AU2009201356B2

AU2009201356B2 - A flue adapter

Info

Publication number: AU2009201356B2
Application number: AU2009201356A
Authority: AU
Inventors: Leon Bogers; Brian Dolly
Original assignee: Rinnai Australia Pty Ltd
Current assignee: Rinnai Australia Pty Ltd
Priority date: 2009-04-07
Filing date: 2009-04-07
Publication date: 2016-01-21
Anticipated expiration: 2029-04-07
Also published as: AU2009201356A1

Abstract

A flue adapter for location in a combustion product flow 5 path that extends between the exhaust of a gas combustion appliance and a natural draught flue. The adapter includes an inlet for receiving hot combustion products exhausted from the gas combustion appliance, and at least one outlet through which to pass combustion products from 10 the adapter into the lower end of the flue. The adapter deviates at least part of the flow direction between the inlet and flue so that t he velocity of the combustion products in the overall flow path direction is reduced by the adapter. N:\Melboume\Cases\Patent\79000-79999\P79551.AU\Specis\P79551.AU Spocification 2009-4-7.doc 7104/09

Description

- 1 A FLUE ADAPTER Field of the invention The present invention relates to a flue adapter for 5 use in a combustion gas flow path that extends between the exhaust of a gas combustion appliance and a flue. Background Gas combustion appliances are commonly used in many 10 applications for heating purposes. In these appliances, a mixture of gaseous hydrocarbons (such as methane, propane and/or butane) and air are burnt, with the heat produced by combustion used to heat a fluid, such as water, oil or air, which in turn can be used for heating the building or 15 to supply hot water to amenities throughout the building. One common application is water heaters in commercial buildings for the provision of hydronic heating and/or for hot water supply to amenities. Instantaneous hot water 20 heaters can be desirable in this application because the water can be heated quickly on demand. A flue is required to safely discharge combustion products produced by gas combustion appliances in 25 applications in which the appliances are located in an enclosed space, such as in a plant room. Excessive spillage of combustion products into the plant room may be hazardous and may cause asphyxiation. It should be noted that combustion products include combustion gases and 30 particulates entrained within the combustion gases. 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 2 Some gas combustion appliances use atmospheric burners in which air enters the combustion chamber by natural draught in the combustion chamber, by the venturi effect created by the flow of the gas fuel, or a 5 combination of the two, and without mechanical assistance. A characteristic of these types of appliances is that the combustion products flow rise through a flue as a result of the natural buoyancy of the hot combustion products. Flues of this type are often referred to as a "natural 10 draught flue". The higher temperature combustion products compared with ambient conditions at the outlet end of the flue, combined with the overall elevation from the inlet to the outlet of the flue, cause the combustion products to rise through the flue. 15 A natural draught flue does not need to be sealed because the flow of combustion products within the flue tends to cause ambient air to be drawn into the flue. Furthermore, the flow velocity of combustion products 20 within the flue tends to be relatively low, and the velocity is only created by the natural buoyancy of the hot combustion products. An increasing number of gas combustion appliances are 25 available with either air being forced into the combustion chamber (and thus the combustion chamber is charged with air at positive pressure), or an extraction fan provided in the exhaust to draw air through the combustion chamber. In both cases, the combustion products have a relatively 30 high velocity as they exit the exhaust of the appliance. Advantages of these systems are their smaller physical size relative to appliances with atmospheric burners, and more complete combustion of gas, which is desirable for 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 3 efficiency considerations. These types of gas combustion appliances are commonly referred to as a "forced flue" or "powered flue" appliances because the combustion products are exhausted from the appliance into the flue at a 5 positive pressure relative to ambient. A powered flue appliance cannot be used with a natural draught flue for a number of reasons, including the risk of spillage of combustion products. Due to the 10 costs associated with refitting a pre-existing flue, powered flue appliances are rarely used with pre-existing natural draught flues. 15 Summary of the invention The present invention provides a flue adapter for location in a combustion product flow path that extends between the exhaust of a gas combustion appliance and a natural draught flue, the adapter comprising: 20 an inlet for receiving hot combustion products exhausted from the gas combustion appliance; at least one outlet through which to pass combustion products from the adapter into the lower end of the flue; and 25 a chamber disposed between the inlet and having a vent to draw dilution air into the chamber for mixing with the hot combustion products, wherein the adapter deviates at least part of the flow direction between the chamber and the outlet such that the velocity of the combustion 30 products in the overall flow path direction is reduced by the adapter. 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 4 In an embodiment in which the overall flow path is vertical, and the velocity of combustion products is reduced by the adapter such that, under ordinary operating conditions, the combustion products rise up the flue as a 5 result of natural buoyancy. The at least one outlet may be arranged so that the combustion products are expelled from the adapter transversely to the inlet flow direction received from the 10 appliance. The adapter may further comprise a baffle to change the flow direction of combustion products passing from the inlet to the outlet of the adapter. The baffle may be 15 positioned adjacent to the at least one outlet. In certain embodiments, the vent may be positioned below the chamber to allow flue spillage products to exit the adapter. 20 The combined cross sectional area of the inlet and the vent may be less than the cross sectional area of the flue downstream and adjacent to the adapter. 25 In certain embodiments, wherein the cross sectional area of the vent is less than the cross sectional area of the inlet. In certain embodiments, the adapter can further 30 comprise: an outer tube with first and second ends; an inner tube that passes through the first end of the outer tube, the inner tube having a first end that 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 5 defines the inlet and a second end that terminates within the outer tube; and an annular gap between the outer and inner tubes that defines the vent. 5 The chamber may be formed within the outer tube downstream of the second end of the inner tube. In some embodiments, the at least one outlet is in 10 the form of a plurality of openings in the side wall of the outer tube. The adapter can also further comprise an annular ring disposed around the inner tube to direct flue spillage 15 products away from the adapter. In certain embodiments in which the diameter of the outer tube is less than the internal diameter of the flue, the adapter can further comprise a second annular ring 20 disposed about the outer tube and extending between the outer tube and the inner wall of the flue. In certain embodiments, the adapter can additionally comprise a tube that surrounds the at least one outlet 25 and, in use, forms part of the lower end of the flue. Brief description of the drawings In order that the invention may be more easily 30 understood, an embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which: 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 6 Figure 1: is a perspective view of a flue adapter according to an embodiment of the present invention; Figure 2: is a side elevation view of the flue 5 adapter of Figure 1; Figure 3: is a perspective cross sectional view of the flue adapter of Figure 1; Figure 4: is a cross sectional view of the flue adapter of Figure 1, which is installed 10 with a gas combustion appliance and a flue; Figure 5: is a cross sectional view of a first plant room, which includes a natural draft flue, several gas combustion appliances, and several flue adapters of Figure 1; 15 Figure 6: is an enlarged, exploded view of Region A in Figure 5; and Figure 7: is a cross sectional view of a second plant room, which includes a powered flue, several gas combustion appliances, and 20 several flue adapters of Figure 1. Detailed description Figures 1 to 3 show a flue adapter 10 according to an 25 embodiment of the present invention. Figure 4 shows that flue adapter 10 disposed in a combustion product flow path that extends between the exhaust of a gas combustion appliance 100 and a flue 120. The gas combustion appliance 100 illustrated is a water heater, however it 30 will be appreciated that the present invention is not limited to use in connection with this type of appliance. 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 7 As shown in Figure 4, the appliance 100 is of the type that has a forced draught burner 102 that is charged with air pressurized by a fan 104. The hot combustion gases rise through the exhaust pipe 106 due to the 5 pressurized flow of the air and gas into the burner 102. As also shown in Figure 4, the combustion product flow path, as defined by the exhaust pipe 106 and the lower end of the flue 120, is generally vertical. 10 The flue adapter 10 receives the hot combustion products (which are at positive pressure relative to ambient) expelled from the powered flue appliance 100 at a relatively high velocity. The adapter 10 has an outlet through which to pass combustion products from the adapter 15 into the flue 120. The adapter 10 deviates at least part of the combustion product flow direction between the inlet and flue so that the velocity of the combustion products in the overall flow path direction is reduced by the adapter. 20 Thus, in ordinary operating conditions, the adapter 10 lowers the velocity of the combustion products in the overall flow path direction. In other words, the velocity of combustion products flowing within the flue 120, 25 immediately downstream of the adapter 10, is lower than that of the combustion products in the exhaust pipe 106 of the appliance 100. In this way, the combustion products can rise up the flue 120 as a result of natural buoyancy of the combustion products in a manner substantially 30 similar to that of an appliance with an atmospheric burner that is provided with a similar gas fuel delivery rate. 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 8 In this embodiment, the outlet is arranged so that the combustion products are expelled from the adapter 10 transversely to the inlet flow direction received by the adapter 10. 5 The adapter 10 has an outer tube 14 with a first (lower) end and second (upper) end, and an inner tube 16 that passes through the lower end of the outer tube 14. The lower end of the inner tube 16 defines an inlet 18 of 10 the adapter 10 and, in situ, connects to the exhaust pipe 106 of the appliance 100. Thus, the hot combustion gases enter the adapter 10 through the inner tube 16. As shown most clearly in Figure 3, the upper end of the inner tube 16 terminates within the outer tube 14. 15 A vent 20 is formed between the outer and inner tubes 14, 16. Induced ambient air can be drawn into the adapter through the vent 20. The flow of induced air is indicated in Figure 4 by arrows D. Enabling induced ambient air to 20 be drawn into the chamber 12 facilitates undisturbed operation of the appliance 100 in the event of pressure fluctuations in the flue 120. During a period of reverse flow conditions in the 25 flue 120, combustion products can flow from the flue 120 back into the adapter 10. The vent 20 provides a means for the combustion products to exit the adapter 10. This allows the appliance 100 to continue to operate with minimal disturbance for a period of time. 30 In addition, when the appliance 100 has not been operating for a significant period of time, the gases within the flue 120 become cold. In this situation, there 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 9 is no natural buoyancy of the gases within the flue, which means that combustion products from the appliance 100 are not drawn up the flue. The vent 20 provides a means for combustion products to "spill" from the adapter 10 until 5 the flue 120 becomes sufficiently warm that the gases have a natural buoyancy. The size of the vent 20 may be selected to achieve a desired ratio of ambient air to combustion gas to be drawn 10 into the adapter 10. Alternatively or additionally, the size of the vent 20 can be selected to allow a certain maximum rate of reverse flow to exit the adapter 10. The adapter 10 further has a chamber 12, within which 15 hot combustion products can be mixed with the induced ambient air drawn in through the vent 20, to form a diluted combustion product mixture. In this embodiment, the chamber 12 is formed within the outer tube 14 downstream of the second (upper) end of the inner tube 16. 20 Induced air enters the chamber 12 through the vent 20 co axially with the hot combustion products, and in the same direction. The combined cross sectional area of inlet 18 and vent 20 is less than the cross sectional area of the flue pipe 120 downstream and adjacent to the adapter 10. 25 In this embodiment, the at least one outlet is in the form of openings 22 formed in the side wall of the outer tube 14. In normal operating conditions, the combustion products exit the adapter 10 through the openings 22 in a 30 direction that is transverse to the inlet flow direction received by the adapter 10. Accordingly, the combustion products enter the lower end of the flue 120 in a direction that is transverse to the flow direction within 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 10 the flue 120. As previously mentioned, the combustion products can then rise up the flue 120, as a result of natural buoyancy, in a manner that is substantially similar to that of an appliance with an atmospheric burner 5 that is provided with a similar gas fuel delivery rate. The adapter 10 includes a baffle 24 that closes the outer tube 14 adjacent the upper end of the outer tube. The baffle 24 acts to change the flow direction of 10 combustion products between the inlet and outlet of adapter 10, so that these products are expelled from the adapter 10 in a transverse direction to the inlet flow direction received from the appliance 100. The chamber 12 is formed within the outer tube 14 and between the upper 15 end of the inner tube 16 and the baffle 24. The flue adapter 10 is provided with an annular constricting ring 34 that is connected to the internal wall of the outer tube 14 and extends radially inwardly 20 towards the inner tube 16. The constructing ring 34 reduces the cross sectional area of the vent 20, and thus limits the flow of induced dilution air D into the chamber 12 to optimise the flow characteristics of diluted combustion products mixture. 25 As shown in Figure 4, the diameter of the outer tube 14 is less than the internal diameter of the flue 120. The adapter 10 further includes an annular ring 26 that is disposed about the outer tube 14 and extends between the 30 outer tube 14 and the inner wall of the flue 120. The annular ring 26 is sized so as that the peripheral edge 28 of the annular ring 26 fits within the inner wall of the flue 120. A series of tabs 30 extend radially outwardly 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 11 from the annular ring 26 to locate the adapter 10 with the annular ring 26 at the base of the flue 120. The appliance 100 shown in Figure 4 is a co-axial 5 flow style appliance, in which the flow direction of fresh intake air entering the appliance 100 and the flow direction of exhaust combustion products exhausted from the appliance 100 are parallel, but in the opposite direction to one another. In Figure 4, the flow of intake 10 air is indicated by arrows R, and the flow of combustion products is indicated by arrows P. To achieve these flow directions, the combustion products exit the appliance 100 through an exhaust pipe 106 and the intake air enters the appliance through an annular space 108 that surrounds the 15 exhaust pipe 106. To vertically separate the intake air R from the induced dilution air D, a second annular ring 32 is mounted about the inner tube 16 between the lower ends of 20 both the outer and inner tubes 14, 16. The second annular ring 32 directs flue spillage products away from the appliance 100, which minimizes the opportunity of the flue spillage products being drawn into the appliance 100 through the annular gap 108, instead of fresh intake air 25 required for combustion. As would be appreciated, flue spillage products being drawn into the appliance 100 would adversely affect combustion. Many applications that require installation of 30 multiple powered flue type appliances involve the replacement of pre-existing gas appliances with atmospheric burners in plant rooms provided with a common natural draft flue. The flue adapters of the present 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 12 invention simplify these replacements because much of the existing natural draft flue system infrastructure, and provisions for appliance ventilation, can remain in place. 5 Figures 5 and 6 show a plant room 250 with a typical natural draught flue 200 for directing combustion gases produced by eight appliances 100 (4 appliances mounted back to back) out of the plant room 250. As shown in Figure 6, each of the appliances 100 is provided with a 10 flue adapter 10 according to the embodiment described in connection with Figures 1 to 4. The flue 200 is formed with eight flue terminals 202 that each connects one of the flue adapters 10 to a common 15 flue header pipe 204. Flue gases then move from the header pipe 204 to the flue pipe 206, and subsequently exit through the flue cowl 208. A condensate drain 210 is provided at the lower end of the flue pipe 206. 20 As previously described, each of the appliances 100 is of the type that has a powered flue. The combustion products from each appliance 100 enter the respective flue adapter 10, which reduces the velocity of the combustion products in overall flow path direction. In this way, the 25 combustion products can rise up the lower end of the flue terminal 202 due to natural buoyancy of the combustion products. Figure 7 show a plant room 350 that is fitted with a 30 typical powered flue 300 for directing combustion gases produced by eight appliances 100 (4 appliances mounted back to back) out of the building. Each of the appliances 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 13 100 is provided with a flue adapter 10 according to the embodiment described in connection with Figures 1 to 4. The flue 300 is formed with eight flue terminals 302 5 that each connects one of the flue adapters 10 to a common flue header pipe 304. The flue header pipe 304 is connected to an intake air pipe 306, which receives fresh intake air from external of the building. The intake air pipe 306 includes a damper 308 for throttling the intake 10 air flow as required. Flue gases can move from the header pipe 304 (with any intake air from the intake air pipe 306) to the flue exhaust pipe 309, which has a discharge opening 310 to 15 direct flue gases externally of the building. The flue exhaust pipe 309 has an extraction fan 312 that creates a negative pressure within the flue header pipe 304. In certain embodiments, the adapter can also include 20 a tube that surrounds the at least one outlet. In use of the adapter the tube forms a part of the lower end of the flue. The tube may be dimensioned so that the peripheral edge of the annular ring fits within the inner wall of the tube. 25 In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as 30 "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15

Claims

1. A flue adapter for location in a combustion product flow path that extends between the exhaust of a gas 5 combustion appliance and a natural draught flue, the adapter comprising: an inlet for receiving hot combustion products exhausted from the gas combustion appliance; at least one outlet through which to pass combustion 10 products from the adapter into a lower end of the flue; and a chamber disposed between the inlet and the outlet, and having a vent to draw dilution air into the chamber for mixing with the hot combustion products, 15 wherein the adapter deviates at least part of the flow direction between the chamber and the outlet such that the velocity of the combustion products in the overall flow path direction is reduced by the adapter. 20 2. A flue adapter according to claim 1, wherein the overall flow path is vertical, and the velocity of combustion products is reduced by the adapter such that, under ordinary operating conditions, the combustion products rise up the flue as a result of natural buoyancy. 25

3. A flue adapter according to either claim 1 or 2, wherein the at least one outlet is arranged so that the combustion products are expelled from the adapter transversely to the inlet flow direction received from the 30 appliance.

4. A flue adapter according to any one of claims 1 to 3, further comprising a baffle to change the flow direction 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 15 of combustion products passing from the inlet to the outlet of the adapter.

5. A flue adapter according to claim 4, wherein the 5 baffle is positioned adjacent to the at least one outlet.

6. A flue adapter according to any one of claims 1 to 5, wherein the vent is positioned below the chamber to allow flue spillage products to exit the adapter. 10

7. A flue adapter according to claim 6, wherein the combined cross sectional area of the inlet and the vent is less than the cross sectional area of the flue downstream and adjacent to the adapter. 15

8. A flue adapter according to either claim 6 or 7, wherein the cross sectional area of the vent is less than the cross sectional area of the inlet. 20 9. A flue adapter according to any one of claims 6 to 8, further comprising: an outer tube with first and second ends; an inner tube that passes through the first end of the outer tube, the inner tube having a first end that 25 defines the inlet and a second end that terminates within the outer tube; and an annular gap between the outer and inner tubes that defines the vent. 30 10. A flue adapter according to claim 9, wherein the chamber is formed within the outer tube downstream of the second end of the inner tube. 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15 - 16 11. A flue adapter according to either claim 9 or 10, wherein the at least one outlet is in the form of a plurality of openings in the side wall of the outer tube. 5 12. A flue adapter according to any one of claims 9 to 11, further comprising an annular ring disposed around the inner tube to direct flue spillage products away from the adapter. 10 13. A flue adapter according to any one of claims 9 to 12, wherein the diameter of the outer tube is less than the internal diameter of the flue, and the adapter further comprises a second annular ring disposed about the outer tube and extending between the outer tube and the inner 15 wall of the flue.

14. A flue adapter according to any one of claims 1 to 13, further comprising a tube that surrounds the at least one outlet and, in use, forms part of the lower end of the 20 flue.

15. A flue adapter substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. 7032703_1 (GHMafters) P79551.AU RDEVAN 21/10/15