GB2040034A - Natural ventilators - Google Patents

Abstract

A natural ventilator surmounting a ventilator gap 14 in the roof of a building has convex outer side walls 30 and an upwardly divergent sided central structure 32 above spaced ventilator throat walls 38, all following the axis of the gap 14. Upper edges 50 of the throat walls 38 are outwardly flared to train air to each side of the central structure 32 and curved or bent upper baffles 64 guide air past upper edges 52 of the central structure. Those upper edges 52 are also preferably curved to assist and train air flow in avoiding turbulence. Also curved guides 60, 62 can be provided in from the ventilator throat into airways to each side of the central structure 32. The latter guides 60, 62 are shown pivotted to be capable of blocking-off the ventilator gap. The ventilator may be for a foundry. <IMAGE>

Description

SPECIFICATION Natural ventilators The invention relates to the ventilation systems of the so-called 'natural' type where airflow through a building is principally controlled by the heat generated within the building, i.e. the airflow is not powered by fans associated with the venilation system. Such systems are also called 'gravity flow' systems.

Such ventilating systems comprise air exit structures which are mounted above ventilation gaps or 'throats' in the roofs or buildings. Such ventilators are frequently disposed along the ridge of a ridged roof building above an elongated ventilation gap and are referred to as roof ventilators. Such roof ventilators, in operation, exhaust large volumes or air at low velocity into the atmosphere. The roof ventilator structure consists of a large static superstructure above the roof which functions to direct the exhausting air from the building and also functions to inhibit ingress of moisture and atmospheric debris into the building through the ventilator throat.

This latter function is referred to as weatherproofing.

Baffle-elements of prior art ventilator structures accomplished the weatherproofing function but interfered with the air flow efficiency.

An object of the invention is to provide a natural ventilator structure which achieves a better compromise in the conflict between the need for weatherproofing and the desirability for achieving efficient air flow characteristics for the exhausting air through the ventilator structure.

Toward this end, the present invention combines certain features in an otherwise commonplace roof ventilator which includes a ventilator gap extended in the roof of the building and an improved ventilator structure which is mounted above the ventilator gap.

The structure includes: two spaced parallel ventilator throat walls extending along the ventilator gap, said throat walls having outwardly flared upper lips; two spaced, parallel vantilator side walls each disposed outwardly of a different one of the ventilator throat walls, and together constituting a pair of inwardly concave surfaces extending parallel to the longitudinal axis of the ventilator gap;; a central longitudinal structure between the ventilator side walls and above the ventilator gap, the said central longitudinal structure being formed from a pair of upwardly diverging surfaces which are joined at lower edges, parallel to the longitudinal axis of the ventilator gap and symmetrically disposed above the ventilator gap, the free outer edges of the divergent surfaces being disposed at approximately that level above the ventilator gap where the inwardly concave ventilator side walls are spaced farthest apart; and two elongate curved or bent airflow guiding vanes, each disposed between outer edges of a different one of said divergent surfaces and the adjacent ventilator side wall, and each extending from a level above the adjacent free outer edge to a level below that adjacent free outer edge.

Recent experiments with ventilator prototypes have indicated that the airflow improvements occur when the following features are used together in a roof ventilator: First, the provision of outwardly flared upper lips on the ventilator throat walls tends to minimise generation of turbulance at the upper rim of the ventilator throat; Second, the upwardly diverging surfaces of the central longitudinal structure splits the exiting air flow uniformly; Third, curved or bent air flow guiding vanes tend to distribute the exhaust air across the available area of the ventilator structure without substantial turbulence.

The aforementioned features in combination can ensure that there is no straight line for rain access from the upper edge of the ventilator side walls and/or the upper edge of the elongate curved or bent air-guiding vanes into the ventilator throat.

Preferably, said free outer edges of the upwardly diverging surfaces have arcuate or bent extensions terminating at a level below upper edges of said curved or bent air flow guiding vanes. These edge extensions constitute a fourth feature to minimise generation of turbulence in the central region of the ventilator structure.

These four features should be combined with the ventilator side walls in such fashion that the available cross-sectional area for air flow at every level through the ventilator structure is at least as great as the cross-sectional area of the ventilator gap. Preferably, such cross-sectional area progressively increases at least above the level of the outer edges of the upwardly diverging surfaces i.e. tangent or extension lines from end parts of the outer side walls and adjacent arcuate or bent edge extensions of the upwardly divergent surfaces make an acute angle.

Normally, the spacing between the two free edges of the upwardly diverging surfaces is wider than the ventilator gap. The central longitudinal structure combines with the curved or bent air flow guiding vanes, the ventilator side walls and the ventilator throat walls to provide weatherproofing for the resulting ventilator structure.

In one embodiment the central longitudinal structure forms a central gutter above the lower edge connection of the two surfaces for collecting and diverting atmospheric moisture and debris. In an alternative embodiment the central longitudinal structure may be capped with a domed or ridged roof surface for diverting atmospheric moisture and debris outwardly away from the ventilator gap.

In an alternative embodiment, optional airflow guiding vanes may be disposed near the upper level of the ventilator gap between the throat walls and flared to each side of said lower edge connection.

These optional airflow guiding vanes preferably are pivoted or hinged to function as ventilator closing members for use when the ventilator is inactive.

The elongate curved or bent airflow guiding vanes may be closer to the outer ends of the upwardly diverging surfaces than to the ventilator side walls and then serve to increase efficiency of the ventilator (see Figure 4).

Specific embodiments of the invention will now be described with reference to the accompanying drawings in which: Figures land 1A are plan and isometric views respectively of a natural ventilator installation on a ridged roof building; Figure 2 is an end elevation of the structure shown in Figure 1; Figure 3 is a diagrammatic section along the line A-A of Figure 1; Figure 4 is a diagrammatic section, similar to Figure 3, showing a particular prototype ventilator.

Figures 1, 1A and 2 show an industrial installation for a factory or workshop, such as a foundry, wherein a building 10 typically has dimensions of 40 metres long by 20 metres wide and about 10 metres high to the ridge of a roof 12. Over a substantial portion of the length of the roof 12, there is a central ventilator gap 14 above which is mounted the roof ventilator structure 18 which is customarily formed from several interconnected modules 20. Ventilation air inlets for the building 10 are provided by louvred grills 22 in the side walls and/or end walls. The ventilator structure 18 is secured to the structural framework of the building 10 and includes interior steel structural framing members, not shown. Suitable flashing members are installed at 16 (Figure 2) to provide a weather resistant assembly.

The dimensions, proportions and general nature ofthe activities carried on within a building will determine the required size of the ventilator gap 14 and the size of the air inlets such as louvred grills 22.

In general the central gap 14will have a width of one to five metres. The width of the gap 14 is further dependent upon the efficiency of the ventilator structure 18. The improvements resulting from the present invention are significant since improved air flow efficiency permits the use of smaller size ventilators which are less expensive in themselves and which require less building reinforcement for support, thus providing a further cost saving.

Characteristic features of the ventilators employing this invention are shown in Figure 3. The ventilator structure 18 is fabricated from sheet metal elements which are fastened to structural steel framing members, not shown. The ventilator includes ventilator side walls 30 of generally convex shape. The ventilator gap 14 includes interior ventilator throat walls 24 and exterior ventilator throat walls 38 which include flashing members 40, extending over the building roof 12, and outwardly flared upper lips 50. The ridge 26 of the building is indicated by the intersection of the broken lines 28.

A central longitudinal structure 32 is fabricated from a first surface 46 and a second surface 48 which diverge upwardly and are connected (42) at lower edges extending parallel to the ridge 26. The central longitudinal structure 32 is disposed symmetrically above the ridge 26 of the building. The first surface 46 and second surface 48 have upwardly arcuate outer edge extensions 52 which are disposed at a level above the ridge 26 approximating that level where the ventilator side walls 30 are farthest apart as indicated by the broken line 34. A pair of curved or bent airflow guiding vanes 64 is disposed, one each between an arcuate outer edge extension 52 and the adjacent ventilator side wall 30. The upper edge 65 of each curved or bent airflow guiding vanes 64 is positioned above the broken line 34, i.e. above the level of the arcuate outer edge extensions 52.The bottom edge 66 of each curved or bent airflow guiding vane 64 is positioned below the broken line 34, i.e. above the level of the arcuate outer edges 52.

It will be observed that the bottom edges 68 of the ventilator side walls 30 are disposed outwardly and below the outwardly flared upper lips 50. It will further be observed that the arcuate outer edge extensions 52 are disposed above and outside the outwardly flared upper lips 50. It will further be observed that the bottom edges 66 of the arcuate or bent air flow guiding vanes 64 are disposed so that they are vertically above an inner surface of the ventilator side wall 30 whereby any moisture which may collect on the curved or bent air flow guiding vane 64 will drop onto the inner surface of a ventilator side wall 30 and thence will be diverted by the roof flashing 40 to run off over the ridged roof 12.

As shown in Figure 3, the first surface 46 and the second surface 48 combine at 42 to form a gutter which collects atmospheric moisture and debris falling between the arcuate outer edge extensions 52. Suitable means, such as a downspout, not shown, are provided for diverting accumulated moisture and atmospheric debris from the gutter above the apex 42. As an alternative embodiment, the central longitudinal structure 32 may be provided with a ridged or domed roof surface 44 which combines, at its edges, with the surfaces 46,48 to form two water diverting channels 54.

The curved or bent air flow directing vanes 64 preferably are curved in relatively small size ventilators and preferably are bent in large size ventilators, the bending being carried out in successive bends so as to minimise turbulence of the exhaust air flowing through the ventilator.

As an optional further embodiment of the present invention, airflow guiding vanes 60,62 may be disposed one each between a ventilator throat wall 38 and the position 42. In the open position as shown in Figure 3, the optional airflow guiding vanes 60 provide some slight improvement in airflow efficiency through the ventilator structure 18. However' in their closed positions as shown in the phantom outline 60', 62' or 60", the optional airflow guiding vanes serve to close off the ventilator structure 18 when not in use. In one alternative closed position, the optional airflow guiding vanes 60', 62' close off the air flow space between the ventilator throat wall 38 and the adjoining one of the surfaces 46,48. In the other alternative closing position, the optional air flow guiding vanes 60" close off the ventilator gap 14 independently of the central longitudinal structure 32.

Prototype testing Prototype ventilator structures constructed as indicated in Figure 4 and operated at flow rate Reynolds numbers from 18,000 to 4000,000 across the throat gave a discharge coefficient from 0.6 to 0.65, which is significantly and surprisingly better than hitherto for natural ventilators (approximately 0.4 to 0.5) especially with very low air speeds.

In Figure 4, arc centres A, B, C, D are positioned as shown for establising the circular shape of (A) the arcuate throat rim 50; (C) the arcuate outer edge extensions 52; (D) the curved air flow guiding vane 64; and (B) the ventilator side walls 30. The upper edge 65 of the curved airflow guiding vane 64 is a flat surface.

It will be noted that the spacings between extensions 52 and the side walls 30 are each at least one half of the throat width.

For Figure 4 there was a ratio of length to throat width of above 4.0.

The ventilators as shown in the drawings are mounted symmetrically in and along the ridge of a ridged roof. They could, however, also be used offset from the ridge but parallel thereto, or at an angle to the ridge, particularly at right angles extending down from the ridge. Also they can be used on flat roofs.

Claims (12)

1. A natural ventilator in the form of a structure surmounting a ventilator gap in the roof of a building, comprising: two spaced parallel ventilator throat walls extending along the ventilator gap, said throat walls having outwardly flared upper lips; two spaced, parallel ventilator side walls each disposed outwardly of a different one of the ventilator throat walls, and together constituting a pair of inwardly concave surfaces extending parallel to the longitudinal axis of the ventilator gap; a central longitudinal structure between the ventilator side walls and above the ventilator gap, the said central longitudinal structure being formed from a pair of upwardly diverging surfaces which are joined at lower edges, parallel to the longitudinal axis of the ventilator gap and symmetrically disposed above the ventilator gap; the free outer edges of the divergent surfaces being disposed at approximately that level above the ventilator gap where the inwardly concave ventilator side walls are spaced farthest apart; two elongate curved or bent air flow guiding vanes, each disposed between a different one of said arcuate outer edges of the divergent surfaces and the adjacent ventilator side wall, and each extending from a level above the adjacent free outer edge to a level below that adjacent outer edge.

2. A natural ventilator according to claim 1, wherein said free outer edges of the upwardly diverging surfaces have arcuate or bent edge extensions terminating below upper edges of said curved or bent air-flow guiding vanes.

3. A natural ventilator according to claim 2, wherein tangent or extension lines from end parts of the ventilator side walls and adjacent arcuate or bent extension of the upwardly diverging surfaces make an arcuate angle to ensure that available crosssectional area for airflow thereabove progressively increases.

4. A natural ventilator according to claim 1,2 or 3, wherein lower edges of the said airflow guiding vanes are disposed outwardly from the said outwardly flared upper lips of the throat walls and further disposed vertically above the lower inner surfaces of the adjacent ventilator side wall.

5. A natural ventilator according to claim 2, wherein a ridged or dome-shaped cap is provided above the said central longitudinal structure and gutters are provided along each side of the central longitudinal structure between the dome or cap and the adjoining arcuate or bent outer edge extension.

6. A natural ventilator according to any preceding claim, wherein the minimum spacings between the free outer edges of the upwardly diverging surfaces and the adjacent inwardly concave surfaces are each at least one half of the width between the throat walls.

7. A natural ventilator according to any preceding claim, wherein the coefficient of dishcarge exceeds 0.6.

8. A natural ventilator according to any preceding claim, wherein two spaced elongate airflow guiding vanes are disposed each extending between a different one of the ventilator throat walls and the joined lower edges of the central longitudinal structure.

9. A natural ventilator according to claim 8, wherein the last-mentioned two airflow guiding vanes are pivotal between a first position wherein they assist the flow of air upwardly through the ventilator throat and an alternative position wherein the said air flow guiding vanes obstruct the ventilator throat.

10. A natural ventilator according to any preceding claim, wherein the elongate curved or bent air-guiding vanes are closer to outer ends of the upwardly diverging surfaces than to the ventilator side walls.

11. A natural ventilator according to any preceding claim for use in connection with a ridged roof building wherein the ventilator gap extends along the ridge of the roof.

12. A natural ventilator arranged and adapted to operate substantially as herein described with reference to and as shown in the accompanying drawings.