GB2298039A - Safety device for heating appliance - Google Patents

Abstract

A gas or liquid fuelled heating appliance comprises a main burner and a secondary burner. An oxygen depletion sending device 15 includes the secondary burner and is adapted to generate a control sign when the oxygen supply to the secondary burner has diminished to a threshold level. Means is provided for transmitting said control signal to fuel supply control means of the main burner for interrupting the flow of fuel thereto. The secondary burner is adapted to draw combustion air 17,19 from a remote location so that the sensing device senses oxygen depletion at said location.

Description

A HEATING APPLIANCE This invention relates to a heating appliance using gas or liquid fuel.

It is well known for such a heating appliance to comprise a main burner for space or water heating. Combustion products, including carbon dioxide and carbon monoxide which are potentially harmful to health, are vented to atmosphere through exhaust passages of the appliance which are connected to a flue or chimney. If the flue or chimney is obstructed, the combustion gases will be vented into the room in which the appliance is located through alternative flow paths in the appliance with consequent risk to the health of an occupant of the room, particularly if the room is poorly ventilated.

It has been previously proposed to provide in said alternative flow paths of the appliance temperature sensing devices for generating a control signal in response to an increase in temperature resulting from combustion gases being diverted into said paths during faulty operation as described above. The control signal is used to interrupt the supply of fuel to the main burner which is thus extinguished.

It is also known to equip a secondary or pilot burner, which is normally used for igniting the main burner, with an oxygen depletion sensing device comprising a thermocouple or flame rectification device so associated with the pilot burner that on depletion of the oxygen supply in the vicinity of the pilot burner flame the effect of the pilot flame on the thermocouple or rectification device is changed and a control signal for interrupting the fuel supply to the main burner is generated. Although more satisfactory than temperature sensing devices oxygen depletion sensing devices have the disadvantage that the main burner is only extinguished when the atmosphere in the vicinity of the pilot flame is oxygen deficient by which time the concentration of exhaust gases in the room may already have risen to an unacceptable level.

It is an object of the present invention to provide a gas or liquid fuelled heating appliance utilising an oxygen depletion sensing device wherein the aforesaid disadvantage is obviated or mitigated.

According to the present invention there is provided a gas or liquid fuelled heating appliance comprising a main burner, a secondary burner, an oxygen depletion sensing device including the secondary burner and adapted to generate a control signal when the oxygen supply to the secondary burner has diminished to a threshold level, and means for transmitting said control signal to fuel supply control means of the main burner for interrupting the flow of fuel thereto, characterised in that the secondary burner is adapted to draw combustion air from a remote location so that the sensing device senses oxygen depletion at said location.

The secondary burner, which is preferably a pilot burner, may be connected to said remote location by a tube which is preferably perforated for removal of condensate. The appliance is preferably so constructed that exhaust gases are vented to atmosphere in a first flow path during normal operation but follow a second flow path if the first path (which will be connected in use to a flue or chimney) is obstructed. The remote location from which combustion air for the secondary burner is drawn is preferably in said second flow path.

The oxygen depletion sensing device preferably comprises a thermocouple or flame rectification device so arranged that on depletion of the oxygen supply to said threshold value the effect of the secondary burner flame on the thermocouple or rectification device is changed so that said control signal is generated.

The invention has useful application to an appliance comprising a space heater combined rearwardly thereof with a central heating boiler, both the heater and the boiler being provided with main and secondary (preferably pilot) burners. In this case, one or both of the secondary burners may be adapted to draw combustion air from a remote location (which may be the same location for each secondary burner). An oxygen depletion sensing device is provided for the or each secondary burner to which combustion air is supplied in this way. In the case where only a single oxygen depletion sensing device is provided incorporating one of the secondary burners the control system may be adapted to enable both main burners to be extinguished by the control signal generated by the single sensing device.

The invention will now be further described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic view from the front of a combined room heater (shown in dashed line) and back boiler of a central heating system, in accordance with the invention; Fig. 2 is the same view with the room heater removed; Fig. 3 is the same view of the back boiler with the front thereof removed to reveal the burners; Figs. 4 and 5 are respectively front and (enlarged) rear views of the room heater shown in Fig. 1; Figs. 6 and 7 are diagrammatic side views of the combined room heater and back boiler appliance of Figs. 1 to 5 illustrating (in Fig.

6) the flow of exhaust gases from the back boiler in normal operation and (in Fig. 7) the flow of exhaust gases when the flue or chimney is obstructed.

Figs. 8 and 9 show a floor standing boiler in accordance with the invention in normal operation (Fig. 8) and with obstructed exhaust flow (Fig. 9); Figs. 10 and 11 show a wall mounted boiler in normal operation (Fig. 10) and with obstructed exhaust (Fig. 11); Fig. 12 shows a pilot burner forming part of an oxygen depletion sensing device for use in appliances in accordance with the invention; and Fig. 13 is a schematic representation of relevant parts of a combined room heater and back boiler heating system as illustrated in Figs 1 to 7.

Referring now to the drawings, Fig. 1 shows a space or room heater 1 combined with a central heating or back boiler 2. The room heater 1 is shown in greater detail in Figs. 4 and 5 and is of conventional design save in that the main burner 3 thereof has a pilot burner 4 in accordance with the invention. The back boiler 2 is likewise of conventional design with a main burner 5 and modified pilot burner 6. The main and pilot burners 3, 4 and 5, 6 are supplied with gas in conventional manner and in each case the pilot burner 4, 6 serves to ignite the main burner 3, 5 when required. The combustion gases contain noxious components such as carbon dioxide and carbon monoxide which are deleterious to health and must therefore be properly vented to atmosphere.In the case of the back boiler 2 the gases rise through a heat exchanger 7 and leave the top of the boiler casing 8 through a flue connection 9 (as indicated by the arrows in Fig. 6). In the case of the room heater 1 the combustion gases rise over the conventional ceramic heat radiating elements 10 to flow rearwardly through a box-shaped exit duct 11 which fits into an opening 12 in the back boiler 2 and terminates in the vicinity of the flue connection 9. Combustion gases from the room heater 1 will therefore be vented to atmosphere through the flue connection 9 during normal operation. If the flue is obstructed gases from the room heater 1 will flow along substantially the same paths as indicated by the arrows in Fig. 7 in the case of the back boiler gases.

Each pilot burner 4, 6 forms part of an assembly shown in Fig.

12. A bracket 13 mounts the pilot burner 4, 6 the end of which extends horizontally to direct the pilot flame 14 onto a thermocouple 15 mounted on the bracket 13 adjacent an electrode 16. The electrode 16 is connected to an electrical power supply and serves to generate a spark for igniting the pilot flame 14 when required. The thermocouple 15 forms part of an oxygen depletion sensing device of known design, for example as sold under the trade mark OXYPILOT by The SIT Company of Padava, Italy. Such devices make use of the fact that the characteristics of the pilot flame change as the oxygen supply reduces. In the case of the illustrated device the pilot flame 14 plays on the thermocouple 15 to permit gas to be supplied to the respective main burner 3, 5.If, as a result of inadequate oxygen in the air supply to the pilot burner 4, 6, the characteristics of the pilot flame 14 change (e.g. the flame lifts or is extinguished) the thermocouple 15 generates an output signal which is transmitted to gas supply control means (not shown) of the respective main burners 3, 5 so as to interrupt the gas supply and extinguish the burners.

Primary combustion air for the pilot burner 4, 6 is drawn through a tube 17 from a remote location 18 at the outer end of the tube 17 (in the case of the back boiler 2) and through a tube 19 from a remote location 20 (in the case of the room heater 1). The remote locations 18, 20 are respectively adjacent one side of and centrally below the exhaust duct 11 of the room heater 1 in the paths taken by the gases when the flue is obstructed (see Fig. 7). The primary combustion air for the pilot flame 14 is thus drawn in each case from a region in which oxygen will first be depleted on obstruction of the flue.

As shown in Fig. 12, the tube 17, 19 may have a drain hole 21 for draining condensate. A further combustion air inlet 22 for the pilot burner 4, 6 may be provided in the gas supply pipe thereto. Air entering the inlet 22 from the vicinity of the pilot burner 4, 6 is likely to be less deficient in oxygen than the air at the remote location 18, 20 and therefore serves to dilute the effect of oxygen reduction at these remote locations.

The floor standing boiler shown in Figs. 8 and 9 has a primary combustion air intake 23 for the pilot burner (not shown) forming part of an oxygen depletion sensing device as shown in Fig. 12. The tube 23 opens at a remote location 24 from which normal atmospheric air is supplied when the exhaust gases of the boiler are venting to atmosphere through the flue as indicated by the arrows in Fig. 8.

When the flue is blocked the exhaust gases escape from the appliance along flow paths traversing the remote location 24 as indicated by the arrows in Fig. 9.

Similarly, Figs. 10 and 11 show a wall mounted boiler in which the pilot burner (not shown) is connected by a tube 5 to a remote location 26 from which primary combustion air for the burner is drawn.

In normal operation exhaust gases escaping through the flue in the direction of the arrows shown in Fig. 10 do not contaminate this primary combustion air but when the flue is blocked the exhaust gases are diverted into different flow paths as indicated by the arrows in Fig. 11 to contaminate the location 26 thereby reducing the oxygen content of the primary combustion air supplied to the pilot burner.

Fig. 13 shows a main burner 30 and a pilot burner 31 of a room heater (not shown) and a main burner 32 of a back boiler (not shown).

The pilot burner 31 forms part of an oxygen depletion sensing device as shown for example in Fig. 12. The main burner 32 of the back boiler is also associated with a pilot burner (not shown) but in this case the pilot burner does not form part of an oxygen depletion sensing device. Also shown in Fig. 13 are a gas control tap 33 for the burners 30, 31 of the room heater, and a back boiler gas control valve 34 under the control of a back boiler control circuit 35. As shown by the lines in the drawing, electrical connections exist between the oxygen depletion sensing device including the pilot burner 31 on one hand and the room heater control tap 33 and the back boiler control circuit 35 on the other hand.The control tap 33 and the control circuit 35 are so designed that when the sensing device incorporating the pilot burner 31 generates a control signal indicating that the available oxygen has diminished to a threshold value the control tap 33 is closed so as to interrupt the flow of gas to the main burner 30 of the room heater and the back boiler control circuit 35 shuts down the back boiler burner 32 by closing the back boiler control valve 34.

The oxygen depletion sensing devices described above may be arranged to emit a control signal whether or not the gas fire burner and/or back boiler burner are operative. Thus, for example, the sensing device on the room heater burner may shut down the back boiler burner even if the room heater is inoperative.

It will be appreciated that numerous changes may be made without departing from the scope of the invention as defined in the appended claims. Thus, for example, the tubes for drawing primary combustion air into the secondary or pilot burners may be branched so as to draw air from two or more different locations. The tubes may also open at different locations at which it is useful and convenient to sense oxygen depletion. The oxygen depletion sensing device as described comprises a thermocouple but it may alternatively comprise a flame rectification device. Although Figs. 4 and 5 have been described as views of the room heater shown in Fig. 1, i.e. in combination with the back boiler, it will be appreciated that such a room heater may be used independently of the back boiler but with a similar flue arrangement.

Claims (9)

CLAIMS:

1. A gas or liquid fuelled heating appliance comprising a main burner, a secondary burner, an oxygen depletion sensing device including the secondary burner and adapted to generate a control signal when the oxygen supply to the secondary burner has diminished to a threshold level, and means for transmitting said control signal to fuel supply control means of the main burner for interrupting the flow of fuel thereto, characterised in that the secondary burner is adapted to draw combustion air from a remote location so that the sensing device senses oxygen depletion at said location.

2. An appliance as claimed in claim 1, wherein the secondary burner is connected to said remote location by a tube.

3. An appliance as claimed in claim 2, wherein the tube is perforated for removal of condensate.

4. An appliance as claimed in any one of the preceding claims, wherein exhaust gases are vented to atmosphere in a first flow path during normal operation and follow a second flow path if the first path is obstructed, and said remote location is in said second flow path.

5. An appliance as claimed in any one of the preceding claims, wherein the secondary burner is a pilot burner for use in igniting the main burner.

6. An appliance as claimed in any one of the preceding claims, wherein the oxygen depletion sensing device comprises a thermocouple or flame rectification device so arranged that on depletion of the oxygen supply to said threshold value the effect of the secondary burner flame on the thermocouple or rectification device is changed so that said control signal is generated.

7. An appliance as claimed in any one of the preceding claims, wherein a space heater combined rearwardly thereof with a central heating boiler are each provided with main and secondary burners, and at least one of said secondary burners adapted as aforesaid to draw combustion air from a remote location forms part of an oxygen depletion sensing device as aforesaid.

8. An appliance as claimed in claim 7, wherein a single oxygen depletion sensing device as aforesaid forming part of one of said secondary burners is adapted to control the fuel supply to both main burners.

9. A gas or liquid fuelled heating appliance substantially as herein described with reference to the accompanying drawings.