GB2120778A

GB2120778A - Outlet device for an air conditioning system

Info

Publication number: GB2120778A
Application number: GB08303677A
Authority: GB
Inventors: Frederick Hugh Howorth
Original assignee: Howorth Air Engineering Ltd
Current assignee: Howorth Air Engineering Ltd
Priority date: 1982-05-20
Filing date: 1983-02-10
Publication date: 1983-12-07
Also published as: GB8303677D0

Abstract

Baffle means 20 surrounding an air outlet 25 are provided with a plurality of perforations 23, 24 through which a proportion D, E of incoming sterile air will pass to enter room 17. This creates a positive outward air pressure around the baffle means 20 and substantially prevents perimeter entrainment of ambient air and mixing of sterile air and ambient air, so that a sterile air zone subsists beneath the air outlet. <IMAGE>

Description

SPECIFICATION Outlet device for air conditioning system This invention relates to an outlet device for use in an air conditioning system.

Air conditioning systems usually regulate the temperature, moisture content and/or purity of air within buildings or parts of buildings e.g. rooms or corridors, hereinafter for convenience all referred to as rooms, by supplying air of requisite quality through ducts and outlet devices to said rooms. In many cases, air conditioning systems also actively remove air which is probably no longer of the correct quality. However, in certain instances, e.g.

hospital operating theatres, the air supplied by the relevant system is simply allowed to diffuse out of the room through doors or other apertures.

A conventional outlet device for an air conditioning system may comprise a simple chamber at the end of an air supply duct. The chamber opens into a room through an aperture in a wall or ceiling surface and extends therefrom to provide a diffuser in the form of an inclined deflector plate to influence the direction of air flow.

When air is emitted from the aforesaid outlet device, the jet of air entering the room from the diffuser gives rise to an area of high pressure in its path and thereby induces ambient air to move towards and become entrained all around the perimeter of the diffuser which is, in comparison, a low pressure area.

Thus, the ambient air rapidly mixes with the emitted air.

When the function of the air conditioning system is the control of temperature and humidity of the air in the room, i.e. climatic control, such rapid mixing is desirable to maintain the required conditions and to minimize draughts caused by a temperature difference between the incoming air and the ambient air. However, when the required function is not climatic control, but the establishment of a clean air zone, e.g. in a hospital operating or treatment room or in a room where medicines are prepared, perimeter entrainment of contaminated ambient air should be prevented.

Air in an operating theatre is a vehicle for bacterial and gaseous contaminants either generated within the theatre or brought in from outside, for example by movement of people and air. Since many of these airborne contaminants may be harmful to patients or to those who work in the operating theatre, it will be appreciated that, on medical grounds, their removal is desirable. In particular, mixing of contaminated air with incoming sterile air and resultant recirculation of contaminants should be minimized.

An object of the present invention is therefore the provision of an outlet device which will allow air to be emitted from an air conditioning system without, or with a minimum of, perimeter entrainment of ambient air so that the mixing of contaminated ambient air with sterile incoming air is substantially obviated.

Pursuant hereto, the present invention provides an outlet device for use in an air conditioning system , said device comprising a chamber having a diffuser in the form of baffle means surrounding an outlet, said baffle means being provided with a plurality of perforations through which air may pass in order to create a positive outward outward pressure around said diffuser and prevent perimeter entrainment of ambient air.

Preferably, the baffle means converge and the perforations are distributed evenly around said baffle means.

Filter means advantageously extend across the chamber in order to ensure sterility of the air emitted from the diffuser.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a part-sectional diagrammatic side view illustrating a conventional outlet device mounted in a ceiling; Figure 2 is a view similar to Fig. 1 illustrating a preferred embodiment of the outlet device according to the present invention mounted in a ceiling; Figure 3 is a view from beneath the device shown in Fig. 2; Figure 4 is a view similar to Fig. 2 but illustrating another embodiment of the invention; and Figure 5 is a view similar to Fig. 2 illustrating a further embodiment of the invention.

As shown in Fig. 1, one type of conventional outlet device comprises a chamber 13, of substantially rectangular cross-section, having a diffuser in the form of four outwardly inclined deflector plates 10 surrounding an opening 18. The chamber 13 is, in use, mounted at the end of an air supply duct 14 of an conditioning system and is seated in an aperture 11 in a false ceiling 12 such that the plates 10 extends into a room 1 7 beneath the ceiling 1 2. When the air conditioning system is operating, air is emitted from the duct 14, through the chamber 1 3 and the opening 18, into the room 17, e.g. an operating theatre, and is deflected by the plates 10 so as to spread outwards as indicated by the arrows A.

In comparison to the high pressure area arising immediately beneath the deflector plates 10 due to the outflow of air, regions 1 5 around the perimeter of the plate 10 are at relatively low pressure so that ambient air tends to flow into the latter regions 15, as indicated by the arrows B. Thus the ambient air mixed with the incoming air in an area around the edges of the deflector plates 10, as indicated by the arrows designated B + A.

The drawing also indicated how the air emitted from the diffuser is deflected outwardly when it reaches the floor 16.

As previously discussed, such perimeter entrainment of ambient air must be avoided in certain outlet devices such as those emitting sterile air into operating theatres, as mixing of contaminated ambient air with clean incoming air is undesirable. Moreover, contaminated air is easily deflected inwardly by a person moving towards the central clean air zone of the room 1 7 from outside said zone.

A preferred embodiment of an outlet device according to the present invention is illustrated in Figs. 2 and 3. This device is shown mounted in a similar manner to the conventional diffuser of Fig. 1, that is to say seated in an aperture 11 in a false ceiling 1 2 and located at the end of an air supply duct 14.

However, in this case, the device comprises a chamber 13, of substantially rectangular cross-section having a diffuser, also of substantially rectangular cross-section, in the form of converging baffle means surrounding an outlet 25 which comprises a perforated plate.

The baffle means consists of four perforated deflector plates or baffles 20 which are arranged so as to form a rectangle and incline inwardly to define the rectangular outlet 25.

Each plate 20 comprises a region 21, adjacent the surface of the ceiling 12, which is inwardly inclined at an angle of approximately 27 to the vertical and has four horizontally arranged rows of small perforations 23. Towards its outer edge, each plate 20 is bent inwardly to form a further region 22 which is inclined at an angle of approximately 48 to the vertical and has two horizontally arranged rows of perforations 24 somewhat larger than the perforations 23 in the region 21. These perforations 23, 24 are evenly distributed around the regions 21, 22. A HEPA (high efficient particulate air) filter 26 extends across the chamber 1 3 above the level of the plates 20.

When the air conditioning system is in use, air flows from the duct 14, through the HEPA filter, where any residual particulate contaminants are removed, and is emitted into a room 17, e.g. an operating theatre, by way of the plates 20. The majority of the air passes through the outlet 25 at a high rate of flow, as indicated by the arrows C. Nevertheless, sufficient resistance is offered to the airflow by the perforated plate forming the outlet 25 that some air is forced to flow through the perforations 23, 24 of the baffle means. The arrows D indicate a low rate of air flow through the small perforations 23 and the arrows E indicate a medium rate of air flow through the larger perforations 24.

In this manner, there is a positive outward pressure of air all around the perimeter of the perimeter of the diffuser so that entrainment of the ambient air in this region and mixing of contaminated ambient air with sterile incoming air is prevented. The outward deflection of the air when it reaches a floor 16 is indicated in Fig. 2.

The invention is not limited to the foregoing details and variations are possible. For example, the diffuser may be substantially circular in cross-section, as illustrated in Fig.

4. Also, as illustrated in that same drawing, the outlet 25 may be formed of a foamed plastics layer resting on, and possibly attached to a supporting wire mesh. Furthermore, the baffles may diverge, as shown in Fig. 5. In each of these Figs, the same reference numerals have been used as in Figs. 2 and 3 to denote similar parts.

The size of the perforations may vary as appropriate from one region of the baffles to another (not necessarily as illustrated) so that a sufficient air flow is achieved, dependant on the air source velocity, to prevent perimeter entrainment of ambient air. However, in some cases, the perforations may all be of equal size. Also, provision of a HEPA filter and a more steeply inclined outer edge region of each plate or baffle are optional and may be dispensed with in further embodiments of the invention.

Moreover, of course, the size, shape and number of the plates or baffles may differ. For example, there may be one angled plate or baffle or several plates fastened together thereby forming a diffuser of substantially circular cross-section, or 3, or 5 plates or baffles forming diffusers of triangular, pentagonal or other polygonal cross-section.

Claims

1. An outlet device for use in an air conditioning system, said device comprising a chamber having a diffuser in the form of baffle means surrounding an outlet, said baffle means being provided with a plurality of perforations through which air may pass in order to create a positive outward pressure around said diffuser.

2. An outlet device as claimed in claim 1 wherein the baffle means converge.

3. An outlet device as claimed in claim 1 or 2 wherein the perforations are distributed evenly around the baffle means.

4. An outlet device as claimed in claim 1, 2 or 3 wherein the perforations vary in size from one location on the baffle means to another so as to achieve a sufficient air flow through the baffle means to create a positive outward pressure all around the perimeter of the diffuser.

5. An outlet device as claimed in any preceding claim wherein filter means extend across the chamber.

6. An outlet device substantially as hereinbefore described with reference to and as illustrated in Figs. 2 and 3 or in Fig. 4 or in Fig. 5 of the accompanying drawings.