GB2088030A - Hot water cylinder - Google Patents

Abstract

A hot water cylinder (10) has a chamber (16) at its lower end, the chamber being defined between upper and lower inwardly domed walls (14, 15) and having respective supply and exhaust means (20, 21 and 17) in communication therewith. The supply means is in the form of a heat exchanger having coils (21), with the end (22) of the heat exchanger extending into and terminating in the chamber (16). Both the heat exchanger and the wall (15) are made of high heat conductivity material and the surface area of the wall (15) is made sufficiently large so that, in use, there is a good transfer of heat from a heat exchange medium in the chamber to water in contact with and just above the surface of the upper chamber wall (15). This arrangement ensures that no layer of cold water remains at the bottom of the cylinder, as occurs with conventional cylinders, with the result that the water in the cylinder is more efficiently and evenly heated, thereby eliminating stratification in the cylinder. <IMAGE>

Description

SPECIFICATION Hot water cylinder This invention relates to a hot water cylinder principally for a domestic heating system.

In such a system, a boiler is normally employed to heat water for circulation through radiators positioned in the rooms of the house. Water for washing could be heated directly by the boiler, but 'it can also be heated indirectly in a conventional cylinder to which cold water is fed from the cold water tank. Several alternative suitable heating methods could be used to heat the water in the cylinder, but perhaps the commonest method is to arrange a heat exchanger in the form of a coiled copper pipe in the cylinder and to pass hot water heated by the boiler, through the coiled pipe. Heat is thus transferred from the water in the coiled pipe to the cold water in the cylinder, which cold water is thus heated so that it can be drawn off from the cylinder for washing.Conventionally, cold water enters the cylinder at the bottom thereof and heated water is drawn off at the top of the cylinder.

Although the last decade has seen improvements and advancements in the design and performance of such items as radiators and heat controls for domestic heating systems, the design of the hot water cylinder has not similarly been improved. As a result, conventional cylinders now suffer from several disadvantages which hinder efforts to provide an efficient and economically acceptable domestic heating system.

Most conventional cylinders have a capacity of approximately 25 gallons or 113.6 litres. As will be explained however, due to their construction it is unlikely that they contain more than 16 to 18 gallons or 72.7 to 81.8 litres of heated water, the remaining water being, at best, only luke warm. It can thus be appreciated that if such conventional cylinders were more efficient so that substantially all the stored water was heated, the size of the cylinders could be reduced, whilst still providing sufficient heated water.

In such a conventional cylinder, the heating coil is usually arranged so that its lowermost heating portion is spaced some distance above the bottom of the cylinder. As a result of this positioning and of the unnecessarily large amount of water to be heated, it is found that a cold or tepid layer of water remains at the bottom of the cylinder, the volume of such water obviously increasing in proportion to the increase in the spacing of the coil from the bottom of the cylinder. Typically the volume of such cold water may be of the order of one quarter of the capacity of the cylinder.

Even if the lowermost heating portion of the coil were to be placed closer to or even at the bottom of the cylinder, it is not believed that this problem of a layer of cold or tepid water would be overcome. This is because the coldest water will always tend to collect at the bottom, this collection being exacerbated by the fact that the cold water inlet is also normally positioned at or near the cylinder bottom. Accordingly a large heat transfer surface area is required to heat this lower layer of cold water and it is considered that the lowermost coil portion would still not provide this large surface area required, even if positioned at or near the cylinder bottom.

In addition to this layer of cold water at the bottom of the cylinder, it is also found that with conventional cylinders stratification, i.e. layers of water at different temperatures, occurs throughout the cylinder. This makes meaningful temperature control of the cylinder impossible.

A further problem is that a conventional cylinder has only a iimited heat transfer capability, i.e. it is not capable of absorbing the total heat output of the boiler. As a result, the boiler short cycles, i.e. switches off and on more often than it would with a cylinder having a greater heat transfer capacity. Accordingly the boiler operates inefficiently due to such short cycling.

Finally, the disadvantages mentioned lead to a relatively long heat-up time for the water in the cylinder. Typically it takes over 40 minutes to heat-up the water in the cylinder from cold and only slightly less for re-heat. An improvement in such times without any substantial increase in energy expended is clearly desirable.

The object of the invention is thus to provide a hot water cylinder which overcomes or at least reduces some or all of the disadvantages referred to.

According to the invention a hot water cylinder comprises a chamber defined between a lower wall and an upper wall, inlet and outlet means for conveying water to be heated, in use, to and from the cylinder, respective supply and exhaust means for conveying a heat exchange medium to said chamber from outside the cylinder and from said chamber to the outside of the cylinder, one of said supply means and said exhaust means including a heat exchange surface so as to transfer heat, in use from said heat exchange medium to said water in the body of the cylinder, and one of said walls of said chamber acting as a heat exchange surface to transfer heat, in use, from the heat exchange medium in the chamber to the water in contact therewith in the cylinder.

Preferably the lower wall of the chamber closes the end of the cylinder which is lowermost, in use, and desirably said upper wall of the chamber acts as said heat exchange surface to transfer heat from the heat exchange medium in the chamber to the water in contact therewith.

By virtue of this arrangement the water at the bottom of the cylinder is now heated, as it is in a heat exchange relationship with the heat exchange medium by way of the upper wall of the chamber, which has a relatively large heat transfer surface area.

The invention will now be described, by way of example, with reference to the accompanying drawing, the single figure of which is a schematic side view of a hot water cylinder of the invention, showing the internal structure thereof.

The drawing shows a copper hot water cylinder 10 of substantially conventional external shape except at its lower end. The cylinder comprises a cylindrical body 11 with a domed top 12 from which an outlet 13 extends. The lower part of the cylinder has a similar, inwardly domed bottom wall 14, the wall thickness of which is such that the configuration of the bottom wall is also present within the cylinder.

An upper wall 1 5 is fixed in the cylinder a short distance above the bottom wall 1 4 thereof. The wall 1 5 is also inwardly domed, as shown, with substantially the same radius of curvature as the wall 14. Together the two walls 14 and 1 5 define a chamber 1 6 therebetween, the chamber having a relatively small capacity as compared to that of the cylinder 10. For example the vertical separation of the walls 14 and 15 may be only about 2.54 cm compared to the cylinder height of about 91.4 cm. However the chamber capacity can be greater or smaller as required.

An outlet pipe 1 7 extends from the centre of the upper wall 15 of the chamber substantially radially of the cylinder through the side wall thereof, where it is connected, in use, to an exhaust line (not shown). The pipe 17 exhausts hot water from the chamber 16 defined between the walls 14 and 15. Any air in the chamber can escape by way of suitable escape means provided in said exhaust line (not shown) connected to the pipe 17 outside the cylinder.

At a position in the cylinder side wall just above the junction of the chamber wall 1 5 with the cylinder interior, there is provided a radially disposed inlet 18 for feeding cold water into the cylinder. Immediately in front of the inlet, in the cylinder, but spaced slightly therefrom is a curved cowl or baffle 1 9, the purpose of which will hereinafter be explained. The inlet 1 8 is, in the example illustrated, disposed in the cylinder wall at a position 180 therearound from the outlet pipe 17.

At a position slightly below the junction of the cylinder body 11 and the domed top 12, an inlet pipe 20 extends through the cylinder side wail and into the cylinder interior. The position of entry of the inlet pipe 20 is, in this example, at the same angular position around the cylinder as the outlet pipe 1 7. The inlet pipe 20 is in the form of a heat exchanger having several coils 21 arranged centrally in the interior of the cylinder. The end of the inlet pipe 20 is arranged to extend vertically into the chamber 16 at a position offset from the centre of the upper wall 1 5 so that it terminates adjacent the bottom wall 14. The extremity 22 of the pipe 20 is arcuately shaped, as shown. The heat exchanger would be made of a material of good heat conductivity.

In use, the cylinder is connected in a domestic heating system. Cold water is fed from the cold water tank into the cylinder 10 through the inlet 18 and this water, heated as will be described, can be drawn off through the outlet 1 3 for washing and the like, as required. Hot water, heated directly by a boiler of the heating system, is fed through the inlet pipe 20 into the chamber 1 6, the hot water passing through the coils 21 before reacing the chamber 16, so that in the conventional manner, heat is transferred from the hot water in the coils to the cooler water in the middle and upper parts of the cylinder in particular.

The extremity 22 of the inlet pipe 20 is arcuately shaped, so that it will direct hot water generally downwardly, so that it will not flow out of the outlet pipe 1 7 without spending some time heating the chamber walls. Moreover the shape and disposition of the extremity of the pipe tends to cause the hot water to flow around the outer peripheral portion of the chamber, thereby contributing to the heating of the chamber. Water flows out of the chamber 1 6 via the outlet pipe 1 7 to be returned to where it is re-heated by the boiler before being fed back to the inlet pipe 20.

The cold water flowing into the cylinder through the inlet 1 8 impinges on the baffle 1 9 which causes the cold water to divide into two streams which flow in opposite directions around the domed wall 1 5. This flow enables the cold water to extract heat from the hot water in the chamber by way of the wall 1 5 which, like the coils 21, would be made of a good heat conducting material, such as copper. The relatively large heat transfer surface area of the wall 1 5 is particularly advantageous in this heat transfer process. Typically such surface area would be of the order of 0.1 sqm. The wall 15 would be made of material of high heat conductivity.

As the inlet 1 8 is positioned at the upper side of the chamber there is no possibility of any cold water not being heated by the chamber 16, so that the previously noted problem of a lower layer of cold water remaining unheated in the cylinder is overcome.

Although in the example described the inlet pipe 20 is provided with coils, any suitable alternative heat exchange surface could be provided instead. However coils are preferred as they present a large surface area for heat transference. Similarly the heat exchange surface constituted by the wall 15 could be of a shape other than domed. Moreover the periphery of the lower part of the chamber 15 could be in the form of a convex cross-section annulus, such a shape being particularly suitable, since any debris in the chamber would then tend to collect at the bottom of the annulus.

A further change from the embodiment described could be the reversal of the hot water inlet and outlet, so that the hot water was fed in through the pipe 17 and taken out through the pipe 20. In addition the water fed through inlet 1 8 could be heated rather than cold. Moreover the heat exchange medium, if desired, be other than water.

The inlet and outlets 18, 1 3 can be disposed in positions other than at or near the top and bottom of the cylinder, if desired.

The cylinder capacity is of the order of 1 8 gallons or 81.8 litres. This reduced cylinder capacity together with the much improved heating at the bottom of the cylinder, means that the whole of the water in the cylinder is heated to much the same temperature top to bottom, thus avoiding stratification. In addition the increased heat transfer efficiency of the cylinder eliminates short cycling of the boiler associated therewith.

Tests carried out with the cylinder of this invention have produced a time of 26.5 minutes to heat the whole contents from cold, with a re-heat time of 1 7.5 minutes following a total draw off of 17.5 gallons or 79.5 litres These times are a considerable improvement over times obtained with conventional cylinders. Moreover the whole test was completed without the boiler short cycling and with comparatively little stratification.

Accordingly all the mentioned disadvantages of conventional cylinders are reduced or eliminated with the cylinder of the present invention.

In an alternative construction, the chamber is much bigger than the chamber 1 6 illustrated, having for example, a vertical height of 30.48 cm compared to a cylinder height of approximately 106.7 cm, with the cylinder diameter also being increased from 35.6 cm to 45.7 cm.

In addition a further difference is that the inlet pipe 20 joins the upper chamber wall at the centre thereof, with a spreader being disposed centrally about 2.54 cm beneath said upper wall. The spreader, which has a hole in its centre, has a minimum diameter of 30.48 cm. The hole allows air to pass therethrough and up through the inlet pipe 20. The spreader is designed to spread the hot water supplied by the pipe 21 on the underside of said spreader, thus giving a good secondary spread of hot water where it is most useful.

Instead of the outlet pipe 17 leading from the centre of the top of the wall 1 5, the outlet pipe 1 7 from the chamber is, in this alternative embodiment, disposed almost at the bottom of the chamber, and extends radially out of the cylinder wall.

If necessary the cylinder could have a temperature probe in the body of the cylinder above the chamber.

One or more of these features mentioned in relation to the alternative construction, could of course be incorporated in the cylinder illustrated instead of, or in addition to, the features shown.

Claims (12)

1. A hot water cylinder comprising a chamber defined between a lower wall and an upper wall, inlet and outlet means for conveying water to be heated, in use, to and from the cylinder, respective supply and exhaust means for conveying a heat exchange medium to said chamber from outside the cylinder and from said chamber to the outside of the cylinder, one of said supply means and said exhaust means including a heat exchange surface so as to transfer heat, in use, from said heat exchange medium to said water in the body of the cylinder, and one of said walls of said chamber acting as a heat exchange surface to transfer heat, in use, from the heat exchange medium in the chamber to the water in contact therewith in the cylinder.

2. A cylinder as claimed in claim 1, in which, in use, all the water contained in the cylinder is above said upper wall of the chamber.

3. A cylinder as claimed in claim 1 or claim 2, wherein said lower wall of the chamber closes the end of the cylinder which is lowermost, in use.

4. A cylinder as claimed in any one of claims 1 to 3, wherein said upper wall of the chamber acts as said heat exchange surface to transfer heat, in use, from the heat exchange medium in the chamber to the water in contact therewith.

5. A cylinder as claimed in any one of the preceding claims, wherein said upper wall of the chamber is domed inwardly of the cylinder and extends across the whole diameter of the cylinder.

6. A cylinder as claimed in claim 5, wherein said lower wall of the cylinder is also inwardly domed in the same manner as said upper wall, with a constant spacing therebetween defining said chamber.

7. A cylinder as claimed in claim 5, wherein said inlet means is arranged in a side wall of the cylinder at a position slightly above the junction of said upper wall of the chamber with the cylinder interior, said inlet means being provided with a baffle to cause water supplied through the inlet means to split into two streams, which flow, in use, in opposite directions around the domed upper wall.

8. A cylinder as claimed in any one of the preceding claims, wherein said heat exchange surface of said one of said supply and said exhaust means is provided by a heating coil disposed in the interior of the cylinder, one end of said coil extending into said chamber and the other end thereof extending through the side wall of the cylinder at a position remote from said chamber.

9. A cylinder as claimed in any one of the preceding claims, wherein the other of said supply and exhaust means extends from the upper wall of the chamber through the said wall of the cylinder at a position adjacent said chamber.

10. A cylinder as claimed in claim 8, wherein said end of the coil is arcuately shaped to direct water, in use, to flow towards the periphery of the chamber.

1 A cylinder as claimed in any one of claims 1 to 8, wherein said coil extends into the centre of the chamber upper wall, and a baffle is disposed just below said wall, in the chamber, said baffle having a central hole therein directly below said coil so that air in the chamber can escape through said hole and up through said coil.

12. A hot water cylinder substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.