GB2290602A - Hot water tank with electrically heated jacket - Google Patents

Abstract

The apparatus includes a copper water tank 2 around which is arranged a heating device 12 for heating liquid in the tank. The device includes electrically insulating, but thermally conductive, sheets (16, 18) between which electrical resistance wire 14 is arranged. When current is supplied to the wire 14, heat is dissipated thereby and conducted through the tank wall to heat water in the tank. A thick, thermally insulating sheet 34 restricts loss of heat to the outside. The wire is arranged as shown in Fig. 3 so that 60% of the heat output of the device is emitted in the bottom third. Suitable materials for the various sheets of the device are given. <IMAGE>

Description

HEATING APPARATUS This invention relates to a heating apparatus and particularly, although not exclusively, relates to a heating apparatus for heating a fluid, for example water in a domestic hot water storage tank.

Known hot water storage tanks include an electrical resistance heating element positioned within the tank, towards an upper end thereof. The element is arranged to heat water in the tank to a high temperature in the range 800C to 90"C. When heated water is standing in the tank ready for use, it loses heat at a relatively high rate.

Additionally, before use by a person, the water must be cooled by adding cold water. Both of these factors highlight the inefficiency of known hot water storage tanks.

Furthermore, the heating elements of known hot water storage tanks are integral components thereof, and cannot easily be replaced or transferred to other tanks for heating fluids therewithin.

It is an object of the present invention to provide a heating apparatus which may alleviate some of the problems associated with known heating apparatus.

According to the invention, there is provided heating apparatus for a fluid, the apparatus comprising a receptacle for fluid and an electric heating device, the device being associated with an outside face of the receptacle for heating fluid in the receptacle.

The device is preferably held against an outside face of the receptacle. The device is preferably held against an outwardly facing wall of the receptacle. The device may be held against a circumferential wall of the receptacle.

For example, the receptacle may be cylindrical and the device may extend circumferentially around the cylindrical wall. The cylindrical receptacle is preferably circularly cylindrical. The device is preferably in the form of a jacket which extends around the receptacle.

The device is suitably arranged to conduct heat to the receptacle.

The receptacle is preferably for a liquid. The receptacle preferably includes an inlet for cool liquid and an outlet for heated liquid. Preferably, the receptacle is a domestic water storage tank arranged to supply heated water to domestic appliances, for example baths, showers and wash basins.

Said device is preferably arranged to be releasably secured to the receptacle. Said device is preferably arranged to be moved between a first extended state in which it may be arranged substantially flat and a second reduced state in which it may be arranged around the receptacle.

Preferably, the heating device includes a resistive element arranged to become heated when a current passes therethrough. Said resistive element preferably comprises a metal or metals. Preferably, said resistive element comprises an alloy of, for example, iron, chromium and aluminium. Said resistive element preferably comprises a wire.

Said heating device is preferably arranged to deliver more heat to a lower part of the receptacle than to an upper part of the receptacle. Where the device includes a resistive element, preferably a greater area and/or a greater length of resistive element is adjacent the lower part of the receptacle than adjacent the upper part of the receptacle. Preferably, the resistive element is of substantially constant cross-section along its length and the element comprises a multiplicity of turns, wherein turns adjacent the lower part of the receptacle are closer to one another than turns adjacent the upper part of the receptacle.

Said heating device preferably comprises a first electrically insulating member which is positioned between the receptacle and the resistive element. Said first electrically insulating member is preferably in the form of a panel. Said panel preferably overlies the resistive element. Said panel is preferably made of a sheet material. Said panel is preferably made of a flexible and/or elastic material. Said resistive element is preferably secured to the first electrically insulating member, for example by adhesive means.

Said heating device preferably also includes a second electrically insulating member, suitably in the form of a panel. Said resistive element is preferably secured to the second insulating member, for example by adhesive means.

Said resistive element is preferably positioned between said first and second electrically insulating members.

Said first and/or said second electrically insulating members may have an electrical resistivity at 230C of greater than 0.1 Ohms.cm. Preferably, the resistivity is greater than 1.0 Ohms.cm and is, more preferably, greater than 5.0 Ohms.cm.

Said first and/or said second electrically insulating members are preferably thermally conductive. The thermal conductivity of the members may be greater than 0.05 Wm1 K1.

Said first and/or said second electrically insulating members preferably can resist temperatures of at least 5000C and, more preferably, of at least 6000C.

Said first and/or second electrically insulating members preferably independently have a width of at least 0.1 mm and, more preferably, of at least 0.15 mm. The width is preferably less than 20 mm, more preferably less than 10 mm.

Said first and/or second electrically insulating members are suitably made of a micanite material.

Said heating device preferably includes a thermally insulating layer arranged between the resistive element and the outside. Said thermally insulating layer is preferably arranged to restrict the passage of heat from the resistive element to the outside. Thus, the device is arranged so that heat can flow predominantly to the receptacle and the fluid therein.

The device is preferably arranged to heat fluid in the receptacle to at least 300C and, more preferably, to at least 400C. The device preferably includes control means for controlling the temperature of fluid in the receptacle. Said control means may be operable to limit the temperature of fluid within the receptacle to less than 90 C, preferably to less than 75"C and, more preferably, to less than 600C.

The invention extends to a method of heating fluid in a receptacle, the method comprising associating an electric heating device with an outside face of the receptacle so that the heating device is arranged to heat fluid in the receptacle.

The invention extends to a method of converting an existing receptacle for fluid to a heating apparatus as described above, the method comprising associating an electric heating device with an outside face of the existing receptacle so that the heating device is arranged to heat fluid in the receptacle.

The invention extends to a central heating system including a heating apparatus as described herein in combination with a space heater, for example a panel heater.

The invention extends to an electric heating device arranged to be associated with an outside face of a receptacle for heating fluid in the receptacle Der se.

The invention extends to the use of an electric heating device for heating fluid in a fluid receptacle.

Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side elevation, partly in cross-section of a heating apparatus including a water tank and a heating device; Figure 2 is a top plan view of the apparatus of Figure 1; Figure 3 is a plan view partly in cross-section of the heating device in an extended state; Figure 4 is a cross-section along line IV-IV of Figure 3 (with details omitted in the interests of clarity); and Figure 5 is a detailed view of the area within region V of Figure 5.

Referring to Figure 1, the apparatus includes a water tank 2 of standard design, in that it is made of copper and has a water inlet 4 towards its lower end 6 and a water outlet 8 at its top end 10. The heating device 12 of the apparatus is in the form of a jacket which is wrapped circumferentially around cylindrical outside wall 14 of the tank 2 and secured in position. The heating device 12 includes an electrical resistance heating element which is arranged to become heated when a current is flowing through. The device is arranged to conduct the heat to the outside wall 14 of the tank which, in turn, conducts heat to the water in the tank.

The apparatus is described in greater detail below.

The heating device 12 comprises electrical resistance wire 14 located between sheets 16, 18 which are formed from a material which is electrically insulating but is reasonably thermally conductive. Electrical connectors 20, 22 are provided for connecting a power supply to the wire 14.

The resistance wire 14 is suitably made of an alloy of iron, chromium and aluminium. One such wire is sold by IMI Scott Limited under the Trade Mark CROMALOY A. The properties and length of the wire used are selected according to the heat output required. For a 500W heating device, a 5.95m length of 0.30mm diameter wire having a resistivity of 18.86 ohms/metre may be used.

The resistance wire 14 is arranged in the convoluted pattern shown in Figure 3 so that the heat emitted per unit area of the device increases on moving from the top 24 to the bottom 26 of the device. In this respect, it will be noted from Figure 3 that the spacing between adjacent turns of the wire 14 decreases on moving from top 24 to the bottom 26.

The device 12 is suitably arranged so that about 60% of its heat output is emitted by the resistance wire 14 disposed in the lowest third of the device.

The sheets 16, 18 of the heating device 12 are formed from 0.2 mm thick sheets of PERMIC 505.3 (Trade Mark) which is a bonded multi-layer rigid micanite material obtainable from COGEBI of Huysmanlann 65, B1651 LOT, Belgium. The material is able to resist 700"C in continuous service and can intermittently be raised to 8000C and beyond, without adverse effect. The electrical resistivity of the material at 230C is greater than 10 ohms.cm. The material also has reasonable thermal conductivity of about 0.3 Wm1K1.

The resistance wire 14 is fixed between the sheets 16,18 by respective flexible ceramic carrier sheets 26, 28 each of which is coated on both sides with an acrylic based adhesive material 30. Such coated ceramic sheet is sold under the trade Mark APOLLO.

A 5mm thermal insulation sheet 34 of Micropore (Trade Mark) insulation material is fixed on the outside face of sheet 16 by means of an adhesive coated carrier sheet 32 of the type described above.

The heating device 12 is made as follows. Carrier sheet 28 is secured by means of its lower adhesive layer 30 to the sheet 18. Then, wire 14 which has been wound into the desired configuration in a jig, is applied to the upper adhesive layer 30 of carrier sheet 28. The carrier sheet 26 is then secured by means of its lower adhesive layer 30 to the sheet 16 and then its upper adhesive layer is pressed against the wire 14. The arrangement is pressure rolled to secure the layers together. The sheet 16 and the carrier sheet 26 includes 7 mm holes (not shown) aligned with connectors 20, 22 of wire 14 in order to allow a power supply to be connected to the wire. The thermal insulation sheet 34 is subsequently secured by means of carrier sheet 32 to the sheet 16.

The assembly described is then housed in a nylon or similar material envelope. One transverse end, e.g. end 40, of the envelope is stitched to a moulded plastics box (not shown) which houses a thermostat, neon "on/off" light, switched receiver/transmitter unit and electrical connections, including a fly earth wire.

Fixing strips (not shown) are secured, by stitching, to the other transverse end, e.g. end 42, of the envelope.

The fixing strips are resilient and are arranged to pass through and be secured within openings in the moulded box in order to securely fix the device 12 in position around a tank.

The device 2 may be arranged around an existing hot water tank 2 with sheet 18 closest to the tank wall. The device is secured in position using the resilient fixing strips.

In use, power is supplied to the wire 14 so that it heats up. Heat is conducted from the wire, through sheet 18, to the wall of the tank. The wall of the tank then conducts heat to the water in the tank. Since the heat emitted per unit area of the device increases on moving from the top 24 to the bottom 26 of the device, the water towards the bottom of the tank is heated more rapidly than that higher up. Consequently, heated water from the bottom of the tank is convected upwardly and water from the top of the tank moves downwardly, leading to turbulence in the tank and, therefore, a more rapid heating of the whole body of the water in the tank.

The device 2 is arranged to heat the mass of water in the tank to a temperature of about 50"C to 550C and the thermostat of the device controls the supply of power to the wire 14 to maintain the water in this temperature range. It should be appreciated that lower energy is required to maintain the water in the stated range compared to the known arrangements wherein the temperature may be maintained in the range 8 OOC to 90 C and, furthermore, the heated water can be used in, for example a bath, without the need for the water to be cooled by addition of cold water.

When wire 14 of the device heats up, it expands slightly. It is important for spaced apart elongate parts 40 of the device not to move laterally to any appreciable degree since there will be a risk that such movement may result in the parts fusing together which will affect the effective resistance of the wire. As shown in Figure 5, the lateral movement is restricted by sheets 26, 28 being slightly curved around the wire.

Devices 2 may be manufactured in different sizes for use with tanks of different sizes. Although a device 2 has been described for securement circumferentially around a circularly cylindrical water tank, a device 2 may be arranged to be secured around a tank of any shape or size.

Furthermore, a device 2 may be provided in the form of a pad arranged to be secured to a face of a vessel to which it is desired to supply heat. For example, a device 2 may be secured to a wall of a diesel fuel tank in order to stop the fuel freezing in cold weather conditions.

The device 2 includes a switched receiver/transmitter unit as mentioned above. The unit communicates with a central control unit, suitably using mains borne signalling operating in conformity with EN 50065-1:1992.

A user may, using the central control unit, programme the device 2 to operate when desired, in order to make maximum use of off-peak electricity tariffs.

The device 2 may be integrated into a central heating system which may also include electric panel heaters each being controlled by the central control unit.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (25)

1. A heating apparatus for a fluid, the apparatus comprising a receptacle for fluid and an electric heating device, the device being associated with an outside face of the receptacle for heating fluid in the receptacle.

2. Apparatus according to Claim 1, wherein the device is held against an outside face of the receptacle.

3. Apparatus according to Claim 1 or Claim 2, wherein the device extends around a circumference of the receptacle.

4. Apparatus according to any preceding claim, wherein the receptacle is cylindrical.

5. Apparatus according to any preceding claim, wherein the receptacle is a domestic water storage tank arranged to supply heated water to domestic appliances.

6. Apparatus according to any preceding claim, wherein the device is arranged to be releasably secured to the receptacle.

7. Apparatus according to any preceding claim, wherein the device is arranged to deliver more heat to a lower part of the receptacle than to an upper part of the receptacle.

8. Apparatus according to any preceding claim, wherein the device includes a resistive element of substantially constant cross-section along its length, wherein the element comprises a multiplicity of turns with turns adjacent the lower part of the receptacle being closer to one another than turns adjacent the upper part of the receptacle.

9. Apparatus according to Claim 8, wherein the device comprises a first electrically insulating member which is positioned between the receptacle and the resistive element.

10. Apparatus according to Claim 9, wherein said resistive element is secured to the first electrically insulating member.

11. Apparatus according to Claim 9 or Claim 10, wherein the device includes a second electrically insulating member arranged so that the resistive element is positioned between said second member and said first member.

12. Apparatus according to Claim 11, wherein said first and/or said second electrically insulating members have an electrical resistivity at 230C of greater than 0.1 Ohms.cm.

13. Apparatus according to Claim 11 or Claim 12, wherein said first and/or said second electrically insulating members have a thermal conductivity of greater than 0.05cm1 K'.

14. Apparatus according to any preceding claim, wherein said device includes a thermally insulating layer arranged outside a or said resistive element.

15. Apparatus according to any preceding claim, wherein the device is arranged so that heat can flow predominantly in a direction towards the receptacle and the fluid therein.

16. Apparatus according to any preceding claim, wherein the device includes control means for controlling the temperature of fluid in the receptacle, said control means being operable to limit the temperature of fluid within the receptacle to less than 900C.

17. A method of heating fluid in a receptacle, the method comprising associating an electric heating device with an outside face of the receptacle so that the heating device is arranged to heat fluid in the receptacle.

18. A method of converting an existing receptacle for fluid to a heating apparatus according to any of Claims 1 to 16, the method comprising associating an electric heating device with an outside face of the existing receptacle so that the heating device is arranged to heat fluid in the receptacle.

19. A central heating system including a heating apparatus according to any of Claims 1 to 16 in combination with a space heater.

20. An electric heating device arranged to be associated with an outside face of a receptacle for heating fluid in the receptacle Per se.

21. Apparatus substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.

22. A method of heating fluid substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.

23. A method of converting an existing receptacle substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.

24. A central heating system substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.

25. An electric heating device substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.