GB1594745A

GB1594745A - Liquid heating installation

Info

Publication number: GB1594745A
Application number: GB2142/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-01-21
Filing date: 1978-01-19
Publication date: 1981-08-05
Also published as: DK26978A; NO140148C; SE7800731L; NL7800706A; NO770186L; FI780152A; NO140148B; SE424228B

Description

(54) LIQUID HEATING INSTALLATION (71) I, BJÖRN FOSSMO MAGNUSSEN, a Norwegian subject, of Sidraapeveien 36u, N-7000 Trondheim, Norway, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a liquid heating installation comprising a hot liquid storage tank and a heat exchanger connected together for circulation of hot liquid from the heat exchanger to the storage tank and cooler liquid to flow from the storage tank back to the heat exchanger.

Such arrangements are often operated over long periods at a fraction of their maximum capacity. This is the case, for example, with central heating installations for private residences, where a water heater which is designed, for example, for 20 kW utilises only a few hundred watts over the parts of each year. Under such operating conditions, however, known water heaters have a very low efficiency. This is due to the source of heat being operated intermittently over short operating periods interposed by relatively long rest periods which permit loss of heat, partly from the mass of the structure of the heat exchanger and partly from hot water which circulates through the heat exchanger.

In practice, use is generally made of a heater which switches on for short periods, with long off intervals therebetween to cover the losses.

Some such installations comprise both a burner for solid, liquid or gaseous fuel and an electrical heating element. In such an arrangement, a significant portion of the supplied energy is lost to air flowing through the heat exchanger even if only electrical energy is supplied. With conventional water heating installations this loss can only be eliminated by blocking the flue gas outlet.

The principal object of the invention is to provide an improved liquid heating installation which will operate with a satisfactory degree of efficiency over its whole range of operation up to its maximum capacity and in which it is possible to heat the liquid within the storage tank with electrical energy without involving loss of heat as a result of induced flow through the heat exchanger so that a flexible transition between electrical heating and heating by other means such as burners is possible.

With this object in view, the present invention provides a liquid-heating installation comprising a hot liquid storage tank and a heat exchanger connected together for circulation of hot liquid from the heat exchanger to the storage tank and cooler liquid to flow from the storage tank back to the heat exchanger, in which the heat exchanger comprises a heating chamber surrounded by concentrically-disposed inner and outer liquid jackets communicating with one another only at their lower ends and the upper ends of which are connected separately with the storage tank at the same height; this has the effect that liquid circulation to the storage tank is precluded in the absence of supply of heat to the heating chamber and that upon supply of heat to the heating chamber liquid circulation occurs by hot liquid rising in the inner liquid jacket and passing to the storage tank whilst cooler water from the storage tank passes to the outer liquid jacket, downwards in the latter, to transfer to the inner liquid jacket.

In the installation of the invention liquid circulation through the heat exchanger ceases when no heat is applied to the heating chamber, and the quantity of energy which is stored in the heat exchanger is minimised.

Both these features serve to reduce the heat loss from the heat exchanger when the heat source supplying heat to the heating chamber is turned off. A further advantage lies in the face that it is possible to include one or more additional said heat exchangers, each of similar construction but, if desired, designed for operating with heat sources or burners, these each being coupled to the hot liquid storage tank which is then common to all of the heat exchangers, without this involving extra energy losses. Furthermore it is an advantage that, with the case where the heat exchanger involves products of combustion being passed through a flue, all flue gas-contacted surfaces are repidly heated above the dew point of the gas so that the danger of corrosion is reduced.

The concentrically-disposed inner and outer water jacket arrangement in the heat exchanger of the installation of the invention has the advantage that it provides a relatively small flow area for the liquid being heated whilst at the same time maintaining the possibility of self-circulation.

By providing for the outer liquid jacket to constitute the exterior of the heat exchanger, heat losses from the heating chamber are minimised.

Since the liquid jackets are connected to the storage tank by a feed conduit and a discharge conduit respectively, at the same height there is formed thereby an effective liquid lock which makes it unnecessary to have special valves for preventing water circulation when heat is not supplied to the heating chamber.

The invention will be described further, by way of example, with reference to a preferred embodiment which is illustrated in the accompanying drawing, in which the single figure is a schematic side view of a water heating installation according to the invention, with the heat exchanger shown in section.

The illustrated installation comprises three main components, namely a hot water storage tank 11, a heat exchanger 12, and a burner 13 for a liquid fuel. The hot water storage tank 11 is of conventional construction.

The heat exchanger 12 comprises tubular concentrically-disposed water jackets, namely an inner water jacket 15 and an outer water packet 16 each having a wall spacing, for example, of less than 5 mm. The burner 13 can be of known construction and is fed with fuel, such as heating oil or gas, through a fuel conduit 14.

The lowermost portion 19 of the outer water jacket 16, which projects down below the inner water jacket 15, is of conical configuration, tapering towards a soot chamber 20 having a tubular wall 21 which extends downwards from the bottom end of the outer water jacket 16. The soot chamber 20 opens upwards towards a heating chamber 18 surrounded by the jackets 15 and 16 and is closed downwards by a detachable bottom cap 22.

The two water jackets 15 and 16 form between them an annular gas passage 23 which is connected to the combustion chamber 18, at the lowermost end of the latter, via an annular entrance 24. Flue gas from the combustion chamber 18, after passing upwards through the passage 23, flows out of the heat exchanger 12 through a flue gas escape or an outlet piece 25 extending radially through the uppermost portion of the outer water jacket 16.

The water jackets 15 and 16 are each constructed with thin double shells or walls of steel plate and form separate annular ducts of small volume. A double-walled, insulating lid 17, which at the same time serves as a holder for the burner 13, forms the upper end walls of the jackets 15, 16, of the heating chamber 18 and of the passage 23.

The water jackets 15 and 16 communicate directly with each other through a connection conduit 26, at the lower edge of the inner water jacket 15, this conduit 26 crossing the entrance 24. The water jackets 15, 16 are advantageously mechanically connected by a bracing stay 27 which is disposed diametrically opposite the connection conduit 26.

The water jackets 15 and 16 are also coupled to the hot water tank 11 by two coaxial couplin pipes 28 and 29 respectively, embodying a ange connection 30.

Air for combustion is supplied to the burner via an opening 31. In addition to the elements which are mentioned above, the heat exchanger 12 is provided with heat insulation which can be fitted in known manner.

The described installation operates in the following manner: On starting up, water in the inner water jacket 15 is rapidly heated to, boiling, which occurs at about looc, dependent upon the pressure in the system, and steam is formed. As a result, an aqueous vapour column is produced in the inner water jacket 15 and this is lighter than the water column in the outer water jacket 16. This starts circulation ot the water which rises in the inner water jacket 15, which circulation continues through the inner coupling pipe 28, the hot water storage tank 11, and the outer coupilng pipe 29 so as to provide a continuous flow of water to the outer water packet 16.This supply of water maintains the imbalance in the water columns in the jackets 15, 16 and ensures continuous water circulation without pumping from the outer water jacket 16 to the inner water jacket 15 through the connection conduit 26. When the burner 13 is turned off, the temperature of the water in the heat exchanger 12 is higher than the temperature of the water in the hot water storage tank 11. The water circulation will therefore continue until the excess heat from the heat exchanger 12 has been transferred to the water in the tank 11 to achieve temperature equilibrium. Thereafter the water Jackets 15, 16 act as an effective water lock which prevents passage of hot water from the hot water storage tank 11 to the heat exchanger 12.

During operation of the burner 13, combustion gas from the heating chamber 18 flows through the annular entrance 24 and passes up through the passage 23 so that it heats up both the inner wall of the outer water jacket 16 and the outer wall of the inner water jacket 15. By virtue of the higher combustion gas temperature and the greater heat transfer surface, the inner jacket 15 receives more heat than the outer jacket 16.

This ensures that a stable liquid circulation is maintained. Moreover, the heat transfer surface is large in relation to the combined volume of materials and liquid, so that it is possible to achieve high heat transfer whilst keeping the stored heat present in the heat exchanger relatively low. Consequently, it is unnessary to form the heat exchanger with special transfer surfaces such as ribs or the like. The advantage is thereby obtained that the heat stored in the materials of the heat exchanger is kept at the lowest possible temperature, which minimises heat loss dur mperiods when the burner is switched off.

In the described embodiment, the water jackets 15 and 16 are made of thin plate or comprise thin-walled pipes, for example stainless steel, which in each jacket are closely adjacent to one another. Both the quantity of metal of, and the volume of, the jackets and hence the auantity of water they will hold, is minimised in this way, and of course these quantities should be as low as practically possible. In an installation having an output of the order of 20 kW, the thickness of the material should preferably be below about 2 mm, while the volume of the two water jackets ought to be from five to seven litres, but preferably less than five litres. With this a series of advantages are obtained.The most important advantage appears to be, as mentioned above, that the heat energy which is received in the mass of the heat exchanger 12, including the amount of water in the water jackets 15 and 16, is minimal during operation, and is stored at the lowest possible temperature. As a result the quantity of heat which can be emitted in rest periods and hence the loss of heat is minimal. By virtue of the low volume of water and the special design of the heat transfer surfaces, the water temperature is brought rapidly up to boiling point and circulation is initiated without the danger of overheating any surfaces of the heat exchanger.

The coaxial coupying of the water jackets 15 and 16 to the hot water storage tank 11 by means of the pipes 28 and 29 at the same height provides the water lock and prevents hot water from being drawn back from the hot water storage tank and emitting heat through the heat exchanger 12 when the burner 13 is not in operation.

Comprehensive tests have shown that an installation corresponding to the illustrated embodiment has a far higher degree of efticiency in its low output range than corresponding known installations.

Direct electrical heating of the stored water in the hot water storage tank 11 can be effected during appropriate periods when there is relatively little need for hot water, or when special tariff conditions make this of interest.

In the illustrated embodiment flexible operation of the installation with oil and electricity can be carried out without special measures being taken to avoid heat losses to air flowing through the heat exchanger 12. If desired, it is possible to couple, to the hot water storage tank 11, one or more further heat exchangers 12 so that the tank 11 is common thereto. These further heat exchangers may be adapted for operation with different fuels, for example, waste paper, coke and coal, without involving any extra heat loss when these units are not in operation.

The coaxial connection 30 simplifies mounting and dismounting of the heat exchanger 12 so that it can be treated as a separate unit, something which is an advantage on possible repair and maintenance work or replacement. At the same time is simplifies the coupling-up of a new heat exchanger to the already-existing hot water storage tank 11.

The location of the soot chamber 20 at the bottom of the heat exchanger 12 facilitates in-situ cleaning of the heating chamber 18.

Cleaning can also be readily carried out after dismounting the whole of the heat exchanger unit.

The liquid heating installation according to the invention can be employed for heating water for a number of purposes, such as sanitary purposes, household purposes and industnai purposes, as well as for the operation of central heating radiators. In principle, the installation of the invention can also be employed for heating liquids or liquid mixtures and suspensions other than water.

The water jackets 15, 16 can, if desired, be made of corrugated plates or can be composed of thin walled pipes. The heat exchange 12 can employ more than two water jackets, especially in larger installations, that is to say installations significantly above 20kW. Within the scope of the invention as defined by the following claims various modifications may be made, which some are mentioned above. The circulation through the water jackets can, for example, additionally be controlled by a valve which closes when the burner is disconnected. This can be accomplished simply, for example by employing a temperature sensor in the heating chamber 18 as control means.

The heat exchanger 12 or the heat exchangers can be arranged differently, relative to the hot water storage tank 11, from what has been illustrated. For example, the or each heat exchanger 12 could be arranged within the tank 11 with appropriate thermal insulation being provided therebetween.

WHAT 1 CLAIM lS:- 1. A liquid-heating installation compris

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. inner water jacket 15. By virtue of the higher combustion gas temperature and the greater heat transfer surface, the inner jacket 15 receives more heat than the outer jacket 16. This ensures that a stable liquid circulation is maintained. Moreover, the heat transfer surface is large in relation to the combined volume of materials and liquid, so that it is possible to achieve high heat transfer whilst keeping the stored heat present in the heat exchanger relatively low. Consequently, it is unnessary to form the heat exchanger with special transfer surfaces such as ribs or the like. The advantage is thereby obtained that the heat stored in the materials of the heat exchanger is kept at the lowest possible temperature, which minimises heat loss dur mperiods when the burner is switched off. In the described embodiment, the water jackets 15 and 16 are made of thin plate or comprise thin-walled pipes, for example stainless steel, which in each jacket are closely adjacent to one another. Both the quantity of metal of, and the volume of, the jackets and hence the auantity of water they will hold, is minimised in this way, and of course these quantities should be as low as practically possible. In an installation having an output of the order of 20 kW, the thickness of the material should preferably be below about 2 mm, while the volume of the two water jackets ought to be from five to seven litres, but preferably less than five litres. With this a series of advantages are obtained.The most important advantage appears to be, as mentioned above, that the heat energy which is received in the mass of the heat exchanger 12, including the amount of water in the water jackets 15 and 16, is minimal during operation, and is stored at the lowest possible temperature. As a result the quantity of heat which can be emitted in rest periods and hence the loss of heat is minimal. By virtue of the low volume of water and the special design of the heat transfer surfaces, the water temperature is brought rapidly up to boiling point and circulation is initiated without the danger of overheating any surfaces of the heat exchanger. The coaxial coupying of the water jackets 15 and 16 to the hot water storage tank 11 by means of the pipes 28 and 29 at the same height provides the water lock and prevents hot water from being drawn back from the hot water storage tank and emitting heat through the heat exchanger 12 when the burner 13 is not in operation. Comprehensive tests have shown that an installation corresponding to the illustrated embodiment has a far higher degree of efticiency in its low output range than corresponding known installations. Direct electrical heating of the stored water in the hot water storage tank 11 can be effected during appropriate periods when there is relatively little need for hot water, or when special tariff conditions make this of interest. In the illustrated embodiment flexible operation of the installation with oil and electricity can be carried out without special measures being taken to avoid heat losses to air flowing through the heat exchanger 12. If desired, it is possible to couple, to the hot water storage tank 11, one or more further heat exchangers 12 so that the tank 11 is common thereto. These further heat exchangers may be adapted for operation with different fuels, for example, waste paper, coke and coal, without involving any extra heat loss when these units are not in operation. The coaxial connection 30 simplifies mounting and dismounting of the heat exchanger 12 so that it can be treated as a separate unit, something which is an advantage on possible repair and maintenance work or replacement. At the same time is simplifies the coupling-up of a new heat exchanger to the already-existing hot water storage tank 11. The location of the soot chamber 20 at the bottom of the heat exchanger 12 facilitates in-situ cleaning of the heating chamber 18. Cleaning can also be readily carried out after dismounting the whole of the heat exchanger unit. The liquid heating installation according to the invention can be employed for heating water for a number of purposes, such as sanitary purposes, household purposes and industnai purposes, as well as for the operation of central heating radiators. In principle, the installation of the invention can also be employed for heating liquids or liquid mixtures and suspensions other than water. The water jackets 15, 16 can, if desired, be made of corrugated plates or can be composed of thin walled pipes. The heat exchange 12 can employ more than two water jackets, especially in larger installations, that is to say installations significantly above 20kW. Within the scope of the invention as defined by the following claims various modifications may be made, which some are mentioned above. The circulation through the water jackets can, for example, additionally be controlled by a valve which closes when the burner is disconnected. This can be accomplished simply, for example by employing a temperature sensor in the heating chamber 18 as control means. The heat exchanger 12 or the heat exchangers can be arranged differently, relative to the hot water storage tank 11, from what has been illustrated. For example, the or each heat exchanger 12 could be arranged within the tank 11 with appropriate thermal insulation being provided therebetween. WHAT 1 CLAIM lS:-

1. A liquid-heating installation compris

ing a hot liquid storage tank and a heat exchanger connected together for circulation of hot liquid from the heat exchanger to the storage tank and cooler liquid to flow from the storage tank back to the heat exchanger, in which the heat exchanger comprises a heating chamber surrounded by concentrically-disposed inner and outer liquid jackets communicating with one another only at their lower ends and the upper ends of which are connected separately with the storage tank at the same height so that liquid circulation to the storage tank is precluded in the absence of supply of heat to the heating chamber and that upon supply of heat to the heating chamber and that upon supply of heat to the heating chamber liquid circulation occurs by hot liquid rising in the inner liquid jacket and passing to the storage tank whilst cooler water from the storage tank passes to the outer liquid jacket, downwards in the latter, to transfer to the inner liquid jacket.

2. An installation as claimed in claim 1 wherein the liquid jackets each have a wall spacing of less than 5 mm.

3. An installation as claimed in claim 1 or 2, wherein the combined volume of the liquid jackets is less than 5 litres.

4. An installation as claimed in claim 1,2 or 3 wherein the walls of the liquid jackets are of a material having a thickness of 2 mm or less.

5. An installation as claimed in any preceding claim wherein the outer liquid jacket forms the exterior of the heat exchanger.

6. An installation as claimed in claim 6 wherein the liquid jackets are connected to the hot water storage tank by means of coaxial coupling pipes.

7. An installation as claimed in any preceding claim wherein a burner is arranged at the top of the liquid jackets, and a soot chamber having detachable lower door is provided at the bottom of the jackets.

8. An installation as claimed in any preceding claim further including, in connecting conduits between the liquid jackets and the hot water storage tank, a valve which is closed in the absence of heat supply to the heating chamber.

9. An installation as claimed in any preceding claim wherein the heat exchanger is disposed within and thermally insulated from the hot water storage tank.

10. A liquid heating installation substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.