GB2153504A - Water heating apparatus - Google Patents

Abstract

Water heating apparatus comprises a hot water tank containing primary water heated by for example a boiler. There is a heat exchange coil 46A and B in the tank and secondary water is passed through the coil to be heated by the primary water. There is an expansion chamber 46C located in the water tank and it is in communication with the secondary water in the coil so as to accommodate thermal expansion thereof. <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 claims as a heating apparatus of the type set forth) having a tank which acts as a thermal store for a body of 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 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 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 overheats and expands.The expansion chamber will take up this expansion as reiated 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 it would not be allowable to have mains pressure in the tank even if it were permissable to use the tank to 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 taking account of thermal expansion of the water in the secondary circuit, and in accordance with the invention, the provided in a heating apparatus of the type set forth a thermal expansion chamber comprising a closed housing in hydraulic connection with the secondary water circuit.

Typically, the closed housing may be a short vertical pipe containing air in the top of same, and the bottom being in hydraulic communication with the secondary circuit. By this means, thermal expansion can be readily accommodated in view of the fact that only a relatively small volume of secondary water is subjected to the heating in the thermal storage tank, and therefore only a small amount of thermal expansion need be accommodated.

As the secondary water circuit is an open circuit, there is no need to isolate the air in the expansion chamber from the secondary water, because the secondary water is constantly being replenished as it is used, and there will be no danger of any rusting resulting from oxygen absorption in the water, since the secondary is completely non-ferrous.

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 eleva tion of heating apparatus accoring to a second embodiment of the present invention; 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 are temperature gradient bands 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'numeral 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 temperature 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 cavity 18, and is in two groups of coils 46A towards the bottom of the cavity 18, and 46B towards the top of the cavity. The group of coils 46B is in the hottest region of the water in cavity 18, and the spacing of the coils 46A, 46B is of particular advantage 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.

The expansion of the secondary water is taken care of by the closed expansion tube 46C which is hydraulically connected to the coils 46B. The secondary water passes through the expansion tube 46C which is sealed and contains air in the space 47. Reference 49 indicates the water level in the expansion tube. The tube can be made relatively small and of the same material as the heat exchange coild, and as the secondary water is constantly being replaced and replenished, there is no disadvantage in having direct contact between the air in space 47 and the secondary water. The expansion of the secondary water is accommodated by compression of the air in the space 47.

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.

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 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 there is an expansion chamber in hydraulic communication with the secondary water to accommodate thermal expansion of the secondary water.

2. Heating apparatus according to claim 1, wherein the expansion chamber is a short closed cylindrical chamber having a head space above water which comprises the secondary water.

3. Heating apparatus according to claim 2, wherein the expansion chamber is located inside the water tank.

4. Heating apparatus according to claim 3, wherein the expansion chamber is connected to the heat exchanger coil at the top of the water tank where the secondary water will be at its hottest.

5. Heating apparatus according to any preceding claim, wherein the chamber is defined by a short vertical pipe closed except for an inlet and an outlet both atthe bottom end of the pipe, for the inflow and outflow of secondary water.

6. Heating apparatus of the type set forth substantially as hereinbefore described with reference to the accompanying drawings.