IE20180514A1 - An instantaneous electric water heater, a heat exchanger and an electric shower - Google Patents

Abstract

An instantaneous electric water heater having a heat exchanger comprising a generally helical heating element (14, 15) disposed within a chamber (12), the chamber (12) being in fluid communication with a water inlet (13a) and a water outlet (13b), and a flow diverter (20) to divert an incoming water flow towards the heating element (14, 15) in a direction substantially parallel to the axis of the helix, or to the main axis of the chamber (12).

Description

Field of the invention This invention relates generally to the field of electric showers and associated water heaters and relates, more specifically, to heat exchanger configurations which are used as part of such arrangements.

Overview of the Prior Art lnstantaneous electric water heaters, of the type which provide heated water on request, are found commonly in domestic sanitarylablutionary environments, in showers, hand wash heaters and the like. In simple terms, the electrical power input and/or flow rate of the water can be adjusted in order to regulate an outlet temperature, with a variety of electric heating elements being known, to perform the water heating operation.

Typically, the electric heating element takes the form of a helical or spiral device, so as to maximise the “heating” surface area, within a given surrounding space - the chamber, or “heater can”. Differing configurations of helical heating elements are known, with the most common being an arrangement in which one is situated above the other. Power can be applied to either of the elements individually, or to both, thus regulating the total heating power which is available to the incoming water, within the chamber.

It is important for the water flowing within the chamber to be heated as uniformly (i.e. evenly) as possible, because areas of stagnant flow give rise to “hot spots” on adjacent parts of the heating element, which can precipitate early failure of the element, and create undesired and excessive build up of scale. It is also important for the flowing water to come into contact with as much of the external surface of the heating element as possible, so as to maximise the heat transfer which occurs between the element, and the incoming water.

A significant amount of the known prior art is concerned with a helical flow of water through the heater can, whereby the speed and direction of the flow around the outside of the heating element induces a flow from inside the coils.

This can reduce the build up of heat where there is no direct flow. With such arrangements the positioning of the water inlet connection to the heater can is vital, to obtain the optimum flow path.

Summarv of the Invention In accordance with a first aspect of the present invention, a heat exchanger for an instantaneous electric water heater having first and second electric heating elements, each substantially in the form of a double helix, the turns of the first and second elements being of different diameters, and with at least part of the smaller diameter helix being disposed within and substantially concentric and substantially coaxial with, the larger diameter helix. in accordance with a second aspect of the present invention, we provide an instantaneous water heater comprising heater exchanger according to the first aspect of the invention. in accordance with a third aspect of the present invention, we provide an electric shower comprising any of the features of the first or second aspects of the invention.

Further features of the first, second and third aspects of the invention are set out in the various claims appended hereto.

Detailed Description of the invention and Overview of the Drawings Specific but non—limiting embodiments of the present invention will now be described in further detail, but strictly by way of example only, by reference to the accompanying drawings, of which FIGURE 1 is a perspective, cut away view of an instantaneous electric water heater in accordance with the invention; FIGURE 2 is a cutaway, front view of the arrangement of Figure 1; FIGURE 3 is a sectional view of the arrangement of Figures 1 and 2; FIGU RE 4 is a perspective view, in enlarged form, of the flow diverter shown in Figures 1 to 3; FIGURE 5 is a perspective view of one of the heating elements shown in Figures 1 to 3; and FIGURES 6, 7 and 8 are computer generated flow/temperature images to illustrate water flowpaths and water temperatures, at different positions in the heat exchanger shown in Figures 1 to 3, and at different power settings.

Referring first to Figure 1, there is shown a heater can assembly 10 of the type which is commonly used in instantaneous water heaters, such as electric showers. As such heater cans are well known in this field, as are the other component parts of water heaters/electric showers, such other components are not shown in this description, but it will of course be clear to one skilled in the relevant art as to how the elements of the present invention can be incorporated into (and co-operate with) such a heater/shower arrangement.

The heater can assembly comprises a housing 11 which defines an internal chamber 12, through which water passes during the heating process.

Incoming (i.e. cold/substantially unheated water) enters the chamber via a tangentially disposed inlet 13g and exits the chamber at 131;. As explained below, the tangential nature of the inlet is not necessary —— other inlet directions will also function perfectly well. in generally conventional manner, the incoming water flows up the inside of the chamber 12, over the heating elements 14 and 15 which, in this embodiment, are both in the form of a double helix. in generally conventional manner, the helical heating elements are made up of a coil/length of resistance wire, held within a protective sheath, with the sheath containing an electrically insulating component such as a compressed MgO (magnesium oxide) powder.

Whilst the illustrated double helix configuration is preferred, other generally helical configurations are also possible. In addition, it is not necessary for there to be two elements, in conjunction with the flow diverter (20), as explained below.

The free ends 14a_, 14_b, 15a_ and 15b of the elements are all disposed towards the top of the chamber 12, by virtue of the “returned” configuration of the helices, as shown more clearly in Figure 5.

As shown most clearly in Figures 2 and 3, the incoming water, having been heated during its upward flow (over and around the elements 14 and 15), then passes over a “weir” configuration (shown generally at 16), before passing back down through the centre of the chamber, via an outlet tube 17, towards the outlet 13b. in this example, the heater can assembly 10 has a generally cylindrical configuration, with the outlet tube 17 being substantially coaxial with the body of the chamber 12.

The arrangement further comprises a flow diverter 20, in the form of a perforated plate 21, featuring a number of apertures 22 which extend therethrough. The plate 21 is disposed, in use, above the level of the water inlet 13a, such that the incoming water (directed in this specific example generally tangentially, as it enters through inlet 13a) first enters a diverting chamber 23 before it can pass through to the main body of the heat exchanger chamber 12.

The plate 21 has an outer edge 24 which, although not shown in the figures, is a very close fit against the internal surface of the lower part of the chamber 12. This means that the vast majority of the water which enters through the inlet 13a_ passes through to the main body of the chamber 12 through the various apertures 22, in the plate 21. Some water (a very small proportion of the overall incoming flow) may pass through the small gap between the edge of the plate and the wall of the chamber, but this has no noticeable effect on the operation of the flow diverter, or the successful performance of the invention. A watertight fit (perhaps using a peripheral seal) is also envisaged, however.

Around the outer edge 24 of the plate 21 are disposed a number of upstanding legs 25 which serve as spacers, as described below. The central part of the flow diverter 20 comprises an upstanding collar 26 which (as shown best in Figures 1 and 4) is provided with a number of radially—outwardly extending fins 27.

As shown best in Figures 1 and 4, the plate 21 is generally circular in configuration, with the apertures 22 lying generally on two concentric circles, with one set of apertures being further radially spaced from the centre than the other.

The effect of this is that unheated water, which is incoming through the inlet 13g, passes through the apertures 22 substantially as a number of ‘‘linear columns”, such that the initial transverse/tangential direction (in this specific example) of the incoming water is translated (diverted) to a generally upward direction, with no (or a minimal) lateral component.

What this means, in practice, is that the water entering the main body of the chamber moves into and through the chamber in a direction which is substantially parallel to the axis of the helix — which, in this example, is coincident with the main vertical axis of the chamber.

The disposition of the two concentric sets of apertures (in the plate 21) means that it is possible to guide the incoming water flow towards particular parts of the heating elements, which are positioned above the flow diverter 20. in this preferred embodiment, the two heating elements 14 and 15 (both having a double helix configuration) are “nested” together, with the diameter of the element 14 being greater than the diameter of the element 15. This gives rise to a heating element having a quadruple helix configuration. As Figure 3 makes especially clear, the effect of this is that the “inner” heating element 15 is able to move axially, relative to the heating element 14, because the lateral distance between the outermost parts of the turns of the inner element 15 is less than the lateral distance between the innermost parts of the turns of the outer element 14. This permits a sliding (translational) movement of one, within the other. This not only facilitates manufacture/installation of the two double-helical heating elements, but also ensures that no direct contact occurs between the turns of the elements, thus allowing unimpeded water flow over, and between them. It will be understood that other relative lateral distances might prevent sliding/translational movement, but the applicants have found that relative axial movement is still possible, by rotating one of the elements with a “screwing” action. This allows the two elements to become “nested”.

As Figure 3 makes clear, the radial positions of the apertures 22 have been chosen to correspond with the radial positions of the turns of the two elements 14 and 15.

This means that the (substantially linear flowing) water, passing through the apertures 22, will come into immediate contact with the turns of the elements, thus maximising the heat transfer which can then occur.

The substantially linearlaxial flow then continues, meaning that the water remains in contact with the elements for longer, providing an improved degree of heat transfer.

In more detail, the applicants understand that a flow pattern emerges which, although substantially linearlaxial (in that the water moves without any substantial degree of rotational or lateral movement), can best be described as “slalom-like”. By this, it is meant that the water flows between the inner and outer turns of the two elements (see Figure 3, for example), with the water flowing (in part) around and over the outside surfaces of the inner element, and around and over the inside surfaces of the outer element. This is shown (schematically) by the broken line “S” in Figure 3. Because the water effectively flows overlaround both the elements 14 and 15, the applicants have found that, even with only one element energised (i.e. using a “half power” setting), significant and effective heat transfer can still be achieved, providing a suitable (and adequate) temperature of hot water, at the outlet. lt will be understood that directlexact alignment of the apertures and turns is not required, and that a substantial benefit can still be obtained if there is some “overlap” in terms of the radial position of the apertures and the elements’ turns.

As shown in particular in Figures 2 and 3, the legs 25 (formed from a high melting point material such as a polysulphone - PPS —— as is the rest of the flow diverter 20) upstand from the plate 21 (at its outer edge) and serve as a spacer, preventing the turns of the heating elements from coming into contact with the walls of the housing 11.

The central collar 26 of the flow diverter also serves a useful purpose, in that it can receive the outlet tube 17 through its central passage 26_a. Thus, during manufacture, the central passage 26g can either be used a guide (to receive the outlet tube 17) or, where the outlet tube is preinstalled, the flow diverter 20 can be “dropped down” over the outlet tube 17, thus ensuring that the flow diverter is located at the correct position (and substantially horizontal), towards the bottom of the chamber 12. Once that has been done, the helical heating elements 14 and 15 can be dropped into the chamber 12, around the central outlet tube 17, with the upstanding legs 25 serving both to locate the lower turns of the heating elements and also to maintain a space between the elements and the inner walls of the housing 11. it is also envisaged that the flow diverter and outlet tube could be provided as a single component (i.e. integral with one another) so that, during assembly of the water heater, the combined assembly is first placed in the heater can, with the heating element(s) then being placed around it.

The fins 27, which extend radially from the collar 26 of the flow diverter 20, assist in inducing/maintaining a substantially linear flow of water, especially insofar as the water exits through the innermost circle of apertures 22.

Figures 4B and 4C show a modified version of flow diverter 20 in which many of the parts are identical to those shown in Figure 4A.

However, the modified version of Figures 4B and 4C differs by the presence of a plurality of downwardly extending baffles 50 which, in this particular embodiment, take the form of substantially cylindrical pegs having a part- spherical lower end. These pegs 51 are disposed, when the assembly is complete, in the diverting chamber 23 (see Figure 3) and act to “break—up” the flow of incoming water which enters the diverting chamber through the inlet 13a. The effect of this is that the incoming flow is also slowed down, meaning that, through the rotational/tangentiaI/lateral aspect of the flow’s movement will have been when the water passes apertures 22, any reduced, thus helping the water fiow (downstream of the plate 21) to adopt a substantially linear/axial configuration. It will be appreciated that other configurationslpositionings of baffles/pegs are also envisaged, and that each peg need not be cylindrical, in cross-section.

Referring next to Figure 5, which shows (in perspective view) one of the two double~helical elements of Figures 1 to 3, it can be seen that the turns A and B (which together define a pair) are spaced closer to each other than are the pairs, themselves. In other words, the configuration is such that a substantial gap (shown at C) is present, in addition to a smaller (but still functionally useful) gap D between the turns A and B, themselves. This allows water to flow both between and around the pairs, and (to some degree) between and around the turns (A and B) which make up each pair.

Referring again to Figures 2 and 3, it can be seen that the elements 14 and 15 are positioned such that the helices of one element fit into the gap C (as shown in Figure 5) of the other element, creating a space between the coils of the inner element 15 and the outer element 14 which is of a similar size to the gap D (see Figure 5) between the pair of turns A and B. This is important as it enables water to flow freely, both through the pairs (defined by turns A and B) of each element 14 and 15, and between the turns which make up each element 14 and 15.

Figure 5 also shows that the double helix configuration has a “returned” character, in that the lowermost part of the helix (shown generally at E) does not terminate in free ends, but instead has the effect of “returning” the helix so that both free ends (shown at F) are disposed at a substantially similar location. This is useful as it enables a convenient connection of the free ends to a source of electrical power.

Where two “nested” heating elements (as shown in Figures 1 and 2) are employed, this means that all four free ends can be disposed at the same location, thus obviating the requirement for any “return leg” of the element which could othenrvise take up space, either outside or within the helices.

Referring lastly to Figures 6, 7 and 8, these show, in schematiclcomputer generated form, the effect of the heating element configuration, in conjunction with the flow diverter, on the fluid flowpaths and temperatures, at different positions within the heater can assembly.

Figures 6, 7 and 8 are similar, differing only by virtue of the power which has been applied to the heating elements — Figure 6 is based on an input power of 9.5 kilowatts, Figure 7 illustrates the effect of an input power of 8.5 kilowatts and Figure 8 shows the effect of an input power of 10.5 kilowatts. ln each case, the ambient (i.e. incoming) water temperature is 20°C, with the outlet (i.e. heated) temperature being 41°C.

What these images show is that positioning the apertures 22 (of the plate 21) “in register” with the turns of the helical heating elements (so that they are in line with one another, in an axial direction) maximises the contact between the incoming (relatively cold) water flows and the hot outer surfaces of the elements. Reducing any tangential/swirling motion of the incoming water also reduces the tendency of the water flows to move towards the walls of the chamber 12 (where less heating can occur) and has been found to lead to a more even heating of the body of water (as contained within the chamber), with acceptable outlet temperatures being attainable even with reduced power settings. Equally as importantly, the occurrence of “hot spots” has been found significantly to be reduced, which is likely to reduce the failure rate of any shower units in which the heat exchanger is present. it will be understood that although Figures 1, 2 and 3 show a flow inlet which is tangential to the inner wall of the housing 11, a significant advantage of the flow diverter 20 is that a tangential (or indeed radial) inlet direction is not necessary, because the flow diverter has the effect of changing the incoming This provides significantly greater design freedom, as regards the location, direction flow direction, before the water interacts with the heating element(s). and construction of the incoming water feed, and its connection to/interaction with the heater can housing.

Overall, the various features of the invention, in isolation and in combination with each other, provide for an efficient, safe and compact heat exchanger assembly, and which can easily be constructed, with the components adopting their correct position, within the heater can housing.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

Claims (6)

1. A heat exchanger for an instantaneous electric water heater having first and second electric heating elements, each substantially in the form of a double helix, the turns of the first and second elements being of different diameters, and with at least part of the smaller diameter helix being disposed within and substantially concentric and substantially coaxial with, the larger diameter helix.

2. A heat exchanger according to claim 1 wherein pairs of the first element's turns are axially offset from pairs of the second element's turns.

3. A heat exchanger according to claim 1 or claim 2 wherein each heating element has a returned configuration such that the free ends thereof are disposed at a substantially common location.

4. A heat exchanger according to claim 1, 2 or 3 further comprising a chamber in which the helices are disposed, the free ends of the heating elements being disposed substantially towards a top part of the chamber.

5. An electric shower comprising the heat exchanger of any one of claims 1 to 4.

6. An instantaneous electric water heater including the heat exchanger according to any one of claims 1 to 5. ANNE RYAN & CO. AGENTS FOR THE APPLICANTS