opening may be provided in the region of the base of the reservoir 12, forming the lower closed end to the annular air gap 20, leading to a drain, to allow any water which collects in the gap 20 to drain away.

The pipes 14 and 16 may be formed from metal or a plastics material which is resistant to the flow of heat therealon s so as to further limit the transfer of heat from 10 to 12.

In Fig 2 an air gap 24 exists between the two reservoirs to impede the transfer of heat therebetween and the pipes 14 and 16 are secured to the upper reservoir by means of thermally insulating plastics material collars 26, 28 respectively to impede transfer

therebetween. In other respects Fig 2 is similar to Fig and the same reference numerals have been employed.

Fig 3 shows an embodiment of the present invention, in which a temperature sensor is shown at 48 for detecting if the temperature of the water in 12 exceeds a different threshold such as 39 C, above which microbiological growth can occur of harmful organisms which can promote disease.

In Pig 3 expansion pipe 16 is shown bent over at 30 to form an inverted Ubend to bring the discharge end beyond the wall of the sleeve 18. A float operated valve 32 and float 34 on an arson 36 is shown for controlling the flow of cold water from a supply main feed 38, and an immersion heater 40 is shown in the lower reservoir 10. The two reservoirs are separated by insulating material 42 although they may be separated alternatively by an air gap. Heat transfer is further reduced by forming the pipe 14 from a plastics material.

A lid 44 covers the open end of the reservoir 12.

A temperature sensor is shown at 46 for connecting to an electrical circuit (not shown), for generating a control signal if the temperature of the water in 10 exceeds a given temperature. It can also be used to control the current to the heater 40.

The sensor 48 incorporates, and controls the operation of, a normally closed switch, shown connected in an electrical circuit shown in Fig 4 which can generate an audible or visible (or both) alann and/or interrupt the supply of energy to the heater 40. The switch 48 opens if the temperature sensed exceeds a predetermined value -e.g. 39 C. The circuit includes a device for integrating an electrical signal with time, the electrical signal being a constant voltage produced when the temperature sensitive switch 48 detects an overtemperature condition in 62, and the generation of an alarm signal, and/or the interruption of the

energy to the heater 40, may be delayed until the integration has reached a predetermined value. As shown in Fig 4 opening switch 48 allows a DC voltage V (from a suitable source of DC 49) to charge up a capacitor 50 via a resistor 52. If the capacitance of 50 is large and the resistive value of 52 is high, the voltage across 50 will only rise slowly with time. The same voltage V is developed across a potentiometer 54 the tapping of which serves as a reference voltage for a differential amplifier 56. The other input to 56 is derived from the junction 58 between 50 and 52.

The amplifier 56 is arranged to generate an output current only when the voltage at 58 exceeds that at the tapping of 54. By adjusting the position of the tapping so the time taken for this to occur can be increased or decreased.

While the timing circuit shown in Fig 4 will allow for a delay of up to 2 or 3 minutes, it is not ideal for longer delays. If longer periods of time are required a pulse generator and digital counter may be employed instead, adapted to produce an output signal when the counter overflows, and adapted to be reset to zero at the start of each delay period.

The output current can be used to drive one or more of a speaker or buzzer or bell or lamp, shown in dotted outline at 60, to produce an audible or visible alarm. It can also be used to operate a relay 62 having a winding 64 and normally closed contacts 66. When the relay operates the normally closed contacts 66 open.

The normally closed contacts 66 are wired in a supply line to the heating element 40 in series with a fuse 68, an ON/OFF switch 70 and the normally closed contacts of the temperature sensing device 46. The power supply 72 is typically the AC mains supply.

Relay 64 is preferably a latching relay which once activated holds contacts 66 open, irrespective of the current flowing through the relay coil, so preventing continued operation of heater 40.

The relay is typically capable of being manually reset.

The alarm 60 may also include a visible display which also latches, to show that an output current has been generated by 56. Alternatively the normally open switch 66 may be a changeover switch, the normally open contacts of which, when closed, connect the AC supply 72 to a bulb 74 in series with a fuse 76. The fuse 76 may be connected as shown, or may be connected to the junction between the switch 70 and fuse 68, so that it is isolated when 70 opened.

It will be seen that when the temperature in 12 drops below the temperature at which 48 operates, the contacts 48 will short out 56 and reduce the voltage across 50 to zero. A discharge resistor 59 may be provided so that the capacitor is not short circuited (which can cause damage) but the relative values of 52 and 59 are chosen so that the resulting voltage across 50, when 48 is closed, is well below that of the tapping of potentiometer 54, so that 56 will revert to its quiescent state and the output current will drop to zero, or a very low value insufficient to operate the alarm device or the relay.

Claims

1. A water heater comprising upper and lower reservoirs in which cold water is stored in the upper reservoir for feeding the lower reservoir which contains water heating means, with an interconnecting passage for transferring cold water from the upper reservoir to the lower to maintain the level therein and an expansion pipe to permit heated water forced out of the lower reservoir by expansion to return to the upper reservoir, wherein means is provided to thermally separate the body of water in the upper reservoir from the expansion pipe to reduce the transfer of heat from the expansion pipe to the water in the upper reservoir, further comprising temperature sensing means for sensing the temperature of the water in the upper reservoir and adapted to produce a response if the temperature of the water therein rises above a predetermined level.

2. A water heater as claimed in claim 1 wherein the sensing means activates an alarm and/or activates valve means to inhibit the flow of water from the lower reservoir.

3. A water heater as claimed in claim 2 wherein the alarm may be visual or audible or both.

4. A water heater as claimed in claim 2 or 3 wherein means is provided for indicating to the user why the system will not allow hot water to flow therefrom.

5. A heater as claimed in any of claims 1 to 4 wherein the temperature sensing means is adapted to control the operation of the heating means in the lower reservoir, to turn it off if an over-temperature condition is sensed in the upper reservoir.

6. A water heater as claimed in any of claims 1 to 5 wherein means is provided for integrating the temperature excess with time and the generation of an alarm and/or the inhibition of hot water flow from the lower reservoir, and/or the turning off of the

heating means in the lower reservoir, is deferred until the integration reaches a predetermined value.

7. A water heater as claimed in any of claims 1 to 6 wherein the temperature sensing means comprises a metal alloy junction or semiconductor device whose electrical characteristics vary with temperature.

8. A water heater as claimed in any of claims 1 to 7 wherein the temperature sensing means comprises an electrical circuit which includes a device whose electrical charactristics change with temperature, and the circuit generates an electrical control signal in response to a change in those characteristics indicative of an excess of temperature above the said predetermined level.

9. A water heater as claimed in claim 8 wherein the electrical circuit includes a timing device which is reset when the temperature condition is exceeded and if the temperature is still in excess of the predetermined value after the tinning device has timed out to a predetermined interval of time, a control signal is generated.

10. A water heater as claimed in any of claims 1 to 9 wherein the alarm is generated proximate to the installation.

11. A water heater as claimed in any of claims 1 to 9 wherein the alarm is generated at a remote location.

12. A water heater as claimed in claim 11 wherein an identifying signal is transmitted with the signal generating the alarm, to indicate where the installation is located in which the upper reservoir water temperature has triggered the alarm.

13. A water heater as claimed in any of claims 1 to 9 adapted to monitor whether the water temperature in the upper reservoir has exceeded the predetermined level during a

period of time, wherein a latching temperature sensing means is used, which only activates if the design temperature for die upper reservoir has been exceeded.

14. A water heater as claimed in claim 13 wherein the latching temperature sensing device includes or comprises a visible chemical composition or device which changes colour or changes from transparent to translucent, or becomes opaque, if its temperature rises beyond a given temperature.

IS. A water heater as claimed in any of claims 1 to 14 wherein the means to thermally separate the body of water in the upper reservoir from the expansion pipe comprises a sleeve which surrounds the expansion pipe to at least the depth of the water in the upper reservoir.

16. A water heater as claimed in claim 15 wherein the sleeve is spaced from the expansion pipe by an air gap, and forms around the expansion pipe an annular chamber.

17. A water heater as claimed in claim 16 wherein the annular chamber is open at its upper end and closed at its lower end.

18. A water heater as claimed in claim 15, 16 or 17 wherein the sleeve is formed from thermally insulating material.

19. A water heater as claimed in claim 15 wherein the sleeve is formed from thermally insulating material and is in contact with the expansion pipe.

20. A water heater as claimed in claim 17 wherein a drain is provided for draining any water which collects in the annular chamber around the expansion pipe.

21. A water heater as claimed in any of claims 15 to 20 wherein the expansion pipe at least where it extends into the upper reservoir is formed from a material having low thermal conductivity relative to that of copper.

22. A water heater as claimed in claim 15 wherein the expansion pipe is formed from metal and the sleeve is cylindrical and is also formed from metal and has an internal diameter which is substantially greater than the outside diameter of the expansion pipe and extends from the base of the upper reservoir to a height therein which is greater than the depth of water in the upper reservoir, the sleeve and the pipe being coaxially arranged so that the sleeve is spaced from the pipe by the same distance around the whole of its circumference, and the spacing is selected so as to ensure that under normal conditions, with the annular space between the pipe and the sleeve filled with air, the transfer of heat from the wall of the pipe to the wall of the sleeve is insufficient to cause any significant rise in temperature of the water in the upper reservoir which surrounds the sleeve.

23. A water heater as claimed in claim 22 wherein a collar of a material having a low thermal conductivity relative to that of copper surrounds the expansion pipe where it extends through a wall of the upper reservoir, to separate the pipe from the wall.

24. A water heater as claimed in claim 23 wherein a similar collar of a similar low thermal conductivity material surrounds the feed pipe from the upper reservoir to the lower reservoir, around the pipe where it extends through a wall of the upper reservoir, to separate the pipe from the wall.

25. A water heater as claimed in any of claims 15 to 24 wherein the upper end of the expansion pipe is bent over to form an inverted U-bend, or is otherwise extended, so that if water is forced up the expansion pipe due to excess temperature in the lower reservoir, it will be discharged in a generally downward direction, clear of the sleeve.

26. A water heater as claimed in any of claims 15 to 25 wherein the level of cold water in the upper reservoir is maintained at a predetermined level by water level responsive

valve means which permits the inflow of cold water into the upper reservoir only if the level of water therein is below the said predetermined level.

27. A water heater as claimed in claim 26 wherein the valve means is a float operated valve.

28. A water heater as claimed in claim 1 constructed arranged and adapted to operate substantially as herein described with reference to the accompanying drawings.