GB2381062A

GB2381062A - A flue fan unit

Info

Publication number: GB2381062A
Application number: GB0216135A
Authority: GB
Inventors: Simon Guy Somerset Cartwright
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-07-18
Filing date: 2002-07-12
Publication date: 2003-04-23
Also published as: GB0216135D0; GB0117585D0

Abstract

A flue fan unit 10 adapted to engage the external terminus of a flue 20, comprising an inlet tube 40 attached to an upper housing which has side vents 80, at least one fan 150 and fan motor 140 and a cowling 90. Preferably, the fan has an upper impeller 160 which draws air through upper inlet vents 81 and directs it onto a lower impeller 170 which draws exhaust gases from the inlet tube 40 and expels it through lower outlet vents 82. Positioned within inlet tube 40 may be an orifice plate 50 with pitot ports 60, 70 positioned on either side of it. The ports 60, 70 are preferably linked to a controller (220, fig 5), comprising a differential pressure sensor (221, fig 5), which can increase the fan speed or disable exhaust gas generating means such as a boiler (200, fig 5). Preferably a switch (210, fig 5) is provided to switch on the fan 150 which creates the pressure difference across plate 50. The invention is concerned with the increase of gas flow-rate through a flue by using a fan.

Description

Flue Fan Unit The present invention concerns fan units adapted for mounting on top of flues, flues having same mounted on them, methods of increasing the rate of flow through a flue using same, and methods of exhausting gases from a flue using same.

Flues are used to convey smoke and exhaust gases from gas fires, boilers and suchlike to the open air, sometimes as part of chimney structure rising from a building.

Modem buildings such as homes and office blocks typically do not have large chimney structures, instead having relatively small, light and insubstantial structures where the flue terminates to allow gases and smoke, etc. , to escape. A cowling covers the top of the flue so that gases, etc. , are exhausted through the side-gap between the flue and cowling and the entrance of rain and other matter (e. g. bird droppings) into the flue is hindered.

In the case of boilers, they are typically connected via a boiler head to a flue.

Boiler manufacturers specify a minimum negative pressure which must be exerted upon the boiler exhaust gases in order for the boiler to operate safely and efficiently. This is typically achieved by having a flue of an appropriate size and capacity. Additional boilers can be connected into an existing flue by means of an appropriate boiler head modification, at which point the total negative pressure exerted on the boilers by the flue may not be sufficient and the boilers might not be able to operate safely or efficiently. The control apparatus for boilers typically includes a pressure sensor which measure the negative pressure exerted on the boiler's exhaust gases, the control apparatus shutting down the boiler if the negative pressure is not great enough, thereby ensuring safe boiler operation.

In such cases where an increased negative pressure must be exerted through a flue and the flow rate through the flue increased, a number of options are currently

available-a new flue can be added, although this can be extremely costly and inconvenient. Alternatively, a fan can be installed in the bottom of the flue near the boiler head to increase the negative pressure on the boiler or boilers and increase the rate of flow through the flue. Such systems are referred to as"Flue Dilution Fans"and exist in two basic formats. A first one involves the installation of a fan in the flue adjacent to the boiler head, and each boiler is provided with a balancing damper. The second involves the provision of a fresh air inlet to the boiler head and a fan in the flue adjacent the boiler hear, with fresh air being brought into the boiler head by the fan, passing each boiler flue to create a sufficient negative pressure on each boiler, and then exiting via the main flue.

Both systems, which are industry standard (see e. g. JCB Control Systems Limited product literature, www. jcb-controls. co. uk), require a fan unit to be placed in the bottom of the flue adjacent the boiler head and boilers.

However, such fans are inherently expensive to install since they require modification to the flue itself, which can be a time-consuming process. In addition, the relatively high gas pressure immediately above the fan can result in a shortening of the lifespan of the flue. The exertion of a positive pressure within the flue is also potentially dangerous since any damage to or holes in the flue can result in the leakage of potentially noxious gases from the flue into surrounding brickwork and masonry and from there into inhabited spaces.

It is also known to position fans on the top of chimney stacks and such fans are produced by the likes of Exhausto (Exhausto, Denmark; www. exhausto. com). However, these fans are designed to be sit on brick chimney stacks and do not fit (without time consuming modification) flue pipes. They are designed to increase flow from chimneys for solid fuel fires, which is highly variable, and not for gas or oil boilers. There is absolutely no suggestion of detecting the rate of flow through the fan, nor of the safety features this provides-there is no inlet tube and therefore no opportunity to have an orifice

plate and pitot ports, and since the units are designed for use with solid fuel fires, it is impossible anyway to switch the fires on or off in the same way that can be done with boilers. Prior art chimney fans are typically unsuitable for flues since they are often heavy and could therefore damage flues, particularly small domestic flues.

The present invention overcomes the prior art disadvantages and provides a flue fan unit with additional advantages.

According to the present invention there is provided a flue fan unit adapted to engage the external terminus of a flue, comprising an inlet tube attached to an upper housing having side vents, at least one fan and fan motor and a cowling.

The fan may have upper and lower impellors, and the side vents may also optionally comprise fan outlet vents and fan inlet vents, the lower impellor urging exhaust gases from the inlet tube through the lower side vents, and the upper impellor urging air into the upper housing through the upper vents and onto the lower impellor.

This fan arrangement provides the significant advantage of providing a flow of cooling air onto the lower impellor which exhausts hot gases from the flue. The amount of cooling air blow onto the lower impellor changes with the rate of gas flow through the lower impellor, so as greater quantities of gases pass through it, more cooling air is blown onto it. This provides the significant advantage of extending the reliability and lifespan of the fan and motor, which are connected upwardly of the upper impellor-the fan is sufficiently cool at this point that it does not conduct too much heat to the fan motor. The cooling effect also means that the fan can be constructed of relatively light materials such as aluminium with lower melting points than heavier materials such as steel.

The flue fan units of the present invention are typically mounted vertically on top of flues. However, they can equally be mounted horizontally e. g. on flues which terminate on a side wall of a building.

Where directions such as"upper"and"side"are used, unless stated otherwise this is made in the context of a vertically orientated flue fan unit, and the terms should clearly be construed as appropriate for flue fn units in non-vertical orientations.

Aluminium displays plastic-like properties at approximately 340 C, and the fan of the present invention, when made of aluminium, is able to operate safely and continuously exhausting gases with temperatures up to e. g. 300 C.

Thus the flue fan unit of the present invention can be constructed from aluminium and be extremely lightweight and suitable for mounting on a wide range of flues without its weight damaging them or requiring additional support to be provided for the flue.

The inlet tube may have located within it an orifice place having upper and lower surfaces and having positioned at the upper and lower surface respectively first and second pitot ports.

The flue fan unit may additional comprise control means for exhaust gas generating means (e. g. a boiler or boilers), the control means comprising a differential pressure sensor engaged with the first and second pitot ports and arranged such that if a predetermined difference in pressure does not exist between the first and second pitot ports when the fan motor is causing the fan to rotate, the exhaust gas generating means is disabled.

The control means can alternatively be provided so that instead of being linked to the exhaust gas generating means, it is simply used to switch the flue fan unit on and off. In either embodiment, the control means can also be provided with alarm means, for example a light, LED, buzzer or suchlike which is activated if the predetermined difference in pressure does not exist between the first and second pitot ports.

Orifice plates and pitot ports are not provided as part of existing chimney or flue fan units. Their inclusion provides an important safety advantage, namely the ability to ensure that there is a sufficient flow of gases through the inlet tube and therefore through the flue and that the flue is therefore not blocked. Flow is determined by detecting a pressure differential between the pitot ports on either side of the orifice plate.

In combination with control means for the exhaust gas generating means (such as a boiler or boilers), this provides an additional safety feature helping to ensure the safe operation of the exhaust gas generating means.

In such a case the e. g. boiler is switched on by first switching on the fan to cause a flow through the flue such that an adequate pressure differential between the first and second pitot ports to prevent the boiler being disabled by the differential pressure sensor is generated. The boiler is then switched on and exhaust gases generated and exhausted from the flue.

The flue fan unit may additional comprises pressure sensing means locatable in the flue adjacent the exhaust gas generating means, the control means controlling the fan motor, and being arranged such that if the pressure detected by the pressure sensing means reaches a first level the rate of turning of the fan is increased.

Thus the flue fan unit can be configured not only to prevent the e. g. boiler from working when the flue is blocked, but can also respond automatically to the amount of exhaust gases being generated and respond by increasing and decreasing fan speed as necessary. If increasing the fan speed fails to achieve a desired pressure, the e. g. boiler or boilers can be shut down. This is not only energy efficient, but also an extremely important safety feature.

Thus the flue fan unit of the present invention may additionally comprise exhaust gas generating means connected to the control means, and the flue.

Also provided according to the present invention is a flue fan unit according to the present invention mounted at the external terminus of a flue.

Also provided according to the present invention is a method for increasing the maximum rate of gaseous flow through a flue, comprising mounting a flue fan unit according to the present invention at the external terminus of the flue.

Also provided according to the present invention is a method of exhausting gases from a flue, comprising mounting a flue fan unit according to the present invention at the external terminus of the flue.

The invention will be further apparent from the following description, with reference to the several figures of the accompanying drawings, which show, by way of example only, one form of flue fan unit.

Of the Figures:

Figure 1 shows a front view of a flue fan unit of the present invention mounted on a flue (section shown); Figure 2 shows a section through a flue fan unit of the present invention; Figure 3 shows side vents of a flue fan unit of the present invention; Figure 4 shows an inlet pipe and orifice plate; Figure 5 shows the arrangement of boiler, flue, flue fan unit and control means; and Figure 6 shows a second embodiment of the present invention, incorporating a constant pressure regulator.

As can be seen from the Figures, in a first embodiment the flue fan unit 10 is mounted at the external terminus of flue 20 and comprises base 30 to which is connected inlet tube 40 containing orifice plate 50 and fist and second pitot ports 60,70. Side vents 80 are attached to base 30 and top cowl 90 is attached to the top of side vents 80. Base 30, side vents 80 and top cowl 90 together define the upper housing of flue fan unit 10. Within the upper housing, mounting ring 100 is attached to side vents 80 between upper fan inlet vents 81 and lower fan outlet vents 82. Attached to mounting ring 100 is secondary inlet 110 upon which is located frame 120 and motor base 130. Motor 140 is located in motor base 130 and fan 150 is attached to it. Fan 150 comprises upper impellor 160 and lower impellor 170 arranged so that as fan 150 is rotated by motor 140, air is urged downwards from upper impellor 160, and radially outwards from lower impellor 170.

Fan input lead 180 is connected to and controls motor 140.

Flue fan unit 10 is optionally secured to flue 20 by securing screw 190.

Base 30, inlet tube 40, top cowl 90, secondary inlet 110 and motor base 130 are constructed from spun aluminium, ensuring their symmetry and simple construction of the flue fan unit 10. Orifice plate 50 is also made from aluminium. Pitot ports/pitot tubes 60,70 are made from stainless steel, as is side vent 80, which is made as a sheet of stainless steel and spot-welded to form a ring.

A typical total weight for a flue fan unit 10 is 12-13 kg. Various sizes (i. e. diameters) of inlet tube 40 can be attached to base 30, meaning that flue fan unit 10 can be adapted to fit any size of flue simply by using the appropriate size of inlet tube 40there is no need for modification of any other part. By ensuring a close or tight fit between flue 20 and inlet tube 40, gases are prevented from escaping between them and instead are exhausted via fan 150. The weight of flue fan unit 10 helps ensure that inlet tube 40 seals the top of flue 20, preventing the escape of gases.

The operation of a flue fan unit 10 of the present invention is shown in Figure 5. Flue fan unit 10 is mounted on flue 20 which in turn is connected to boiler 200.

Instead of being connected directly to boiler 200, boiler control means 210 are connected by boiler control connection 230 to flue fan unit control means 220 which in turn is connected to motor 140 via fan input lead 180. Control means 220 incorporates a differential pressure switch 221 (Beck GmbH, Germany; www. beck-sensors. com; model 930.8x) which is connected to pitot ports/pitot tubes 60,70 and is able to determine any pressure difference between the upper and lower surfaces 51,52 of orifice plate 50.

Control means 220 is connected to boiler 200 via boiler control connection 240.

In use, differential pressure switch 221 is set to the pressure level appropriate for the desired minimum rate of flow through flue 20. Boiler control means 210 comprising a timer and thermostat controls when boiler 200 is to be turned on and off To turn on boiler 200, boiler control means 210 switches on the flue fan unit control means 220, which switches on fan motor 140, causing fan 150 to rotate. Upper impellor 150 causes air to be drawn in through upper fan inlet vents 81 and blown onto lower impellor 170, providing a flow of cooling air onto it as shown by arrow 250. The rotation of lower impellor 170 causes gases in flue 20 to be drawn into inlet tube 40, through hole 260 defined by orifice plate 50 (passing pitot ports 70 and 60 in turn) and to be exhausted through lower fan outlet vents 82 as shown by arrow 270. The flow of gases past orifice plate 50 and pitot ports 70,60 causes a pressure difference between the upper and lower faces 51,52 of orifice plate 50, detectable by differential pressure switch 221 via pitot ports 60,70.

When a sufficient pressure difference is detected, indicative of adequate gaseous flow along flue 20, differential pressure switch 221 switches on boiler 200 via boiler control connection 240. Hot exhaust gases from boiler 200 are then urged from flue 20 by lower impellor 170 of flue fan unit 10 and cooling air is blown onto lower impellor 170 by upper impellor 160, thereby keeping it, upper impellor 160 and motor 140 cool, preventing their overheating and prolonging the operational lifespan of flue fan unit 10.

When boiler 200 is to be switched off by boiler control means 210, this is effected via flue fan unit control means 220 which keeps fan motor 140 running for a short extra period to ensure that all exhaust gases in flue 20 have been expelled.

If flue 20 becomes blocked at any time, or fan motor 140 or fan 150 fail, then the lack of flow past orifice plate 50 is detected by differential pressure switch 221, which causes boiler 200 to be switched off.

In a second embodiment, pressure sensor 280 is placed in flue 20 adjacent boiler 200 and is connected to constant pressure regulator 290, which in turn is connected to flue fan unit control means 220 and acts to ensure that a constant negative pressure is maintained in the flue adjacent boiler 200 by varying the speed of motor 140 according to the detected negative pressure. If, for example, boiler 200 creates too many exhaust gases then the negative pressure will be insufficient and even if differential pressure switch 221 detects an adequate flow past orifice plate 50, boiler 200 is shut down.

To modify an existing flue 20, the cowling is removed from its external terminus and flue fan unit 10 of any of the above embodiments (with an inlet tube 40 of an appropriate diameter) is mounted on flue 20. Control means 210,220 are then easily re-wired as shown in the Figures and boiler 200 (and therefore flue fan unit 10) switched on.

An existing flue 20 can also be modified as above but without the modification of the boiler control means 210, instead flue fan unit 10 simply being provided to enhance flow through the flue, and not control the boiler. In such cases flue fan unit control means 220 can include a warning light, LED and/or buzzer etc. which is activated in the event of differential pressure switch 221 not detecting an adequate pressure difference and therefore gas flow.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible, without departing from the scope thereof as defined by the appended claims.

Claims

1. A flue fan unit adapted to engage the external terminus of a flue, comprising an inlet tube attached to an upper housing having side vents, at least one fan and fan motor and a cowling.

2. A flue fan unit according to claim 1, said vents comprising fan outlet vents and fan inlet vents, said fan having upper and lower impellors, said lower impellor urging exhaust gases from said inlet tube through lower side vents, and said upper impellor urging air into said upper housing through upper vents and onto said lower impellor.

3. A fan unit according to either one of claims 1 or 2, said inlet tube having located within it an orifice plate having upper and lower surfaces and having positioned at said upper and lower surfaces respectively first and second pitot ports.

4. A flue fan unit according to claim 3 additionally comprising control means for exhaust gas generating means, said control means comprising a differential pressure sensor engaged with said first and second pitot ports and arranged such that if a predetermined different in pressure does not exist between said first and second pitot ports when said fan motor is causing said fan to rotate, said exhaust gas generating means is disabled.

5. A flue fan unit according to claim 4, said control means being arranged such that the enabling of said exhaust gas generating means comprises the step of switching on said fan to generate a sufficient pressure difference between said first and second pilot ports that said differential pressure sensor will not disable said exhaust gas generating means, and enabling said exhaust gas generating means.

6. A flue fan unit according to claim 4, additional comprising pressure sensing means locatable in said flue adjacent said exhaust gas generating means, said control means controlling said fan motor, and being arranged such that if the pressure detected by said pressure sensing means reaches a first level the rate of turning of said fan is increased.

7. A flue fan unit according to claim 6, being arranged such that if said pressure detected by said pressure sensing means remains at or above said first level for a predetermined period of time or if it reaches a second level, said exhaust gas generating mens is disabled.

8. A flue fan unit according to any one of claims 4 to 7, said exhaust gas generating means comprising at least one boiler.

9. A flue fan unit according to any of the preceding claims, mounted at the external terminus of a flue.

10. A method of increasing the maximum rate of gaseous flow through a flue, comprising mounting a flue fan unit according to any one of claims 1 to 8 at the external terminus of said flue.

11. A method of exhausting gases from a flue, comprising mounting a flue fan unit according to any one of claims I to 8 at the external terminus of said flue.