GB2362451A

GB2362451A - Flue blockage detection

Info

Publication number: GB2362451A
Application number: GB0107969A
Authority: GB
Inventors: Patrick James Collins; David James Swift
Original assignee: AGA Consumer Products Ltd
Current assignee: AGA Consumer Products Ltd
Priority date: 2000-03-31
Filing date: 2001-03-30
Publication date: 2001-11-21
Anticipated expiration: 2021-03-30
Also published as: GB0007733D0; GB2362451B; GB0107969D0; IE20010330A1

Abstract

A heating appliance 2, for example a cooking stove or range and/or a hot water boiler, in which fluid fuel is burned at a burner 6 in combustion chamber 4 to produce hot products of combustion which can flow as indicated by arrows 12 to a flue system. The flue system comprises a first flue pipe 20 having a portion of inverted U-shape 22 entering an upper end of a second flue pipe 26 connected to its lower end 28 to eduction means 32 comprising a driven fan 34. The eduction means draws flue gas along the flue system. A conduit 48 has an horizontal lower end 50 opening to atmospheric air and an upper end 52 opening into the flue pipe 20 just before the inverted U 22 so that dilution air is drawn along conduit 48 in a first direction indicated by arrow C to enter the flue system. An impedance of or obstruction to discharge of the flue gases from the second pipe 26 can cause them to be diverted down the conduit 48 to flow in an opposite or second direction indicated by arrow D towards the opening 50. Gas flow observing means 62, comprising pairs of heat sensitive semiconductor diodes, is mounted just outside the conduit opening 50 to detect a diverted flow of products of combustion down the conduit 48 in direction D and provides a signal indicating the obstruction.

Description

2362451 1 AN HEATING APPLIANCE This invention concerns an heating

appliance in which fuel is burned to produce hot products of combustion.

The heating appliance may comprise burner means for burning fluid fuel. The fluid fuel may be liquid fuel, for example heating oil, or the fluid fuel may be fuel gas, for example natural gas.

In one form the heating appliance may be a cooking range or stove and/or a boiler to produce hot water, for example, for washing and/or for central heating purposes.

The heating appliance may comprise flue means along which aforesaid products of combustion can flow as flue gases for discharge, and eduction means to draw the said flue gases along the flue means. The flue means and eduction means may be as disclosed in our co-pending British patent application published under no. GB 2 330 899A on 05 May 1999. Should the flue means become obstructed so discharge of the flue gases is impeded or blocked, this can give rise to a potentially damaging or dangerous condition within the appliance and in its vicinity.

An object of the invention is to provide an heating appliance in which impedance or blockage of a discharge of the flue gases is rendered apparent whereby measures may be taken in response to obviate or mitigate a potentially damaging or dangerous condition arising.

According to the invention there is provided an heating appliance in which 30 fuel is burned to produce hot products of combustion, said appliance 2 comprising flue means along which said products of combustion can flow as flue gases for discharge, eduction means to draw said flue gas along the flue means, conduit means having an inlet opening to atmospheric air and an outlet opening into said flue means upstream of said eduction means whereby dilution air drawn along the conduit means in a first direction can enter the flue means to mix with flue gases therein, the arrangement being such that an impedance of or obstruction to discharge of aforesaid flue gases can cause a diversion of flow of products of combustion along the conduit means in an opposite second direction towards said inlet, and gas flow observing means to detect a diverted flow of products of combustion along the conduit means in said second direction and provide a signal indicative of said impedance or obstruction.

Said gas flow observing means may comprise temperature sensitive means responsive to temperature obtaining at or in the vicinity of the temperature sensitive means, said temperature depending on whether dilution air is entering the conduit means or flue gases are flowing therealong in said opposite direction.

The temperature sensitive means may be disposed adjacent to said inlet. Preferably, the temperature sensitive means is disposed externally of the conduit means.

The temperature sensitive means may comprise semiconductor means. The semiconductor diode means may comprise first semiconductor diode means and second semiconductor diode means so arranged that when dilution air enters the conduit means the first and second semiconductor diode means are at substantially the same temperature, but when flue gases are passing along the conduit means in said second direction and reach the flow observing means the temperature obtaining at 3 the second semiconductor diode means is higher than that obtaining at the first semiconductor diode means. Thus, in relation to the flow of dilution air along the conduit means, the second semiconductor diode means may be downstream in relation to the first semiconductor diode means.

The first and second semiconductor diode means may each comprise at least one semiconductor diode. Preferably, the first and second semiconductor diode means each comprises a plurality of semiconductor diodes. The first and second semiconductor diode means may each comprise the same number of semiconductor diodes. Each of the semiconductor diode means may comprise at least two said semiconductor diodes in electrical series.

Said semiconductor diode means has/have forward voltage applied thereto and forward electrical current(s) flow(s) through the semiconductor diode means from current source means providing substantially constant current.

A first voltage drop across the first semiconductor diode means may differ from a second voltage drop across the second semiconductor diode means when temperatures obtaining at the first and second semiconductor diode means differ, and,voltage observing means may be provided to observe a difference between the first and second voltage drops indicative of a said impedance or obstruction.

The heating appliance may further comprise fluid fuel burner means whereat burning fluid fuel produces said hot products of combustion.

The eduction means may comprise driven fan means for use in causing drawing of said flue gases along the flue means.

4 The heating appliance may comprise control means to control operation of the burner means and/or speed at which said fan means is driven. Said control means may be responsive to occurrence of a said signal indicative 5 of said impedance or obstruction to increase the speed of the fan means. The control means may be responsive to occurrence for at least a predetermined period of time of a said signal indicative of said impedance or blockage to cause supply of fuel to the burner means to be reduced or shut-off.

The invention will now be further described by way of example with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic fragmentary view of an heating appliance formed according to the invention; Figure 2 is a diagrammatic view, drawn to a larger scale, of part of the appliance in Figure.l.; Figure 3 is a diagrammatic view, drawn to a still larger scale, of part of the appliance in Figure. 1 viewed along direction A; Figure 4 is a diagrammatic and fragmentary view along direction B (Figure. 1) of the eduction means, and Figure 5 is an electronic circuit providing, or forming at least part of, the gas flow observing means.

With reference to the drawings, in which like reference numerals identify like or comparable parts, an heating appliance 2 may be a hot water boiler to provide hot water for washing and/or central heating purposes or it may be a cooking stove or range, or as shown in Figure.1 a combination of both. The appliance 2 comprises a fire or combustion chamber 4 including a burner 6 for burning fluid fuel, for example heating oil or fuel gas, supplied along a supply pipe 8 including a fuel supply control valve 10. The burning fuel produces hot products of combustion indicated by arrows 12 which circulate in manner known per se through the appliance to heat a water boiler or heat exchanger and/or one more cooking hot plates 14 for pans and/or one or more heated cabinets or ovens, for example 16 and 18 having respective roofs 16A, 18A and respective floors 16B, 18B. The hot products of combustion form flue gases leaving the appliance 2 by a flue system comprising a first flue pipe 20 having a portion 22 of inverted U-shape entering an upper end 24 of a wider diameter second flue pipe 26 having a lower end 28 connected by piping 30 to eduction means 32 which may be as disclosed in our co-pending British patent application published under no. GB 2 330 899A.

The eduction means 32 comprises a rotatable fan 34 which may be driven at variable speed by a motor 36, for example an electric motor. The fan 34 discharges air drawn thereinto from atmosphere into a flue chamber 38 comprising two venturi regions 40, 42 at opposite sides of a cylindrical flue nozzle 44 leading from the piping 30 and having about half its underside cut away at 46 over a part of the nozzle length. Air propelled by fan 34 flows along the venturi passages 40, 42 causing a reduction of pressure at the nozzle 44 thereby drawing flue gases from the appliance 2 for discharge from the chamber 38, normally to atmosphere. A conduit 48 has an open inlet end 50 below oven floor 18B and ascends to an outlet end 52 through which the conduit opens into flue pipe 20 just upstream, in relation to normal flue gases flow through the pipe 20, of the U-part 22 and thus upstream of the eduction means 32. When the flue is operating 6 properly, dilution air from atmosphere, is drawn (as indicated by arrows 56 in Figure.3) into the inlet end 50 of the conduit 48 via louvres 58 in appliance casing 60 and flows along the conduit in direction C to mix with flue gases in pipes 20 and 26 to dilute and/or cool these gases.

Should an impedance, or blockage, or other malfunction occur in the flue system, for example in pipe 26 or eduction means 32 so that extraction of the flue gases is impeded or stops, the continued creation of products of combustion in the combustion chamber 4 can result in the flue gases diverting down conduit 48 in direction D to emerge from the inlet end 50.

This condition could be potentially damaging and dangerous, possibly even lethal. But the appliance 2 includes a safety system to inhibit danger or damage occurring. The system comprises gas flow observing means 62 disposed outside the conduit 48 and adjacent to the inlet 50.

The gas flow observing means comprises two pairs of semiconductor diodes 64A, 64B and 66A, 66B, for example signal diodes, mounted on a circuit board or substrate 68, the diodes of each pair being in electrical series and having a forward voltage applied thereto between lines 70, 72.

All the diodes are substantially similar and affected by the same temperature change in substantially the same electrical manner. For example the voltage drop across each diode may change by substantially the same amount X volts (v) per degree Celsius, and X may be about 2.5mv/'C. Line 74 including the diodes 64 includes a constant current source 76 and line 78 including the diodes 66 includes constant current source 80. The forward current from each of the constant current sources may be substantially the same. Thus when the diodes 64 are at the same temperature as the diodes 66 signals, (for example voltage signals) on lines 82 and 84, representing voltage drops across each pair of diodes 7 respectively, may be substantially the same. The signals on lines 82, 84 are input to a differential amplifier 86, which may be an operational amplifier, in a control 88 comprising a computer or microprocessor 90.

When the flue system is functioning normally, air flow 56 cools both pairs of diodes 64, 66 equally, and the differential amplifier 86 observes substantially no difference between the signals on line 82 and 84. Thus the supply of fuel to the burner 6 continues via valve 10 as otherwise desired, and the fan 34 operates at the normal or desired speed, for example 1800 revolutions per minute (r.p.m). In the event of the flue system becoming blocked or impeded downstream of conduit outlet 52, hot flue gases can become diverted along the conduit 48 and flow in direction D to emerge at inlet 50 to impinge on the diodes 64A, 64B first thus raising the temperature thereof to a higher value that of the diodes 66A, 66B since they are now downstream of the diodes 64 and any flue gases reaching the diodes 66 will be cooler due to mixture with air outside the conduit. The temperature difference between the diodes 64 and 66 gives rise to a difference or error between the values of the signals on lines 82 and 84, for example the voltage drop across the "hot" diodes 64 may be less than that across the "cold" diodes 66, and the differential amplifier 86 is arranged to give an output on line 92 to the microprocessor 90, the value of which output may be a function of the error. On occurrence of said error, or an error of a pre-determined value, the control 88 may respond and issue a signal on line 94 to vary the speed of the fan 34. For example the fan speed may be increased with a view to increasing the suction effect on the flue system in an effort to clear the obstruction therein. For example the fan speed may be increased, from say a normal operational speed, for example about 1800 r. p.m., up to a pre-determined maximum speed, for example about 3600 r.p.m. The fan speed increase may occur in pre-determined increments, 8 for example increments of about 200 r.p.m., over a pre-determined period of time provided the error signal continues at a value requiring the control 88 to keep increasing the fan speed. Should the error substantially disappear, or fall below a pre-determined value, the control 88 may function to cause the fan speed to reduce towards its normal operating speed. On the other hand should the fan speed attain its aforesaid maximum value, then at a pre-determined time, for example at expiry of a pre-determined time period after the fan 34 starts to be driven at its maximum speed (which period may be substantially sixty seconds) the control 88 may issue a signal on line 96 to close, or preferably shut, the fuel supply control valve 10 to reduce or stop combustion in the chamber 4.

Two diodes in each line 74, 76 increases sensitivity, but if desired only one diode in each line may be used. On the other hand the same number of diodes in excess of two may be used in each of the lines 74, 76.

Advantages of using diodes:- (1) low Cost, (2) modern manufacturing methods can produce diodes of substantially identical performance, (3) fast reaction to temperature change, (4) low mass so that heat is not retained, (5) robust construction, and (6) easy to obtain and install.

9

Claims

CLAIMS:

1. An heating appliance in which fuel is burned to produce hot products of combustion, said appliance comprising flue means along which said products of combustion can flow as flue gases for discharge, eduction means to draw said flue gas along the flue means, conduit means having an inlet opening to atmospheric air and an outlet opening into said flue means upstream of said eduction means whereby dilution air drawn along the conduit means in a first direction can enter the flue means to mix with flue gases therein, the arrangement being such that an impedance of or obstruction to discharge of aforesaid flue gases can cause a diversion of flow of products of combustion along the conduit means in an opposite second direction towards said inlet, and gas flow observing means to detect a diverted flow of products of combustion along the conduit means in said second direction and provide a signal indicative of said impedance or obstruction.

2. An heating appliance as claimed in Claim 1, in which the gas flow observing means comprises temperature sensitive means responsive to temperature obtaining at or in the vicinity of the temperature sensitive means.

3. An heating apparatus as claimed in claim 2, in which said temperature depends on whether dilution air is entering the conduit means or flue gases are flowing along the conduit means in said opposite direction.

4. An heating appliance as claimed in Claim 2 or Claim 3, in which the temperature sensitive means is disposed adjacent to said inlet.

5. An heating appliance as claimed in any one of Claims 2 to 4, in which the temperature sensitive means is disposed externally of the conduit means.

6. An heating appliance as claimed in any one of Claims 2 to 5, in which the temperature sensitive means comprises semiconductor diode means.

7. An heating apparatus as claimed in Claim 6, in which the semiconductor diode means comprises first semiconductor diode means and second semiconductor diode means so arranged that when dilution air enters the conduit means the first and second semiconductor diode means are at substantially the same temperature, but when flue gases are passing along the conduit means in said second direction and reach the flow observing means, the temperature obtaining at the second semiconductor diode means is higher than that obtaining at the first semiconductor diode means.

8. An heating appliance as claimed in Claim 7, in which, in relation to the flow of dilution air along the conduit means, the second semiconductor diode means is downstream in relation to the first semiconductor diode means.

9. An heating appliance as claimed in Claim 7 or in Claim 8, in which the first and second semiconductor diode means each comprise at least one semiconductor diode.

10. An heating appliance as claimed in any one of Claims 7 to 9, in which the first and second semiconductor diode means each comprises a plurality of semiconductor diodes.

11 11. An heating appliance as claimed in any one of Claims 7 to 10, in which the first and second semiconductor diode means each comprises the same number of semiconductor diodes.

12. An heating appliance as claimed in any one of Claims 6 to 11, in which said semiconductor diode means has/have forward voltage applied thereto and forward electrical current(s) flow(s) through the semiconductor diode means from current source means providing substantially constant current.

13. An heating appliance as claimed in any one of Claims 7 to 11, or as claimed in Claim 12 when appended to Claim 7, in which a first voltage drop across the first semiconductor diode means differs from a second voltage drop across the second semiconductor diode means when temperatures obtaining at the first and second semiconductor diode means differ, and voltage observing means is provided to observe a difference between the first and second voltage drops indicative of a said impedance or obstruction.

14. An heating appliance as claimed in any one preceding claim, in which the heating appliance further comprises fluid fuel burner means whereat burning fuel produces said hot products of combustion.

15. An heating appliance as claimed in any one preceding claim, in which the eduction means comprises driven fan means for use in causing drawing of said fluid gases along the flue means.

12

16. An heating appliance as claimed in Claim 14 and/or in Claim 15, in which the heating appliance comprises control means to control operation of the burner means and/or speed at which said fan means is driven.

17. An heating appliance as claimed in Claim 16, in which the control means is responsive to occurrence of a said signal indicative of said impedance or obstruction to increase the speed of the fan means.

18. An heating appliance as claimed in Claim 16 or in Claim 17, in which the control means is responsive to occurrence for at least a predetermined period of time of a said signal indicative of said impedance or blockage to cause supply of fuel to the burner means to be reduced or shut-off.

19. An heating appliance as claimed in any one preceding claim, in which the appliance is a water boiler and/or a cooking stove or range.

20. An heating appliance in which fuel is burned to produce hot 20 products of combustion, said heating appliance being substantially as hereinbefore described with reference to the accompanying drawings.