GB2275325A

GB2275325A - Water heating devices

Info

Publication number: GB2275325A
Application number: GB9402844A
Authority: GB
Inventors: Thomas Henry Bell
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-02-18
Filing date: 1994-02-15
Publication date: 1994-08-24
Anticipated expiration: 2014-02-15
Also published as: GB9402844D0; GB9303264D0; GB2275325B

Abstract

A heating device for hot water in a cylinder tank (18) comprises an electrical heating element received within a casing (26) and a thermostat (28). An open-ended sleeve (30) is carried by an adapter (34) fitted to the tank. An annular passage (38) defined by the sleeve (30) around the heater communicates at its upper region with a pipe (40) which leads to an expansion pipe (42) above the level of the top of the tank by for example a distance of 600mm. The enhanced rate of circulation of the heated water brought about by the extra head of water achieved will be found to provide a small quantity of hot water in a short time. It will also be found that there is little tendency for the heated water to mix with the normal sluggish circulation of unheated water in the tank. In an alternative construction, the sleeve (30) is secured directly to the thermostat (28). A pump may aid the circulation. <IMAGE>

Description

WATER HEATING DEVICES The invention is concerned with improvements in or relating to water-heating devices, particularly but not exclusively to domestic water-heating devices of the kind known as immersion heaters.

In the use of known immersion heaters, an elongate electric heating element, for example of nickel-chromium wire, is provided with an outer casing which, in becoming heated by the element, in turn heats the water in a cylindrical tank. Water heated by the casing rises in the tank and is replaced by cold water from below. The resulting circulation of water results in the gradual heating of the body of water in the tank downwardly from an upper region thereof to a lower end of the element, little or no circulation taking place below that level.

An adjustable thermostat normally controls the operation of the heating element.

In situations in which it is not required to heat the whole quantity of water in the tank, the use of a conventional full length heater element is inefficient since in order to obtain reasonably hot water, the major portion of the tank capacity needs to have reached a relatively high temperature at which it is not subject to the cooling effect of unheated water in circulation. For example, it may take nearly 2 hours using a 3 kW heater to heat a 90 litre tank of water from 10 C to say 60"C. This is not convenient where only a small quantity of water is required for example for washing dishes.

One solution to this problem has been suggested in which a second heating element is provided within the casing which is less than half the length of the main element. This is not an ideal solution since the combined output of the two elements is not normally greater than that of the single element and therefore the rating of the smaller element is so low that much of the anticipated benefit of only having to heat a relatively small volume of water at the top of the tank is lost. For example, a 1.5 kW short heating element may take 1.5 hours to heat 30 litres of water to 60"C. If an up-rated device is to be used, a revised electric wiring operation is required.

However, a 3 kW short heating element may still take 40 minutes to achieve a 60"C water temperature.

The present invention provides a water-heating device comprising an elongate heating means received within an outer sleeve and adapted to be immersed in a tank of a water heating system, said sleeve having an opening at a free end portion thereof adapted to act as an inlet for water within the tank to be heated and providing an at least part-annular passage around the heating means, communication being provided between said passage at an opposite end portion of the sleeve and an outlet for heated water, said outlet being arranged at an elevated level with respect to the tank that ensures the maintenance in use of a vertical head of water sufficient to provide a greater circulating pressure of heated water in an upper region of the system compared with that of unheated water at a lower level in the tank.

Preferably the outlet leads to a conduit connecting with an expansion pipe or other vent provided at the upper portion of the tank, thus enabling heated water to leave the tank and to be returned thereto from an elevated level with respect to the tank.

Advantageously, said sleeve may be mounted at said opposite end portion thereof to an adapter device capable of insertion between an aperture in the tank through which the heater means is intended to pass, and a mounting member of the heater means.

If preferred, the sleeve may be secured to the tank wall or, alternatively, to the heater device itself.

There will now be described an example of a device according to the invention. It will be understood that the description which is to be read with reference to the drawings is given by way of example only and not by way of limitation.

In the drawings: Figure 1 is a schematic view illustrating an example of the prior art; Figure 2 is a similar view of a device according to the invention; and Figure 3 is an exploded view of parts of the device of Figure 2.

The device shown in Figure 1 illustrates a known example of a two-element water heating device 2 fitted to a domestic cylinder tank 4. The heater device is received in a threaded aperture 6 at an upper portion of the tank 4 and comprises a head portion 8, a full length heating element 10 and a shorter heating element 12. An expansion pipe 14 is provided, with a draw-off pipe 16 leading to hot water taps of the system (not shown). When the element 10 is operated the water partakes of a circulating movement represented by arrows A in that Figure. It will be observed that vertical distance through which the circulation takes places, H, is determined by the effective height of the element 10 when operated to heat the major proportion of the water.Thus when element 10 is operated the force of circulation of the water is greater than when the element 12 is in use, since the circulation path is that shown by the arrows B, thus heating a smaller amount of water. Circulation of water in a tank is caused by the differing densities of hot and of cold water and is also influenced by the height of the rising (heated) volume of water and of the falling (cooler) volume of water. The greater is the height, the greater will be the circulation force or pressure.

However, it will be found that unless an element of sufficiently high rating is positioned at the top of the tank a rapid build-up of hot water is not achieved because the circulation within the tank (arrows A or B) is too sluggish, and the circulation pressure too low without the use of a moderate size pump.

Figure 2 shows a device according to the invention in which a tank 18 is provided with a threaded aperture 20 in which an immersion heater device 22 is received. The heater device 22 comprises a long length element 24 received within a casing 26, and a head portion 28 including a thermostat 29 (Figure 3). An open-ended sleeve 30 is provided which surrounds the casing 26 of the element 24 so as at least to extend the full length thereof or to extend beyond a tip 32 thereof as shown in the Figure. In an example, the sleeve 30 may be provided already secured to the heater portion 28 for direct insertion into the aperture 20, so as to be effectively integral with the tank, but in the present example the element 24 and casing 26 are part of an existing device including the head portion 28 which would normally be threaded directly into the aperture 20. The sleeve 30 is thus in the form of a conversion device, enabling a standard "immersion" element to be readily converted into a device according to the invention.

To this end, the sleeve 30 is provided on an annular adapter member 34 (Figure 3) which is received within the threaded aperture 20 and itself is internally threaded at 36 to receive the head portion 28. An annular passage 38 is thus formed around the casing 26 into which water is drawn in a path shown by arrows C. Because of the relatively small volume of water being heated in the passage 38, the heat transfer is very rapid. For example, a litre of water will be raised in temperature from 10 C to 60"C by means of a 3 kW heating element in approximately 1.5 minutes.

If it is desired for some reason to use a higher rated element, perhaps up to 10 kW, it may be found beneficial if the rate of circulation of heated water is still further increased by the additional action of a small pump, the operation of which will tend to eliminate the risk of premature cut-out by the thermostat 29 due to a localised build-up of heated water at an unrepresentatively high temperature. It will be understood that the capacity of a pump used in the above context may be small compared with that normally required in the context of prior art arrangements.

At the upper portion of the passage 38, hot water enters the adapter 34 and passes along a laterally extending pipe 40 which leads from the device 22 externally of the tank 18 and is connected to an expansion pipe 42 of the tank at a level which in the present example is at least 600mm above the level of the top of the tank 18. Water drawn through the heated passage 38 is thus fed to the pipe 40 and from there to the pipe 42 from which it flows downwardly into the upper region of the tank where it tends to accumulate in sufficient quantity that, when a hot water tap elsewhere in the system is turned on, water is drawn from draw-off pipes 44 or 44', hot water being available within a very short time of switching on the immersion heater.Moreover, the enhanced rate of circulation of the heated water is sufficiently greater than the sluggish circulation of colder water in the remainder of the tank that the heated water does not readily mix with the unheated water and therefore is not unduly cooled by it.

When the full tank is required to be heated, the additional vertical distance of water flow shown at H' in Figure 2 in comparison with the distance H of Figure 1 results in a greatly enhanced rate of circulation within the tank including the region at the open lower end of the sleeve 38.

However, where the situation of the tank prevents the vertical distance H' from being arranged to reach an optimum height, achievement of the required effect may be ensured by the provision of a small capacity pump.

Thus the use of the invention provides a device capable of supplying not only small quantities of hot water very rapidly, by minimizing the mixing of heated and unheated water, but also of building up a supply of hot water within the tank without requiring the bulk of the water present in the tank to be at a predetermined temperature before acceptably hot water becomes available.

Various modifications may be made within the scope of the invention as defined by the following claims.

Claims

1. A water heating device comprising an elongate heating means received within an outer sleeve and adapted to be immersed in a tank of a water heating system, said sleeve having an opening at a free end portion thereof adapted to act as an inlet for water within the tank to be heated and providing an at least part-annular passage around the heating means, communication being provided between said passage at an opposite end portion of the sleeve and an outlet for heated water, said outlet being arranged at an elevated level with respect to the tank that ensures the maintenance in use of a vertical head of water sufficient to provide an increased circulating pressure of heated water in an upper region of the system compared with that of unheated water at a lower level in the tank.

2. A device as claimed in claim 1 wherein the outlet leads to a conduit arranged to connect with an expansion pipe or vent provided at the upper portion of the tank, permitting heated water to leave the tank and to be returned thereto from an elevated level with respect to the tank.

3. A device as claimed in either one of claims 1 and 2, wherein said sleeve is mounted at said opposite end portion thereof to an adapter device capable of insertion between an aperture in the tank through which the heater means is intended to pass, and a mounting member of the heater means.

4. A device as claimed in either one of claims 1 and 2, wherein said sleeve is secured to the tank wall.

5. A device as claimed in either one of claims 1 and 2, wherein said sleeve is secured to the heater device.

6. A device as claimed in claim 2 wherein said outlet provides a flow path from the at least part annular passage through said conduit to a point at least 600mm above the upper portion of the tank, said path then leading downwardly into the upper portion of the tank.

7. A water heating device substantially as hereinbefore described with reference to an as shown in Figures 2 and 3 of the drawings.