GB2274702A

GB2274702A - Convector open fires

Info

Publication number: GB2274702A
Application number: GB9301620A
Authority: GB
Inventors: Mark Edward Crowther; Roy David Holtham; Nigel Philip John Stephens
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1993-01-27
Filing date: 1993-01-27
Publication date: 1994-08-03
Anticipated expiration: 2013-01-27
Also published as: GB9301620D0; GB2274702B; IE940073A1

Abstract

A convector open fire 1 comprises a double-skinned firebox 2 which defines a convective air chamber 8 for heating air, the cross-section of the chamber 8 being proportional to the expected temperature of the air in use passing therethrough. The firebox may be made from low-nickel stainless steel. A tapering flue 30 may have a damper plate (36, Fig 2 not shown) at its inlet, the plate being reciprocated by a pivoted lever (44). Fins 24 may be straight or corrugated and may be perforate. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO OPEN FIRES This invention concerns improvements in or relating to open fire appliances and in particular to convector open fire appliances.

An object of the present invention is to provide a convector open fire giving high amenity together with enhanced efficiency compared with conventional open fire appliances.

According to the invention there is provided a convector open fire including a double-skinned fire box defining within the relatively inner skin a combustion chamber for solid fuel to be burned on a grate located within the chamber, a flue outlet from the chamber, a convection chamber for the passage of air defined between the relatively inner skin and the relatively outer skin, an inlet to the convection chamber at or towards the base thereof, an outlet from the convection chamber at or towards the roof thereof, the cross-sectional area of the convection chamber being proportional to the expected temperature of air in use passing therethrough.

Advantageously, the relatively inner skin of the firebox is provided with extended heat exchange surfaces protruding into the convection chamber, thereby to enhance heat transfer efficiency.

The extended heat transfer surfaces may be provided by fins which may be straight corrugated, straight single strip fins, or single strip fins which are perforated and/or contoured to provide an increased surface area. The fins are secured to the outer wall surface of the inner skin by for example fillet or spot welding, or by any other suitable method giving an extensive and thermal contact. The ratio of the fin depth, ie from tip to root, to the fin pitch may conveniently be 1:1. The fins may extend from the ash collection area beneath the grate to the top of the inner skin.

The flue outlet passes through the roof of the convection chamber and tapers from its mouth towards its exit, thereby maintaining the cross-sectional area of the convection chamber roof and minimising the restriction to convective air flow through the chamber, whilst ensuring in use sufficient capture of combustion products rising from the fire.

Preferably the flue outlet is provided with a damper extending across its mouth, the damper comprising a movable plate actuable by a pivoted lever.

The outlet from the convection chamber is defined in the roof of the firebox and is preferably directed upwardly away from the combustion chamber in order to prevent in use heated air being drawn down into the firebox by air movement towards the flue and the fire.

The firebox may be manufactured from plate material of cast iron, mild steel or low-nickel stainless steel. The choice of low-nickel stainless steel will give a highly reflective surface with aesthetic appeal and improved longevity.

The fire may be provided with a surround which interfaces with the fire to afford not only aesthetic appeal but also complementary functionality particularly with regard to the direction in use of warm air from the outlet of the convection chamber.

By way of example only, one embodiment of convector open fire according to the invention is described below with reference to the accompanying drawings in which: Figure 1 is a cut away isometric diagrammatic view; Figure 2 an orthographic elevation on the arrow A of Figure 1; and Figure 3 is an isometric view of a surround for the fire.

Referring to the drawings, a convector open fire is shown generally at 1 and includes a double-skinned firebox 2 having a relatively inner skin 4 and a relatively outer skin 6 with a convective air chamber 8 defined therebetween. A combustion chamber 10 is defined by the skin 4 and a grate (not shown) is positioned therein at a level 12 with an ash receiving zone 14 therebelow. The zone 14 has a floor 16 beneath which is an air entry channel 18 leading to the convective air chamber 8. A tube 19 extends through and across the entry channel 18 to provide for the passage of a screw (not shown) for fixing the fire to the floor beneath. The channel 18 has an inlet 20 at the front of the fire 1.

The convective air chamber 8 has a cross-sectional area proportional to the temperature of the air passing through it, and it extends from the inlet 20 to an outlet 22 formed at the front of the fire above the combustion chamber 10. The skin 4 forming one bounding wall of the chamber 8 is provided with a plurality of fins 24 extending substantially vertically within the chamber 8 and disposed around the wall at spaced intervals. The fins 24 are suitably secured to the wall by for example welding. The ratio of fin depth to pitch is preferable 1:1 and in the specific embodiment is chosen as 25 mm. The fins 24 extend substantially the full vertical height of the chamber 8 and effectively increase the surface area of the wall in order to enhance heat transfer efficiency.

The convective air chamber 8 is traversed at its top region by a flue duct 30 having a mouth 32 of greater dimension than its exit 34 which latter is of essentially box shape, the duct tapering from the mouth 32 to the exit 34. The outlet 22 of the chamber 8 is close to the flue duct 30 and is upwardly turned away from the combustion chamber 10.

Referring specifically to Figure 2, a flue gas damper in the form of a plate 36 is shown in registration with the flue duct 30 and is reciprocable along and supported by runners 38 located at the margins of the mouth 32 of the duct. The plate 36 carries a spigot 40 which cooperates with the fork end 42 of an operating lever 44 pivoted at 46.

In Figure 3 there is shown a mantel or fire surround 50 which comprises two side members 52 which in use embrace the firebox 2 at each side thereof, the members being interconnected at their upper extremities by a cross beam 54 constituting the mantelpiece. On its under side, the beam 54 is provided with a sloping face 56 which in position over the firebox lies adjacent the outlet 22 of the chamber 8 to provide continuity to the upward direction thereof.

In operation, the convector open fire 1 is used to burn solid fuel, in particular coal, which is formed into a bed and ignited on the grate (not shown) within the combustion chamber 10. Heat from the combustion of the fuel is transferred to the firebox 2 through radiation and conduction. The metal of the firebox heats up and heat is transferred through the skin 4 to the fins 24 which in turn heat the air in the chamber 8 thereby causing air movement. The air movement induces air flow through the inlet 20 into the entry channel 18 of the chamber 8. The air passing through the channel 18 is preheated as it travels beneath the ash receiving zone 14 and thence ascends within the main part of the chamber 8 in heat transfer relation to the fins 24 and the skin 4 thereby having a cooling effect upon the skin 4. The extended heat transfer surface provided by the fins 24 serves to enhance the efficiency.

The heated air continues its upward path through the chamber 8 to the roof thereof where it turns towards the front of the open fire and passes the intersecting flue duct 30 to exit through the outlet 22 into the room in which the fire is located, the temperature of the exiting air being of the order of 2500C. Since the outlet 22 is turned upwardly and the face 56 of the beam 54 assists in positively directing the warm air, substantially no flow of the exhausting air is induced by the natural draught of the fire into the flue duct 30.

The rate of combustion of the firebed on the grate is governed by the draught through the flue duct 30 which is regulated by the plate 36 using the lever 44 to change its position according to requirements. The converging shape of the flue duct 30 from the mouth 32 to its exit 34 ensures that the cross-section of the chamber 8 through which it passes is maintained in order to secure proportionality with the temperature of the air and to minimise the restriction in convection air flow. The relatively large mouth 32 of the duct 30 provides adequate catchment for the smoke arising from the firebed and appropriate draught.

The heat transfer efficiency is further enhanced if the inner skin is manufactured from low-nickel stainless steel which is heat reflective and assists in radiating heat to the room. The use of this material also aestheticises the fire because of its light reflective properties. Furthermore the longevity of the fire is improved by the adoption of the low-nickel stainless steel because of its resistance to surface oxidation.

It has been found that the convector open fire of the present invention has an average measured efficiency of 52% compared with 37% achieved with a British Standard open fire.

Claims

1. A convector open fire including a double-skinned fire box defining within the relatively inner skin a combustion chamber for solid fuel to be burned on a grate located within the chamber, a flue outlet from the chamber, a convection chamber for the passage of air defined between the relatively inner skin and the relatively outer skin, an inlet to the convection chamber at or towards the base thereof, an outlet from the convection chamber at or towards the roof thereof, the cross-sectional area of the convection chamber being proportional to the expected temperature of air in use passing therethrough.

2. A convector open fire according to Claim 1 in which the relatively inner skin of the firebox is provided with extended heat exchange surfaces protruding into the convection chamber.

3. A convector open fire according to Claim 1 or 2 in which the extended heat exchange surfaces are provided by a plurality of fins.

4. A convector open fire according to Claim 3 in which the fins are single strip fins.

5. A convector open fire according to Claim 4 in which the single strip fins are perforated and/or contoured.

6. A convector open fire according to any one of Claims 3 to 5 in which the ratio of the fin depth to the fin pitch is 1:1.

7. A convector open fire according to any one of the preceding claims in which the flue outlet is in the form of a duct which passes through the roof of the convection chamber.

8. A convector open fire according Claim 7 in which the flue duct has a mouth and an exit and the duct tapers from the mouth to the exit.

9. A convector open fire according to any one of the preceding claims in which the flue outlet is provided with a damper.

10. A convector open fire according to any one of the preceding claims in which the outlet from the convection air chamber is defined in the roof of the firebox and is directed upwardly away from the combustion chamber.

11. A convector open fire according to any one of the preceding claims in which the firebox is manufactured from a heat resistant, heat reflective and light reflective material.

12. A convector open fire according to Claim 11 in which the material is low-nickel stainless steel.

13. A convector open fire substantially as hereinbefore described with reference to the accompanying drawings.