GB2404243A

GB2404243A - Burner including fan and silencer arrangement

Info

Publication number: GB2404243A
Application number: GB0317154A
Authority: GB
Inventors: Raymond Rennison
Original assignee: Worcester Heat Systems Ltd
Current assignee: Bosch Thermotechnology Ltd
Priority date: 2003-07-23
Filing date: 2003-07-23
Publication date: 2005-01-26
Anticipated expiration: 2023-07-23
Also published as: IE20030718A1; GB0317154D0; GB2404243B

Abstract

A pressure jet burner 14 within a boiler unit 10 has a housing 16 including an air intake opening, an oil or gas burner positioned in the housing, and a fan 20. The fan is arranged to draw air in through the air intake opening in order to provide an air supply to the burner, and the air intake also includes a silencer 22 fitted to the housing which is used to reduce noise generated by the fan. The silencer may include a tuned cylindrical tube 26 comprising a pipe 28 of a length between 20 and 200 mm and diameter between 20 and 50mm, and may further include a chamber 24 positioned between the tuned tube and the air intake. The tube may extend along or adjacent to the burner housing exterior, and the chamber may be used to direct the air flow into the housing air intake, the direction of flow into the housing changing by 180 degrees. The silencer may include acoustic insulation 30 positioned inside the pipe 28, which may be in the shape of a tube and formed from foam material. Ambient air may enter the pipe at an inlet 34 and flow into the silencer 22 which is in fluid communication with the chamber 24, the air intake, and the burner housing.

Description

Improvements in or relating to a pressure jet burner This invention

relates to a pressure jet burner and, more particularly, to a pressure jet burner having a silencer.

Oil- and gas-fired boiler assemblies are well-known. These utilise oiland gas- fired burners. Pressure jet burners use a fan to generate a sufficient air flow across the burner, thereby promoting combustion.

However, it has long been a problem that the fan in conjunction with the air being drawn in causes an unsatisfactory level of noise. This problem is particularly apparent with arrangements having an air intake which draws air from the interior of a building, since the air intake opening permits unrestricted or substantially unrestricted noise propagation.

Attempts have been made to soundproof the interior of boiler assemblies to suppress fan and air noise, but with only marginal success.

The present invention seeks to provide an improved solution to this problem.

According to a first aspect of the present invention, there is provided a pressure jet burner comprising a housing having an air intake opening, an oil or gas burner positioned in the housing, a fan for drawing air into the housing through the air intake opening, and a silencer fitted to the air intake opening of the housing, the silencer, in use, acting to reduce noise generated by the fan.

Preferable and/or optional features of the first aspect of the invention are set forth in claims 2 to 11, inclusive.

According to a second aspect of the present invention, there is provided a boiler assembly having a pressure jet burner in accordance with the first aspect of the invention.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a boiler assembly, in accordance with the second aspect of the invention and shown with the top case panel and front cover removed for clarity, including a first embodiment of a pressure jet burner, in accordance with the first aspect of the invention, having a silencer; Figure 2 is a schematic view showing part of the silencer depicted in Figure 1 from one end; Figure 3 is a longitudinal sectional view along line A-A of the part of the silencer shown in Figure 2; Figure 4 is an end schematic view showing part of a silencer of a second embodiment of a pressure jet burner, in accordance with the first aspect of the invention; and Figure 5 is a side view of the silencer shown in Figure 4. s

Referring firstly to Figures I to 3, there is shown a boiler assembly to (with top case panel and front cover removed for clarity) which comprises a boiler body 12 and a pressure jet burner 14 located in the boiler body 12. The pressure jet burner 14 has a burner housing 16, a gas- or oilfired burner (not shown) housed in the burner housing 16, and an electrically operated fan 20 also housed in the burner housing 16.

The burner housing 16 includes a single air intake opening (not shown) in a side facing the front of the boiler body 12. The size of the air intake opening is adjustable.

The fan 20 is arranged to draw air in through the air intake opening, thus IS providing an air supply to the burner, and to exhaust from the housing 16 through an exhaust outlet (also not shown).

The arrangement so far described is conventional and well-known.

The pressure jet burner 14 also comprises a silencer 22 mounted externally on the burner housing 16 and positioned over the air intake opening. The silencer 22 comprises a chamber 24, which extends from the air intake opening of the housing 16, and a tuned tube 26 connected to and in fluid communication with the chamber 24.

The tuned tube 26 comprises a, typically metal, cylindrical pipe 28 having a length preferably in the range of 20 millimetres (mm) to 200 mm, and acoustic insulation 30, in the form, for example, of foam material, positioned inside the cylindrical pipe 28. The foam material, in this case, is closed cell foam material, but may be open cell foam material or any other suitable material.

The acoustic insulation 30 is a tube defining a pipe bore 32 along which air drawn by the fan 20 can flow. A first end 34 of the pipe bore 32 acts as an inlet for ambient air to flow into the silencer 22, and the second end 36 is in fluid communication with the chamber 24. The diameter of the pipe bore 32 is preferably in the range of 20 mm to 50 mm.

The chamber 24 is a, typically metal, duct having only two openings, one opening 38 leading from the second end 36 of the tuned tube 26 and the other opening 40 leading to the air intake opening of the housing 16. Both chamber openings 38, 40 are in one surface 42 of the chamber 24, thus causing the flow path of air being drawn into the burner housing 16 to be diverted through, or substantially through, 180 from leaving the tuned tube 26 to entering the air intake opening of the burner housing 16.

The use of the chamber 24 allows the tuned tube 26 to extend along, or adjacent to, one side 44 of the burner housing 16, instead of projecting directly away from the burner housing 16. Consequently, the pressure jet burner 14 can remain compact and the boiler body 12 does not need to be enlarged. However, the chamber 24 could be dispensed with.

In preliminary tests, it was found that a conventional 25kW boiler assembly 10, as described above and without the silencer 22, typically ran at or around 52 dBA (A-weighted decibel) with the boiler assembly sitting on the ground, all case panels and front cover in place, and with readings taken 1 metre (m) in front of the front cover and at a height of 1.5m above ground level. When using silencers 22 of various dimensions, the following results were obtained: Outside Diameter Inside Diameter Length Noise Level when running (mm) (mm) (mm) (dBA) 27 30 45 33 30 47.8 36 62 46.7 36 132 46.4 The 'Outside Diameter' is the outside diameter of the tuned tube 26; the 'Inside Diameter' is the diameter of the pipe bore 32; and the 'Length' is the length of acoustic insulation 30, which may be different from the overall length of the tuned tube 26 in order to allow for connection of the tuned tube 26 to the chamber 24, for example as shown in Figure 1 where the tuned tube 26 is attached to the chamber 24 using a jubilee clip 46.

As can be seen from the results of these preliminary tests, a significant reduction in noise levels of up to 7 dBA was achieved by adjusting the length and/or cross-sectional area of the tuned tube 26.

Referring now to Figures 4 and 5, a modification to the tuned tube 26 of the silencer 22 of the first embodiment is shown. The acoustic insulation 30 is omitted and the diameter of cylindrical pipe 28' of this silencer 22' is reduced so that the internal bore diameter corresponds to the pipe bore diameter of the acoustic insulation 30. The tests described above were repeated, and similar levels of noise reduction were achieved.

Similar noise reduction was also achieved when the chamber 24 was omitted from the silencer 22 and tuned tube 26 was directly positioned over the air intake opening of the burner housing 16.

Although the chamber 24 can be omitted from the silencer 22/22', the chamber 24 is beneficial in diverting the flow path so that the silencer 22/22' can be entirely accommodated within an existing boiler body 12. The chamber 24 is therefore advantageous in providing a flow path which, at least in part, extends at an angle to the flow path defined by the tuned tube 26/26'.

It is envisaged that the chamber could be unitarily formed with the tuned tube; and at least part of the silencer could follow an arcuate path. These measures help to reduce air flow restrictions.

The inlet to the tuned tube may also be belled to increase the volume of air able to be drawn into the silencer by the fan.

The tuned tube may also have a shape other than cylindrical. For example, the tuned tube may have a square or rectangular cross-section.

It is also conceivable that the silencer, while still being fitted to the air intake opening, could project internally into the burner housing, rather than projecting externally. This would provide a far more compact arrangement of pressure jet burner.

The tuned tube of the silencer could also project internally into the silencer chamber, instead of projecting externally therefrom as previously described.

It is thus possible, by the provision of a tuned tube silencer, to significantly reduce the noise generated from air being drawn into a pressure jet burner by the associated fan.

The embodiments described above are given by way of example only, and further modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims. For example, where the pressure jet burner has a different power rating, a silencer having a tuned tube suitable for reducing noise associated with that burner is provided.

Claims

1. A pressure jet burner comprising a housing having an air intake opening, an oil or gas burner positioned in the housing, a fan for drawing air into the housing through the air intake opening, and a silencer fitted to the air intake opening of the housing, the silencer, in use, acting to reduce noise generated by the fan.

2. A pressure jet burner as claimed in claim 1, wherein the silencer comprises a tuned tube having a length and/or cross-sectional area which is/are selected to reduce noise associated with operation of the fan.

3. A pressure jet burner as claimed in claim 2, wherein the tube of the silencer is a cylindrical pipe.

4. A pressure jet burner as claimed in claim 3, wherein the length of the pipe is in the range of 20 millimetres (mm) to 200 mm, and the diameter of the pipe is in the range of 20 mm to 50 mm.

5. A pressure jet burner as claimed in any one of claims 2 to 4, wherein the silencer further comprises a chamber which is interposed between the air intake opening of the housing and the tube of the silencer and through which air flows when drawn into the housing by the fan.

6. A pressure jet burner as claimed in claim 5, wherein the flow path defined by the chamber is at least in part at an angle to the flow path defined by the tuned tube.

7. A pressure jet burner as claimed in claim 5 or claim 6, wherein the chamber diverts the air being drawn into the housing through or substantially through 180 .

8. A pressure jet burner as claimed in any one of claims 2 to 7, wherein the tuned tube extends along or adjacent to an external surface of the housing.

9. A pressure jet burner as claimed in any one of the preceding claims, wherein l 0 the silencer includes acoustic insulation.

10. A pressure jet burner as claimed in claim 9, wherein the acoustic insulation is in the form of a tube.

l l. A pressure jet burner as claimed in claim 9 or claim 10, wherein the acoustic insulation is foam material.

12. A pressure jet burner substantially as hereinbefore described with reference to the accompanying drawings.

13. A boiler assembly having a pressure jet burner as claimed in any one of the preceding claims.