WO2009040558A2

WO2009040558A2 - An improved water heater

Info

Publication number: WO2009040558A2
Application number: PCT/GB2008/003307
Authority: WO
Inventors: Andrew Hunt
Original assignee: Baxi Heating (Uk) Limited
Priority date: 2007-09-27
Filing date: 2008-09-26
Publication date: 2009-04-02
Also published as: WO2009040558A3; GB0718985D0; EP2205907A2; WO2009040558A9; GB2456289A

Abstract

An electric heating element (20), the element (20) comprising; an electrically non-conducting support comprising a plurality of segments (22), each segment (22) being moveably connected to two neighbouring segments (22) and capable of one dimensional motion in respect thereto, the outer surface of each segment (22) including a ridge (27) extending helically about the segment (22), the ridges (27) of neighbouring segments (22) co-operating together to form a helical channel a first electrically resistive wire (21) heating portion helically wound about the support within said helical channel, the segments (22) defining a further channel along the axis of the helix, said further channel retaining a second electrically resistive wire (21) heating portion spatially separated from the first resistive wire portion, the first and second portions being operatively connected to define an electrical pathway.

Description

AN IMPROVED WATER HEATER

Field of the Invention

The present invention relates to the field of domestic and industrial hot water heaters. Li particular, the invention concerns a heating element for use in such heaters.

Background to the Invention

A large proportion of domestic and small industrial water heaters, heat the water by means of a resistive electric element. Such heaters are typically used to supply hot water for the water supply and also for use as a thermal carrier for a heating system within a building.

In order to prevent the element from coming into contact with the water, the element is housed within a tubular casing made of a thermally conductive material. As such materials are normally also electrically conducting steps also need to be taken to keep the element away from the casing.

This arrangement does however lead to difficulties during maintenance work carried out on the boiler; the maintenance work can be carried out either on a routine basis or to address a problem which has arisen with the boiler.

The principal difficulty is due to the need to gain access to the element without causing damage thereto. Where the casing is rectilinear then the problem is not too great. However many casings, in order to improve the efficiency and power of the heater are curved. Unless care is taken when designing the curves, it is difficult, if not impossible to remove or insert the element without causing damage. The result is that time is expended and a replacement element and casing is often required. Many conventional elements are formed into a loop for convenience of allowing current to enter and leave the element. The loop allows the entry and exit points to be located in close proximity to each other. Such loops however can on occasions cause difficulties, as objects can easily snag on them.

It is an object of the present invention to address the above problems and provide a more serviceable yet flexible heating element.

Summary of the Invention

According to a first aspect of the invention there is provided an electric heating element, the element comprising

a non-conducting support comprising a plurality of segments, each segment being moveably connected to two neighbouring segments and capable of one dimensional motion in respect thereto, the outer surface of each segment including a ridge extending helically about the segment, the ridges of neighbouring segments co-operating together to form a helical channel

a first electrically resistive wire heating portion helically wound about the support within said channel,

the segments defining a further channel along the axis of the helix, and retaining a second electrically resistive heating portion, the first and second portions being operatively connected to define an electrical pathway.

The above arrangement provides a flexible element which can be easily inserted into and held in spaced arrangement from a curved element housing.

The element does not moreover require a looped housing as the outward and inward current sections are maintained within the same structure. The segments are preferably formed of a ceramic material and are therefore robust and capable of withstanding high temperatures.

Brief Description of the Drawings

The invention will now be described with reference to and as illustrated by the accompanying drawings which show by way of example only one aspect of a heating element. In the drawings:

Figure 1 illustrates a water heater, known from the prior art;

Figure 2 illustrates an element housing;

Figure 3 is an expanded view of the support shown in Figure 2, including a heating wire;

Figure 4a and 4b are perspective views of a segment of an element; Figure 5 is a perspective view of a casing; and

Figure 6 illustrates an element and casing within a water heater.

Detailed Description of the Invention

The general layout of a water heater 10 is shown in Figure 1.

The heater 10 comprises an outer steel casing 11 which houses and supports amongst other things, a water tank 12. Typical volumes retained by the water tank are from 50-1000 litres. The water heater for which the invention is suited can be of the type known as a mains unvented heater but also a low pressure vented heater. Often a baffle is provided floating on the surface of the water to reduce absorption of the air in the gap into the water.

Two elements 13,14 are provided in the tank 12 to ensure even heating of the water volume. The lower of the two elements 14 is curved into a right angled configuration and inserted into the water such that the free arm of the element 14 is orientated vertically downwards. This configuration allows firstly for a longer element to be provided and therefore a greater heat flux into the water.

Secondly, water is heated both across the tank 12 and at different depths within the tank 12. This latter feature is particularly useful, due to the higher density of cold water which would otherwise remain in the unheated region at the bottom of the tank 12.

Curved resistive-heating elements are however difficult to form particularly where the current carrying part of the element is of appreciably thickness.

Moreover, the water must of course be kept away from direct contact with the electric current. Conventionally therefore, the element is housed within a heat conductive sheath, usually made of steel. This leads to the additional problem that the element itself needs to be separated from the conductive metal sheath and so prevent short circuits. Since air is an efficient insulating material, spatial separation of the element from the sheath is sufficient.

A difficulty therefore arises when carrying out maintenance work. In order to inspect the element this needs to be withdrawn from the sheath. Unless both the element and the sheath have the same, constant curvature then withdrawal and reinsertion will be very difficult. The element in Figure 1 usually needs to be completely removed and replaced, and because it is in the form of a loop the element is only extracted with difficulty.

The element housing and element 20 shown in Figures 2 and 3 overcome the above difficulties by providing a flexible protective housing for a resistive-type heating wire 21. The element 20 has a series of ceramic support segments 22. The central portion 23 of a segment is generally cylindrical in shape defining an outer surface 24 on which the wire 21 can rest. Ceramic materials are suited to the task of providing a support as they are both electrically insulating and also capable of withstanding the high temperatures generated by the passage of current. Moreover, the precursor materials can be moulded into the shapes required, yielding upon final treatment a hard, robust ceramic.

As illustrated more clearly in Figure 4, one end of the segment 22 extends outwardly in the form of a half disc 25 The opposite end of the segment 22 has a recess 26 of complementary size and shape to accommodate the disc 25 when in use.

The segment 22 further comprises a rigid portion of a helix flight 27. In the example illustrated each segment includes one full turn of the flight, but the number of turns can be chosen to suit the particular task. As can be seen from

Figure 3, neighbouring segments 22 are so aligned that the flights 27 join up to form a continuous helix. If required, the segments can include, for example, notches and protrusions to facilitate correct alignment.

The helical flights 27 define a helical channel shown by arrow A in Figure 2 in which a heating wire 21 is located. The individual turns of the wire 21 are thereby separated from one another by the flights, ensuring that short circuits do not occur. Moreover the helix flights 25 prevent the wire 21 from touching an outer protective casing, again preventing short-circuits.

Each segment 22 also defines a substantially cylindrical hole 28 along its central axis, each hole 28 being of a sufficient breadth to accommodate the heating wire 21. The holes 28 combine together, when the segments 22 are linked together, to form a channel along the length of the element 20. The channel thereby formed houses the return portion of the wire 21. It will be appreciated that the two portions of the wire 21 will normally be parts of the same wire, formed into the appropriate shape. Where required however, the two portions can be separate wires joined together at a junction within the element 20.

In the above embodiment therefore, the return portion of the wire 21 is separated from the outward portion residing on the helical channel. The free ends of the wire 21 can be housed in a suitable plug and socket arrangement enabling easy connection with the other parts of the heater and with the mains electricity supply. The element 20 is flexible and can be fitted easily into a curved casing without the need for the casing having a loop to accommodate the return portion of the wire.

When required therefore, an assembled element is pushed inside a heat conductive casing 50, as illustrated in Figure 5. Any one dimensional curvature of the casing can be easily handled due to the relative motion possible between neighbouring segments. The conductive wire is protected from the casing due to the profile of the ceramic segments and their combining together to form a channel in which the wire sits.

The completed assembly can be seen in Figure 6 in which the casing 50 and element 20 are shown in section within a water tank 12.

In order to service the element, the reverse procedure is carried out. To do this the casing, along with the element, can be removed from the heater. Alternatively, the element can be removed with the casing still in situ within the heater. Once inspection has taken place, the element can be replaced.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention.

Claims

1. An electric heating element (20), the element (20) comprising;

an electrically non-conducting support comprising a plurality of segments

(22), each segment (22) being moveably connected to two neighbouring segments (22) and capable of one dimensional motion in respect thereto, the outer surface of each segment including a ridge (27) extending helically about the segment, the ridges (27) of neighbouring segments (22) co-operating together to form a helical channel

a first electrically resistive wire (21) heating portion helically wound about the support within said helical channel,

the segments (22) defining a further channel along the axis of the helix, said further channel retaining a second electrically resistive wire (21) heating portion spatially separated from the first resistive wire portion, the first and second portions being operatively connected to define an electrical pathway.

2. An element according to Claim 1, wherein the support is formed of a ceramic material.

3. An element according to Claim 1 or Claim 2, wherein the helical ridge (27) on each segment describes an integer number of turns.

4. An element according to Claim 3, wherein the helical ridge (27) describes a single turn.

5. An element (20) according to any preceding Claim wherein each segment has at a first end a projection (25) and at a second end a recess (26) of complementary shape to the projection, the projection (25) engaging with the recess (26) of a neighbouring segment enabling, relative one- dimensional motion of the two segments.

6. An element according to Claim 5 wherein the projection (25) is a semi- circular disc.

7. An element according to either Claims 5 or Claim 6, wherein the projection includes an aperture (28) allowing passage therethrough of the second resistive wire.

8. An element according to Claim 7, wherein the projection is hollow.

9. An element according to any preceding claim wherein the resistive wire is continuous within the element (20).

10. An element substantially as herein described with reference to the accompanying drawings.