GB2061476A

GB2061476A - Flue Gas Water Heater

Info

Publication number: GB2061476A
Application number: GB7932175A
Authority: GB
Original assignee: Fear R R
Current assignee: Fear R R
Priority date: 1979-09-17
Filing date: 1979-09-17
Publication date: 1981-05-13

Abstract

A water heater 4 is intended to form part of a chimney flue. The water heater 4 has a duct 5 and chamber around the duct 5. The water heater also has a male connection member 8 and female connection member 7 for engaging corresponding female and male connection members 3 and 2 of flue sections 1. In use, water flows through the chamber as indicated by the arrows 15 and is heated by hot flue gases flowing in the direction of the arrow 14. <IMAGE>

Description

SPECIFICATION A Water Heater This invention relates to a water heater for heating water with hot flue gases.

There is known a wide variety of solid fuel, oil and gas fires or burners. Such a fire may comprise an open fire, a back boiler, a closed room heater or a central heating boiler. However, all such fires for domestic use have a maximum efficiency of 70%. This efficiency is the amount of heat extracted by a fire and transferred to a material to be heated, divided by the theoretical maximum amount of heat available from the fuel used. In general, the heat extracted by the fire is used to heat the interior of a building or water or other liquid. Some of the heat, which is not extracted by the fire, is recovered as it passes through the chimney breast into the building in which the fire is located.

The flue gas temperature in domestic heating equipment including such a fire can be up to 455or. It is desirable that as much as possible of this heat which would otherwise be wasted is recovered.

According to one aspect of the present invention there is provided a water heater, intended to form part of a chimney flue, the water heater comprising a duct, a chamber which is disposed around and in thermal contact with the duct and which has an inlet and an outlet for water, and male and female connection members at opposite ends of the water heater for engaging female and male connection members of adjacent flue sections respectively, the arrangement being such that, in use, with the male and female connection members of the water heater engaged with respective female and male connection members of adjacent flue sections of a chimney flue and with the duct thus forming part of a chimney flue through which hot flue gases flow, water is passed through the chamber so that heat is transferred from the hot flue gases to the water flowing through the chamber.

Preferably the chamber is defined between the duct and a wall spaced from and around the duct.

The duct and the wall may be of circular section and the chamber may be annular.

Each of the male and female connection members can be secured to both the duct and the wall.

In recent times, many chimney flues have been constructed using flue linings The material used for these flue linings varies according to the particular use and the maximum flue gas temperature. Details of flue linings of this type can be found in British Standards 567 (1973), 71 5 (1970),835(1973),1181 (1971), and 1289 (1945); and in the following codes of practice: 131(1974); 337 (1963) and 3002 parts 1 and 2.

Some of these chimney flues comprise a plurality of flue sections each of which has a male connector at one end and a female connector at the other end According to another aspect of the present invention there is provided a domestic hot water system including a water heater according to the first-mentioned aspect of the present invention.

For a better understanding of the present invention and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows a vertical section through a water heater according to the present invention; Figure 2 shows diagrammatically part of a domestic hot water system including a water heater in a flue of an open fire; Figure 3 shows diagrammatically part of another domestic hot water system including a water heater in a flue of an open fire with back boiler; Figure 4 shows diagrammatically part of a further domestic hot water system including a water heater in a flue of a boiler; and Figure 5 shows diagrammatically part of a different domestic hot water system including a water heater in a flue of a boiler.

The chimney flue comprises a plurality of flue sections in the form of clay flue linings 1 according to British Standard 1181. In the drawing, one of these flue linings 1 is provided with a male connector 2, whilst the other flue lining 1 is provided with a female connector 3.

A water heater 4 comprises a first inner duct 5 and a second outer duct or wall 6, both of which are made from stainless steel. The two ducts 5 and 6 are joined at their upper and lower ends by connection members 7 and 8 which comprise steel and are welded to the ducts 5 and 6 to define a chamber between the ducts 5 and 6. A tube 9 is disposed around the inner duct 5. A major portion of the tube 9 is formed as a helix 1 0 which contacts the outer surface of the first duct 5. End portions 11 and 12 of the tube 9 pass through openings in the second duct 6 and comprise an inlet and outlet for water respectively.The major helical portion 10 of the tube 9 is surrounded by a layer of insulation material 13, for example glass fibre. the tube 9 has a flattened circular cross-section so that the surface area of the major portion 10 in contact with the outer surface of the first duct 5 is increased with respect to that for a tube of circular cross-section.

The major helical portion 10 of the tube 9 need not necessarily contact the first duct 5, and could instead be proximate the first duct 5 so that heat can readily be transferred from the first duct 5 to the pipe 9.

The connection member 7 comprises a female connector which engages the male connector 2 and the connection member 8 comprises a male connector which engages the female connector 3.

The two connections between the pair of connectors 2 and 7 and between the pair of connectors 3 and 8 are sealed by high alumina flue cement or asbestos.

In use, hot flue gases flow up through the chimney flue in the direction of the arrow 14 and water is passed through the tube 9 as indicated by the arrows 15. The water is at a lower temperature than the flue gases so that heat is transferred from the flue gases through the first duct 5 and the walls of the tube 9 to the water flowing through the tube 9.

In order to improve the insulation around the major portion 10 of the tube 9, a sheet of heat reflective foil can be placed around the major portion 10 and between the major portion 10 and the insulation 13.

In order to extract the maximum amount of heat possible from the flue gases, the water heater should be placed as close to the fire itself as possible, since the flue gases cool down as they travel up the chimney flue due to heat transfer through the chimney flue. In certain situations, however, it may be necessary to locate the water heater some distance above the fire in order not to impair the "chimney effect" due to the column of hot flue gases above the fire which draws air through the fire.

The inside surface of the first duct 5 can be provided with one or more fins to improve heat transfer from the hot flue gases to the duct 5.

Preferably these fins extend axially along the duct 5 so as not to provide too great a flow resistance to the flue gases and so as to enable the chimney flue to be cleaned easily.

The inner cross-sectional shape of the welter heater 4 should correspond to that of the flue sections 1. The outer cross-sectional shape of the water heater 4 need not necessarily correspond to that of the flue sections 1, but should be such as to enable the water heater to be inserted in a cavity in which the flue sections 1 are to be fitted.

The length of the water heater 4 is conveniently an integral number times the standard length of the flue sections 1 to enable the water heater 4 to be substituted for one or more of the flue sections 1 of an existing chimney flue. The length of the water heater 4 will depend upon the conditions existing in a particular chimney flue and the amount of heat that is to be extracted from the hot flue gases.

Figure 2 shows the water heater 4 disposed in a flue 1 6 of an open fire, although the arrangement shown in Figure 2 is also applicable to a flue of a gas radiant fire. It is expected that the hot water will be heated either by an electric immersion heater or by an 'Ascot' type gas heater.

The end portions 11 and 12 of the tube 9 are connected to heating coil 1 7 inside a hot water cylinder, and a heat leak radiator 1 8 is connected in parallel to the heating coil 1 7. The water heater 4 connected in this way provides heat for the hot water supply and hence reduces the amount of electricity or gas used by the conventional heating means.

Figure 3 shows an arrangement similar to that of Figure 2, except that the fire in this case is provided with a back boiler (not shown). The heating coil 1 7 and a heat leak radiator 18 are connected to the back boiler. The water heater 4 is connected to one or more radiators 19, which, for example, could be upstairs radiators and/or a heated towel rail or radiator. Alternatively, the water heater 4 could be connected into the main hot water circuit to boost the effective output of the back boiler.

Figure 4 shows a hot system heated by a boiler 20, which has sufficient heat output to provide heat for a downstairs heating circuit 21 only so as to provide partial central heating. The individual radiators for the downstairs heating circuit 21 are not shown. The boiler 21 also provides hot water for a heating coil 17 in the water tank and a heat leak radiator 18. The water heater 4 is used to heat water for an upstairs circuit 22 so as to complete the central heating system. Again the individual radiators in the circuit 22 are not shown. The water in the circuit 21 is circulated by a pump 23 whilst the water in the circuit 22 relies on gravity circulation.

Figure 5 shows a boiler 20 capable of providing the heat output necessary for a complete central heating system and for the heating coil 1 7. Hot water leaves an outlet 25 of the boiler 20 and flows through a downstairs heating circuit 21 provided with radiations 24.

The water leaving the circuit is relatively cool and flows into the inlet portion 11 of the water heater 4. The water is reheated in the water 4, leaves the outlet portion 12 of the water heater 4 and flows through the upstairs heating circuit 22 provided with radiators 24. The water then returns to the boiler 20 via a pump 26, which pumps the water around the circuits 21 and 22. The water heater 4 can thus enable the boiler 20 to be run at a lower output than normal as the water for the central heating is reheated between the downstairs circuit 21 and the upstairs circuit 22.

Claims

1. A water heater, intended to form part of a chimney flue, the water heater comprising a duct, a chamber which is disposed around and in thermal contact with the duct and which has an inlet and an outlet for water, and male and female connection members at opposite ends of the water heater for engaging female and male connection members of adjacent flue sections respectively, the arrangement being such that, in use, with the male and female connection members of the water heater engaged with respective female and male connection members of adjacent flue sections of a chimney flue and with the duct thus forming part of a chimney flue through which hot flue gases flow, water is passed through the chamber so that heat is transferred from the hot flue gases to the water flowing through the chamber.

2. A water heater as claimed in claim 1, wherein the chamber is defined between the duct and a wall spaced from and around the duct.

3. A water heater as claimed in claim 2, wherein the duct and wall are of circular section and the chamber Is annular

4. A water heater as claimed in claim 2 or 3, wherein each of the male and female connection members is secured to both of the duct and wall.

5. A water heater as claimed in claim 2, 3 or 4, which includes a pipe around the duct and proximate or contacting the duct, the free ends of the pipe comprising the inlet and the outlet for water and the arrangement being such that, in use, water flows through the pipe.

6. A water heater as claimed in claim 5, wherein the pipe has a flattened circular crosssection, a major portion of the pipe is disposed helically around and contacting the duct, and two end portions of the pipe pass through openings in the wall.

7. A water heater as claimed in claim 6, wherein the helical major portion of the pipe is surrounded by a heat reflective foil.

8. A water heater as claimed in claim 7, wherein the space between the heat reflective foil and the wall is filled with glass fibre insulation.

9. A water heater as claimed in claim 5,6,7 or 8, wherein the pipe Is formed of metal.

10. A water heater as claimed in any one of claims 2 to 9, wherein the duct and wall are formed of stainless steel.

11 A water heater as claimed in any preceding claim. wherein the two connection members are formed of steel

12 A water heater substantially as hereinbefore described with reference to, and as shown In, Figure 1 of the accompanying drawings.

13. A water heater as claimed in any preceding claim, when disposed in a chimney flue.

14. A domestic hot water system including a water heater as claimed in any preceding claim.

1 5. A domestic hot water system as claimed in claim 14, substantially as hereinbefore described with reference to, and as shown in, Figures 2, 3, 4 or 5 of the accompanying drawings.