AU772232B2 - Gas fired burner apparatus - Google Patents

Description

WO 00/52387 PCT/AU00/00128 -1- TITLE: GAS FIRED BURNER APPARATUS FIELD OF THE INVENTION The present invention relates to an improved gas fired burner apparatus and more particularly to heating devices having housed gas burners operating with a primary air component supplied from a region within the burner housing.

The invention has been developed primarily as a means of controlling and reducing NO, emissions in gas powered flueless convection space heaters and flued water heaters and will be described hereinafter with reference to such applications. However, it will be appreciated that the benefits are not limited to these uses and that the invention is applicable to any gas fired burner apparatus that operates with a primary air component supplied from an interior region of the gas burner apparatus.

BACKGROUND OF THE INVENTION The control and reduction of harmful emissions from gas fired burners has become increasingly important. At this stage there are no universally accepted standards for various different types of burner in relation to maximum permissible emission levels for the primary pollutants, which are oxides of nitrogen (NOx) and carbon monoxide (CO).

However, there is an aim worldwide to reduce these emission levels wherever possible, particularly NO,, emissions.

To date numerous techniques have been employed to try and reduce NO emissions. Of these techniques the two main categories are most likely the use of catalysts and various means to reduce combustion temperatures. One example of this latter approach is to recirculate hot exhaust products into the primary air infeed to increase the proportion of 'inerts' within the combustion mixture. This has the effect of reducing the overall combustion temperature by slowing the combustion process.

-2- The present invention arises from the surprising discovery firstly, that gas fired appliances that do not use exhaust product recirculation but which induce primary air from a closed region within the appliance housing, actually operate with relatively high primary air inlet temperatures, and secondly that the inclusion of control means to effect a substantial reduction of this primary air temperature results in improved combustion with surprisingly significant reductions in NOx emission levels.

This is a design criteria that appears to have been overlooked in the design of gas fired burner appliances to date. In fact, as described above, some of the current methods used to effect NOx reductions actually serve to increase the primary air inlet temperature.

DISCLOSURE OF THE INVENTION :--According to a first aspect of the invention there is provided a gas fired burner "apparatus including a housing containing a burner, air supply means for drawing ambient air into said housing to be delivered as primary air to said burner, fuel supply oo* •means for supplying fuel to be combined with said primary air to form a combustible fuel/air mixture delivered to said burner, said housing including an interior air supply :.."•region for receiving said ambient air for delivery as primary air in said combustible fuel/air mixture to said burner, said air supply region being located within said housing heat transfer proximity with said burner, said ambient air being heated and the temperature of said primary air being increased in said air supply region, and primary air temperature control means for lowering the temperature of said primary air.

Preferably, the temperature control means is selected from one or more of the following: a forced convection cooling system using dedicated fan means and/or utilising fans forming part of the apparatus associated with the burner; WO 00/52387 PCT/AU00/00128 -3- (ii) convection cooling arising from design changes to the burner and associated apparatus to increase natural convection at or interactively adjacent the air supply region; (iii) the use of insulating means and/or thermal shielding means; and (iv) refrigeration means including liquid conduction cooling systems and evaporative cooling systems; or any combination thereof.

In accordance with a first preferred embodiment of the invention there is provided a gas fired burner apparatus in the form of a heater for heating ambient air in a space to be temperature conditioned, said heater including a housing containing a burner for combustion of a fuel/air mixture and convective heat transfer to said ambient air, said housing including wall means cooperating with said burner to provide substantially segregated interior housing regions having controlled flows of ambient air therethrough, said interior housing regions including an air supply region for receiving ambient air from said space for delivery thereof as primary air in a combustible fuel/air mixture to said burner and a low pressure region for drawing ambient air from said space into the low pressure region for subsequent heating by said bumrner to form circulation air that is discharged from said housing into said space, said air supply region being located within said housing in heat transfer proximity with said burner so as to heat said ambient air in said air supply region and said primary air, said primary air temperature control means including heat removing means for withdrawing heat from said primary air supply region to inhibit heating of said primary air.

Desirably, the heat removing means comprises a fluid connector providing fluid communication between said air supply region and low pressure region for withdrawing heated ambient air from said air supply region and adding the withdrawn heated ambient WO 00/52387 PCT/AU00/00128 -4air to said circulation air, whereby heating of said ambient air within said air supply region and primary air is inhibited and the heat contained in said circulating air is augmented.

In accordance with a second preferred embodiment of the invention there is provided a gas fired burner apparatus in the form of a water heater including: a water tank, a housing containing a burner for combustion of a fuel/air mixture for heat transfer therefrom, the housing including an interior air supply region for receiving ambient air for delivery as primary air in a combustible fuel/air mixture to said burner and a combustion chamber region receiving products of combustion from said burner, said air supply region being located within said housing in heat transfer proximity with said burner, a flue in fluid communication with an outlet from said combustion chamber, configured to provide a low pressure region which operates to draw products of combustion out of said combustion chamber, and heat removing means in the form of ducting means connecting an outlet of said air supply region to said low pressure region of said flue so as to reduce the burner pre-heating effects on the primary air drawn into the burner.

According to a second aspect of the invention there is provided an oxygen depletion sensor configuration for a gas fired burner apparatus according to a first aspect of the invention having a combustion surface made from a porous material such as metallic mesh, said sensor configuration including: a thermocouple having a probe tip at one end and electrical connection means at its other end; a plate or tab adapted to extend over a pre-selected end portion of the combustion surface at which the combustion flame is present but is inherently unstable, the plate having an aperture therein shaped to receive the thermocouple probe tip and to define a WO 00/52387 PCT/AU00/00128 plurality of spaced points that extend in a direction away from said probe tip and said unstable combustion zone; the aperture shape and positioning of the tab and probe tip being configured such that as the oxygen supplied to the burner is depleted, the flame lifts from the mesh under the aperture and progressively retreats from point to point away firom the probe until such time as the flame crosses the tab completely and the probe tip is exposed in a flame free zone.

Preferably the preselected end portion of the combustion surface is that adjacent the air/fuel supply inlet.

Desirably, the aperture is generally star shaped, preferably including an extended narrow passageway located at an end of the aperture remote from the probe tip.

In one preferred form, the porous combustion surface underneath the aperture is modified to have controlled progression of the flame in that region.

BRIEF DESCRIPTION OF THE DRAWINGS Two preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a cut away perspective part view of a first embodiment gas fired space heater in accordance with the first aspect of the invention; Figure 2 is a right hand side end view of the space heater shown in Figure 1; Figure 3 is a longitudinal sectional view of a first embodiment water heater in accordance with the invention; and Figure 4 is a schematic plan view of an oxygen depletion sensor configuration according to a second aspect of the invention.

WO 00/52387 PCT/AU00/00128 -6- PREFERRED EMBODIMENTS OF THE INVENTION Turning firstly to Figures 1 and 2 there is illustrated a gas fired burner apparatus in the form of an unflued space heater shown generally at 1. The heater includes an outer housing 2, the end portions of which have been shown in hidden detail so as to more clearly describe the internal features.

The housing also includes a number of internal walls that serve to segregate the inside of the burner into discrete regions. The first of these walls are the left and right hand end walls 4 and 5. These walls support a cylindrical "mesh" style burner 3 at its longitudinal ends therebetween and simultaneously define within the outer housing segregated left and right hand end regions 6 and 7 the boundaries of which are shown in dotted line.

The gas burner 3 has a lower channel shaped body portion 10 with an upper curved combustion surface 11 that is formed from a suitable mesh material, defining therebetween a cylindrical plenum chamber 12. The burner operates on a combustible fuel/air mixture which is delivered to the plenum 12 by means of a mixing system comprising a gas nozzle shown generally by arrow 13 which operates to inject gas under pressure into a venturi 14 to entrain and mix therewith a primary air component drawn from the end region 6. The gas injection nozzle 13 and inlet to the venturi 14 are located within the left hand end region 6.

The heater 1 also includes a powered fan shown generally at 15. Interacting with the fan 15 and burner 3 are three internal dividing walls 16, 17 and 18 which cooperate to provide further segregated interior housing regions having in use controlled flows of ambient air therethrough. These air flows extend from an inlet shown generally at 19 to an outlet 20 as shown by the paired arrows.

WO 00/52387 PCT/AU00/00128 -7- Referring in particular to the right hand side end view shown in Figure 2, it can be seen that the burner 3 is supported between end walls 4 and 5, internal walls 16 and 17 and the outer housing 2, so as to define a combustion chamber 22 above the combustion surface 11 and a shielded sub-chamber 23 below the burner body 10. In the preferred form illustrated a deflector plate 24 is disposed within the left hand end region below the venturi 13 and above an opening 25 provided in the left hand internal end wall 4.

In the right hand end region 7 primary air temperature control means are provided that include a fluid connector duct 27. The duct extends from a first opening 28 through the right hand end wall 5 into the burner sub-chamber 23, to a second opening 29 also provided in the right hand end wall which communicates with a low pressure region generated by the powered fan In use, primary air is aspirated from the left hand end region 6 into the venturi 14 by injection of gas under pressure via nozzle 13 for mixing and delivery into the burner plenum chamber 12 for subsequent combustion at the burner combustion surface 11. Once the burner 3 has reached normal operating temperatures, it will be appreciated that the surrounding burner components will get and remain reasonably hot. This is due to both convection and conduction from the burner, the latter being exacerbated due to the majority of the burner components being manufactured from metal materials.

In the applicant's prior art version of the illustrated space heater there was no fluid connector duct 27 or deflector plate 24, and the right hand end wall 5 had an opening at its base that aligned with opening 25 in the left hand end wall 4. This created an intemrnal passage enabling air to flow through the sub-chamber 23 to assist in cooling the burner underside and the housing components adjacent the burner. However, it appears that the low pressure region caused by the operation of the venturi caused hot air to be drawn from WO 00/52387 PCT/AU00/00128 -8the sub-chamber 23 into the venturi as primary air. For example, tests conducted on the applicant's current SLE 2 Model Space Heater showed the temperature of the primary air at the venturi inlet to be about 104'C with a resultant NO 2 emission level of approximately 2.6ng/Joule.

By contrast, in the heater of the invention described above, the hot air in subchamber 23 is drawn away from the venturi 13 by means of the suction or negative pressure created by connecting the low pressure region of the fan 15 via the connector duct 27 to the right hand end of the sub-chamber. In this way, air drawn into the venturi tends to be ambient air drawn into the air supply region adjacent the venturi inlet through vents in the outer heater housing rather than hot air from within the housing. This process is assisted by the deflector plate 24 which discourages upward air flow from the opening to the sub-chamber. As there is a continual air flow past this region, preheating effects are minimised.

By comparison, the same current SLE 2 Space Heater altered to include the fluid connector duct and deflector as shown in Figures 1 and 2 showed an inlet primary air temperature of closer to 50C which corresponds to an increase in the density of the primary air of about 10% to 25% and NO 2 emission levels of around Ing/Joule which is a very significant reduction.

Turning next to Figure 3 there is illustrated a second embodiment gas fired burner apparatus in the form of a flued water heater shown generally at 50. Whilst the physical structure is different from that of the flueless space heater, the principle of operation is substantially the same. In this regard the heater 50 has a water tank 51 and an outer housing 52 which includes a gas injection cover plate 53.

WO 00/52387 PCT/AU00/00128 -9- Within the outer housing 51 are internal walls 54 and 55. The first wall 54 is preferably dome shaped and defines the upper surface of a combustion chamber 56. The second wall 55 is an outer insulated skin which extends over the tank 51 to below the first wall 54. This serves to close off the combustion chamber 56 and define an air supply region 57 surrounded by cover plate 53.

Disposed within the combustion chamber 56 is a mesh style surface combustion burner 59 including a venturi 60 which extends through the wall 55 into the air supply region 57 to align with a gas injection nozzle 61. At an outlet to the combustion chamber shown at 62, a central flue 63 extends upwardly which is configured to draw combustion products out of the combustion chamber 56 to an external outlet 63. Also connected to the flue at a low pressure point 64 is a first end of a connector duct 65 which at its other end is attached in fluid communication with the air supply region 57.

In use the burner 59 operates to bum a fuel/air mixture drawn through venturi the products of combustion being drawn out of the combustion chamber to atmosphere by means of the flue 62. The flue may operate simply through the "chimney" effect by utilising the natural draught produced by the buoyancy of the combustion products, or alternatively may be assisted by an extractor fan or the like. This venting of combustion products creates a low pressure region at 64 causing air to be drawn out of the air supply region 57 and into the flue. Fresh ambient air is then drawn into the supply region 57 and into the venturi as by the arrows shown in Figure 3. In this way there is again a continual air flow past the primary air inlet region and preheating effects are reduced.

Whilst the two embodiments illustrated utilise air moving mechanisms already present within the heater structure, that is the powered fan of the space heater 1 and the natural "pull" from the flue of the water heater 50, other embodiments of the invention not WO 00/52387 PCT/AU00/00128 specifically described herein are contemplated that utilise alternative methods of ensuring that air in the air supply region is kept as cool as possible. Such positive temperature reduction means may include: the use of forced convection systems using separate dedicated fan means or the equivalent, the use of sophisticated insulating means and/or thermal shielding means; and suitable forms of refrigeration means or indeed any combination thereof.

Turning finally to Figure 4, there is shown a new and improved oxygen depletion sensor configuration that is particularly suited for use with a gas burner apparatus made in accordance with the first aspect of the invention. In this regard, it was found that the applicant's prior art system would not function reliably when applied to a gas burner apparatus operating with modified combustion characteristics as results from the first aspect of the invention.

In this regard, the prior art system simply comprised a thermocouple having the tip of its probe located at an edge of the combustion surface in a location where, ordinarily, under conditions of oxygen depletion, the flame would commence to lift from that point.

This will cause the flame to retreat in a predictable manner from the probe tip, the resultant drop in voltage from the thermocouple signalling an oxygen depletion situation.

It was found with the gas burner apparatus according to the first aspect of the invention that the retreat of the flame was not as predictable and without that predicability the prior art system was of no use. This prompted extensive investigation which has led to a new configuration which addresses this problem.

Figure 4 shows a gas burner 70 with an oxygen depletion sensor system (ODS) shown generally at 71. The ODS system comprises a thermocouple 72 having at one end a probe tip 73 and at its remote end electrical connection means 74.

WO 00/52387 PCT/AU00/00128 -11 The burner 70 has a porous combustion surface in the form of a mesh 75 which is secured to the burner housing 76 by means of end covers 77 and 78. Extending from end cover 77 is a tab 78. The tab includes an aperture 79 having a generally star shaped configuration defining a centre portion adapted to received the thermocouple probe tip 73 from which extend a plurality of radially extending passages 80 which define at their juncture a plurality of points 81. An extended elongate channel 82 is also provided which extends from a portion of the aperture remote from the thermocouple tip 73 in a direction away from the end cover 77. The aperture 79 is located above the mesh 75 at a location adjacent the air/fuel inlet 83 to the burner where the flame is inherently unstable, as this is the point from which the flame retreats as the oxygen supply to the burner is depleted. In one preferred form an additional layer of mesh material is provided beneath the aperture to "fine tune" the response of the system.

In use, the burner operates with a reasonably even flame across the combustion surface 75, the flame extending through the aperture 79 in the tab such that the thermocouple 72 achieves a steady reading. As oxygen to the burner is depleted, the flame begins to lift from the unstable region within the aperture and advances away from the probe tip 73 toward the centre of the combustion surface. As this happens, it has been found that the flame progresses in a controlled step like manner, the flame effectively adhering to each of the points 81 in succession until the flame traverses the extended elongate channel 82 and finally jumps the end of the tab, thereby exposing the probe tip to a flame free zone. This facilitates a predictable and highly measurable change in the thermocouple output thereby providing a reliable means of sensing an oxygen depletion condition.

WO 00/52387 PCT/AU00/00128 -12- Although the various aspects of the invention have been described with reference to specific examples, it will be appreciated by those skilled in the art that each aspect of the invention may be embodied in many other forms.

Claims (30)

1. A gas fired burner apparatus including a housing containing a burner, air supply means for drawing ambient air into said housing to be delivered as primary air to said burner, fuel supply means for supplying fuel to be combined with said primary air to form a combustible fuel/air mixture delivered to said burner, said housing including an interior air supply region for receiving said ambient air for delivery as primary air in said combustible fuel/air mixture to said burner, said air supply region being located within said housing in heat transfer proximity with said burner, said ambient air being heated and the temperature of said primary air being increased in said air supply region, and primary air temperature control means for lowering the temperature of said primary air.

2. A gas fired burner apparatus according to claim 1, wherein the primary air temperature control means is selected from: 9• o a forced convection cooling system using dedicated fan means and/or *oo utilising fans forming part of the apparatus associated with the burner; (ii) convection cooling arising from design changes to the burner and associated apparatus to increase natural convection at or interactively adjacent the air 9999 oooo supply region; (iii) the use of insulating means and/or thermal shielding means; and (iv) refrigeration means including liquid conduction cooling systems and evaporative cooling systems; or any combination thereof.

3. A gas fired burner apparatus according to claim 1 or claim 2, wherein the temperature of the primary air is reduced to approximately 50% as compared with a similar burner not having said primary air temperature control means. -14-

4. A gas fired burner apparatus according to any one of claims 1 to 3, wherein the temperature of the primary air is reduced to approximately 60% or less as compared with a similar burner not having said primary air temperature control means. A gas fired burner apparatus according to claim 1, wherein said primary air temperature control means includes means for withdrawing heated ambient air from said air supply region prior to delivery to said burner, said air supply region receiving additional ambient air to replace said withdrawn heated ambient air to maintain said fuel/air mixture delivery to said burner and thereby lowering the temperature of said primary air.

6. A gas fired burner apparatus according to claim 5, wherein said housing also .includes a low pressure region, and said primary air temperature control means comprises a fluid connector communicating between said interior air supply region and said low pressure region, said heated ambient air withdrawn from said interior air supply •o• region flowing through said fluid connector into said low pressure region.

7. A gas fired burner apparatus according to claim 6, wherein said apparatus comprises a heater for heating ambient air in a space to be temperature conditioned, and further includes air circulating means for drawing ambient air into said housing to form circulation air, said circulation air being heated and discharged from said housing into said space, and said low pressure region is formed in said housing by said air circulating means.

8. A gas fired burner apparatus according to claim 6, wherein said apparatus comprises a water heater, and further includes exhaust means for venting products of combustion from said burner, and said low pressure region is formed by said exhaust means venting products of combustion.

9. A gas fired burner apparatus in the form of a heater for heating ambient air in a space to be temperature conditioned, said heater including a housing containing a burner for combustion of a fuel/air mixture and for convective heat transfer to said ambient air, said housing including wall means for cooperating with said burner to provide substantially segregated interior housing regions including an air supply region and a low pressure region, said regions having controlled flows of ambient air therethrough, said air supply region receiving ambient air from said space for delivery thereof as primary air in a combustible fuel/air mixture to said burner, said low pressure region receiving ambient air from said space for subsequent heating by said burner to form circulation air that is discharged from said housing into said space, said air supply region OS being located within said housing in heat transfer proximity with said burner so as to "heat said ambient air in said air supply region and said primary air, and primary air °temperature control means including heat removing means for withdrawing heated ambient air from said air supply region prior to delivery to said burner, said air supply 0S region receiving additional ambient air from said space to replace said withdrawn heated ambient air to maintain said fuel/air mixture delivery to said burner and to thereby lower sees ooo6 oooo o S the temperature of said primary air. So

10. A heater according to claim 9, wherein said heat removing means comprises a fluid connector providing fluid communication between said air supply region and low pressure region for withdrawing heated ambient air from said air supply region and adding the withdrawn heated ambient air to said circulation air, whereby heating of said ambient air within said air supply region and primary air is inhibited and the heat contained in said circulation air is augmented.

16- 11. A heater according to claim 10, wherein said wall means include a burner wall that extends in said air supply region and tends to heat ambient air in said air supply region and said primary air. 12. A heater according to claim 10 or 11, wherein said housing has a housing opening through which ambient air from said space passes for receipt in said air supply region, said burner having an air supply means including an air supply inlet located in said air supply region for aspirating ambient air from said air supply region to form a flow of said primary air to said burner, said fluid connector having a fluid inlet connected to said air supply region and a fluid outlet connected to said low pressure region, said fluid inlet being connected to said air supply region at a location remote from said housing opening and said air supply inlet. 13. A heater according to claim 9 or 10, wherein said burner includes a fuel supply 1means for providing a flow of gaseous fuel to said burner and an air supply means including an air supply inlet located in said air supply region for aspirating ambient air 15 from said air supply region to form said flow of primary air in said combustible fuel/air mixture to said burner, and said primary air temperature as measured at said air supply .inlet is reduced about 40% as compared with the temperature of the primary air •o measured at a corresponding location in a similar burner not having said low pressure region of said housing in fluid communication with said air supply region. e0ee 14. A heater according to claim 9 or 10, wherein said burner includes a fuel supply means for providing a flow of gaseous fuel to said burner and an air supply means 0000 :o :including an air supply inlet located in said air supply region for aspirating ambient air o00 from said air supply region to form said flow of primary air in said combustible fuel/air mixture to said burner, and said primary air temperature as measured at said air supply inlet is reduced about 40% to about 60'C or less as compared with the temperature of the -17- primary air measured at a corresponding location in a similar burner not having said low pressure region of said housing in fluid communication with said air supply region. A heater according to claim 9 or 10, wherein said burner includes a fuel supply means for providing a flow of gaseous fuel to said burner and an air supply means including an air supply inlet located in said air supply region for aspirating ambient air from said air supply region to form said flow of said primary air in said combustible fuel/air mixture to said burner, and the density of said primary air in said flow increases in an amount ranging from about 10% to about 25% as compared with the density of primary air in a corresponding flow in a similar burner not having said low pressure region of said housing in fluid communication with said air supply region. 16. A heater according to claim 9 or 10, wherein said burner has a combustion temperature in the range of from about 650 0 C to about 850'C, an air component in the range of at least 110% of the theoretical minimum for complete combustion. !17. A heater according to claim 16, wherein the burner has a combustion load in the 15 range of from about 200 MJoules/m 2 hr. to about 650EC MJoules/m 2 hr.

18. A heater for heating ambient air in a space to be temperature conditioned, said °•heater having a housing containing a burner including a combustion chamber and a """plenum chamber, a fuel supply for providing a flow of fuel gas to said burner, segregated air supply and low pressure regions in said housing having controlled flows •20 of air therethrough, an air supply means for supplying ambient air received in said air supply region, said air supply means including an air supply inlet located in said air :O :supply region for delivering said received ambient air as primary air in a fuel/air mixture to said plenum chamber of said burner, said air supply region being located in heat transfer proximity with said burner so as to heat said ambient air received in said air supply region and said primary air, and air circulation means including a circulating air -18- inlet located in said low pressure region for drawing a flow of ambient air from said space into said housing and low pressure region for subsequent heating and discharge into said space, said low pressure region of said housing being in fluid communication with said air supply region to withdraw therefrom a flow of the heated ambient air prior to delivery to said burner, said withdrawn heated ambient air being replaced by additional ambient air to maintain said fuel/air mixture to inhibit heating of said primary air within said air supply region and said plenum chamber.

19. A method of heating ambient air in a space that is to be temperature conditioned using a heater having a housing containing a burner, said housing having wall means for cooperating with said burner to provide substantially segregated interior housing regions including an air supply region and a low pressure region, comprising the steps of: drawing ambient air from said space into said air supply region to form a flow of i: primary air for combustion with a fuel in said burner, said burner being in sufficiently S•close proximity with said air supply region to heat said ambient air in said air supply 15 region and said primary air; drawing ambient air from said space into said low pressure region and forming a flow of circulation air, heating said circulation air by heat transfer with said burner and discharging said heated circulation air into said space; and transferring heated ambient air, prior to delivery to said burner, from said air 20 supply region to said low pressure region.

20. A method according to claim 19, wherein the step of transferring heated ambient air from said air supply region to said low pressure region results in an increased total ambient air flow into said air supply region.

21. A method according to claim 20, wherein said wall means include a burner wall that extends in said air supply region and tends to heat said ambient air and said primary -19- air in said air supply region, and said increased total ambient air flow tends to cool said burner wall.

22. A method according to claim 19, wherein said burner includes a fuel supply means for providing a flow of gaseous fuel to said burner and an air supply means including an air supply inlet located in said air supply region for aspirating ambient air from said air supply region to form said flow of primary air to said burner, and said primary air temperature as measured at said air supply inlet is reduced about 40% as compared with the temperature of the primary air measured at a corresponding location in a similar burner not having said low pressure region of said housing in fluid communication with said air supply region.

23. A method according to claim 19, wherein said burner includes a fuel supply means for providing a flow of gaseous fuel to said burner and an air supply means including an :"air supply inlet located in said air supply region for aspirating ambient air from said air supply region to form said flow of primary air to said burner, and said primary air 15 temperature as measured at said air supply inlet is reduced about 40% to about 60'C as compared with the temperature of the primary air measured at a corresponding location in a similar burner not having said low pressure region of said housing in fluid communication with said air supply region.

24. A method according to claim 19, wherein said burner includes a fuel supply means o o 0% 20 for providing a flow of gaseous fuel to said burner and an air supply means including an air supply inlet located in said air supply region for aspirating ambient air from said air O osupply region to form said flow of primary air to said burner, and said primary air temperature as measured at said air supply inlet is reduced about 40% to less than about as compared with the temperature of the primary air measured at a corresponding location in a similar burner not having said low pressure region of said housing in fluid communication with said air supply region. A heater according to claim 9 or 18, wherein said burner includes a fuel supply means for providing a flow of gaseous fuel to said burner and an air supply means including an air supply inlet located in said air supply region for aspirating ambient air from said air supply region to form said flow of primary air to said burner, and the density of said primary air in said flow increases in an amount ranging from about to about 25% as compared with the density of primary air in a corresponding flow in a similar burner not having said low pressure region of said housing in fluid communication with said air supply region.

26. A heater according to claim 9 or 18, wherein said burner has a combustion temperature in the range of from about 650EC to about 850'C, an air component in the range of at least 110% of theoretical minimum for complete combustion.

27. A heater according to claim 9 or 18, wherein said burner has a combustion load 15 in the range of from about 200 MJoules/m 2 hr. to about 650 MJoules/m 2 hr.

28. A method of heating a space to be temperature conditioned using a heater having a housing containing a burner including a combustion chamber and a plenum chamber, a fuel supply for providing a flow of fuel gas to said burner, an air supply means including an air supply inlet located in a segregated air supply region within said housing, and an 20 air circulation means including a circulating air inlet located in a segregated low *pressure region within said housing, comprising the steps of receiving ambient air in said air supply region from said space, said burner being in sufficiently close proximity with said air supply region to heat said ambient air in said air supply region, supplying said received ambient air to said air supply inlet to form a flow of primary air to said plenum chamber of said burner, drawing a flow of ambient air from said space into a low -21- pressure region segregated in said housing to form a flow of circulating air for subsequent heat exchange with said burner and discharge back into said space, and transferring heated ambient air, prior to delivery to said burner, from said air supply region to said circulating air to inhibit heating of said primary air within said air supply region and said plenum chamber while augmenting the heat contained in said circulating air.

29. A method of heating a space to be temperature conditioned using a heater having a housing containing a burner, a fuel supply for providing a flow of fuel gas to said burner, an air supply means for receiving ambient air from space to form a flow of primary air to said burner, said air supply means being located in an air supply region located within said housing in heat transfer proximity with said burner to heat said ambient air in said supply region, and an air circulation means, comprising the steps of o: receiving ambient air in said air supply region from said space, supplying said received Sambient air to said air supply inlet to form a flow of primary air to said burner, drawing 15 a flow of ambient air from said space into a low pressure region in said housing to form a flow of circulating air for subsequent heat exchange with said burner and discharge S" back into said space, and transferring heated ambient air, prior to delivery to said burner, "from said air supply region to said circulating air to inhibit heating of said received air within said air supply region and said primary air within said plenum chamber while *555 5555 20 augmenting the heat contained in said circulating air.

30. A gas fired burner apparatus in the form ofa water heater including: a water tank; a housing containing a burner for combustion of a fuel/air mixture for heat transfer therefrom, the housing including an interior air supply region for receiving ambient air for delivery as primary air in a combustible fuel/air mixture to said burner and a -22- combustion chamber region receiving products of combustion from said burner, said air supply region being located within said housing in heat transfer proximity with said burner, a flue in fluid communication with an outlet from said combustion chamber, said flue being configured to provide a low pressure region which operates to draw products of combustion out of said combustion chamber, and heat removing means in the form of ducting means connecting an outlet of said air supply region to said low pressure region of said flue for transferring heated ambient air, prior to delivery to said burner, from said air supply region to said low pressure region so as to reduce the burner pre-heating effects on the primary air drawn into the burner.

31. A gas fired burner apparatus or heater according to any one of claims 1 to 27 or including: a combustion surface made from a porous material such as metallic mesh an oxygen depletion sensor assembly, said sensor assembly including: a thermocouple having a probe tip at one end and electrical connection means at 15 its other end; O a plate or tab adapted to extend over a pre-selected end portion of said combustion surface along which the combustion flame is present during normal operation, the plate having an aperture therein shaped to receive the thermocouple probe tip and to define a plurality of spaced points that extend in a direction away from said 20 probe tip; °the aperture shape and positioning of the tab and probe tip being configured such that as the oxygen supplied to the burner is depleted, the flame lifts from the mesh under the aperture and progressively retreats from point to point away from the probe until -23- such time as the flame crosses the tab completely and the probe tip is exposed in a flame free zone.

32. An oxygen depletion sensor assembly as set forth in claim 31, wherein said burner apparatus includes an air/fuel supply inlet, and said preselected end portion of the combustion surface is adjacent the air/fuel supply inlet.

33. An oxygen depletion sensor assembly as set forth in claim 32, wherein said aperture is generally star shaped.

34. An oxygen depletion sensor assembly as set forth in claim 33, wherein an extended narrow passageway is located at an end of said aperture remote from the probe tip.

35. An oxygen depletion sensor assembly as set forth in claim 34, wherein said 9 9= ~porous combustion surface underneath the aperture is modified to have controlled 9 9 progression of the flame adjacent the aperture.

36. A gas fired burner apparatus substantially as herein described with reference to 9 •15 any one of the embodiments of the invention illustrated in the accompanying drawings.

37. A heater substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings. 9999 9999 9999

38. A method of heating ambient air substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings. DATED this 2 nd Day of February, 2004 BALDWIN SHELSTON WATERS Attorneys for: BOWIN TECHNOLOGY PTY LIMITED