GB2344164A - Ventilator cowl - Google Patents

Abstract

A ventilator cowl in which a baffle structure provides resistance to high rates of flow resulting from high atmospheric wind speeds. The baffle structure is mounted adjacent an outer end of an opening (3) in an external wall of a space to be ventilated. The baffle structure is annular and defines a series of passages each of which extends from an open outer end to a space that is located in register with the outer end of the opening. The arrangement is such that air flowing through the opening must flow through the passages defined by the annular baffle structure. Each of the passages is shaped to resist high rates of flow by causing the direction of flow of air within the passage to change as the air passes along the length of the passage. Each of the passages may be defined between a pair of radially extending walls (11) and a series of four circumferentially extending walls (12,13,14,15). The baffle is located within a housing having inlet louvres (8) at either end.

Description

VENTILATOR COWL The present invention relates to a ventilator cowl, and in particular to a ventilator cowl which can be used to reduce unwanted drafts through ventilator openings.

Fuel burning units such as central heating boilers and gas fired room heaters must be provided with an adequate supply of combustion air. Many such units rely upon the supply of combustion air from the space in which the units are located, for example a boiler room in which a central heating boiler is located or a living room in which a space heater is located. It is normal practice to provide ventilators through the walls of any such spaces so that combustion air can flow through those ventilators to the combustion units. Various regulations have been established to ensure that the ventilators are capable of providing a supply of air appropriate to the particular combustion unit.

Where ventilators are provided in purpose built boiler house walls, if drafts are caused within the boiler house this is not a particular problem. Where ventilators are provided in the walls of living rooms however drafts can be a real problem.

Ventilators are dimensioned to provide an appropriate supply of combustion air assuming that the external wind speed is zero but this is often not the case and in some circumstances high winds can cause very large drafts to enter living rooms through ventilators provided to supply combustion air to combustion units located in those living rooms.

The problem with unwanted drafts associated with ventilators has been addressed by providing ventilator ducts in which baffle plates are incorporated, the baffle plates being located to force air passing through the ventilator to change direction as it progresses along the length of the ventilator. Typically such arrangements incorporate a tubular pipe-like body which in use is inserted in a wall of the space to be ventilated. Baffle walls are provided inside the tubular body. In one arrangement, a series of simple baffle walls are provided spaced apart along the length of the tubular body, each of the baffle walls occupying slightly over half of the crosssectional area of the tubular body. In another arrangement, baffle walls define three passages connected end to end, the intermediate passage conveying air in the opposite direction to the other passages. As a result, air flowing initially axially along the length of the tubular body must turn through a series of corners so as to negotiate the obstructions presented by the baffle walls. Such an arrangement does reduce the magnitude of unwanted drafts to an extent, but unfortunately given that the baffle walls partially obstruct the passage through the tubular body, if the necessary free cross-sectional area of the ventilator for a particular application is to be achieved the outside diameter of the tubular body must be considerably greater than would be necessary if the tubular body was a simple open pipe.

It is an object of the present invention to obviate or mitigate the problems outlined above.

According to the present invention there is provided a ventilator cowl comprising a baffle structure which in use is mounted adjacent an outer end of an opening in an external wall of a space to be ventilated, wherein the baffle structure is annular and defines a series of passages each of which extends from an open outer end to a space that in use is located over the outer end of the opening such that air flowing through the opening must flow through the passages, each of the passages being shaped to cause the direction of flow of air within the passage to change as the air passes along the length of the passage.

The annular baffle structure does not have to define a circular shape. The baffle structure may comprise a base defining an aperture which in use is in register with the opening, a cover spaced from the base, and an array of walls extending between the base and the cover and defining the passages between the base and the cover, the walls being arranged such that air flowing through any passage is caused to flow along a circuitous path. The cover and base may be interconnected by top and bottom walls spaced from and extending respectively over and beneath the baffle walls.

Arrays of walls defining louvres may extend between the top and bottom walls, the louvres being arranged so as to be inclined downwards in the direction away from the baffle walls. Each passage may be defined between a pair of side walls extending inwards from the outer end of the passage and a series of baffle walls spaced apart in the direction of air flow and extending alternately from each of the side walls. The side walls may extend in the radial direction relative to a point which is centrally located in the said space and the baffle walls may extend in the circumferential direction. Each passageway may incorporate for example four baffle walls.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which ; Figure 1 is a perspective outside view of a cowl embodying the present invention; Figure 2 is a vertical section in the plane indicated by lines 2 in Figure l ; Figure 3 is a section through the ventilator cowl of Figure I in the direction indicated by lines 3 in Figure 2; Figure 4 plots the relationship between the average ventilator flow velocity and wind velocity assuming a wind directed against the ventilator cowl in a direction perpendicular to a wall on which the cowl is mounted; and Figure 5 plots the relationship between the pressure differential across the ventilator cowl and energising voltage applied to a fan used to establish that differential pressure.

Referring to Figures I to 3, the illustrated embodiment of the invention comprises a planar cover 1, a planar base 2 in which a circular opening 3 has been formed, a top wall 4, and a bottom wall 5. In use of the device, the wall 4 will be generally horizontal and uppermost. The base 2 will be secured against a wall so that the opening 3 registers with a ventilator pipe extending through the wall on which the cowl is mounted, the ventilator pipe not projecting beyond the ends of the opening in the wall. Figure 3 shows the position of the opening 3 relative to the ventilator pipe 6 extending through an opening in a wall 7.

The cover 1 and base 2 are interconnected by an array of walls best shown in section in Figure 2. Vertically extending louvres are defined along each vertical side edge of the cowl by walls 8 which are inclined downwards towards the side edges of the cover I and base 2. This arrangement prevents for example snow or leaves drifting into the space between the cover I and base 2 and obstructing air flow. A further series of walls extends between the cover 1 and base 2 and defines an annular baffle assembly extending around and radially outwards from the edge of the opening 3. In the illustrated case these further walls define thirteen passageways of identical configuration extending from an outer opening 9 to an inner opening 10. Each passage defined between the openings 9 and 10 is circuitous as a result of the passage being defined between two radially extending walls 11 and a series of four circumferentially extending walls 12,13,14 and 15. Air entering the opening 9 first has to turn through 90 to pass between walls 14 and 15, then has to turn through 180 around the lower edge of the wall 14, then has to turn through 180 around the upper edge of the wall 13, and then has to turn through 90 to pass through the inner opening 10. Given such a passage configuration, any air driven by wind into the opening 9 will lose much of its kinetic energy before entering the space defined within the radially innermost wall 12 over the opening 3. Accordingly the effects of wind speed on flow rate through the cowl will be substantially suppressed.

Figure 4 shows the results of tests conducted to assess the performance of embodiments of the present invention as compared with currently used prior art structures in which baffle walls are formed within a ventilator tube extending through a wall of a space to be ventilated, the baffle walls of the prior art structure defining a first passage section extending towards the inner face of the wall, a second section connected end to end with the first section and extending towards the outer surface of the wall, and a third section connected end to end with the second section and extending to the inner surface of the wall. Figure 4 plots the average flow velocity through the ventilator cowl in metres per second given exposure of the cowl to a wind directly facing the outer surface of the wall through which the ventilator pipe extends.

Curve 16 shows the experimental results achieved with the prior art structure and curve 17 shows the experimental results obtained with an embodiment of the present invention as described with reference to Figures 1 to 3 and sized to provide a free cross-section for the ventilator pipe equal to that of the prior art device responsible for producing the results represented by line 16. Lines 18 and 19 show similar figures for smaller capacity devices respectively in the form of the prior art structure and the embodiment of the invention. The experimental results clearly show that performance of embodiments of the present invention is very much better than that of the conventional baffle structures.

Referring to Figure 5, this shows experimental results achieved using a conventional baffle such as that responsible for the results represented by lines 16 and 18 of Figure 4 and a cowl in accordance with the present invention. The conventional structure produced the results represented by line 20 and the embodiment of the present invention produced the results represented by the line 21. The lines plot the variation of differential pressure across the ventilator for a given applied voltage to a fan pumping air into a chamber from which air could escape through the ventilator cowl. It will be seen that for the same flow rates (corresponding to the same voltages applied to the fan rotor) the conventional baffle structure required a much larger pressure differential. The results represented in Figure 5 were obtained using a conventional baffle located within a ventilator pipe having an internal diameter of 7.5cm and a ventilator cowl in accordance with the present invention fitted over the end of a pipe also of 7.5cm internal diameter. Thus it can be seen that embodiments of the present invention present much less resistance to air flow as compared with conventional devices assuming the same size of ventilator pipe.

It is highly advantageous to be able to meet the ventilation requirement of a particular application using a relatively small diameter pipe. Not only is it easier to find a location appropriate to fit a relatively small pipe as compared with a relatively large pipe, but the installation costs of a small pipe are also substantially less than those of a large pipe. The present invention makes it possible to use a relatively small pipe to meet a particular ventilation requirement whilst at the same time ensuring that drafts are reduced.

Claims (8)

1. CLAIMS 1. A ventilator cowl comprising a baffle structure which in use is mounted adjacent an outer end of an opening in an external wall of a space to be ventilated, wherein the baffle structure is annular and defines a series of passages each of which extends from an open outer end to a space that in use is located over the outer end of the opening such that air flowing through the opening must flow through the passages, each of the passages being shaped to cause the direction of flow of air within the passage to change as the air passes along the length of the passage.
2. 2. A ventilator cowl according to claim 1, wherein the baffle structure comprises a base defining an aperture which in use is in register with the opening, a cover spaced from the base, and an array of walls extending between the base and the cover and defining the passages between the base and the cover, the walls being arranged such that air flowing through any passage is caused to flow along a circuitous path.
3. 3. A ventilator cowl according to claim 1, wherein the cover and base are interconnected by top and bottom walls spaced from and extending respectively over and beneath the baffle walls.
4. 4. A ventilator cowl according to claim 3, wherein arrays of walls defining louvres extend between the top and bottom walls, the louvres being arranged so as to be inclined downwards in the direction away from the baffle walls.
5. 5. A ventilator cowl according to claim 2,3 or 4, wherein each passage is defined between a pair of side walls extending inwards from the outer end of the passage and a series of baffle walls spaced apart in the direction of air flow and extending alternately from each of the side walls.
6. 6. A ventilator cowl according to claim 5, wherein the side walls extend in the radial direction relative to a point which is centrally located in the said space and the baffle walls extend in the circumferential direction.
7. 7. A ventilator cowl according to claim 5 or 6, wherein each passageway incorporates four baffle walls.
8. 8. A ventilator cowl substantially as hereinbefore described with reference to the accompanyingdrawings.