GB2297150A - Gas fire heat exchanger - Google Patents

Abstract

A gas fire comprises heat exchanger located above the gas burner, the heat exchanger defining first and second passageways, the first passageway forming part of a combustion products exhaust between the tubes 21 and the second passageway forming part of an air convection passageway through the interiors of the tubes 21. The heat exchanger is defined by an array of parallel spaced apart tubes 21 extending between upper and lower metal sheets which are secured within a casing to prevent intercommunication between the exhaust and air convection passageways. The ends of the tubes pass through and are deformed to mechanically engage the edges of apertures formed in the metal sheets. (Figure 6).

Description

GAS FIRE The present invention relates to a gas fire, and in particular to a gas fire of the type which produces a simulation of a coal-burning fire in an efficient manner.

Gas fires are known which comprise a casing that is fitted into a wall cavity, a gas burner located in a lower front portion of the casing and arranged to form a radiant heat source, a combustion products exhaust passageway extending from above the burner to an exhaust outlet located in an upper portion of the casing, and an air convection passageway extending from a lower rear portion of the casing to a heated air outlet located in an upper front portion of the casing. It is known to provide a heat exchanger above the gas burner which defines part of the combustions product exhaust passageway and part of the air convection passageway. Air in the air convection passageway is heated in the heat exchanger and improves the amount of heat delivered to the area in front of the fire as compared to the amount of heat lost to the exhaust.

The air convection passageway in the known fires extends from a cavity beneath the gas burner and up a relatively wide cross section passageway adjacent the rear of the casing. At the top of that passageway the air is diverted forwardly relative to the casing through the heat exchanger. Although some improvement in efficiency does result from such an arrangement, the improvement has proved disappointing in available products. It has proved difficult to manufacture heat exchangers which are efficient in use and yet economic to manufacture.

In one known fire the heat exchanger is in the form of an aluminium casting. The surface area of metal heated on one side by the combustion products and cooled on the other side by air is relatively small and thus although in high volume applications the cost per heat exchanger is acceptable the operational efficiency of such an arrangement is not.

An alternative heat exchanger is described in British Patent No.

2238607. This comprises a single array of rectangular section tube the side walls of which are indented to define air passageways therebetween. It may be that such an arrangement is as suggested in the patent specification efficient in operation but this does not seem very likely given that the individual tubes are of relatively short length and relatively small height. Furthermore the tubes, although formed as individual components, must subsequently be welded together. Such procedures would be difficult to achieve at acceptable cost in a sufficiently reliable manner to ensure that no leaks occur which could result in significant volumes of combustion products becoming mixed with the convected air.

It is an object of the present invention to provide an improved gas fire incorporating an air convection system.

According to the present invention there is provided a gas fire comprising a casing, a gas burner located in a lower front portion of the casing and arranged to form a radiant heat source, a combustion products exhaust passageway extending from above the burner to an exhaust outlet located in an upper portion of the casing, an air convection passageway extending from a lower rear portion of the casing to a heated air outlet located in an upper front portion of the casing, and a heat exchanger located above the gas burner, the heat exchanger defining first passageways which together form part of the combustion products exhaust passageway and second passageways which together form part of the air convection passageway, wherein the heat exchanger is defined by an array of parallel spaced apart tubes extending between upper and lower metal sheets which are secured within the casing to prevent intercommunication between the exhaust and air convection passageways, the interiors of the tubes defining the second passageways and the spaces between the tubes defining the first passageways, and the ends of the tubes passing through and being deformed to mechanically engage the edges of apertures formed in the metal sheets.

Thus, in contrast to prior art devices where welded or cast structures of relatively limited surface area are provided, the invention enables a large number of tubes to be inserted in an assembly which can be manufactured in a simple and economical fashion. No welded or cast components are required.

Preferably, the tubes are formed with circumferential ribs adjacent their ends, those ribs bearing against the edges of the apertures defined in the metal sheets. The tips of the tubes extend through the apertures and are bent radially outwards to trap the edges of the apertures between the ribs and the bent tips. No further sealing devices are necessary to make the assembly sufficiently gas tight for the application in which it is used.

Preferably the tubes extend at an angle inclined to the horizontal of at least 300 and preferably 450 or more. Such an orientation of the tubes enables the manufacture of a heat exchanger with a large number of relatively long tubes thus defining a large heat exchange surface. The tubes will project downwards towards the burner to a position in which they can be readily seen from in front of the fire, but providing they are sufficiently closely spaced together, the visual effect is perfectly acceptable, particularly if the tubes are blackened.

The gas burner and associated components, such as a simulated fire bed and gas and electrical controls, are preferably mounted on a sub-assembly that may be secured to a base plate of the casing or removed from the casing for servicing. Such an arrangement makes it extremely easy to install and subsequently service a fire in accordance with the invention. Preferably the simulated fire bed is mounted on a support plate which forms part of the sub-assembly, rear and side edges of the support plate bearing against inner components of the casing when the sub-assembly is secured to the base plate. The contact between the support plate and the inner casing components is sufficient to prevent unacceptable leakage between the area above the burner and the area behind the internal casing components at least part of which forms a section of the convected air passageway.The gas burner and associated gas supply control and monitoring devices may themselves be supported on a sub-frame which may be secured to or removed from the sub-assembly for servicing.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a part cut away side view of an embodiment of the present invention; Fig. 2 is a front view in the direction of lines 2-2 of Fig. 1 in the absence of a heat exchanger and decorative components of the front of the fire; Fig. 3 is a schematic representation of components making up the casing of the embodiment of Figs. 1 and 2 and a sub-assembly which is incorporated in that casing; Fig. 4 is a detailed front view of a heat exchanger incorporated in the embodiment of Figs. 1 and 2; and Figs. 5 and 6 illustrate the manner of attachment of tubes shown in Fig. 4 to sheet metal plates defining the ends of the heat exchanger of Fig. 4.

Referring to Figs. 1 to 3, the illustrated fire comprises a casing having side walls 1, a base 2, and an upper wall 3. A flange 4 extends around the open front of the casing, that flange covering the space between the casing and any recess into which the fire is fitted. An exhaust outlet 5 is defined in a rear wall 6.

Internal components of the casing comprise side panels 7 which taper inwards away from the front of the fire opening, a rear panel 8, and a front cross member 9. The area defined behind the panels 7 and 8 forms the lower portion of a convected air passageway whereas the area in front of these panels receives the bed of a coal-effect gas fire. All of the components of the gas fire other than the casing itself are removable from the casing as part of a sub-assembly as best appreciated from Fig. 3.

Referring to Fig. 3, the sub-assembly comprises a support plate 10, which may be slid onto the upper surface of the base plate 2. An air fan 11 is mounted on an upstanding panel 12 secured to the back of the support plate 10. A gas burner 13 and its associated controls is itself demountably secured to the support plate 10. When mounted on the support plate, the gas burner 13 is located beneath a slot 14 through which burning fuel issues. The slot 14 is provided in a tray 15, the rear and side edges of which define an upwardly extending flange 16 which, when the sub-assembly is inserted into the fire casing, bears against the lower edges of the panels 7 and 8. A silicone rubber edge seal may be mounted on the flange 16. This provides a sufficiently reliable seal to prevent combustion products above the tray 15 leaking into the passageway defined behind the panels 7 and 8. Generally, however, the pressure behind the panel 8 will be greater than in front, avoiding any risk of potentially dangerous leakage. The tray 15 supports thermally insulating fire bricks 17 that form three sides of a space onto which simulated coal may be arranged so as to give a real fire effect.

A heat exchanger 18 is located above the gas burner.

Combustion products from the gas burner follow the path indicated by arrows 19 towards the exhaust aperture 5. Air pressurised by the fan 11 is forced upwards behind the rear panel 8, through the heat exchanger 18 and out of the front of the fire through a louvre assembly, the air following the path indicated by arrows 20. The air travels through an array of parallel circular section tubes extending in a vertical plane perpendicular to the front of the fire and at an angle in that plane of 45 to the horizontal. The flue products pass through the gaps defined between these tubes.

Referring to Fig. 4, the detailed structure of the heat exchanger is illustrated. Thirty eight tubes 21 extend perpendicular to an upper metal sheet 22 and a lower metal sheet 23. The tubes are arranged in five rows, the first (uppermost) row incorporating 4 tubes, the second and fourth rows incorporating 9 tubes, and the third and fifth rows incorporating 8 tubes. Each tube has an outside diameter of l9mm and a wall thickness of 0.9mm, and the minimum spacing between adjacent tubes is 4mm. As can be seen from Fig. 2, the side panels 7 taper outwards in an upwardly direction and the heat exchanger incorporates side panels 24 which close the gap between the array of tubes in each side of the fire casing. The various sheet metal components are secured together by rivets 25.Thus the heat exchanger forms a subassembly of rugged construction which itself is secured by rivets to the side walls of the casing.

Figs. 5 and 6 illustrate the manner in which the upper ends of the tubes 21 are secured to the upper heat exchanger sheet 22.

Exactly the same structure and procedures are used to secure the lower ends of the tubes 21 to the lower heat exchanger sheet 23. The tubes 21 are preformed from aluminium tubing so as to have expanded ribs adjacent their ends, the ends themselves being slightly reduced in diameter from the nominal outside diameter of the tubes. The narrowed ends are then inserted through appropriate apertures in the sheet 22 as shown in Fig. 5. The apertures are dimensioned such that although the tube ends can pass therethrough, the ribs cannot. A tool 26 is then pressed down on the tube end so as to cause the tube end to be splayed radially outwards. As a result the edges of the aperture in the sheet 22 are tightly gripped between the rib adjacent the tube end and the bent over tube end itself. The result is a gas tight mechanical interconnection between the sheet 22 and the tube 21.

The process illustrated in Figs. 5 and 6 can be readily performed in an economic manner. A tool is required having two banks of 38 pressing tool heads, each aligned with a respective tube such that one bank can press the bottom ends of the tubes whilst the other bank presses the upper ends of the tubes. The lower heat exchanger sheet 23 is positioned above the lower bank of tools, the 38 tubes are then positioned in the appropriate apertures in the base sheet 23, the upper heat exchanger sheet 22 is then placed onto the top ends of the tubes, and the tool banks are then urged towards each other so as to cause the necessary deformation of the tube ends. The operation relies entirely upon mechanical interengagement between the components and no soldering, welding or other like processes are required. The final assembly is robust, reliable and economic.

Because of the economic procedures used for the manufacture of the heat exchanger, a heat exchanger can be produced which incorporates a large number of passageways and hence a relatively large surface area through which heat can be exchanged between the combustion products and the convected air. Furthermore, because the tubes 21 are inclined at 450 to the horizontal, the length of the individual tubes can be very much greater than in an arrangement such as that illustrated in patent specification 2238607 where the heat exchanger tubes are arranged at approximately 100 to the horizontal.

Given the length of the tubes 21 they will be visible from in front of the fire above the rear panel 8 but given that the tubes are of relatively small diameter and are packed closely together the visual effect is entirely satisfactory, particularly if the tubes are painted matt black.

Claims (8)

1. A gas fire comprising a casing, a gas burner located in a lower front portion of the casing and arranged to form a radiant heat source, a combustion products exhaust passageway extending from above the burner to an exhaust outlet located in an upper portion of the casing, an air convection passageway extending from a lower rear portion of the casing to a heated air outlet located in an upper front portion of the casing, and a heat exchanger located above the gas burner, the heat exchanger defining first passageways which together form part of the combustion products exhaust passageway and second passageways which together form part of the air convention passageway, wherein the heat exchanger is defined by an array of parallel spaced apart tubes extending between upper and lower metal sheets which are secured within the casing to prevent intercommunication between the exhaust and air convection passageways, the interiors of the tubes defining the second passageways and the spaces between the tubes defining the first passageways, and the ends of the tubes passing through and being deformed to mechanically engage the edges of apertures formed in the metal sheets.

2. A gas fire according to claim 1, wherein circumferential ribs are formed adjacent the ends of the tubes and bear against the edges of the apertures defined in the metal sheets, the tips of the tubes extending through the apertures and being bent radially outwards to trap the edges of the apertures between the ribs and the bent tips of the tubes.

3. A gas fire according to any preceding claim, wherein the tubes are inclined to the horizontal by at least 300.

4. A gas fire according to claim 3, wherein the tubes are inclined to the horizontal by 450.

5. A gas fire according to any preceding claim, wherein the gas burner and associated components are mounted on a sub-assembly that may be secured to a base plate of the casing or removed from the casing for servicing.

6. A gas fire according to claim 5, wherein the associated components comprise a simulated fire bed mounted on a support plate which forms part of the sub-assembly, rear and side edges of the support plate bearing against inner components of the casing when the sub-assembly is secured to the base plate so as to restrict intercommunication between regions behind the inner components of the casing and the area above the support plate.

7. A gas fire according to claim 5 or 6, wherein the gas burner and associated gas supply control and monitoring devices are supported on a sub-frame which may be secured to or removed from the sub-assembly for servicing.

8. A gas fire substantially as hereinbefore described with reference to the accompanying drawings.