GB2367609A

GB2367609A - Fluid heating device

Info

Publication number: GB2367609A
Application number: GB0020605A
Authority: GB
Inventors: Thomas Henry Bell
Original assignee: David Michael Elder
Current assignee: David Michael Elder
Priority date: 2000-08-21
Filing date: 2000-08-21
Publication date: 2002-04-10
Anticipated expiration: 2020-08-21
Also published as: GB2367609B; GB0020605D0

Abstract

The device 10 has a primary hot water storage tank 12 and a secondary external heating tank 14 with a smaller capacity for fluid. The external tank contains a U-shaped electric heating element 16 and a temperature sensing means 18, such as a thermostat. An inlet pipe 20 connects the two tanks together and a further pipe 22 allows circulation of heated fluid back into the primary tank or out through pipe 26 for use. The thermostat has a first end connected to an electrical transducer and a second end positioned upstream (i.e. near to inlet 20) from the first end, although the arrangement may be reversed. The thermostat is positioned longitudinally parallel to the heating element.

Description

HEATING DEVICES

Background of the Invention This invention relates to fluid heating devices. More particularly, though not exclusively, this invention relates to water heating devices wherein there is an improvement in control of heated water temperature, and there is provided an ability to heat a relatively small volume of water from a storage tank.

As conventional electric water heaters seek to heat an entire volume of a tank, it takes a relatively long while to obtain heated water. It is also very wasteful of energy to heat a whole tank when only a small amount of heated water is required. Previously, to address these problems and seek to improve the heating process, a double heating element has been proposed. Furthermore, to seek to improve the heating process, multiple or separate heating elements, or the like, have been developed so that not all of a body of water in a tank has to be heated. For example, if a heating element is provided in an uppermost region of a tank, only a top part of the water will be heated, where from the heated water may be drawn off.

In the prior art there has also been proposed provision of a hot water tank with an external heating tank of smaller volume than the hot water tank so as to allow heating of small amounts of water when desired.

A disadvantage of such prior art is that thermostat (s) have been found not to properly monitor the temperature of heated water. It is believed that this is because the thermostat is constantly cooled by cooler water. I t is an object of at least one aspect of the present invention to obviate or at least mitigate one or more of the aforementioned problems.

It is a further object of at least one embodiment of the present invention to provide an improved control of temperature of heated water from a domestic boiler.

A yet further object of at least one embodiment of the present invention is to provide a means for heating a relatively small volume of water from a domestic hot water tank/boiler.

Summary of the Invention According to a first aspect of the present invention there is provided a fluid heater apparatus comprising: a primary tank; a secondary tank having a heating means and a temperature sensing means; and means allowing fluid communication from the primary tank to the secondary tank; wherein the temperature sensing means has a first end connected to an electrical transducer and a second end, the second end being positioned upstream from the first end.

Herein"upstream"means closer to the fluid communication means.

The fluid heater apparatus may also comprise means allowing fluid communication from the secondary tank to the primary tank.

Preferably, the temperature sensing means is a thermostat, for example, a bimatic strip, rod, or trip thermostat.

Preferably, the fluid heater is a water heater.

Preferably, the heating means is an electric water heater.

In a preferred embodiment, the heating means may be substantially U-shaped and may be suspended from a top portion of the secondary tank with the temperature sensing means preferably situated substantially longitudinally adjacent the U-shaped heating element.

In an alternative embodiment, the first end of the temperature sensing means may be situated at or near an uppermost portion of the secondary tank an electrical connection end or ends of and the heating element may be situated at or near a lowermost portion of the secondary tank adjacent the means for allowing fluid communication from the primary tank to the secondary tank.

Preferably, the secondary tank is substantially cylindrical and optionally has a diameter to length ratio of around 35% to 40%, and preferably a diameter of around

76. 1mm (3 inches) and a length of around 300mm.

It is further preferred if heated water is drawn off from the primary tank by a pipe at or near top portion.

Preferably, there is provided a pump which aids flow of water to and from the secondary tank.

Brief Description of the Drawings An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a sectional side view of an electric water heater according to an embodiment of the present invention; Figure 2 is a sectional side view of an external heating tank of the electric water heater shown in Figure 1 to an enlarged scale; Figure 3 is a top view of an external heating tank shown in Figure 1 to an enlarged scale; Figure 4 is a cross-sectional view along line A-A of Figure 3; Figure 5 is a graph showing water temperature versus time for the water heater of Figure 1 when a thermostat is set to 60 C ; Figure 6 is a graph showing water temperature verus time for the water heater of Figure 1 when the thermostat is set to 65 C ; and

Figure 7 is a graph showing water temperature versus time for the water heater of Figure 1 when the thermostat is set to 70oC.

Brief Description of the Drawings In Figure 1, there is shown a water heater, generally designated as 10, according to an embodiment of the present invention. The electric water heater 10 comprises a primary hot water storage tank 12 and a secondary external heating tank 14, the external tank 14 having a smaller internal volume than the water storage tank 12. As shown in Figure 2, which is an enlarged view of the external heating tank 14, the external heating tank 14 has a U-shaped electric heating element 16 and a thermostat 18. In the present embodiment, for example, a VKL 3000 rod thermostat available from"SUNVIC"may be used. The rod used in the thermostat 18 has a known coefficient of expansion.

As shown in Figure 1, water enters the water storage tank 12 at a bottom portion through inlet 30 e. g. from a header tank. When the heating element 16 is activated (i. e. switched on), the water surrounding the heating element 16 is heated. As the water surrounding the heating element 16 is heated the water expands and becomes buoyant.

This has the result that the heated water ascends and rises up through the external heating tank 14. To replace the

ascending heated water, cold water from the storage tank 14 flows into the external heating tank 14 via inlet 20 to external tank 14. The heated water in the external heating tank 14, as it rises, flows over the thermostat 18 which monitors the temperature of the water. The heated water then rises up outlet 22 and then flows back into a top portion the storage tank 12 via open-vented pipe 24.

Usually a top part of outlet pipe 22 is about 600mm above the top of the storage tank 12 which creates a circulating head. Gravity circulation of the water is therefore set up within the water heater 10. The heated water when it is fed into the top of the storage tank 12"sits"on top of the unheated (i. e. cold) water. Stratification of different temperatures of water may therefore be set up within the storage tank 12. When hot water is required, a tap (not shown) is opened, and hot water is fed out via pipe 26.

Figure 3 shows a top view of a head cap 28 of the external heating tank 14. This shows the orientation of the thermostat 18 to the heating element 16.

Figure 4 shows a cross-sectional view along line A-A of the head cap 28 of Figure 4 which clearly shows outlet pipe 22.

Additionally, the external heating tank 14 used has a diameter of about 76. 1mm (3 inches) whereas previous external heating tanks have used a diameter of 54mm (2

inches). This provides the advantage of reducing the flow rate of water through the external heating tank 14 and gives the thermostat 18 time to heat up and properly monitor the temperature of the heated water. The length of the external heating tank 14 is about 300mm. The overall length from the top of outlet pipe 22 to the bottom of the storage tank 12 is about 2m.

An advantage of the present invention is that the heating element 16 or thermostat 18 may be replaced easily.

This is done by detaching cap 28 at the top of the external heating tank 14, e. g. by screws, bolts or the like, which allows easy access to the heating element 16 and the thermostat 18.

Although not shown in any of the Figures, the water heater 10 may also comprise a small pump either inside the external heating tank 14 or in inlet pipe 20 or outlet pipe 22 which acts to aid the flow of water and may eliminate the need for having a head of hot water in outlet pipe 22 and pipe 24 above storage tank 12.

Figures 5,6 and 7, respectively, show water temperature against the heating element on time in the external tank 14 of Figure 1 wherein the thermostat is set at 60oC, 65 C and 70oC. The lines A, B, and C in Figures 5, 6 and 7 represent measurements taken by thermal couplings placed at a variety of positions in the external tank 14. Line A represents measurements from a thermal coupling

positioned towards a top of the external tank 14, line B represents measurements from a thermal coupling positioned towards a midpoint of the external tank 14, and line C represents measurements from a thermal coupling positioned towards a bottom of the external tank 14. It should be noted that the temperature is maintained below boiling i. e.

100oC. Furthermore, the line A has a"jagged"character which illustrates the thermostats 18 function to switch the heating element 16 on and off and control the temperature of the heated water. The thermostat 18 includes a transducer 19 which switches the heating element (s) on and off in a controlled fashion.

Finally, it should be noted that the present invention meets the new (and old) British and European Standards for thermostats controlling the temperature of heated water and keeping it below 98OC. Previous thermostat arrangements have not met these Standards due to cooler (i. e unheated) water flowing over the thermostat and therefore causing overheating of water.

Example Below is a worked example of the present invention

using a 3kW heater (i. e. the heating element) which has a temperature difference of 22 C between the heated and the unheated water. The flow rate can be calculated as follows:

Flow rate = 3kW (i. e. power of heater) 4. 2 (specific heat X 22 (temperature capacity of water in difference between kilojoules) heated and unheated water) = 0. 032 kg/s (this is the flow rate required to maintain this temperature difference) The circulating pressure per metre of height is then found from the following formula: circulating pressure = 9. 81 (p2-pl) (in Pa per metre of height for head) where p2 = density of return water (kgfm3) pi = density of flow water (kg/m ?) i. e. total circulating pressure 1. 5m x 9.81 x (990.93-980. 29) (head of water) 156. 56Pa To compensate for fittings etc in the pipe and using a 2m pipe, 10% is added to this, i. e. the effective length of the pipe is said to be 2.2m.

The circulating pressure per metre of pipe is then calculated: circulating pressure = total circulating pressure effective length = 156.56 2.2 = 71.16Pa As the frictional loss for a 20mm diameter pipe is 9.5Pa

per metre of pipe which is less than the circulating pressure (71. 16), the system will be satisfactory.

It will be appreciated that the embodiment of the present invention hereinbefore described is given by way of example only, and is not meant to limit the scope thereof in any way.

It will particularly be appreciated that the primary tank/hot water storage tank may be provided with further heating means and further temperature sensing means in a conventional manner so as to allow heating of the whole body of water in the primary tank/hot water storage tank.

It will also be appreciated that while delivery of water to tap (s) from the primary tank may be caused, in the normal way, by the pressure of water from a header tank via pipe 30, flow of hot water from secondary tank to the top portion of the primary tank is caused by gravity convection circulation with the sealed fluid heater apparatus.

Claims

1. A fluid heater apparatus comprising : a primary tank; a secondary tank having a heating means and a temperature sensing means; and means allowing fluid communication from the primary tank to the secondary tank; wherein the temperature sensing means has a first end connected to an electrical transducer and a second end, the second end being positioned upstream from the first end.

2. A fluid heater apparatus according to claim 1 which comprises means allowing fluid communication from the secondary tank to the primary tank.

3. A fluid heater apparatus according to any preceding claim, wherein the temperature sensing means is a thermostat.

4. A fluid heater apparatus according to claim 3, wherein the thermostat is a bimatic strip, rod, or trip thermostat.

5. A fluid heater apparatus according to any preceding claim, where the fluid heater is a water heater.

6. A fluid heater apparatus according to any preceding claim, wherein the heating means is an electric water

heater.

7. A fluid heater apparatus according to any preceding claim, wherein the heating means is substantially U-shaped.

8. A fluid heater apparatus according to any preceding claim, wherein the heating apparatus is suspended from a top portion of the secondary tank.

9. A fluid heater apparatus according to any of claims 7 and 8, wherein the temperature sensing means is situated substantially longitudinally adjacent the U-shaped heating means.

10. A fluid heater apparatus according to any of claims 1 to 6, wherein the first end of the temperature sensing means is situated at or near an uppermost portion of the secondary tank.

11. A fluid heater apparatus according to claim 10, wherein an electrical connection end or ends of and the heating element are situated at or near a lowermost portion of the secondary tank adjacent the means for allowing fluid communication from the primary tank to the secondary tank.

12. A fluid heater apparatus according to any preceding claim, wherein the secondary tank is substantially cylindrical.

13. A fluid heater apparatus according to any preceding claim, wherein the secondary tank has a diameter to length ratio of around 35% to 40%.

14. A fluid heater apparatus according to any preceding claim, wherein the secondary tank has a diameter of around 76. 1mm (3 inches) and a length of around 300mm.

15. A fluid heater apparatus according to any preceding claim, wherein heated water is drawn off from the primary tank by a pipe at or near a top portion.

16. A fluid heater apparatus according to any preceding claim wherein there is provided a pump which aids flow of water to and from the secondary tank.

17. A fluid heater apparatus substantially as hereinbefore described with reference to the accompanying drawings.

18. A method for heating fluid substantially as hereinbefore described with reference to the accompanying drawings.