GB2283314A

GB2283314A - A balanced flue terminal

Info

Publication number: GB2283314A
Application number: GB9322423A
Authority: GB
Inventors: David John Buckles
Original assignee: GAH
Current assignee: GAH
Priority date: 1993-10-30
Filing date: 1993-10-30
Publication date: 1995-05-03
Anticipated expiration: 2013-10-30
Also published as: GB9322423D0; GB2283314B

Abstract

A balanced flue terminal 14 for a burner comprises two concentric tubes. The outer tube comprises two pieces 42, 58; and the inner tube comprises two pieces 40, 46, so that the length of the terminal 14 may be varied by telescoping the respective pieces of the outer and the inner tubes. An insulating sleeve 62 separates the inner tube from the outer tube. In use, exhaust gas from the burner exits via an exhaust duct 32, through the inner tube to the atmosphere. Combustion air enters the burner via the outer tube and an inlet duct 36. Because of the use of concentric tubes, the terminal 14 has relatively small cross section, and the combustion air is warmed by the exhaust gases. The inner tube 46 terminates inside the outer tube 42. The outer tube includes thermal insulation 64 adjacent the end of the tube and air intake openings 44. A tapered body 52 defines an exhaust gas discharge passage 66. <IMAGE>

Description

A Balanced Flue Terminal This invention relates to a balanced flue terminal which serves to admit combustion air and to discharge exhaust gases from a burner. Balanced flue terminals are conventionally used to provide the necessary air/gas handling capabilities to burners mounted on the inside of an external wall of the building. In such cases the balanced flue extends through the thickness of the wall and the end of the flue remote from the burner is located in open air.

The balanced nature of the flue means that external pressures acting on the remote end of the flue affect equally the combustion air drawn in and the exhaust gas discharged so that the operation of the burner is unaffected by the external pressure which may be generated for example by wind blowing past the flue.

Such terminals are typically found where a burner is incorporated in a water-heating boiler, but the invention is not restricted to this application.

According to the present invention there is provided a balanced flue terminal for a burner which has an exhaust gas outlet and a combustion air inlet, the flue terminal comprising two concentric tubes, one forming the exhaust gas outlet and the other forming the combustion air inlet, the tubes being thermally insulated from one another, a junction chamber on the inner (burner) end of the terminal which surrounds the inner tube and is arranged so that the inner tube passes straight through the chamber and so that the outer tube communicates with the interior of the chamber, the chamber having a connection for a burner air duct, and wherein the outer end of the inner tube terminates in an open end located inside the outer tube, the outer tube having a terminal fitting which at least partly encloses the cross-section thereof, and vent apertures through the side wall thereof.

By making the inlet and outlet tubes concentric, a particularly space saving construction is achieved.

Both outlet and inlet tubes can be of square cross-section, of circular cross-section, or of any other cross-section.

The inner tube may be of the same or different crosssectional shape to the outer tube.

To provide the thermal insulation between the two tubes, the inner tube may be double-skinned, with an air gap between the two skins. Alternatively a sleeve of thermally insulating material may be provided around the inner tube.

The terminal fitting of the outer tube preferably includes a tapered body, the apex of which is positioned adjacent the open end of the inner tube.

The inner tube is preferably the exhaust gas outlet and the outer tube the combustion air inlet. Exhaust gases passing along the inner tube are then diverted by the conical body towards the vent apertures.

The outer tube preferably has no vent apertures in the upwardly facing surface thereof.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a boiler with a flue terminal installed through the wall of a building; Figure 2 is a plan view of the boiler shown in Figure 1; Figure 3 is a schematic view of a boiler incorporating a balanced flue terminal in accordance with the invention, with the boiler cover removed and part broken away; Figure 4 is an exploded view of the balanced flue terminal from Figure 3; Figure 4a shows a cross-section through a junction chamber; Figure 5 is a longitudinal cross-section through the flue terminal of Figures 3 and 4; Figure 6 is an end view taken in the direction of the arrow A from Figure 5; and Figure 7 is a side view, to an enlarged scale, of the outer end of the flue terminal.

Figures 1 and 2 show a boiler 10 mounted against an external cavity wall 12 of a building. The boiler has a balanced flue terminal 14 which extends through the wall and has an inlet/outer in the open air on the outside of the wall 12.

The internal construction of the boiler is shown in Figure 3. The boiler has a burner 16 which has to be fed with air for combustion and from which the rpoducts of combustion have to be exhausted. The burner burns fuel in a combustion chamber 18. The heat generated in the combustion chamber is used to heat water in a water jacket 20 surrounding the combustion chamber, and this water is circulated through a heating circuit through pipes indicated at 22, 24. The combustion chamber has an access cover 26, and in Figure 3 an external casing for the boiler is indicated schematically at 28.

The burner 16 has to be fed with air for combustion, and this air is fed through an inlet duct 30. Exhaust gases from the combustion chamber are exhausted through an exhaust duct 32. Both the inlet air duct 30 and the exhaust duct 32 are connected to the balanced flue terminal 14 which will be described in more detail in the following.

Figure 4 shows the exhaust duct 32 connected to a junction chamber 34. The chamber 34 has a fitting 36 to which the combustion air duct 30 can be connected. The junction box 34 is mounted against a back wall 38 of the boiler casing 28 and on the outside of this back wall a balanced flue terminal 14 is fitted.

As will be seen from Figure 4a, the exhaust gas duct 32 extends straight through the junction chamber 34 and ends, outside of the boiler casing, a stub pipe 40. The remaining components of the balanced flue terminal are fitted around this stub pipe 40. It is a requirement of the balanced flue terminal that it should be adjustable in length so that it can be fitted through walls 12 of varying thicknesses, and so both the exhaust gas outlet and the combustion air inlet are constructed in a telescopic manner.

The outer end of the flue terminal, shown in Figure 5, has a square section casing 42 with intake openings 44 in the sides, and a centrally mounted round inner tube 46. The inner tube is supported inside the square section casing by a flange 48 (Figure 5). At the outer end of the terminal, the casing 42 ends in a terminal fitting 50 which has a tapered body 52 held in the mouth of the casing by webs 54 to define a discharge air passage 56.

To assemble the terminal, a square section distance piece 58 is fitted over a square section boss 60 on the junction chamber. An insulating sleeve 62 is fitted over the stub tube 40, and the outer end of the terminal is then slid together with the distance piece 58 in a telescopic manner so that the tubes 40 and 46 telescope together and the tubes 42 and 58 also telescope together. The insulating tube 62 will be cut to length in accordance with the known desired longitudinal extension of the flue terminal before the terminal components are assembled together.

At the outer end of the terminal further insulation is provided at 64.

In use, the exhaust gas leaving the boiler will pass along the inner tube 46 as indicated by arrows 66, and air for combustion will be drawn in along the annular space between the outer and inner tubes, as indicated by arrows 68. As a result of the existence of a chamber 70 at the discharge end of the flue terminal, the exhaust gases are directed towards the outer skin of the rectangular outer casing of the terminal. The outer skin is lined with low thermal capacity insulating/sound absorbing material 64 on all four sides of the chamber. This reduces the sound emitted from the discharge holes 56 and in addition reduces the possibility of condensation which might otherwise occur when starting with a cold uninsulated terminal end on which condensation could form when the gases of combustion are cooled.

The design of the discharge apertures 56 ensures that the hot gases of combustion leaving the terminal are evenly distributed over a large area and are quickly cooled and diluted with external air.

The design of the balanced flue terminal shown in the drawings has a desirably small cross-sectional dimension and is less obtrusive where it passes through the external wall than many other balanced flue terminals. There is also an advantage that the air for combustion flowing as indicated by the arrow 68 is warmed by the exhaust gases.

Claims

1. A balanced flue terminal for a burner which has an exhaust gas outlet and a combustion air inlet, the flue terminal comprising two concentric tubes, one forming the exhaust gas outlet and the other forming the combustion air inlet, the tubes being thermally insulated from one another, a junction chamber on the inner (burner) end of the terminal which surrounds the inner tube and is arranged so that the inner tube passes straight through the chamber and so that the outer tube communicates with the interior of the chamber, the chamber having a connection for a burner air duct, and wherein the outer end of the inner tube terminates in an open end located inside the outer tube, the outer tube having a terminal fitting which at least partly encloses the cross-section thereof, and vent apertures through the side wall thereof.

2. A balanced flue terminal as claimed in Claim 1, wherein the inner tube is of the same cross sectional shape as the outer tube.

3. A balanced flue terminal as claimed in Claim 1 or Claim 2, wherein the terminal fitting of the outer tube includes a tapered body, the apex of which is positioned adjacent the open end of the inner tube.

4. A balanced flue terminal as claimed in any one of the preceding claims, wherein the inner tube is the exhaust gas outlet and the outer tube is the combustion gas inlet.

5. A balanced flue terminal as claimed in any one of the preceding claims, wherein the outer tube has no vent apertures in its upwardly facing surface.

6. A balanced flue terminal as claimed in any one of the preceding claims, wherein the thermal insulation between the tubes is double skinned, with an air gap between the two skins.

7. A balanced flue terminal as claimed in any one of the preceding claims, wherein the exhaust gas outlet and the combustion air inlet are constructed in a telescopic manner.

8. A balanced flue terminal substantially as herein described with reference to any one of Figures 3 to 7.