GB2193569A - Inset simulated solid fuel gas fire - Google Patents

Abstract

An inset, gas fired, live-fuel effect space heater comprises an outer casing 4 the rear and side parts of which are adapted to permit the space heater to be inset in a fireplace opening which contains a conventional 'Milner' firebrick 3, an inner casing 7 positioned within the outer casing 4 and containing a gas- fired, live-fuel effect firebed 8, it being arranged that in use no naked flame or incandescent part of the firebed 8 projects more than 50mm from the fireplace opening, a heat exchanger 13 positioned in the normal flow path of the combustion products 15 from the firebed 8 and from which they are passed to a flue outlet 16, the heat exchanger 13 carrying convection air flowing from between the inner casing 7 and outer casing 4 which is heated by the combustion products 15. Preferably a flue blockage sensor 21 is provided which is positioned adjacent to but not in the normal combustion product flow path of the space heater 1, the sensor 21 preventing the flow of gas to the firebed 8 if the flue outlet 16 becomes blocked. The firebed 8 may include a non- permeable layer having apertures filled with particulate material, or an open-cell ceramic foam layer. <IMAGE>

Description

SPECIFICATION Space heaters This invention relates to space heaters and relates more especially, to an inset, gas-fired, live-fuel effect space heater.

It is commonly required, at the present time, to provide a gas-fired, live-fuel effect space heater that can be inset into a fireplace opening which originally had been designed for an open, solid-fuel e.g. coal fire. Such fireplace openings are usually provided with a firebrick, commonly referred to as a Milner brick, which is normally cemented-in within a larger fireplace opening. With prior art inset space heaters it is required that the firebrick be removed in order to provide sufficient space for the space heater to be inset in the opening and also to provide sufficient space behind the heater for any rubble or other matter that might fall down the fireplace chimney flue.

However, the removal of the firebrick and the associated back-fill material can be a relatively expensive operation which has to be done prior to a space heater being installed.

Therefore the installation of such prior art inset space heaters is not a straight forward operation.

it is an object of the present invention to provide an inset, gas-fired, live-fuel effect space heater that is adapted to be installed in a fireplace opening which retains within it the usual firebrick.

According to one aspect of the present invention there is provided an inset gas-fired live-fuel effect space heater comprising an outer casing the rear and side parts of which are adapted to permit the space heater to be inset in a fireplace opening which contains a conventional firebrick, an inner casing positioned within said outer casing and containing a gas-fired live-fuel effect firebed, it being arranged that in use of said space heater, no naked flame from said firebed or no incandescent part thereof projects more than 50mm from the vertical plane of a fireplace opening in which said space heater is to be fitted, heat exchanger means positioned in the normal flow path of the combustion products from said firebed and from which said products are passed to a flue outlet of said appliance, said heat exchanger means, in use of said appliance, carrying convection air flowing from between said outer and inner casings which is heated by said combustion products.

In this specification, what is meant by a firebrick is the insert that is normally provided in fireplace openings for open, solid-fuel e.g.

coal fires. Such firebricks are commonly referred to as "Milner" or "Chair" bricks and at the present time are defined in accordance with British Standard B.S. 1251.

In a preferred arrangement for carrying out the aforesaid first aspect of the invention, flue blockage sensor means will be provided positioned adjacent to but not in the normal combustion product flow path of said space heater, said sensor means controlling the flow of gas to said firebed if said flue outlet becomes blocked.

According to another aspect of the invention there is provided a firebed for use in a gas-fired, live-fuel effect space heater.

Some exemplary embodiments of the invention will now be described reference being made to the accompanying drawings, in which: Fig. 1, is diagrammatic side view of a space heater in accordance with a preferred embodiment of the invention; Fig. 2, is a perspective, diagrammatic side view of the appliance of Fig. 1 with alternative form of heater exchanger; Fig. 3, is a side view of the appliance of Fig. 2, in which the heater exchanger is provided with baffles; Fig. 4, is a schematic side view of the appliance of Fig. 1 with an alternative form of firebed; Fig. 5, is a diagrammatic side view of the appliance of Fig. 4, with an improved form of fuel bed; -Fig. 6, is a diagrammatic plan view of part of the firebed depicted in Fig. 5; and, Fig. 7, is a block schematic diagram indicating the operation of the flue blockage sensor of Fig. 1.

In Fig. 1 there is shown a gas fire 1 which is adapted to be inset in a fireplace opening which is bounded at the top by a fireplace lintel 2 and at the back by a firebrick 3, sometimes referred to as a Milner or Chair brick. The gas fire 1 consists of an outer casing 4 the upper 5 part of the rear portion of which is inclined towards the front of the fire in order to accommodate the forward protruding part 6 of firebrick 3. Although not shown, the side portions of the outer casing 4 are also angled outwards from the rear of the casing 4 in order to substantially correspond to the sidewalls of the firebrick 3.

Within the outer casing 4 is positioned an inner casing 7, the lower part of which carries a firebed 8 comprising a burner assembly 9 and an inclined bed 10 of simulated solid fuel briquettes (which may alternatively be logs) supported on a plurality of spaced transverse supports 12 of a hard ceramic material. In order to comply with the necessary standards, it is arranged that in use of the gas fire 1 thus far described, no naked flame or incandescent part of the firebed 8 projects more than 50mm from the vertical plane 2, of the fireplace opening in which the gas fire 1 is fitted. The upper part of the inner casing 7 opens into a plate-type heat exchanger 13 which has a number of flue passageways 14 through it, through which the combustion products 1 5 from the firebed 8 pass.After pas sage through the heat exchanger 13 the com bustion products pass through a flue outlet 16 of the fire 1 and thence to a chimney flue 17.

At the lower part of the front face of the fire 1 is provided an air inlet 18 for introduc ing air into the underside of the firebed 8 for combustion purposes and below the air inlet 18 is a further air inlet 19 for introducing air between the outer casing 4 and the inner cas ing 7, which air passes across the bottom of the fire 1, up the back of the fire 1, through the heat exchanger 13 and out through a decorative grille 20 in the upper part of the front face of the fire 1. During its passage through the fire 1 this air is heated and ema nates from the grille 20 as heated convection air.

Under normal circumstances the combustion products 15 from the firebed 8 flow-upwards, through the heat exchanger 13, through the flue outlet 16 and into the chimney flue 17.

However, if for any reason the chimney flue 17 becomes blocked perhaps due to debris falling down the flue 17, there being no space behind the fire 1 for any debris to collect, the combustion products have no alternative but to pass into the room in which the fire 1 is situated. For a short period of time this condition may not be noticed, but if it is prolonged then the room becomes stuffy and creates a drowsy effect upon the occupants which could eventually become dangerous.

In order to overcome this problem, the fire 1 is provided with a flue blockage sensor 21 situated on the outside of a canopy 22 so that it is not in the normal flow path of the combustion products 15. However, if the chimney flue 17 becomes blocked, the com bustion products cannot pass up the flue 17 and so pass out through the front face of the fire 1 and pass over the sensor 21. The sensor 21 thus detects the flue blockage condition and is arranged to cut-off the gas supply to the gas burner 9. The cut-off of the gas supply may be arranged to be temporary so that if the flue blockage clears the gas supply is restored or it may be arranged to be per manently cut-off so requiring the call-out of a serviceman to investigate the reason for the flue blockage.

In Fig. 2 of the drawings there is shown a gas fire which is similar to that of Fig. 1 but in which an alternative form of heat exchanger 13 is used. For the sake of clarity the canopy 22 carrying the flue blockage sensor 21 has been omitted in Fig. 2. In Fig. 2 the heat exchanger 13 is of the cross-flow type which consists of a plurality of generally rectangular tubes 23 which extend from front-to-back in the inner casing 7 of the fire 1 and through which the convection air flowing between the outer and inner casings 4 and 7 respectively pass to emanate from the grille 20. The hot combustion products 15 from the firebed 8 pass upwards between the tubes 23 thereby heating the convection air passing through them.

However, in the heat exchanger 13 of Fig. 2 it is found that the flow of convection air tends to be mainly at the tops of the tubes 23 and also the flow of the combustion products 15 tends to take place mainly around the inner ends of the tubes 23. Because of this the efficiency of the heat exchanger is not as good as it could be. This is rectified in the heat exchanger 13 shown in the gas fire of Fig. 3 by providing one or more baffles 24 which extend across the width of the heat exchanger 13 below the tubes 23 and which have generally vertically disposed fingers 24' which extend upwards between the tubes 23.

The baffles 24 and fingers 24' have the effect of causing the hot combustion products 15 to flow over a greater portion of the tubes 23 thereby increasing the effective heat exchange area.

Similarly, adjacent the inner ends of the tubes 23 is provided a further baffle 25 which extends across the width of the heat exchanger in front of the lower part of each of the tubes 23, the top surface of which is provided with baffle extensions 25' (shown in dashed lines) which extend lengthwise down each of the tubes 23. The baffle 25 and the extensions 25' thereof have the effect of causing the convected air to flow over a greater surface area of the tubes 23 thereby again increasing the effective heat exchange area.

By providing the baffles 24 and 25 the efficiency of the heat exchanger 13 can be significantly increased. A still further increase in efficiency can be achieved by providing for forced flow of the convected air that is passed through the heat exchanger 13. This is achieved in the gas fire of Fig. 3 by means of a tangential-flow type fan 26 which is located in the rear bottom corner of the outer casing 4 between it and the inner casing 7, and which has the effect of increasing the flow of convected air from the air inlet 19 to the heart exchanger 13.

In Fig. 4 there is shown a gas fire 1 similar to that of Fig. 1 but having an alternative form of firebed 8. In Fig. 4 the firebed 8 consists of an open mesh or gauze base 27 which is used to support a layer of particulate material 28 such as Vermiculite or ceramic beads. On top of the layer of particulate material 28 is a grid shaped support 29, typically of a hard ceramic material, and on the support 29 is provided the simulated fuel briquettes 30. A gas/air mixture is provided to the underside of the firebed 8 via a mixer tube 31 and a gas injector 32. Ignition of the gas/air mixture may be achieved by direct spark ignition or from a pilot, although it would be possible using a lighted match. A firebed of this form is found to have an improved live-fuel effect over firebeds of conventional form.

An improved version of the firebed 8 incorporated in the gas fire of Fig. 4 is shown in the gas fire of Fig. 5 which is otherwise identical to that of Fig. 4. In the gas fire of Fig. 5 the firebed 8 is contained in a separate tray 33, shown diagrammatically in plan view in Fig. 6, which is supported on the inclined base 34 of the inner casing 7 of the fire. The tray 33 is formed on its underside in each corner thereof with downward depressions 35 on which the tray 33 is supported so that air is free to circulate around and underneath the firebed 8 to assist aeration.

Within the tray 33 is provided the open mesh or gauze base 27 which supports in succession the particulate material 28, the grid shaped support 29 and the simulated fuel briquettes 30 as in the arrangement of Fig. 4. In order to increase efficiency, the inside walls of the inner casing 7 surrounding the firebed 8 are lined with suitable insulating material 45.

A major difference between the firebeds 8 of Figs 4 and 5, apart from the inclusion of the tray 33 in Fig. 5, is that whereas in Fig. 4 a burner assembly having a single mixer tube 31 and single gas injector 32 is provided, in Fig. 5 two mixer tubes 36 and 37 having respective injectors 38 and 39 are provided, these being more clearly shown in Fig. 6, the mixer tube 36 feeding an inner section 40 of the firebed 8 and the mixer tube 37 feeding the remaining, outer section 41 of the firebed 8. The purpose of providing two separately fed mixer tubes 36 and 37 is two-fold.Firstly, one or other or both of the mixer tubes may be selectively supplied with gas in- order to provide for three different settings of the gas fire and also the gas/air mixture emanating from the two mixer tubes 36 and 37 may be made to be different so that, for example, one section of the firebed can be used to produce a clear hot flame for heating the briquettes 30 but which flame is not very visible, and the other section can be used to produce a not so hot flame but which is more visible, thereby giving a more realistic "real fire" effect. The combined effect of the two sections results in a firebed that radiates a lot of heat and yet which has a realistic "real fire" effect.

One problem with the firebeds described with reference to Figs. 4 and 5 is that in order to achieve an acceptable level of direct radiated heat, it is necessary to incline the firebed so that heat is radiated outwards rather than upwards. However, the amount of inclination that can be achieved is limited by the layer of particulate material, which, if the inclination is too steep, will not remain in place.

One proposed way of overcoming this is to replace the layer of particulate material 28 with a corresponding non-gas permeable layer having a plurality of apertures in it, which may extend widthwise over the area of the firebed 8, the apertures being filled with particulate material, which is thus held in position. It has also been found advantageous to support the open mesh or support base 27 over its area, and one way of doing this is to support it on an apertured sheet, the apertures of which correspond essentially to the apertures in nongas permeable layer.

It is also envisaged that the particulate material may be replaced by a single open-celi, sponge-like layer, perhaps of a ceramic foam which would enable the firebed to be used at relatively steep angles.

The flue blockage sensor 21 hereinbefore described, especially in connection with the gas fire of Fig. 1, may take a number of different forms. One such form is shown in Fig.

7, in which the sensor 21 takes the form of a temperature sensor. The burner assembly 9 of the gas fire is shown having a gas supply 42 applied to it via a gas control valve 43. The gas control valve 43 is controlled by means of a flame sensor 44 in conjunction with the temperature sensor 21. The temperature sensor 21 is arranged so that at normal temperatures it forms a short-circuit but at high temperatures, i.e. those occurring during flue blockage conditions, it goes open-circuit. Conversely, the flame sensor 44 is arranged to be short-circuit when it is subjected to the burner flame, but is open circuit when the burner flame is out.Thus, under normal conditions with the gas fire functioning correctly with correct flue conditions, both the temperature sensor 21 and the flame sensor 44 will be short circuit and the control valve 43 will operate to supply gas to the burner assembly 9.

However, if the temperature of the temperature sensor 21 exceeds its predetermined temperature, as is arranged to happen when flue blockage occurs, then it becomes open circuit and the control valve 43 is operated to cut-off the gas supply to the burner assembly 9. Similarly, if the flame of the burner assembly 9 goes out for any reason, the flame sensor 44 will go open-circuit which will again cause the control valve 43 to cut-off the gas supply to the burner assembly 9.

Instead of a temperature sensor, the flue blockage sensor 21 may take the form of a fusible link which controls a weep line to a gas control valve, such that when the link melts (at a pre-determined temperature) the gas control valve closes to cut-off the gas supply to the burner assembly.

Yet a further alternative is for the flue blockage sensor 21 to take the form of an oxygen sensing pilot. The fire is fitted with an oxygen sensing permanent pilot which controls a flame failure device. The pilot extinguishes when the oxygen level in the combustion air falls to a predetermined level, resulting in clo- sure of the flame failure device and cut-off of the gas supply to the burner assembly.

Although in the embodiments described, a flue blockage sensor 21 has been provided in order to sense a flue blockage condition, this being necessary because of the lack of space behind the fire for any debris etc. that may fall down the chimney flue to collect, it will be appreciated that the gas fire described may be installed in a fireplace opening which does not have any firebrick in it or which, for example, may have only the top part of the firebrick removed, in which case the flue blockage sensor 21 may be dispensed with.

In addition, the firebeds 8 incorporated in the gas fires of Figs. 4 and 5, although ideally suited for use in an inset, live-fuel effect, gas fire as described, might also find application in other types, e.g. non-inset, live-fuel effect, gas fires.

Claims (31)

1. An inset gas-fired live-fuel effect space heater comprising an outer casing the rear and side parts of which are adapted to permit the space heater to be inset in a fireplace opening which contains a conventional firebrick, an inner casing positioned within said outer casing and containing a gas-fired live-fuel effect firebed, it being arranged that in use of said space heater no naked flame from said firebed or no incandescent part thereof projects more than 50mm from the vertical plane of the fireplace opening in which said space heater is to be fitted, heat exchanger means positioned in the normal flow path of the combustion products from said firebed and from which said products are passed to a flue outlet of said appliance, said heat exchanger means, in use of said appliance, carrying convection air flowing from between said outer and inner casings which is heated by said combustion products.

2. A space heater as claimed in claim 1, comprising flue blockage sensor means positioned adjacent to but not in the normal combustion product flow path of said space heater, said sensor means controlling the flow of gas to said firebed if said flue outlet becomes blocked.

3. A space heater as claimed in claim 1 or claim 2, in which said firebed is of unguarded form.

4. A space heater as claimed in any preceding claim, in which said heat exchanger means takes the form of a plate-type heat exchanger.

5. A space heater as claimed in any of claims 1 to 3, in which said heat exchanger takes the form of a cross-flow heat exchanger.

6. A space heater as claimed in claim 5, in which the cross-flow heat exchanger comprises a plurality of tubes extending from front-to-back in said inner casing and through which said convection air flows, said combustion products flowing around said tubes.

7. A space heater as claimed in claim 6, in which the cross-flow heat exchanger comprises baffle means within said tubes for controlling the flow of said convection air.

8. A space heater as claimed in claim 6 or claim 7, in which the cross-flow heat exchanger comprises baffle means disposed on the outside of said tubes for controlling the flow of said combustion air.

9. A space heater as claimed in any preceding claim, comprising fan means for providing for force flow of said convection air.

10. A space heater as claimed in claim 9, in which the fan means comprises a tangentialflow type fan located in the rear bottom corner of said outer casing, between said outer casing and said inner casing.

11. A space heater as claimed in any preceding claim, in which said firebed comprises gas burner means disposed so as to, in use, supply a gas/air mixture under a gas permeable open cell layer thereof, said layer being superposed by means for supporting a bed of simulated solid fuel.

12. A space heater as claimed in claim 11, in which said layer comprises a gas permeable sheet for supporting a layer of particulate material.

13. A space heater as claimed in claim 12, in which the means for supporting said bed of simulated solid fuel comprises a lattice structure disposed on said layer of particulate material.

14. A space heater as claimed in any of claims 11 to 13, in which said firebed is formed in a tray which is located in the base of said inner casing.

15. A space heater as claimed in claim 14, in which the gas burner means is of duplex form.

16. A space heater as claimed in claim 15, in which the gas burner means includes a first burner for affording an inner central burner area of said firebed, and a second burner for affording an outer burner area of said firebed which surrounds said inner central area.

17. A space heater as claimed in claim 11, in which the gas permeable open cell layer comprises a non-gas permeable layer having apertures therein containing gas permeable, open cell material.

18. A space heater as claimed in claim 17, in which the gas permeable, open cell material is particulate material.

19. A space heater as claimed in claim 18, in which the gas permeable open cell layer is superposed on a gas permeable sheet.

20. A space heater as claimed in claim 19, in which the gas permeable sheet is supported on an apertured support sheet, the apertures of which substantially correspond with the apertures in said non-gas permeable layer.

21. A space heater substantially as hereinbefore described with reference to the accompanying drawings.

22. A gas-fired, live-fuel effect space heater including a firebed, comprises gas burner means disposed so as to, in use, supply a gas/air mixture under a gas permeable open cell layer thereof, said layer being superposed by means for supporting a bed of simulated solid fuel.

23. A space heater as claimed in claim 22, in which said layer comprises a gas permeable sheet for supporting a layer of particulate material.

24. A space heater as claimed in claim 23, in which the means for supporting said bed of simulated solid fuel comprises a lattice structure disposed in said layer of particulate material.

25. A space heater as claimed in any of claims 22 to 24, in which said firebed is formed in a tray structure.

26. A space heater as claimed in claim 25, in which the gas burner means is of duplex form.

27. A space heater as claimed in claim 26, in which the gas burner means includes a first burner for affording an inner central burner area of said firebed, and a second burner for affording an outer burner area of said firebed which surrounds said inner central area.

28. A space heater as claimed in claim 22, in which the gas permeable open cell layer comprises a non-gas permeable layer having apertures therein containing gas permeable, open cell material.

29. A space heater as claimed in claim 28, in which the gas permeable, open cell material is particulate material.

30. A space heater as claimed in claim 29, in which the gas permeable open cell layer is superposed on a gas permeable sheet.

31. A space heater as claimed in claim 30, in which the gas permeable sheet is supported on an apertured support sheet, the apertures of which substantially correspond with the apertures in said non-gas permeable layer.