GB2234058A

GB2234058A - Chimney throat restrictors

Info

Publication number: GB2234058A
Application number: GB8914220A
Authority: GB
Inventors: David James Izzard
Original assignee: GRATE GLOW FIRES
Current assignee: GRATE GLOW FIRES
Priority date: 1989-06-21
Filing date: 1989-06-21
Publication date: 1991-01-23
Anticipated expiration: 2009-06-21
Also published as: GB2234058B; GB8914220D0

Abstract

Flow control means (10), e.g. for a decorative fuel effect gas fire, comprise a restrictor (12) adapted to be located at the bottom of a chimney throat (14) to restrict flow therethrough of combustion gases (16) from an open fire (18), the restrictor (12) defining passage means (20) for such gases (16), and guide means (22) for guiding the gases up and towards said passage means (20) which are plunged to aid flow therethrough. The restrictor (12) comprises a plate (26) being a continuation of a plate (24) of guide means (22) and pivotted and balanced to allow chimney debris (64) to build up behind the same and then to release such debris. Second guide means comprising a plate (66) guide combustion gases (76) towards second passage means (75) to reduce spillage of combustion gases (76) from the flow control means (10) and into the room. Sensor means (78) responsive to excess spillage operate a flame cut-out (80). When debris (64) builds up, it forces aside plate (26) and falls against a deflector (68) to a non-operational area (72). <IMAGE>

Description

TITLE FLOW CONTROL MEANS FOR FIRES BACKGROUND This invention relates to flow control means for fires.

Open fires give off fumes of combustion gases which may contain e.g. carbon monoxide. If the fire is in a closed room, there can be a poisonous build-up in the atmosphere. To prevent this, a chimney is provided which can draw the fumes up and away from the fire and the room's atmosphere provided that there is a suitable inlet for replacement air into the room, e.g. an air-brick. The high through-flow needed of the air takes a large amount of heat up the chimney, and, as a result, the efficiency is commonly of the order of 24%. Any substantial reduction in the air flow causes the combustion gases to spill into the room and poison the atmosphere.Even if, e.g., the air brick is absent, the drawing power of the chimney is so great that air is drawn into the room through crevices and gaps, e.g. around windows and doors, and the reduction is nothing like as large as might be expected.

THE INVENTION The present inventor has hit on a combination of features that can ameliorate this position. According to one aspect of the invention there is provided a flow control means as claimed in claim 1. According to another aspect of the invention, there is provided a flow control means as claimed in claim 2. The provision of a restrictor in conjunction with a chimney throat reduces the through-flow of combustion gases from the fire definitively and to a controlled degree. The guide means aids the action of the restrictor and can be used to ensure that there is no spillage of combustion gases into the room, or only to an acceptable degree, e.g. 4 or 5%, frequently about 2%.The through-flow san thereby be reduced to substantially less than 70m3 This substantially increases the temperature of the escaping combustion gases but so reduces the rate of flow thereof that the efficiency can increase by about 507., e.g. to 30 to 35%. Also, with such low flow rates, reduced spillage and a concomitant reduction in the combustion ratio (carbon monoxide to carbon dioxide) to perhaps better than 0.02, e.g.

0.01 or, typically, 0.006, weight in weight, the conventional air brick can be omitted within conventional standards, e.g. British standards and regulations. In an example of fire means incorporating flow control means according to the invention, a reduction of air flow was obtained from 200m. per hour to 54m3. per hour. In any particular case, a fire is first designed having a combustion ratio of the order of 0.01, the restrictor passage flue inlet/is then reduced with the efficiency increasing correspondingly until spillage occurs and the passage in the restrictor is then slightly enlarged. The combustion ratio may then have increased slightly and the fire design is adjusted until the combustion ratio decreases suitably and a check is made that the spillage is within acceptable limits.If necessary the passage, fire design and guide means may be slightly adjusted to obtain minimum combustion ratio, minimum air flow rate and maximum efficiency. The whole of this test is carried out in a closed space, e.g. an unvented factory, so that the chimney produces minimum drawing of its own and so that the fire and flow control means thus produced will have better values of these quantities in practice in an actual house or other building. This adjustment of the design of the flow control means and fire need only be carried out once for any particular design of fire as the chimneys are more or less standard e.g.

in accordance with British Standard 8303:1986, see especially Figure 1.

always However, it is not/necessary to have a particular fire in mind when designing a suitable flow control means embodying the invention since a substantial improvement can be made for any fire by using flow control means embodying the invention with a reasonable size of passage means.

Preferably, if the restrictor is horizontal, the passage means are to be located at or near the remote (back) part of the restrictor while if the restrictor is oblique or vertical, the passage means are to be located at or near the top of the restrictor. In such case, the restrictor itself can help the flow of gas towards the passage means, acting as part of, or helping, the guide means.

The restrictor is preferably located or adapted to be located at or near the bottom of the chimney throat since this provides the most ready access for fixing the restrictor into position.

Generally, the passage means are designed to reduce the flow area to less than 30% of the throat area of the chimney. From around this point, the flow becomes substantially reduced and the efficiency substantially increased, without spillage, provided suitable guide means are used. The optimum flow area of the passage means has been found by experiment to be between 10% and 20% of the throat area, depending of course on the design of chimney and fire and guide means.

While any suitable guide means which will guide the gases towards the passage means can be used, e.g. a tubular opening of constant cross-section, a substantially improved performance is obtained if the guide means are shaped to funnel the flow towards the passage means, giving the flow a substantial degree of streamlining.

The passage means could be simply a gap between a restrictor plate and the side of the chimney throat. However, better flow characteristics appear to result from passage means which comprise one or more of slots and holes. If these passage means are plunged (by which term is meant a degree of streamlining at the inlet side of such slot or hole and an extension thereof on the outlet side, as for example may be produced by a form of punching of the hole or slot, much improved performance is obtained, e.g. the efficiency may increase by up to about 33%. In such case, the co-efficient of discharge might be increased by the plunging from 0.6 to 0.9.

In a preferred embodiment, the restrictor comprises a plate and this is provided with the passage means and forms at least part of the guide means. Such an embodiment is particularly neat as it has one element performing more than one job. It is also versatile as such a design makes for easier adjustment to different conditions.

A frequent difficulty with chimneys of decorative fuel effect gas fires is the likelihood of debris falling down the chimney. Clearly, if a restrictor is placed across the throat of the chimney, then such debris would tend to build up behind the restrictor and could block the passage means, causing the flow control means to malfunction.A particularly ingenious solution to this difficulty is to have the restrictor comrpise a plate pivotted and balanced to allow chimney debris to build up above or behind the same and then to release such debris after it has built up somewhat. (Clearly, the debris could not be allowed to fall through continuously since this would provide an opening in parallel with the passage means and therefore interfere with the proper functioning of the flow control means.) In practice, the balancing is so arranged that the debris can normally build up to a level substantially below the passage means (another reason for putting the passage means at the top of the restrictor), at which point the pivotted plate will rotate and release the debris.This can be deflected by a deflector located therebelow and thus be guided towards a nonoperational (back) part of the appliance, where the debris can gather harmlessly and be removed at intervals.

If second passage means are located above the first-mentioned passage means and second guide means are provided to guide combustion gases towards the second passage means, the second guide means can thereby reduce spillage of the combustion gases from the flow control means even further.

Since the flow control means operates responsively to air flow into the room and gas flow up a chimney, conditions may arise in which such flow is interfered with and there may then be spillage of an unacceptable amount. A safety device for this situation can be provided by sensor means responsive to a level of spillage to provide a signal for the cutting off the fuel supply to the fire, e.g. by operating a standard flame cut-off device, (which when once cut off does not allow the gas to be turned on again until properly lighted.) very Such a sensor may/effectively be placed at the front of the second guide means and at the top thereof since these guide means rapidly increase in temperature in such conditions. For example, their temperature may increase from 1700C to 2400C and the sensor for such an appliance would be set to respond at 2000C.

While fireplaces for solid fuel effect fires are normally built to an official standard (such as the aforementioned B.S.8303:1986, for example), so that a particular size of flow control means embodying the invention may fit quite snugly, actual installations often vary somewhat so that there could be a gap at one or more edges of the flow control means which would be unacceptable because it would interfere with the operation of the passage means. To deal with this type of situation, the flow control means are preferably fitted with adjustable fitting and sealing means for adapting the restrictor to the size of the chimney throat. The sealing means may comprise a noncombustible sealing rope and the adjustment may be provided by angleiron rails along the side and upper edges which (along the upper edge) hold the rope and are themselves adjustably fitted to the restrictor.

PARTICULAR DESCRIPTION Reference will now be made by way of example to the accompanying drawings, in which: Fig.l is a vertical cross section through fire means embodying the invention; and Fig.2 is a half front view of flow control means shown in Fig.l embodying the invention.

Referring to the drawings, flow control means 10 comprise a restrictor 12 adapted to be located at or near a chimney throat 14 to restrict flow therethrough of combustion gases 16 from an open fire 18, the restrictor 12 defining passage means 20 for such gases 16, and guide means 22 for guiding the gases 16 up and towards said passage means 20. If the flow control means are in situ, they may comprise also the chimney throat 14 (and the parts actually fixed to the throat 14 may be somewhat simpler than shown in Fig.l). The passage means 20 are near the top of the restrictor 12 which, as seen in Fig.l, is located at the bottom of the throat 14.

In the embodiment shown in Fig.l, the passage means 20 have a flow area of around 10% of the throat area. The guide means comprise a front plate 24 and a continuation of it in the form of a rear plate 26 which together are shaped to funnel the flow 16 towards the passage means 20. The passage means comprise a slot 20 extending horizontally almost to the sides of plate 26. Slot 20 vertical is plunged, as indicated at 28, being rounded (in/cross section) at the front and extended backwards by a few millimetres. The restrictor 12 comprises plate 26 provided with the passage means 20 and forming at least part of the guide means 22.

The restrictor comprises a back plate 34 mounted first by means of a single bottom central bolt 36 to firebrick 38. The bolt 36 is of a kind which can be inserted through a hole in firebrick 38 and then tightened to collapse a portion 40 at the back and hence hold the bolt to the firebrick. Plate 34 carries side rails 42, each in the form of an angle iron mounted loosely to back plate 34 and adjustably thereto by means of the bolts and slots 44. Two bolts 46, like bolt 40, are used to fix each side rail 42 tightly to the parts of firebrick 38 that form the sides of the chimney or fireplace. Bolts 44 are then tightened in position, engaging threaded holes in rails 42. A similar top rail 48 is held loosely to the top of back plate 34 by bolts and slots 50, the bolts engaging threaded holes in back plate 34.Rail 48 carries non-combustible rope 52 and is pressed tightly against the top firebrick 54 of throat 14 and then the bolts 50 are tightened to hold rail 48 in position. The corner spaces between rails 48 and 42 are filled with fire clay. Thus, a close sealing fit is provided right around back plate 34. Plate 34 has a large slot 56 extending from the bottom part 58 of the firebrick defining throat 14 to a point 60 somewhat above the junction 62 between plates 24 and 26. These plates 24,26 are in fact formed of a single plate with a straight-line bend at junction 62 and a centre of gravity a little below and to the right (as seen in Fig.l) of pivot 32, so that this unit when suspended on pivots 32 will, by its own weight, be urged gently towards firebrick portion 58.It then closes thewhole of slot 56 except for that portion opposite passage 20 and that portion above junction 62. When sufficient debris 64 gathers, this presses plate 26 to the right (until plate 24 hits a guide 66, to be described below). This allows the debris to fall onto the upper side of deflector 68 (fastened by a pair of bolts 70 like bolt 40) and hence pass down to a non-operational area 72 of fire 18.

Except when debris is thus falling, the only passage means through the restrictor is via slot 20, apart from a second passage means now to be described.

Second guide means 66 in the form of a plate extends roughly parallel to plate 24 but beyond this to meet end pieces 74 to which it is sealed forming a canopy or shield. A small amount of the combustion gases 76 enters the space between plate 24 and plate 66, acting as second 75 guide means, up and towards the upper portion/of slot 56 above junction 62.

75 This upper portion constitutes second passage meansA whereby most of the spillage of gases 76 is also led to throat 14. A small amount of spillage, perhaps 2%, may escape into the room but this is negligible for practical purposes. Plate 66 is also carried by back plate 34 to which it is rivetted. Sensor means 78 act in the manner described above to operate a flame cut-out shown schematically at 80. Plate 66 can also serve to carry any required decorative canopy. The end pieces 74 ensure that any gas 76 caught by guide means 66 does not escape but is led up towards the upper part of slot 56 between junction 62 and point 60, constituting said second passage means 75.

The range of movement of rails 42,48 is about 15mm. The whole arrangement fits into the back of a 400mm. or 450mm. chairbrick made to British Standard 1251:1987.

It is found that this embodiment actually improves the pull of the flue, thus reducing spillage of combustion gases into the room.

The placing of the restrictor at the entrance to the throat of the chimney has the following advantages: (a) it can be seen and installed easily without the necessity of breaking into the chimney structure.

(b) at this point, details of the sizes of the chimney are visible and easily known. Above this point, the throat is variable and has an unknown area.

(c) as the entry to the chimney throat is fairly well standardised, the positioning of the restrictor unit at this point allows it to be made to cater for all standard fireback tolerances and tolerances of installation of lintels 54.

It is to be noted that the whole working of the arrangement depends on aerodynamic features and this should be taken into account in design, particularly of the guide means and preferably of the passage means (as described above with reference to plunging) to help streamline flow and reduce or inhibit eddying.

It will be appreciated that the flow control means can comprise the fire itself, which can be sold as a single unit for fitting into an existing fireplace, provided the unit fits exactly into the fireplace, particularly around the edges or at least can be adjusted to do so.

Claims

1. Flow control means comprising a restrictor adapted to be located at or near a chimney throat to restrict flow therethrough of combustion gases from an open fire, the restrictor defining passage means for such gases, and guide means for guiding the gases up and towards said passage means.

2. Flow control means comprising a chimney throat, provided with a restrictor to restrict the flow therethrough of combustion gases from an open fire, the restrictor defining passage means for such gases, and guide means for guiding the gases up and towards said passage means.

3. Means as claimed in claim 1 or 2, in which the passage means are at or near the top or remote part of the restrictor.

4. Means as claimed in any preceding claim, in which the restrictor is located or adapted to be located at or near the bottom of the chimney throat.

5. Means as claimed in any preceding claim, in which the passage means have a flow area less than 30% of the throat area.

6. Means as claimed in claim 5, in which the passage means have a flow area of between 10% and 20% of the throat area.

7. Means as claimed in any preceding claim, in which the guide means are shaped to funnel the flow towards the passage means.

8. Means as claimed in any preceding claim, in which the passage means comprise one or more of slots and holes.

9. Means as claimed in claim 8, in which the passage means are plunged to aid flow therethrough.

10. Means as claimed in any preceding claim, in which the restrictor comprises a plate provided with the passage means and forming at least part of the guide means.

11. Means as claimed in any preceding claim, in which the restrictor comprises a Plate pivotted and balanced to allow chimney debris to build up above or behind the same and then to release such debris.

12. Means as claimed in any preceding claim, comprising second passage means above the first-mentioned passage means and second guide means to guide combustion gases towards the second passage means and to reduce spillage thereof from the flow control means.

13. Means as claimed in any preceding claim, comprising sensor means responsive to a level of spillage to provide a signal for cutting off fuel supply to the fire.

14. Means as claimed in any preceding claim, comprising sealing means to seal the restrictor to the chimney throat.

15. Means as claimed in any one of claims 1 to 13, comprising adjustable fitting and sealing means to adapt the restrictor to the size of the chimney throat.

16. Means as claimed in any preceding claim, in which the guide means are arranged or adapted to be arranged to prevent at least 95% of spillage of gases from the fire.

17. Flow control means substantially according to any example hereinbefore described with reference to or illustrated in the accompanying drawings.

18. Fire means comprising an open fire and flow control means as claimed in any preceding claim for controlling the flow of combustion gases from the fire.

19. Fire means as claimed in claim 18, in which the fire is a decorative fuel effect gas fire.