Supply Air Device For Injection Of Perferably Cold Ventilation Air

Abstract

An air supply device adapted to be mounted in a hung ceiling for injecting cold air from a duct extending parallel to the ceiling surface above the hung ceiling. The device consists of a pressure box having an air distribution chamber in its bottom formed between a pair of perforated plates which operate to distribute the air vertically downward and eliminate any horizontal component generated in the duct. To avoid the fouling of the ceiling surface surrounding the distribution chamber by the dirty secondary room air, airflow gaps are provided surrounding the distribution chamber to inject air streams substantially parallel to the ceiling surface radiating outwardly from the distribution chamber. Airflow-regulating means are provided in each gap and in the distribution chamber to insure mixture of the air with secondary room air so as to avoid the draughts normally experienced from cold air inlet grilles.

Description

This invention relates to a supply air device for injecting preferably cold ventilation air into rooms which should be draught-free in the dwelling zone, It comprises a pressure box mortised in the ceiling of the room, which is connected to a drum system for supply of the ventilation air, said pressure box downwardly being defined by and communicating with the room through an air distribution means.

The supply air device according to the invention is intended primarily for supplying rooms requiring permanent cooling with cold ventilation air. Such rooms may be, for example, large office rooms which owing to heat emission from light fittings and human beings require cooling all the year round, or so-called internal zones which are surrounded on all sides by rooms heated in winter and which include such heat sources that said zones must be cooled even in the coldest days of the winter.

The cold ventilation air is heavy and, after its discharge from the supply air device mounted in the ceiling, it has, therefore, a strong tendency of rapidly sinking to the floor of the room where it causes an unpleasant draught before it is mixed with the room air. The draught problem is particularly great in rooms with a low ceiling height.

An essential object of the present invention is, therefore, to produce a supply air device with a short throw (length). This applies particularly to air directed to the dwelling zone where the air speed must not exceed 0.15 m./sec., but also the air directed along the ceiling surface should have a short throw (length) in order not to cause draught.

The supply air device is intended for use in rooms with a subceiling construction where the pressure box is mounted in the space above the subceiling. For aesthetical reasons, the supply air device must not project downwardly very much from the surface of the subceiling (for embodiments now in use a distance of 20 mm. has been deemed acceptable). Therefore, the pressure box has to be given a small height (at maximum 250 mm.). This implies great difficulties in eliminating the influence of the dynamic pressure of the supplied air before supplying the ventilation air. Furthermore, it must be possible to mortise the supply air device in ceilings covered by square, possibly sound-damping plates, so that the supply air device is used instead of such a plate. Therefore, the device must have a size of, for example, 600.times. 600 mm. The air is supplied to the pressure box through an air duct placed in the space above the subceiling and having a diameter of about 150 mm. Owing to the height dimension of the supply air device, and because for the same reason the supply duct usually is to be connected to one of the sidewalls of the pressure box, the dynamic pressure of the air supplied has a great tendency of being propagated through the air distribution means of the supply air device and giving rise to a concentrated jet of cold air in the room, which is inconvenient from a draught point of view.

Ventilation air injected into a room through a supply air device ejects with itself room air, thereby causing secondary airstreams in the room. The coejected room air, however, is not as clean as the injected ventilation air, but includes a great amount of dust particles which deposit on surfaces swept by the secondary airstreams. Particularly exposed to such deposits are the supply air device surfaces swept by secondary air and the ceiling surface around the supply air device.

The present invention has as its object to produce a supply air device of the aforementioned kind, which independent of the dynamic pressure in the pressure box effects good distribution of the injected cold ventilation air in the room and a short throw length of said air, and which prevents the supply air device proper and the ceiling surface around the same from being fouled. The invention is characterized in that the air distribution means comprises two perforated metal sheets mounted substantially horizontally somewhat spaced from each other and arranged so as together with sidewalls along their edges to enclose a distribution chamber for eliminating obliquely directed speed components in the airstream passing through said metal sheets and for uniformly distributing said airstream, and gaps around the perforated metal sheets outside said sidewalls, said gaps being provided with dampers for controlling the air amount flowing through the gap in question and adapted at opened dampers to inject air fogs substantially in parallel with the ceiling surface of the room.

The air fogs injected through the gaps around the perforated metal sheets eject with themselves the air (amount) flowing into the room through the perforated metal sheets and thereby prevent said air (amount) from directly flowing down into the dwelling zone and causing draft. Since, on the other hand, energy is consumed thereby for deflecting the air injected through the perforated metal sheets, the air fogs injected through the gaps will have a short throw length.

The air distribution in the room can be adjusted by means of the dampers in the gaps.

In addition to the aforesaid advantages it is achieved, that the air injected through the perforated metal sheets prevents the coejected room air from sweeping the supply air device and surrounding ceiling surface and from fouling the same.

Due to the fact that two parallel perforated metal sheets are used for distributing the air injected downwardly into the room, the high dynamic pressure locally prevailing in the pressure box is effectively balanced.

An expedient embodiment of the invention is characterized in that the uppermost of the two perforated metal sheets has a substantially smaller degree of perforation, i.e. a smaller area of air passage, than the lowermost perforated metal sheet, preferably only one-fifth of the perforation degree of the lowermost metal sheet.

This additionally improves the capacity of the air distribution means to eliminate the detrimental effect of the dynamic pressure in the pressure box on the air distribution in the room.

The uppermost of the two perforated metal sheets preferably may be provided with means for adjustably screening off the perforation openings whereby the perforation degree of said metal sheet can be varied. Said screening, for example, may be effected by a similar perforated metal sheet adapted to be moved adjacent the uppermost perforated metal sheet according to above, or by means of exchangeable unperforated metal sheets provided with a single-large opening, in such a manner, that the openings of the exchangeable metal sheets are of different size in relation to each other.

In order to prevent the air fogs ejected from the gaps around the perforated metal sheets to sweep the ceiling surface immediately adjacent the supply air device and to foul said surface by coejected room air, said gaps can be defined toward the ceiling surface by an edge plate projecting from the ceiling surface.

The invention is described in greater detail in the following, with reference to the accompanying drawing showing by way of example an embodiment of a supply air device for applying the idea of the invention, in which drawing

FIG. 1 shows a cross section of the supply air device mounted in a subceiling construction, and

FIG. 2 shows a section through the supply air device along the line II--II in FIG. 1.

In the drawing, the supply air device according to the invention is designated by 1. The supply air device comprises a pressure box 4 mortised in the subceiling 3 of a room 2, which pressure box is connected to a drum system for the supply of ventilation air via an air duct 5. The pressure box 4 is downwardly defined by and communicates with the room 2 through an air distribution means 6. According to the invention, the air distribution means 6 comprises two perforated metal sheets 7 and 8 mounted horizontally somewhat spaced from each other and arranged so as together with sidewalls 9 along their edges to enclose a distribution chamber 10, further gaps 11 around said perforated metal sheets 7 and 8 outside said sidewalls, which gaps are provided with dampers 12 and adapted at opened dampers to inject air fogs 13 substantially in parallel with the ceiling surface 3a of the room. The distribution chamber 10 is intended, in addition to a uniform distribution of the airstream 14 passing through the perforated metal sheets 7 and 8 also to effect the elimination of obliquely directed speed components in said airstream, which components are caused by the dynamic pressure in the airstream supplied through the air duct 5. The dampers 12 are intended for control of the air amount 13 flowing through the gap 11 in question. Hereby the flow pattern in the room 2 can be adjusted in a simple way and the cold ventilation air can so be directed that it does not give rise to draught in the room. The cold airstream 14 downwardly injected through the perforated metal sheets 7 and 8 is ejected together with the air fogs 13 injected through the gaps 11. Hereby said cold airstream is kept away from the dwelling zone and the entire injected air amount is caused to flow along the ceiling surface 3a to which the airstreams are attracted. Owing to the energy loss at the deflection and coejection of the downwardly injected airstream 14, the air fogs 13 have a short throw (length). Room air is also coejected (see the arrows 15), but due to the downwardly injected airstream 14 the room air is prevented from sweeping and fouling the supply air device 1 and the ceiling surface 3a around the same.

The uppermost perforated metal sheet 7 has a substantially smaller degree of perforation than the lowermost metal sheet 8, in order, prior to the injection into room 2, safely to eliminate the obliquely directed speed components caused in the air (amount) flowing through the perforated metal sheets 7 and 8 by the dynamic pressure in the pressure box 4. A ratio of 1:5 between the perforation degrees of the uppermost and lowermost perforated metal sheets has proved to render the best results.

In certain cases it may be suitable that the air passage area of the uppermost perforated metal sheet 7 is adjustable. This can be achieved in different ways. In FIG. 1 an exchangeable perforated metal sheet 16 adapted variably to screen off the perforation openings in the perforated metal sheet 7 is indicated by dashed lines.

In order to prevent the air fog 13 ejected from the gap 11 in question to sweep the ceiling surface immediately adjacent the supply air device 1, the gaps 11 are defined toward the ceiling surface 3a by an edge plate 17 projecting from the ceiling surface. The injected ventilation air, it is true, usually is filtered, but by said edge plate also the remaining dust particles and those from the coejected room air are prevented from appreciably fouling the ceiling surface, because they are caused by the edge plate to spread over a larger area before they meet the ceiling.

An exemplifying embodiment of the invention has been described with reference to the drawing. The invention, however, can be varied in its details within the scope of the following claims.

Claims

I claim:

1. A device for supplying cold air into a room having a subceiling surface with an opening spaced inwardly from the side edges thereof for receiving the air supply device, said device comprising a pressure box positioned above the plane of the ceiling surface and having a cold air duct connected thereto through one side thereof so as to introduce air into said pressure box from a direction parallel to the ceiling surface, said pressure box being mounted in said opening in said ceiling and having a lower portion comprising an air distribution means for introducing cold air from said pressure box into the room, said air distribution means comprising a pair of vertically spaced perforated plates disposed parallel to the plane of the ceiling surface, and sidewalls surrounding said pair of plates and disposed intermediate said plates to define a distribution chamber below said pressure box which eliminates any lateral component of airflow from the air duct to thereby uniformly direct the airflow from said distribution box vertically downward into the room for mixture with the secondary room air, said sidewalls of said distribution chamber being spaced from the sides of said pressure box to provide airflow gaps surrounding said distribution chamber, said sidewalls providing guiding surfaces in said gaps for directing airflow from said pressure chamber outwardly from said air supply device substantially parallel to the ceiling surface of the room to avoid a flow of secondary room air along the ceiling surface surrounding said device.

2. An air supply device according to claim 1 wherein the perforations of the upper of said pair of plates provide a smaller airflow area than the perforations of the lower of said plates.

3. An air supply device according to claim 1 including means cooperable with the perforated plate to variably screen off the airflow openings therethrough.

4. An air supply device according to claim 1 wherein said pressure box has edge plates depending below the ceiling surface and confronting the sidewalls of said distribution box in spaced relation to cooperate with said sidewalls to direct the air from said gap at a level spaced below the ceiling surface immediately surrounding said air supply device.

5. An air supply device according to claim 1 including damper means in said airgaps to control the force of the air discharged through said gaps selectively around the periphery of said device.

6. A device according to claim 5 wherein said opening is square and said airgaps comprise four gaps disposed along the respective sides of the square openings, said damper means including a separate flap valve in each gap.