WO2004081463A1

WO2004081463A1 - Potable water heating system

Info

Publication number: WO2004081463A1
Application number: PCT/GB2004/001019
Authority: WO
Inventors: Alan Harris; Duncan Bennett; Steven Hollis
Original assignee: Ez-Hot Limited
Priority date: 2003-03-13
Filing date: 2004-03-10
Publication date: 2004-09-23
Also published as: GB0305760D0

Abstract

A water heating system is provided which includes a tank (10) for storing water with heating means (20) located therein. A sleeve (22) is provided around the heating means (20) with clearance provided therebetween. The sleeve (22) has an inlet at a bottom end thereof and an outlet at a top end thereof and, in operation of the heating means, a convection flow path is generated in the water in the tank from the inlet of the sleeve, through the sleeve to the outlet, the water passing over the heating element to be heated thereby, the water from the outlet of the sleeve being returned to the receptacle (10) and/or being supplied to one or more locations to meet a demand for hot water. The receptacle (10) is pressurised to allow rapid flow of hot water through the system.

Description

Potable Water Heating System

This invention relates to a potable water heating system of the type wherein a storage tank containing water has an immersion heater by which the water is heated. Such systems are mainly used for the heating of domestic hot water, but the invention can be applied to industrial and commercial establishments.

The most commonly used water heating system of the above type comprises an electric immersion heater simply inserted in storage cylinder which is gravity fed with supply water from a supply tank at atmospheric pressure. When the heating element is operative, the water around the element is heated, and when heated it rises ih the cylinder causing the colder water under the element to drift up by convection and it in turn to be heated. As a result there is a gentle circulatory convection flow of the water in the cylinder, until the whole of the water is heated to a thermostatically controlled temperature.

The problem with the above described known type of system is that the heating is slow, and if there is a demand at a tap for hot water whilst the heating of the water is taking place, it is often the case that the water supplied at the tap never reaches a satisfactorily high enough temperature.

Attempts have been made to overcome this problem, and one such attempt is set forth in UK patent application No. 2275325. The solution in that patent specification is to provide that the iinmersion element is disposed in the cylinder in oblique manner, which is not in itself new, and in addition there is a sleeve around the element in order to create a flow passage between the element and the inside of the sleeve. When the element is activated, the water in the passage in the vicinity of the element is heated and as the sleeve has an inlet for the water at the bottom, and an outlet for the water at the top, so there is established a water flow from top to bottom through the sleeve, again as a result of convection, but enhanced by providing that the gravity head of water in the tank between the top and bottom of the sleeve is serving only to drive the smaller body of water in the sleeve. As a result, the heated water flows quicker than in the case of the conventional arrangement, and heating of the water takes place quicker, and by directing the small amount of heated water emerging from the sleeve outlet when there is a demand at a tap, so hot water can be supplied at the tap quicker and for longer periods.

However, even the system of this prior patent application does not give optimum performance. It still takes too long to heat the whole tank, and the hot water oudet temperature desirably needs to be higher, and at the oudet when there is a demand for hot water, the hot water needs to be supplied in the shortest possible time. Also, it is desired that there should be an ample supply of hot water over as long a period as possible.

A similar system is disclosed in FR804227 but in this system the water to be heated does not pass directly over the heating element, thereby reducing the efficiency of water heating. In addition, the sleeve is provided at an upper part of the water tank and water is returned to a lower part of the tank. This creates problems in the circulation of water in the system since cold water cannot be forced easily through hot water, thereby increasing the time taken for hot to be supplied in the system.

A further problem with conventional potable water heating systems is that whatever method is used to increase the efficiency of water heating, health and safety standards need to be met since the water needs to be fit for human or animal consumption. For example, GB2209821 discloses a central heating system which provides a neutral gas above a water level in a water tank which is separated from the water level by an immiscible fluid, such as oil, to increase the water heating efficiency of the system and provide an internal space for expansion of water. However, such a method is clearly unacceptable for use in a potable drinking water system.

The present invention seeks to provide a system which addresses and obviates or mitigates the above mentioned problems.

According to the invention there is provided a potable water heating system, said system including a receptacle for storing water with heating means located therein, a sleeve being provided around the heating means with clearance provided therebetween, said sleeve having an inlet at or adjacent a bottom end thereof and an outlet at or adjacent a top end thereof and, on operation of said heating means, a convection flow path is generated in the water in the tank from the inlet of the sleeve, through the sleeve to the outlet, the water passing directly over the heating element to be heated thereby, the water from the outlet of the sleeve being returned to the receptacle and/or being supplied to one or more locations to meet a demand for hot water, characterised in that the receptacle is pressurised.

By providing a pressurised system, and the pressure in the receptacle/ tank is typically the mains pressure of the cold water supply, considerable advantages accrue. Thus, the temperature to which the water can be heated can be considerably increased compared with a gravity system (approx. 90°C compared with approx. 60°C), therefore much more heat can be stored. This means that much more hot water can be supplied, for example for washing, over a given period. By pressurising the system, the flow rate of the water through the sleeve is increased, and hot water can be supplied much quicker after a demand has been made. In particular, even if the water in the tank is cold and a demand is made for hot water, as soon as the element is activated, hot water of a satisfactory temperature is supplied more or less straight away.

The system typically pressurises itself as a result of heating of the water in the receptacle.

The receptacle is typically in the form of a water tank and the heating means is typically in the form of an elongated immersion heater. The immersion heater is furύier typically provided in a substantially vertical orientation in the water tank and surrounded by the sleeve.

The clearance between the sleeve and the heating means is sufficient to allow the flow of heated water therealong.

Preferably the sleeve is substantially continuous along its length thereof, thereby preventing loss of heated water from the sleeve, and greatly enhancing benefits from stratification effects.

Further preferably the sleeve has substantially equal dimensions along the length thereof so as to provide a substantially even flow of water through the sleeve.

In one embodiment the sleeve is provided along a substantial length of the receptacle. Thus, for example, the inlet of the sleeve can be provided adjacent a base of the receptacle and the outlet of the sleeve can be provided at or adjacent a top of the receptacle, a space being provided between the base of the receptacle and the inlet of the sleeve to allow sufficient water to enter and flow through the sleeve to achieve the advantages of the present invention.

Preferably the heating means are provided substantially along the entire length of the sleeve, thereby maximising the volume of water that can be heated at any particular time.

Water is typically returned to the receptacle adjacent the top thereof and heated water typically exits the tank adjacent the top thereof, tiiereby increasing the circulation of water in the receptacle.

Preferably also the temperature to which the water is heated is thermostatically controlled to avoid flow blockage as a result of steam generation in the sleeve.

Preferably a temperature and/or pressure valve means is provided in the system to limit the pressure and/or temperature in the receptacle.

Further preferably a thermal cut out stat is provided in the system and yet further preferably a thermal fuse is provided in the system. The thermal fuse is typically located between two spaced apart locations on the heating means.

In one embocliment two or more of die thermostat, pressure and/or temperature release valve means, thermal cut out stat and thermal fuse are provided. Each is typically set to blow/be activated at spaced apart temperatures, thereby providing at least two levels of redundancy or safety in the system. In a preferred embodiment, all four levels of redundancy or safety are utilised in the system.

Because the system is a high efficiency system, it runs at much higher temperatures and so die tiiermostatic control is effected to ensure that steaming of the water in the sleeve does not take place. If steaming does happen, the system is likely to block.

The oudet preferably leads to a pipe above and outside the tank, the pipe containing the thermostat, and leading to a return pipe which returns the heated water to die tank, unless there is a demand for hot water, in which case the hot water is not returned to the tank, but is diverted through a branch pipe leading to the hot water supply circuit, and eventually to the location of die demand.

Since die system of d e present invention forms a closed system, when the water in the water heater tank expands as it is heated, the pressure in the water system also increases. Whilst the pressure/temperature relief valve means can be used to relieve excess pressure, expansion means can be provided for a more constant relief of thermal expansion in the system. In one embodiment the expansion means is in the form of an expansion receptacle. This is typically located on the outside of the heater jacket on die cold water inlet pipe. The expansion receptacle can be formed from steel or any other suitable material. The lining material of the expansion receptacle can be formed from rubber or any other suitable material. The size of the expansion receptacle used depends on the size of the water tank. In one embodiment the expansion receptacle is approximately 2.5% of the capacity of die water tank. An embodiment of the present invention will now be described with reference to the accompanying drawings, wherein;-

Figs. 1 and 2 are respectively a front view and a side view of a system of the present invention;

Fig. 3 is an enlarged view of the top of the cylinder shown in Figs. 1 and 2;

Fig. 4 is an exploded view of the immersion heating assembly shown in Figs. 1 and 2,

Fig. 5 shows a modified form of sleeve of the immersion heating assembly; and

Fig. 6 is a graph showing the improved performance to be achieved by embodiments of the present invention.

Referring to die drawings, in the embodiment shown in Figs. 1 and 2, there is illustrated a potable water heating system. This system typically forms part of a larger system which is connected to a mains water supply and which also includes a plurality of outiets, typically in the form of taps, located at required locations in a premises.

The water heating system is a closed system which pressurises itself upon heating due to expansion of water in the system. The system has a cylinder 10, made for example in copper, for holding the water to be heated, and surrounding the cylinder 10 is a thermal jacket 12, of known construction. The cylinder is held in a casing 14 of the configuration shown. The dimensions shown in die drawings are the relevant dimensions of a specific design. These dimensions are of course exemplary and are not intended to limit the invention, as clearly the unit could be of any suitable size.

The cylinder 10 is domed at the top and bottom, and for stability die bottom rests on a base 16 of die casing 14.

The top of the cylinder is provided with a fitting 18 whereby an elongated heating element 20 is suspended from the top of the cylinder, and extends down into the interior of the cylinder 10. Surrounding the fitting with clearance is an open ended sleeve or shield 22, also typically of copper. The sleeve 22 extends from the fitting 18 to a position approximately coincident with the bottom of the heating element.

In ti is example, die heating element is an electric immersion heater type, and it, the sleeve 22 and the fitting 18 are shown in more detail in Fig. 4, to which reference is now made. The fitting comprises basically two rings 18A and 18B which in use are screwed together. Ring 18B is brazed or otherwise fixed to the top of the sleeve 22, which in turn is brazed or otherwise fixed to the top of the cylinder 10, and ring 18A is adapted to be screwed to the ring 18B. The screw design in the fitting 18 is such that the rings are simply screwed together by hand to make the fitting, but when they are so screwed together and the fitting is hot (which happens when the system is functional) they lock and can only be unscrewed when the fitting is cooled. When the fitting is made, it traps between the rings 18A, 18B, a plate 24 of the heating element. This plate 24 also supports die terminals 26, 28 of the electric element 20, and an eartii terminal 30. An oudet pipe 32 is provided in the plate 24 so that water which flows through the sleeve 22 and over the element 20 and heated thereby can flow through this pipe 32 and exit the fitting 18.

When it exits the fitting 18 the hot water enters one leg of an T shaped union 34 (Fig. 3) which houses a thermostat 35 set to control the operation of the element 20. From the other leg of the union 34, a short pipe 36 feeds the heated water to a T shaped union 38 in a vertical discharge pipe 40 having a second T shaped union 42. Oudet 44 from union 42 is for feeding hot water to consumption points such as domestic taps. If there is no demand from a consumption point, the hot water is returned via pipe 40 to the top of the cylinder 10 as shown by arrow 46.

The cylinder is pressurised. That is to say when the system is running, the pressure inside the cylinder 10 is at a pre-determined level, such as for example the cold water mains pressure, the cold mains water being supplied tiirough an inlet 50 shown in Fig. 1. Behind this inlet there is a cold water deflector plate which serves to direct the incoming cold water to the optimum location for best circulation and heating of the water. The cylinder 10 also has a drain outiet 48, which is normally closed but can be opened to drain die system for maintenance and repair. At the top of pipe 40 the union 38 houses a temperature and pressure relief valve 52 which opens in the event of the cylinder pressure or water temperature exceeding a predetermined value. These values can be adjusted.

By virtue of the system being pressurised, the water can be heated up to much greater levels tiian in gravity feed systems, with the advantages referred to herein. When the heating element is operational, the water in the sleeve directiy surrounding the element 20 is heated rapidly due to the high running temperature. As a result, the hot water rises in the sleeve 22, and is replaced by fresh cold water flowing into the sleeve 22 at the bottom end. An upwards flow of water through the sleeve 22 is immediately established, and because the system is pressurised, and higher temperatures are used tiiis flow is much faster than in a gravity fed system. If there is no demand from the consumption points, die heated water is returned to the cylinder 10, and quickly the entire volume of water in the cylinder 10 is heated up to a high temperature, for example in die order of 90°C. The thermostat cuts off the heating element when the temperature in the cylinder reaches a "cylinder satisfied" level, and at tiiis level, steam generation in the sleeve is avoided. If there is a demand at a consumption point, the heated water can flow direct to die consumption point through outlet 44, even if the rest of the water in d e cylinder 10 is cold. Thereby, heated water of a satisfactory temperature can be supplied almost on demand. The principle is that only a small volume of water (that in the sleeve 22) is heated at any instant, and because high temperatures and a pressurised system are used, heating is extremely rapid. This leads, as will be demonstrated herein, to previously unachievable efficiencies. The system is therefore both an in line system, by which hot water can be supplied directly on demand, regardless of the state of the store, and also when the store is fully charged, hot water can be supplied in large quantities.

Fig. 5 shows a slight modification to the design of the sleeve bottom end. In this case, the sleeve is closed at the bottom end by means of a cap, but to provide the inlet for the water there is a branch pipe 56 in the sleeve 22, as shown, and water enters the sleeve 22 through this inlet pipe 56. Other designs are possible. The cylinder will be sized to suit the application, and currentiy it is believed that most domestic applications will be served by a range of cylinder sizes, and two heating element sizes for each cylinder size. By way of example only, die cylinder sizes may be 14, 44, 65 and 120 litres (approx. equivalent to 4, 12, 17 and 32 US gallons) each adapted to be fitted witii a 3Kw or a 6Kw immersion electric heater.

In a further example of the present invention, in addition to the thermostat temperature control means 35 and the temperature and pressure relief valve 52, a further level of redundancy can be provided so as to provide a further safety mechanism in the event that the thermostat 35 and valve 52 fail. This further level of redundancy is in the form of a cut out stat 33 which is typically wired in series to the main thermostat. The cut out stat can be located on hot water oudet 32. It is typically set at 120 degrees Centigrade and therefore is activated if there is water in the tank and the thermostat (typically set at 94°C) and valve 52 (typically set at 105°C) fail. However, if there is no water in the tank and the power in the system is switched on, a fourth level of redundancy or safety is required. This can be in the form of a thermal fuse temperature control means 39 which in one example is set at 150°C. Thus, if the heating element in the tank fails, the thermal fuse ensures the element goes to earth (i.e. it prevents the cylinder from becoming electrically live). The thermal fuse can be located between the two legs of the heating element.

Fig. 6 shows graphically the improved performance that can be achieved witii the heating system of the present invention. The systems tested to produce the graphs of Fig. 6 were systems in which the cylinder was not provided witii tiiermal insulation, and so even better results can be expected to be achieved witii lagged production models. Referring now to Fig. 6, which is largely self explanatory having regard to die wording thereon, the graphs illustrate the heating and delivery characteristics of three specific prototype heating systems according to the invention, referenced I (32 US Gallon 6KW Heater (240V x 30A), II (32 Us Gallon 3KW Heater (110V x 30A) and III (4 US Gallon 3KW Heater (110V x 30A). All of the systems are shown as being heated from a cold condition 1, when the water in the cylinder is at 12°C. The heating element is now switched on, and the water is heated by the circulation discussed above. At this time, no hot water is being drawn off. Heating continues until the "cylinder satisfied" point 2 is reached (Hot water 'on' at 2.0 US Gallons /min). At this point the water in the store is at the required temperature set by the thermostatic controls and as the system is pressurised this temperature is in the order of 90°C, which is much higher than in conventional systems. To reach this condition took approximately 19 minutes, which again is much faster than conventional systems.

The rest of the curves show the conditions which apply as hot water is drawn off at maximum rate. During this draw off, heat continues to be supplied via the heating element.

As can be seen, for a 4 US gallon cylinder, 5 gallons can be drawn off in some 4/5 minutes before the draw off temperature reaches 40°C, which is considered a minimum. With the 32 gallon cylinder using a 3Kw heater, 60 US gallons could be drawn off in approximately 30 in. before the minimum temperature was reached, and for the 32 gallon cylinder witii a 6Kw heater, 120 gallons could be drawn off before the minimuπi temperature was reached. In all cases in practice, the outiet for the hot water would be supplied to an automatic mixer valve to which cold water is also supplied so that the hot and cold water are mixed to varying degrees automatically so that the final outputted mixed water is at a sensibly constant pressure and temperature. Such automatic mixing valves are well known.

It can be seen therefore that the invention provides a high efficiency combined in line and storage water heating system, giving outputs and efficiencies not achievable in the conventional gravity fed systems currentiy available.

Claims

Claims:

1. A potable water heating system, said system including a receptacle (10) for storing water with heating means (20) located therein, a sleeve (22) being provided around die heating means (20) with clearance provided therebetween, said sleeve (22) having an inlet at or adjacent a bottom end thereof and an oudet at or adjacent a top end thereof and, on operation of said heating means, a convection flow path is generated in the water in the receptacle from the inlet of the sleeve, tiirough the sleeve to the outlet, the water passing directiy over the heating element to be heated thereby, the water from the outiet of the sleeve being returned to the receptacle (10) and/or being supplied to one or more locations to meet a demand for hot water, characterised in that the receptacle (10) is pressurised.

2. A system according to claim 1 characterised in that thermostatic control means are provided in or associated with the receptacle (10) to allow thermostatic control of the water temperature.

3. A system according to claim 2 characterised in that the outlet of the sleeve leads to a pipe (32, 34) above and external to the receptacle, the pipe containing the thermostatic control means.

4. A system according to claim 3 characterised in that the pipe (32, 34) leads to a return pipe which either returns the heated water back to die receptacle if there is no demand for the heated water or diverts the heated water to one or more branch pipes (44) if there is demand for the heated water at one or more locations.

5. A system according to claim 1 characterised in that pressure and temperature relief valve means (52) are provided.

6. A system according to claim 1 characterised in that a thermal cut out stat means (33) is provided.

7. A system according to claim 1 characterised in that thermal fuse means (39) are provided between at least two spaced apart locations on die heating means (20).

8. A system according to a preceding claim characterised in that two or more of the thermostatic control means (35), temperature and/or pressure relief valve means (52), thermal cut out stat means (33) and thermal fuse means (39) are provided and each are set to be activated at spaced apart temperature settings.

9. A system according to claim 1 characterised in that the receptacle (10) is a water tank and the heating means (20) is in the form of an elongate immersion heater located in said water tank within the sleeve.

10. A system according to claim 9 characterised in that the elongated immersion heater (20) is located in a substantially vertical orientation in the water tank (10).

11. A system according to claim 1 characterised in that the sleeve (22) is substantially continuous along its length.

12. A system according to claim 1 characterised in that the sleeve (22) has substantially equal dimensions along its length.

13. A system according to claim 1 characterised in that sleeve (22) is provided along substantially the entire length of the receptacle (10) with a space provided adjacent the inlet of the sleeve and the base of the receptacle sufficient to allow the flow of water through the sleeve.

14. A system according to claim 1 characterised in that the heating means (20) are provided along substantially the entire length of the sleeve

(22).

15. A system according to claim 1 characterised in that water is returned to the receptacle (10) adjacent a top thereof and heated water is removed from the receptacle adjacent a top thereof.

16. A system according to claim 1 characterised in that attachment means for attaching the heating means and the sleeve to the receptacle includes two annular members (18A, 18B), one annular member for attachment to the sleeve (22) and this annular member and/or the other annular member for attachment to the receptacle (10), and a portion (24) of the heating means being located between the two annular members (18A, 18B) when said members are brought into engagement with each other to secure the heating means (20) in position.

17. A system according to claim 16 characterised in that the heating means portion (24) supports electrical terminals (26, 28) of the heating means, including an earth terminal (30).

18. A system according to claim 1 characterised in that the receptacle (10) is pressurised at mains water pressure.

19. A system according to claim. 1 characterised in that an inlet (50) is provided in the receptacle (10) for directing a cold mains water supply therein.

20. A system according to claim 19 characterised in that the inlet (50) is provided adjacent a lower portion of the receptacle (10).

21. A system according to claim 1 characterised in tiiat a drainage outiet (48) is provided in the receptacle (10).

22. A system according to claim 4 characterised in that the return pipe and/or one or more branch pipes (44) are provided with one or more temperature and/or pressure relief valves (52) which open in the event of the cylinder pressure and/or water temperature exceeding a pre-determined value.

23. A system according to claim 1 characterised in that the bottom of the sleeve (22) is closed by closure means and the inlet is provided in the form of a pipe (56) located adjacent the bottom of the sleeve (22).