GB2153503A - Water heating apparatus - Google Patents

Abstract

The present invention provides a heating apparatus wherein the heating tank contains a primary water which is heated and secondary water is heated by the primary water in being passed through heating coil means 46A and B contained in the primary water. The secondary water comes from the mains, enters the heat exchange coil means and then leaves, heated, for supply to a consumption point such as water taps. The heating coil means comprises two relatively narrow heating coils well spaced apart inside the body of primary water, and the heating of the primary water is by means of a circulating boiler or the like drawing water from the bottom of the primary body, heating same and returning it to the top of the primary body in the vicinity of the upper heating coil. <IMAGE>

Description

SPECIFICATION Water heating apparatus This invention relates to water heating apparatus, and in particular is concerned with water heating apparatus of the type (referred to hereinafter and in the appended claims as "heating apparatus of the type set forth") having a tank which acts as a thermal store for a body of water (primary water) which is or can be selectively circulated around a flow heating circuit, such as a small bore central heating system in a domestic dwelling. The heat is added to the body of the primary water in the tank by any appropriate heating means, which may be either inside the tank but preferably will be external of the tank and will be a boiler or solar heating means through which the primary water from the tank is circulated and by which the primary water is heated.

Reference is made in the above to "primary" water because the present invention concerns heating apparatus of the type set forth having a secondary water circuit, and that secondary water circuit includes a heat exchange coil which is inside the thermal store tank. The secondary water passes through the coil and receives heat from the heated primary water in the tank which surrounds the coil, and the heated secondary water which issues from the coil is for consumption i.e. at domestic water taps, washing machines, or for general purposes.

It can been seen therefore that the heating circuit through which the primary water flows is in fact a closed circuit in that the water which passes through the heating system is returned to the tank, whereas in the secondary water circuit the cold water, which may be supplied directly from the mains, passes through the heat exchanger coil and receives heat from the primary water in the tank, and then the heated secondary water is consumed, and therefore the secondary water circuit is an "open" circuit.

The above arrangement is in fact somewhat opposite to what is currently used in domestic hot water systems. Currently, the hot water tank receives water from the mains after it has passed through a water break, which is required by law in the United Kingdom, which may be an expansion tank having a flow control valve. Water is drawn directly from the hot water tank for general consumption. The heating system is a separate circuit and the water therein is heated directly by the boiler.

The purpose of the break tank in the supply of mains water to the hot water tank in the conventional system is to ensure that the water in the hot water tank will essentially be at atmospheric pressure, or at least at a low pressure, and domestic hot water tanks in the United Kingdom currently are therefore of the "non-pressure" type. However, nearly all other countries in Europe operate on pressurised supply systems, which involves bringing the water at mains pressure directly to the hot water tank, through appropriate pressure reducing valves and non-return valves to prevent back flow or contamination from the tank to or in the mains supply. Such systems require the use of a large volume expansion chamber in order to avoid explosions and burst tanks. The expansion chamber is required for the case where the water in the water tank over heats and expands.The expansion chamber will take up this expansion as related to the maximum possible expansion of the water in the water tank calculated on the volume of the water tank. As the total volume of the tank is relatively large, then a large expansion chamber is required. The expansion chamber comprises a sturdy vessel containing a diaphragm to one side of which is a volume of inert gas, in particular nitrogen, and to the other side of the diaphragm, hydraulic communication is made with the body of water in the water tank.If British domestic hot water tanks were therefore converted to receive the supply direct from the mains, then depending upon the allowable internal pressure in the hot water tank, so the tank would require an expansion chamber as described, a pressure regulating valve in order to step down the mains pressure would not be allowable to have mains pressure in the tank even if it were permissible to use the tank in a pressure system and filters.

With heating apparatus of the type set forth however, because the mains supply water, the secondary water, passes through the heat exchanger coil to receive its heat, only a relative small volume of the secondary water i.e. that in the coil, will be heated, and therefore the danger of explosion is considerably reduced, because the expansion of a small volume of water is correspondingly small.

The present invention is concerned with enabling the most effective heat transfer between the body of water in the tank, and water in the heat exchanger coil which is also contained in the tank.

When the heat exchanger is in the form of a plurality of equally spaced coils, it has been found that the most effective heat transfer is not achieved. When the primary water in the tank is heated, it will tend to be hotter at the top than at the bottom and when there is no flow of secondary water, and heat exchange is taking place, then the standing water in the coils of the heat exchanger will be temperature graded in an upwards direction from the bottom coil to the top coil, and when the secondary water is used, then the temperature of water issuing from the tap will soon decline.

It has been found that by using the present invention, discharge of secondary water at a more consistently high temperature can be achieved over a longer period, and this is achieved in accordance with the present invention in that the heat exchanger comprises a length of heat exchange tubing located inside the tank so as to be immersed in the primary water, and the tubing is coiled into at least two groups of coils which are spaced in the height direction of the tank, so that one of the groups will be near the top of the tank, and the other near the bottom of the tank.

This arrangement has been found to give improved performance in that effective stratification of the primary water in the tank is obtained i.e. the water in the tank remains relatively quiescent and the water at the top of the tank remains hotter than that at the bottom, and because of this the secondary water at a consistently higher temperature and for a longer time can be delivered from the system.

The groups of coils may be connected by a straight length of the pipe, and preferably the heat exchange pipe is in copper.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, wherein: Figure 1 is a diagrammatic, sectional side elevation of heating apparatus according to one embodiment of the present invention; Figure 2 is a diagrammatic, sectional side elevation of heating apparatus according to a second embodiment of the invention; Figure 2A is a diagram for the purposes of ex plaining the relative disposition of the heat exchange coils in the tank; Figures 3, 4 and 5 indicate methods of controlling the flow of primary water through the heating circuit driven by the apparatus; and Figure 6 shows graphically the performance of the apparatus according to either of the embodiments of the invention shown in Figures 1 and 2.

Referring to the drawings, in Figure 1 is shown a tank 10 which comprises an inner casing 12 of copper or like material, cladding 14 of insulation, such as fibre-glass, and an outer case 16 of galvanised mild steel.

The tank 10 defines two cavities, namely a main cavity 18, and an expansion overflow cavity 20.

The cavity 18 contains primary water which is circulated around a flow heating circuit through go and return pipes 22 and 24, the direction of flow being indicated by arrows 26. The primary water in cavity 18 is heated by means of a small (approx. 3 Kw) open flue gas circulator 28 which circulates the primary water therethrough as indicated by the arrows 30. Cold water is supplied to the cavity 20 through pipe 32 and float controlled valve 34, and flows from the cavity 20 into cavity 18 through down pipe 35. Reference 36 illustrates an over flow in cavity 20, whilst expansion pipe 38 enables water to flow from the cavity 18 and the cavity 20 when the water in cavity 18 expands.

By drawing primary water from the bottom of cavity 18, and by passing it through the gas boiler 28 to heat same and then injecting the heated water into the top of the cavity 18, the water in cavity 18 becomes hotter at the top than at the bottom, and hence the water becomes "stratified" in that there is a temperature gradient over bands of water levels from bottom to top of the cavity 18.

As water is drawn off to the heating system through pipe 22, so the hottest water at the top of the tank is immediately fed into the heating system, adding to efficiency. Reference numral 40 indicates a pump for circulating the hot water around the heating system 22, 24. Finally, in relation to the heating system, there is a bleed pipe 42 from pipe 24 to bleed a variable amount of the returning, cooler water in pipe 24 through a control lable mixing valve 44 back into the line 22 without circulating through the cavity 18, whereby the tem perature of the water flowing along pipe 22 can be controlled.

In said cavity 18 is a pipe 46, which is in fact a heat exchange pipe, and this pipe is immersed in the primary water in cavity 18, and is in two groups of coils, one 46A towards the bottom of the cavity 18, and one 46B toward the top of the cavity. The group of coils 46B is in the hottest region of the water in cavity 18, and the spring of the coils is of particular advantage as explained with reference to Figure 2A, providing that the secondary water which is in the pipe 46, is heated more strongly in the coils 46B so that when the secondary water is outputted through pipes 48, it is at the correct temperature.The secondary water is inputted into a lower group of coils 46A through an inlet pipe 50, which may be supplied directly from the mains through suitable pressure reduction and non-return valves in order to ensure that the secondary water will be at the correct pressure, and that it will not flow back into the mains supply, which could cause contamination. The output pipe 48 is directed to consumer points in the domestic dwelling, such as hot water taps, and a washing machine supply.The secondary water is heated in passing through the two coils 46A and 46B, but the secondary circuit also has a bleed pipe 52 which has a one-way valve 54 leading to a control valve 56 by which a controlled and variable amount of cold water bled from the line 50 is mixed with hot water issuing from the group of coils 46B, to control the temperature of the hot water which is eventually discharged from the domestic taps.

In the arrangement shown in Figure 1, the expansion cavity 20 is integral with the tank 10, and the boiler 28 is mounted on or adjacent the tank. In the arrangement shown in Figure 2, the system is essentially the same, except that the expansion cavity is replaced by a separate expansion tank 20A which may be remotely located, and the boiler is a balanced flue gas circulator 28A, which again is remotely located. Other components already described in relation to Figure 1 operate in the same manner as described in relation to Figure 1, and are designated with the same reference numerals.

An additional pump 30A is required for circulating the primary water through the boiler 28A.

Referring now to Figure 2A, this figure shows the two coils 46A and 46B and the relative dispositions within the body of water in the cavity 18. The figure also shows particularly prepared dimensions for the tank water and coils. The body of water is indicated as being a cylinder outlined by line 18A.

The diameter is shown as being D and the height as H. The disposition of the coils 46A and 46B in the body of water 18A is significant for achieving the advantageous effect of the invention. Thus, the coils 46A and 46B preferably are symmetrically disposed around the centre line 19, and are spaced by a distance S which is greater than the height L1 or L2 of the respective coils 46A or 46B. Height L1 and L2 preferably are the same. Height L1 and L2 are related to the height H in the following ratio range; 1:3 to 1:7 and preferably approximately 1:5.

Equally, the diameters D1 and D2 of the coils 46A and 46B are preferably related to the diameter D of the body of water within the following ratio range; 2.5:5 to 3.5:4 and preferably approximately 3:4.

Diameter D1 is preferably but need not be the same as diameter D2.

Finally, the height S is probably related to the height H to be in the following ratio range; 1:2 to 1:4 and preferably approximately 1:3.

Designing the coils 46A and 46B and their positions within the body of water 18A provides advantageous results in that hot water can be drawn from the upper coil 46A for a longer period.

Although reference has been made in the above to the body of water 18A being cylindrical clearly this is not a necessary requirement and the coils 46A and 46B need not be circular.

Figures 3, 4 and 5 show various control systems for the control of the heating circuit 22, 24. In the arrangement of Figure 3, the mixing valve 44 is shown as being simply manually controlled by a controller 60, and a pump 40 is controlled by a simple on/off switch 62, which is in turn controlled by a thermostatic radiator valve on the main living room radiator or at any other suitable location.

In the arrangement of Figure 4, the mixing valve 44 is automatically controlled by means of a room sensor 64, the pump 40 again being controlled as described in relation to Figure 3.

Heating can of course be controlled in a more conventional fashion using a time clock and conventional room thermostat 66 and 68 as shown in Figure 5, these two components controlling the pump 40, so that the pump 40 runs during the time that is set by the time switch, and as long as the room thermostat does not detect that the room temperature is above the predetermined level.

The embodiments operate in that the fluctuating demands for heating and hot water are evened out by storing energy produced when demand is low and discharging it when demand is high. An important feature of the design is that the secondary water can be supplied directly from the mains at conventional flow rates without the need for nonreturn valves, temperature and pressure safety relief valves or expansion vessels.

Typically, the cavity 18 will contain 160 litres of primary water which is maintained at a temperature approximately 80"C at the top of the cavity.

With such an arrangement, and a heating load of 2.5 KW, two 70 litre baths at a flow rate of 15 litres per minute with a 30 minute with a 30 minute interval between the two whilst maintaining the hot water draw temperature above 45"C can be drawn, as shown in Figure 6, and during this period the room temperature remains between 20 and 22"C.

Although the apparatus described has particularly good application for small start-up homes, there is no reason why the principle cannot be used for any dwellings.

Claims (6)

1. Heating apparatus of the type set forth wherein the heat exchange coil for the secondary water is in the form of two coils which are substantially spaced within the primary water, and connected by a length of pipe also in the primary water.

2. Apparatus according to Claim 1, wherein each coil has a height which is a fraction of the height of the body of primary water so as to fall within the ratio range as follows; 1:3 to 1:7.

3. Apparatus according to Claim 1 or 2, wherein the said heating coils are spaced by a height related to the height of the primary water so that the said spacing as related to the height of the primary water is within the ratio range as follows; 1:2 to 1:4.

4. Apparatus according to any preceding claim, wherein the width dimension of each coil is related to the width dimension of the body of water so as to lie within the following ratio range; 2.5:4 to 3.5:4.

5. Heating apparatus according to any preceding claim including means for heating the water which draws the water from the bottom of the primary body of water, heats same, and returns it to the top of the body of the primary water whereat the upper of the said heating coils is located.

6. Heating apparatus substantially as hereinbefore described with reference to the accompanying drawings.