GB2304183A

GB2304183A - Gas-fired heating appliance

Info

Publication number: GB2304183A
Application number: GB9516269A
Authority: GB
Inventors: Michael Morley
Original assignee: Hepworth Heating Ltd
Current assignee: Hepworth Heating Ltd
Priority date: 1995-08-08
Filing date: 1995-08-08
Publication date: 1997-03-12
Anticipated expiration: 2015-08-08
Also published as: GB9516269D0; GB2304183B

Abstract

A gas fired heating appliance incorporates means for shutting down the appliance in the event of a flue blockage comprising means for directing combustion products diverted from the flue into contact with sensing means (19) adapted to generate a signal in response to the presence of combustion products, and means operable in response to the signal generated to cut off the gas supply to the appliance. The sensing means is preferably located in a sensing zone (28) of relatively small area or extent such that essentially all the combustion products entering the zone come into close contact with the sensing means. Preferably the sensing zone is defined by a recess in an edge of a plate member over which the diverted combustion products are directed, whereby the products pass into the zone before clearing the remainder of the edge.

Description

GAS FIRED HEATING APPLIANCES This invention relates to gas fired heating appliances.

Combustion products from gas fired heating appliances are generally exhausted to atmosphere through a chimney or flue forming part of or connected to the building in which the appliance is installed and to which the appliance is connected by means of a flue outlet. Occasionally chimneys or flues can be become blocked and the relevant regulations require in such circumstances that the appliance must shut down safely.

Previously proposed arrangements for this purpose have suffered from somewhat erratic operation and there has been a difficulty in ensuring satisfactory operation over the full range of heat settings at which such appliances are designed to operate.

It is an object of the present invention to obviate or mitigate these disadvantages.

According to one aspect of the invention there is provided a method of shutting down a gas fired heating appliance in the event of a flue blockage, comprising constraining combustion products diverted from the flue to flow through a sensing zone, generating a signal in response to the presence of combustion products in said zone and utilising said signal to cut off gas supply to the appliance.

The invention also provides a gas fired heating appliance incorporating means for shutting down the appliance in the event of a flue blockage comprising means for directing combustion products diverted from said flue to a sensing zone, means for sensing the presence of combustion products in said zone, means for generating a signal in response to said sensing, and means operable in response to said signal to cut off the gas supply to the appliance.

Preferably said sensing zone is of relatively small area or extent such that essentially all the combustion products entering said zone come into close contact with said sensing means.

Preferably said sensing zone is defined by a recess in an edge of a plate member over which said diverted products are directed, whereby the products pass into said zone before clearing the remainder of said edge. The plate member advantageously forms part of a draught diverter adapted to provide an alternative flow path for combustion products in the event of downdraughts from an unblocked flue or of flue blockage.

Said sensing means preferably comprises temperature sensitive switch means located in said zone and operable on actuation to interrupt current flow in an electrical circuit acting on valve means operable to control supply of gas to the appliance.

Preferably said valve means is maintained in a normally open position by electromagnetic means the current supply to which is cut off upon operation of said sensing means.

Preferably said circuit incorporates a thermocouple disposed adjacent to a gas burner of the appliance and operable on heating to generate an electrical current in said circuit, whereby in the event of said burner failing to ignite or being extinguished, current flow in said circuit ceases and said valve means operates to cut off gas supply to the appliance.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammtic drawings, in which: Fig. 1 is a vertical cross-section through one form of gas fired heating appliance according to the invention showing the flow of combustion products during normal operation; Fig. 2 is a view similar to Fig. 1 showing the flow of combustion products in the event of flue blockage; Fig. 3 is an enlarged perspective view of the rear of the appliance showing various details; and Fig. 4 is a diagram of an electrical circuit incorporated in the appliance.

Referring to the drawings, the appliance comprises a combustion chamber 5 incorporating a simulated fuel bed 6. A gas burner assembly 7 is mounted below and in front of the fuel bed 6, combustion of fuel at the burner surface generating gas flames which act upon the fuel bed to produce an incandescent glowing effect simulating a coal or log fire. Combustion products generated by combustion of the gas at the burner surface pass upwards and rearwards through the combustion chamber 5 as indicated by the arrows in Fig. 1 to a rear housing 8 incorporating an outlet duct 9 adapted in use to be connected to a chimney or flue (not shown). In normal operation of the appliance products of combustion derived from the burner 7 pass upwardly and rearwardly through the combustion chamber 5, housing 8 and outlet 9 and are discharged to atmosphere through the chimney or flue.

The housing 8 is open at its lower end and serves as a draught diverter ensuring that during normal operation any downdraughts from the chimney or flue are prevented from passing through and out the front of the appliance but are caught in the chamber 8 and discharged from its lower end.

As best seen in Fig. 3, a supply of gas for combustion purposes enters the appliance through a supply pipe 14 connected to a control valve 15 mounted on the rear of the appliance and adapted to be manually operated by a control knob (not shown) at the side of the appliance. Outlet pipes 17A and 178 are connected between the control valve 15 and the burner 7. The control valve incorporates a valve member (not shown) normally maintained in an open position by an electromagnet whereby to allow flow of gas from the supply pipe 14 through pipes 17A and 17B to the burner 7.

A thermocouple 18 is positioned adjacent to the burner 7 so as to be heated by the gas flames when the burner is in operation. The thermocouple 18 is connected in circuit with an electromagnetic coil associated with the control valve 15 and with a sensing assembly 19 mounted on the rear of the housing 8.

During normal operation of the appliance, heating of the thermocouple 18 by the flames from the burner 7 generates an electrical current which energises the electromagnetic coil, thus maintaining the control valve in its open position and permitting gas supply to the burner 7.

For this purpose the thermocouple comprises an outer tubular casing 18A and an inner wire 18B connected together at the end adjacent the burner 7 and insulated from one another throughout the remainder of their lengths. At its other end the casing 18A is connected to earth via the body of the valve 15 and the wire 18B is connected to one end of the electromagnetic coil, the other end of which is earthed. Intermediate the ends of the thermocouple a junction block 20 is provided by means of which the inner wire is connected by supply and return wires 21A and 218 to a thermally sensitive switch 25 mounted on a bracket 26 secure to the rear surface of the housing 8. The switch member 25 is normally maintained in a closed position to complete the circuit and maintain the valve 15 in its open position.

Immediately below the bracket 26 a recess 27 is formed in the lower edge 8A of the casing 8. The recess 27 defines a sensing zone 28 through which diverted combustion products pass in the event of blockage of the chimney or flue as will be described hereafter. The presence of hot combustion products in the zone 28 energises the thermal control switch 25 thereby breaking the electrical circuit and causing the control valve 15 to close and cut off gas supply to the burner 7.

Fig. 2 shows the flow of combustion products through the appliance in the event of blockage of the flue. Thus, as shown by the arrows in Fig. 2, combustion products cannot discharge through the outlet 9 and are instead directed downwardly through the casing 8. In the absence of the recess 27, the products would flow over the lower edge 8A of the casing 8 in a somewhat erratic manner making it difficult to sense the presence of diverted combustion products sufficiently promptly or accurately. By virtue of provision of the recess 27, diverted combustion products first discharge from the housing 8 into the zone 28 defined by the recess and are thereby brought immediately into contact with the control switch 25 resulting in shut down of the appliance.

Provision of the zone 28 defined by the recess 27 in the lower edge of the casing 8 is particularly advantageous in ensuring effective operation of the unit throughout the full range of heat settings for which such units are normally designed. At low heat settings the ambient temperature at the rear of the appliance is relatively low and in the absence of the recess 27 spillage of diverted gases can occur at varying points along the lower edge of the casing 8 so that detection may be delayed resulting in an excessive period of operation under blocked flue conditions. Conversely when the appliance is running at its maximum heat output, the ambient temperature at the rear of the appliance is generally substantially higher and this can result in generation of false signals and unnecessary shut down of the appliance.Adjustment to accommodate one condition can aggravate the other making it extremely difficult to attain satisfactory operation under all conditions.

By virtue of the arrangement described, diverted combustion products reach the upper end of the recess 27 and spill into the sensing zone 28 before reaching the lower edge 8A of the casing at other points. Moreover by the provision of a sensing zone of relatively small area or extent, essentially all the combustion products entering the zone come into close contact with the sensing means. Diverted flue gases are therefore constrained to discharge from the housing directly adjacent the location of the control switch 25, thereby ensuring rapid response to a flue blockage condition and greatly facilitating setting of the sensitivity of the switch to operate satisfactorily irrespective of the heat output setting of the appliance.In a typical arrangement the recess 27 may be approximately 30mm wide by 15mm high in a draught diverter of about 315mm in width. The dimensions of the recess may however be varied dependent on the sensitivity of the thermal switch or other sensing device employed and on other factors.

Thus during normal operation of the appliance combustion products from the burner 7 pass upwardly and rearwardly through the main casing 5, casing 8 and duct 9 to the chimney or flue. In the event of downdraught conditions combustion products are diverted downwardly through the casing 8 and discharged at its lower end.

This does not result in activation of the shut down mechanism since the combustion products are diluted by air entering the appliance from the flue. In the event of a flue blockage preventing exhaust of combustion products through the outlet 9, they are diverted downwardly within the housing 8 and, by virtue of the provision of the cut out 27 spill into the zone 28 before reaching the lower edge 8A of the casing. The combustion products are thus directed directly to the vicinity of the switch 25 which is thereby actuated to cause closing of the valve 15 and cut-off of gas supply to the burner 7.

Various modifications may be made without departing from the invention. For example the size, shape and position of the cut out 27 may be varied or other means may be provided for channelling diverted combustion products directly to the location of the switch 27 or other sensing means. The arrangement for supply of gas to the appliance and for cutting off the supply following actuation of the sensing means may be varied and more than one burner may be provided.

Moreover while reference has been made herein primarily to a gas fire, the invention may also be applied to a combined gas fire and back boiler unit.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

aalimS:

1. A gas fired heating appliance incorporating means for shutting down the appliance in the event of a flue blockage comprising means for directing combustion products diverted from said flue into close proximity with sensing means adapted to generate a signal in response to the presence of combustion products, and means operable in response to said signal to cut off the gas supply to the appliance.

2. An appliance according to claim 1 wherein said sensing means is located in a sensing zone of relatively small area or extent such that essentially all the combustion products entering said zone come into close contact with said sensing means.

3. An appliance according to claim 2 wherein said sensing zone is defined by a recess in an edge of a plate member over which said diverted products are directed, whereby the products pass into said zone before clearing the remainder of said edge.

4. An appliance according to claim 3 wherein said plate member forms part of a draught diverter adapted to provide an alternative flow path for combustion products in the event of downdraughts from an unblocked flue or of flue blockage.

5. An appliance according to any of claims 2 to S wherein said sensing means extends over substantially the full width of said sensing zone.

6. An appliance according to any preceding claim wherein said sensing means comprises temperature sensitive switch means operable on actuation to interrupt current flow in an electrical circuit acting on said means to cut off the gas supply to the appliance.

7. An appliance according to claim 6 wherein said means to cut off the gas supply comprises valve means incorporated in said circuit and maintained in a normally open position by electromagnetic means the current supply to which is cut off upon operation of said sensing means.

8. An appliance according to claim 6 or 7 wherein said circuit also incorporates a thermocouple disposed adjacent to a gas burner of the appliance and operable on heating to generate an electrical current in said circuit, whereby in the event of said burner failing to ignite or being extinguished, current flow in said circuit ceases and said valve means operates to cut off gas supply to the appliance.

9. A gas fired heating appliance substantially as hereinbefore described with reference to the accompanying drawings.

10. A method of shutting down a gas fired heating appliance in the event of a flue blockage, comprising constraining combustion products diverted from the flue to flow into close proximity with a sensing means, generating a signal in response to the presence of combustion products at said sensing means and utilising said signal to cut off gas supply to the appliance.

11. A method according to claim 10 wherein said sensing means is located in a draught diverter through which combustion products flow in the event of a downdraught or a flue blockage, the method including constraining the combustion products to first pass into the vicinity of said sensing means before discharge from the diverter.

12. A method according to claim 10 or 11 wherein said sensing means is disposed in a sensing zone through which diverted combustion products are directed, substantially all of the products passing through said zone coming into contact with the sensing means.

13. A method of shutting down a gas fired heating appliance in the event of a flue blockage substantially as hereinbefore described.

14. Any novel subject matter or combination including novel subject matter disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.