Dual Plenum For Ventilating Ceilings In Clean Rooms

Abstract

A bounded clean air space within a room is provided by a dual plenum located directly above the clean air space, the plenum formed of the pre-existing room ceiling, a lower plenum ceiling and plenum walls, and divided into two chambers by a membrane, the inner chamber being a supply chamber for providing clean air to the clean air space, and the outer chamber providing a supply source for air delivered through a slot extending around the periphery of said lower plenum ceiling. An air curtain which laterally bounds the clean air space is formed by the air supplied through the slot, which air is removed through peripheral air openings at the bottom of the room.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention lies in the field of clean room systems and, more particularly, means for providing an air curtain laterally surrounding a clean space within said room and means for providing clean air to such space.

2. Description of the Prior Art

In present day technology, there is an increasing need for clean rooms supplied with a downflow of air at a relatively low velocity, and for providing such a clean room area in a relatively small space within a larger preexisting room, with free access to the inner clean room space. In many applications, such as hospitals and industrial laboratories, the clean area can be confined to a limited space, making it theoretically unnecessary to provide the high volume of clean air which would be necessary to maintain the entire room in a clean state. A system for ventilating and maintaining clean a portion of a room is shown in U. S. Pat. No. 3,380,369, issued to Claes Gustaf Allander on Apr. 30, 1968. The Allander system provides that a portion of the total air supply to the room is directed to a peripheral slot in the ceiling thereof encompassing the extreme outer limits of the desired clean space, with return air ducts placed along the lower edges of the walls of the room, thereby creating a high velocity air curtain which effectively partitions the larger space of the room into an inner clean area and an outer uncontrolled, or dirty area. The remaining portion of total air supply is introduced through a perforated ceiling into the central area, which is then fed with downflow air at a relatively low velocity. In this system, contaminants from the outer area cannot reach the central area since they are aspirated into the high velocity peripheral air curtain and carried downward and out through the return air grills, while any contaminant particles generated within the clean area are carried downward by the low velocity air.

The practical difficulty with the system as described in the patent to Allander lies in adapting it to an existing room. It is difficult, if not impossible, in most cases to have the air supply slot means extending through the ceiling. Further, room ceilings are of varying heights, and placement of the slot within the existing ceiling would constrain the design engineer with respect to the required pressure in order to obtain the desired flow rate. Accordingly, it is desirable to provide the air supply slot means in a position below the preexisting ceiling, and to provide an economical and easily installed dual plenum in the space between the preexisting ceiling and the slot means, the outer chamber providing for introduction of the air through the slot means to form the air curtain, and the inner chamber providing for introduction of the low velocity clean air.

SUMMARY OF THE INVENTION

It is a purpose of this invention to provide an efficient, simple, inexpensive, and easily installed plenum extending downwardly from the ceiling of a room, which plenum provides an efficient ventilating system which utilizes a minimum of space.

It is another purpose of this invention to provide separate inner and outer air chambers within one plenum, the outer chamber feeding a slot encompassing the lower periphery of the plenum.

It is a further purpose of this invention to provide a closed loop airflow system utilizing two air supply sources fed by a common air return.

It is a further purpose of this invention to provide means to control the quality of air cleanliness in a central space of a preexisting room, while allowing for free access to such space.

It is a further purpose of this invention to maintain only a limited space within a room as a clean space, thereby reducing the cost and size of the required clean air equipment.

Accordingly, this invention provides for a plenum connected to the ceiling of a room, said plenum being divided into an inner and outer chamber by an airtight membrane, the downward side of said plenum being perforated, and spaced from the plenum sidewalls so as to provide a slot encompassing such downward side, said slot being in connection with and fed by air introduced into said outer plenum chamber, the air passing through said slot cooperating with peripheral air return means at the bottom of the room to provide an air curtain encompassing a space in the room below said plenum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an elevation view of a preexisting room having a dual plenum connected to the ceiling thereof, with a diagrammatic representation of the air flow in the room.

FIG. 2 is a plan view taken from the plane indicated 2--2 in FIG. 1.

FIG. 3 is a detailed view of the connections at the peripheral slot.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, an elevation view of a room is shown having a ceiling 20, sidewalls 21, and a floor 22. Suspended from the ceiling, preferably from the center thereof, are plenum walls 25 which may be supported by brackets 26. Plenum wall 25, as seen in FIG. 2, encompasses a closed space. It may be of any contour, but preferably of the same contour as the room in which placed, e.g., of a rectangular contour for a typical rectangular room. Suspended from the ceiling 20 and placed within the lower edge of plenum wall 25 is the downward member of the plenum, referred to as plenum ceiling 27, typically comprised of perforated panels suspended by T-bars which in turn are attached to ceiling 20 by wires. Ceiling 27 is perforated to permit flow of air therethrough, and in combination with plenum wall 25 and the enclosed portion of ceiling 20 forms a plenum 28. The space confined by plenum 28 in relation to the overall room can be adjusted to suit the needs of the particular application, with plenum ceiling 27 designed according to the height at which it is desired to introduce clean air into the portion of the room directly below it, and the surface area of the plenum ceiling 27 being designed to accommodate that inner portion of the room below which is to be maintained in a clean state.

The separation between plenum ceiling 27 and plenum wall 25 forms an air slot 30 which extends in a closed loop around the periphery of plenum ceiling 27. A membrane 31 is connected at the slot to the outside of plenum ceiling 27, and extends upwardly and inwardly to the ceiling 20 where it is attached, thereby separating plenum 28 into two chambers, an inner plenum 33 and an outer plenum 34. The membrane 31 is preferably of fabric which can be attached easily and conveniently, and provide an airtight separation of the two chambers. As shown in FIG. 3, the membrane may be connected to a steel channel 40 by a U-shaped metal or plastic retainer 41, the steel channel 40 in turn being connected to plenum ceiling 27. A plurality of spacers 42 may be used to maintain the slot between plenum ceiling 27 and the plenum wall 25. The membrane may be connected to the ceiling 20 by any conventional means which affects an airtight connection.

Air is introduced into the inner plenum chamber 33 through one or more clean air distributors 45, the number and location of such distributors being determined in accordance with the size of the plenum chamber, and the total of flow rate required. The air which is brought in through the distributors 45 under pressure, is effectively converted by the perforated ceiling into a low velocity downward flow, typically of 20 cubic feet per minute per square foot. Outer plenum chamber 34 is supplied with air under pressure by ducts 46, the air under pressure being channeled through slot 30 which effectively acts as an orifice which converts the air pressure into velocity, producing a jet of downward air surrounding the periphery of plenum ceiling 27.

Located at the bottom of the room, preferably in sidewalls 21 just adjacent to the floor 22, is a peripheral return air opening 50 which enters into the hollow interior of walls 21, providing a return path for the air from duct 30, as well as for the air that has passed through plenum ceiling 27. The arrows, as shown in FIG. 1, indicate directions of airflow. The air is returned upward through the hollow interior of walls 21 and fed into return air ducts 55 mounted just below ceiling 20. The ducts 55, which extend continuously around the perimeter of the room, feed into a collection duct 56 which is connected to one or more fans which clean and purify the air prior to resupplying same to the two plenum chambers.

In operation, air which is to be introduced into the clean space is purified to the desired degree and introduced through sleeves 48 into distributors 45, which in turn distribute the air throughout inner plenum 33, from whence it passes downwards into the clean space below. Simultaneously, air is provided under pressure to outer chamber 34, which is emitted through slot 30 downward at a relatively high velocity. The closed path between slot 30 and return air opening 50 gives rise to an air curtain which surrounds and defines a clean space 60 bounded laterally by the air curtain, above by plenum ceiling 27, and below by floor 22. Both the clean air and the air which provides the air curtain are channeled through peripheral opening 50 up the hollow interior of walls 21 through return air ducts 55 to collection duct 56, and thence through fans and conditioners not shown back to the two chambers of the plenum.

In practice, it will frequently be desirable to add an outer ceiling 62, generally on the same level as plenum ceiling 27, thereby creating space 65 surrounding the plenum. Space 65 may be used to provide additional space for location of normal building facilities such as piping, wiring, plumbing, etc., and for supports for lights or other apparatus as desired. Outer ceiling 62 preferably is comprised of panels of the same material as comprise plenum ceiling 27, and is designed such that plenum ceiling 27 and outer ceiling 62 give the appearance of a continuous ceiling, interrupted only by slot 30.

It is seen from the above that the system as thus described is adaptable to any preexisting room, and can be designed to accommodate any three dimensional space within such room. By dividing the plenum with a one-piece flexible membrane, two airtight chambers are provided, one central and one peripheral, so as to separately supply relatively high velocity and relatively low velocity air for the air curtain and clean area respectively.

Claims

What is claimed is:

1. A system for providing a clean space freely accessible from without, comprising:

a room having a ceiling, a floor, and sidewalls, which encompass and define said room;

a second ceiling, suspended from said ceiling and being perforated and of smaller area than said ceiling;

connecting means for supporting said second ceiling from said ceiling;

a plenum wall displaced from and encompassing said second ceiling and extending from the level of said second ceiling to said ceiling, said plenum wall cooperating with said ceiling and said second ceiling to form a plenum;

membrane means, connected from said ceiling within said plenum to the periphery of said second ceiling, for dividing said plenum into an outer plenum chamber and an inner plenum chamber;

slot means between said second ceiling and said plenum wall, and encompassing said second ceiling and engaging said outer plenum chamber, for providing an outlet for air from said outer plenum chamber; first air supply means for providing air under pressure into said outer plenum chamber; and

air return means at the lower part of said room for drawing and maintaining said air in a high velocity flow downward from said slot, thereby forming a continuous air curtain laterally surrounding a space within said room, said space being bounded above by said second ceiling and below by said floor.

2. The system as described in claim 1, wherein said air return means comprises intake grills located peripherally at the bottom of said sidewalls.

3. The system as described in claim 1, comprising a third ceiling at the level of said second ceiling and extending from said plenum wall to said sidewalls, said second and third ceilings together completely encompassing the lateral cross section of said room.

4. The system as described in claim 1, wherein said second ceiling is placed at the center of said room, and said clean space is centered in said room and encompasses a space substantially less than that of said room.

5. The system as described in claim 1, wherein said second ceiling contains perforations, and comprising second air supply means for supplying clean air into said inner plenum chamber and through said perforated ceiling into said clean space, and said air return means comprises ducts for recirculation of the combined air supplied from said inner and outer plenum chambers.

6. The system as described in claim 5, wherein said sidewalls are hollow, which hollow sidewalls form part of said air return means and function as ducts carrying said combined air for recirculation.

7. The system as described in claim 1 wherein said slot means comprises spacers between the periphery of said second ceiling and said plenum wall.

8. The system as described in claim 1 wherein said connecting means for supporting said second ceiling comprises T-bars connected to said ceiling by wires.

9. The apparatus as described in claim 1, wherein said membrane means converges downwardly and outwardly toward said plenum wall.