GB2254679A

GB2254679A - Waterheating system

Info

Publication number: GB2254679A
Application number: GB9206990A
Authority: GB
Inventors: Richard Martyn Griffiths
Original assignee: IMI RANGE Ltd
Current assignee: IMI RANGE Ltd
Priority date: 1991-04-10
Filing date: 1992-03-31
Publication date: 1992-10-14
Anticipated expiration: 2012-03-31
Also published as: GB2254679B; GB9206990D0

Abstract

An unvented mains pressure hot water storage cylinder (1) includes an internal "bubble top" (19) defined by a separately formed chamber (18) for accommodating expansion of the secondary hot water (2) contained in the cylinder. This dispenses with the need for the expensive, cumbersome external diaphragm-type of expansion vessel conventionally used and avoids the potential problems associated with alternative internal bubble top arrangements in which the cylinder itself serves to trap the air bubble. The chamber (18) may be located within the bounds of heat exchanger (13) and secondary water may enter the cylinder (1) via the chamber (18). <IMAGE>

Description

Waterheating System This invention relates to waterheating systems and more particularly to so-called unvented hot water storage systems.

Whilst unvented hot water storage systems containing in excess of 15 litres of stored hot water have only relatively recently been permitted in the United Kingdom, they are now in quite common use here and their construction and mode of operation are well-known.

Reference is made to, for example, our TRIBUNE (Registered Trade Mark) system. Briefly, such a system includes a storage vessel, such as a copper or steel cylinder, for containing secondary (ie. useable) water heated directly by an immersion heater or indirectly by a remote boiler, as in conventional low pressure (vented) cistern fed systems. Unvented hot water storage systems differ, however, from conventional vented systems in that the secondary hot water is delivered to its points of use by mains, or reduced mains, pressure water instead of by water contained in feed cistern. This has the advantage that there is no need to instal a secondary feed and expansion cistern, for example in a loft, and that the hot water issues at a relatively high flow rate, which is beneficial especially in the case of showers.However, such a system does have disadvantages, mainly the need to provide a number of safety and control devices including, in particular, a large external diaphragm-type expansion vessel which is required to accommodate the expansion of the secondary water as it heats up under static conditions. Such expansion vessels are cumbersome and expensive and the diaphragm is prone to premature failure compared with the other components of the system.

Recently, there has been a proposal to substitute the external, diaphragm-type expansion vessel with an internal "bubble top". In that arrangement, a large bubble of air is trapped in and by the top part of the cylinder and accommodates expansion of the secondary water simply by becoming compressed. As will be appreciated, this overcomes the above disadvantages, but it has the drawback that the top part of the vessel interior is constantly subjected to high temperature water or water vapour (typically at about 650C) in the presence of oxygen which is likely to give rise to corrosion problems.In addition, the use of such a bubble top is inconvenient from the point of view of siting the temperature relief valve, which is another safety device required in unvented storage systems, because it cannot, as is convenient and normal, be located at the top of the cylinder since it must be in actual contact with the secondary water in the vessel.

Further, the use of such a bubble top gives rise to design problems on account of the fluctuating water level at the top of the cylinder. Furthermore, such an arrangement could be considered to be a pressure vessel whereby conventional means of achieving safety by using temperature control may not be acceptable or appropriate as there is an additional hazard due to the containment by the cylinder itself of air under pressure.

It is an object of the present invention to provide an unvented hot water storage system wherein the means for accommodating expansion of secondary hot water is, broadly, of the internal bubble-top type but wherein the problems associated with the recent proposal described above are eliminated or at least significantly mitigated.

According to the present invention, therefore, there is provided, in and for an unvented hot water storage system, a hot water storage vessel including an internal bubble-top for accommodating expansion of the secondary water contained, in use, in the vessel, characterised in that the bubble-top is comprised in a separately formed chamber located within the vessel, said chamber having an opening communicating its interior with the interior of the vessel, the arrangement being such that, in use, an enclosed air space will be defined above said opening by the chamber walls and the surface of the quantity of secondary water that enters the chamber via said opening.

Preferably, the chamber is substantially cylindrical, being closed at the top and open at the bottom so as to afford said opening.

In a preferred embodiment, the chamber is located in an upper region, preferably adjacent to the top, of the storage vessel and preferably has a basal opening that is above and laterally at least co-extensive with the heating means located in the vessel, such as one or more electric immersion heaters or a heat exchanger coil.

In another embodiment, the incoming mains cold water pipe is connected to the chamber, with its inlet opening into the air space and so arranged that, upon a demand for secondary hot water, the incoming mains cold water will impinge either directly on the chamber wall or directly onto the water surface within the chamber whereby dissolved air will be released into the air space and so continually replenish the air therein. In such an embodiment, the opening in the chamber (for example the bottom, open end of the substantial cylindrical chamber referred to above) should of course be located in a lower region of the vessel, preferably adjacent the base thereof, so that most of the secondary hot water contained in the vessel may, if necessary, be utilised.

This embodiment has the additional advantage that, whilst the incoming mains cold water will enter the chamber at a relatively high velocity, it will thence enter the vessel at a relatively low velocity and so not disturb stratification of the secondary hot water contained in the vessel. Preferably the air space in the chamber includes a conical, or other suitably shaped, baffle onto which the incoming mains water impinges and which is arranged to cause the water to flow down the walls of the chamber and so flush away any corrosion deposits thereon.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a diagramatic view of a conventional unvented hot water storage system, such as our TRIBUNE system; Figure 2 is a similar view to that of Figure 1 including a vessel having a bubble top in accordance with the invention; Figure 3 is a similar view to that of Figure 1 including a vessel having an alternative bubble top in accordance with the invention; and Figure 4 is a detailed view of an alternative design of "bubble top" chamber suitable for use in the system shown in Figure 3.

Referring firstly to Figure 1, a conventional unvented system comprises, as is well known in the art, a lagged cylinder 1, for example of copper or steel, for storing secondary hot water 2 typically at about 60-65 C. In a domestic context the capacity of the cylinder 1 is usually between 80 and 210 litres, depending on the likely demand for hot water. The secondary hot water 2 is conveyed to points of use via an outlet pipe 3 connected to the top of the cylinder 1, by means of pressurised cold water connected to the mains supply by a pipe 4.The pipe 4 includes a strainer 5, a pressure reducing valve 6, usually set at around 2 bar gauge (ie. 3 bar absolute), a non-return valve 7, a diaphragm-type expansion vessel 8 (typically able to accommodate from 3 to 7 litres of expanded secondary water, depending on the capacity of the cylinder 1) and an expansion relief valve 9. The system further comprises a temperature relief valve 10 whose outlet, together with the outlet of the expansion relief valve, leads to a tundish 11. The secondary water 2 may be heated directly, for example by an electric immersion heater 12, and/or indirectly by a remote boiler via a coiled heat exchanger 13 located in the cylinder 1.In addition, the system includes an energy cut out device 14 that, in the event of the secondary hot water 2 attaining too high a temperature, prevents further heating of the secondary water 2 by closing a motorised valve 15 located in the primary circuit 16 of a boiler-heated system. The valve 15 is also actuable by a cylinder thermostat 17, typically set at 60 to 650C. Where the water 2 is heated by an immersion heater, a cut out device 14' is incorporated in the heater 12 and the water temperature is controlled by a thermostat 17' also incorporated in the heater 12.

As already noted, the above system, and its components, are well-known to those skilled in the art and need not be further described herein. For further details, however, the reader is directed to, for example, our TRIBUNE brochure. As already noted also, the use of the expansion vessel 8, or of the alternative bubble top previously proposed, has certain drawbacks and these may be substantially eliminated by adopting the expansion arrangements shown in Figures 2 to 4 of the drawings.

Referring to Figure 2, and in accordance with the present invention, instead of expanded secondary water being accommodated in the expansion vessel 8 (which is dispensed with) it is accommodated in an internal bubble top chamber 18 located near the top of the cylinder I.

The chamber 18, which is dome-shaped and is closed at its upper end but is completely open at its lower end, is rigidly located in place by a number of spaced tabs 22 brazed or otherwise secured to the chamber 18 and to the internal surface of the cylinder 1. The chamber 18 may, of course, be located in place by alternative means; for example it may be rigidly suspended from the top end of the cylinder 1 by a short, radially apertured hollow stem that communicates with the outlet pipe 3, the secondary water 2 flowing, on demand, from the cylinder 1 into the pipe 3 via the stem and the aperture(s) therein.

When, after installation of the system, the cylinder 1 is first filled (by turning on the mains supply to pipe 4), the water level in the cylinder will gradually rise and when it reaches the base of the chamber 18 it will trap the air contained in the chamber. The level of water in the cylinder 1 will continue to rise until the cylinder 1, and the secondary water distribution pipework, is full. At the same time the water level in the chamber 18 will rise, compressing the trapped air, until the pressure of the trapped air counterbalances the pressure in the secondary system, typically about 2 bar gauge. The ensuing trapped air space 19 is thus available to accommodate thermal expansion within the secondary water system under static conditions during service, ie. when hot water is not being drawn off and the water in the cylinder 1 is being heated up.As will be apparent, the chamber 18 needs to be so dimensioned that the bubble in it, ie. the air space 19, is sufficiently large that the maximum possible amount of expansion can be accommodated and in any given case appropriate dimensions may be determined by simple calculations.

During service, when there is a demand by the user for hot water 2, cold water in the pipe 4 drives hot water, at high pressure, from the cylinder 1 through supply pipe 3 to the point of demand.

We have found it preferable to locate the chamber 18 above the coiled heat exchanger 13 whereby any loss of air from the space 19, for example because of dissolution thereof in the secondary water 2, will be more or less replenished when, during continual re-heating of the water 2, dissolved air is driven out of the water 2 immediately surrounding the coil 13 and rises in the form of bubbles into the air space 19. In brder to maximise the amount of rising air received in the space 19, the diameter of the lower open end of the chamber 18 is, as shown, significantly greater than the external diameter of the coiled heat exchanger 13.

Referring to Figure 3, the expanded secondary water is accommodated in an internal bubble top chamber 18 located coaxially within the coil 13 (which has been omitted for clarity).

The chamber 18 is cylindrical and is closed at its upper end but is open at its lower end adjacent to the base of the cylinder 1. The mains cold water feed pipe 2 serves to support the chamber 18 and sealingly passes through an aperture formed in the closed upper end of the chamber 18 and extends slightly into it. Establishment of the bubble top within the chamber 18 is the same as described with reference to Figure 2.

During service, when there is a demand by the user for hot water 2, cold water issues from the pipe 4 and drives hot water, at high pressure, from the cylinder through supply pipe 3 to the point of demand. The cold water issuing from the pipe 4 cascades onto the water surface 20 in the chamber 18 and the turbulence causes dissolved air to be released, whereby the bubble will be continually replenished.

Referring to Figure 4, the air space 19 includes a conical baffle 21 secured, in spaced relationship, to the internal wall of chamber 18, and the apex of which is located directly beneath the outlet of the pipe 4. The baffle 21 thus directs the incoming cold water onto the internal walls of the chamber 18, as indicated by the arrows, whereby any corrosion deposits and/or scale thereon will be flushed away.

Reverting to Figures 2 and 3, whilst the expansion relief valve 9 is shown to be present, it may be possible to dispense with same because its major function is to cope with expansion water in the event that the expansion vessel used in prior unvented systems fails. Also, with reference to Figure 3, the cold water feed pipe 4 may be connected to the cylinder in the conventional way, instead of via the chamber 18, as is indicated by the dotted lines in Figure 3, in which case the chamber 18 may be located higher up, for example as in the embodiment shown in Figure 2.

Claims

CLAIMS:

1. In or for an unvented hot water storage system, a hot water storage vessel including an internal bubble top for accommodating expansion of the secondary water contained, in use, in the vessel, characterised in that the bubble top is comprised in a separately formed chamber located within the vessel, said chamber having an opening communicating its interior with the interior of the vessel, the arrangement being such that, in use, an enclosed air space will be defined above said opening by the chamber walls and the surface of the quantity of secondary water that enters the chamber via said opening.

2. A hot water storage vessel according to claim 1 wherein the chamber is in the form of an inverted cup whose lower, open end defines said opening.

3. A hot water storage vessel according to claim 2 wherein the chamber comprises a hollow circular cylinder that is closed at the top and open at the bottom so as to afford said opening.

4. A hot water storage vessel according to claim 3 wherein the top closure is domed.

5. A hot water storage vessel according to any one of claims 1 to 4 wherein the chamber is located in an upper region of the vessel above the heating means for the secondary hot water.

6. A hot water storage vessel according to claim 5 wherein the chamber is located adjacent to the top of the vessel.

7. A hot water storage vessel according to claim 5 or claim 6 wherein, laterally, the said opening is at least co-extensive with the said heating means.

8. A hot water storage vessel according to any one of claims 1 to 7 wherein the chamber is rigidly suspended from the top of the vessel.

9. A hot water storage vessel according to claim 8 wherein the chamber is rigidly suspended from the top of the vessel by a radially apertured hollow stem that communicates with the secondary water outlet of the vessel such that, in use, secondary water flows, on demand, from the vessel outlet via the stem and the radial aperture(s) therein.

10. A hot water storage vessel according to any one of claims 1 to 4 wherein the chamber is located in a central or lower region of the vessel.

11. A hot water storage vessel according to claim 10 wherein the mains cold water inlet is connected to the chamber and opens into the air space.

12. A hot water storage vessel according to claim 11 wherein the incoming mains cold water is arranged to impinge directly onto the surface of the water within the chamber.

13. A hot water storage vessel according to claim 11 wherein the incoming mains cold water is caused to impinge onto the internal walls of the chamber and thence onto the surface of the water within the chamber.

14. A hot water storage vessel according to claim 12 wherein the chamber includes, within the air space, a baffle onto which the incoming mains water initially impinges and which serves subsequently to direct the water towards, and into contact with, the wall(s) of the chamber.

15. A hot water storage vessel according to claim 14 wherein the baffle is substantially conical.

16. In or for an unvented, mains pressure hot water storage system, a hot water storage vessel substantially as hereinbefore described with reference to, and as illustrated in, Figure 2, Figure 3 or Figure 3 as modified in accordance with Figure 4, of the accompanying drawings.