US 3487766 A
Description (OCR text may contain errors)
Jan. 6, H970 W. B. WOOD 3Afi7fifi CLEAN ROOM HAVING SUBSTANIIALLY VERTICAL AIR FLOW THEREIN Filed Jan. 12, 1968 f2 /4 .f, I @J m W W I kw I EH-=- E; H6. 2 20 INVENTOR. MWU'ER EMUGE W000 (1 and 1W L fl/S United States Patent 3,487,766 CLEAN ROOM HAVING SUBSTANTIALLY VERTICAL AIR FLOW THEREIN Walter Bruce Wood, Bridgeville, Pa., assignor, by mesne assignments, to American Air Filter Company, Inc., a corporation of Delaware Filed Jan. 12, 1968, Ser. No. 697,362
Int. Cl. F24f 7/06, 13/06 US. Cl. 98-31 11 Claims ABSTRACT OF THE DISCLOSURE A clean room is provided having a substantially vertical air flow from the ceiling down to a perforated floor which overlies a series of vertical chambers. The chambers act to direct air in a vertical direction and counter horizontal air flow or other turbulences which otherwise tend to disturb the air flow.
Background of the invention It has become the practice in a number of technological areas such as, for example, electronics and space technology to provide so-called clean rooms in which precision equipment, components, and the like can be assembled in an atmosphere having minimum amounts of impurities such as airborne dust, dirt and the like. Such a clean room normally has filtered, purified air admitted into the room from the ceiling and withdrawn from the room at the floor to remove any dirt, etc. This downward flow also acts to prevent dirt, which may be on the floor, from contaminating materials in the room by being conveyed ofl? the floor onto the material which condition might well occur if the air flow was other than downward. Ideally, therefore, the air should enter the room via regularly spaced intervals throughout the entire ceiling and then pass directly down to corresponding openings in the floor so that the air flow is entirely vertical and no cross currents or turbulences are built up which would tend to allow contamination generated from any internal source to be transmitted in a horizontal plane throughout the room.
However, the usual practice is to connect the openings in the floor to a common duct which, in turn, feeds the air into a circulating pump which purifies the air and circulates it back to the room via the ceiling. This has created problems because the openings in the floor do not normally draw equally from the various portions of the room. To overcome this, elaborate battling systems have been used. However, even such baflling systems are still easily unbalanced by persons moving about the room, repositioning of furniture and the like.
This unbalancing and unequal drawing of air can be easily explained in terms of venturi effect created at each opening from the room into the duct. As the air is collected in the farthest corner of the room (with respect to the circulating fan) it rushes through the duct beneath other, closer, openings and a suction or venturi effect is created drawing excessive amounts of air through the closer openings which, in turn, is usually compensated for by bathing or the like. Therefore, the amount of air passing through a given opening in the floor is dependent upon the amount of air passing through the other openings in the floor, particularly upon those other openings which are spaced a further distance from the circulating fan. Repositioning of furniture such as movement of a chair or the like, as well as movement of personnel in the room, can cause temporary starvation of air fiow through any one opening or group of openings in the floor which can cause unbalance in the system thereby causing horizontal, or at least nonvertical air currents to be generated.
Quite surprisingly, it has now been found that a clean room can be constructed which will provide substantially vertical and possibly a columnar or laminar air flow in the room.
Summary of the invention -In accordance with the invention, a system for vertically directing air flow in a clean room comprises an enclosed space having a wall with a ceiling portion and a fioor portion and means for circulating the air downwardly into the enclosed space from the ceiling and means in the floor portion for controlling the direction of flow of the air in the enclosed space and for removing the air from the space. The means for controlling the direction of flow of the air comprise a plurality of parallel vertical chambers. The chambers interconnect between a series of openings in the floor leading from the enclosed space into the chambers and a second series of openings at the opposite end of each chamber leading into a collection duct. The air can be recirculated from the collection duct back into the enclosed space through the ceiling by suitable means.
Brief description of the drawings FIGURE 1 is a cross-sectional schematic view of a clean room using the invention.
FIGURE 2 is an isometric partially broken away view of a lower corner of the clean room and the vertical chambers beneath the floor.
FIGURE 3 is a cross-sectional portion of FIGURE 1 along lines 3-3 showing the chambers.
Detailed description As previously stated, the invention provides a substantially vertical downward air flow of air in a clean room. Referring now to FIGURE 1, a clean room is generally indicated at 2 comprising an enclosed space 4, an air collection assembly 6 comprising the floor of the clean room, and a collection duct 8 beneath collection assembly 6 which collects the air from the assembly and passes it to circulating and filtering means 10. This can be any suitable fan and filtering means or the like including means for controlling temperature, humidity and the like such as are Well known in the art. The clean air then passes through duct 12 into duct 14 which is located above ceiling 16. Ceiling 16 is provided with regularly spaced openings (not shown) to admit the air downwardly in a vertical direction into enclosed space 4. Ceiling 16 can be any conventional porous: ceiling such as is well known in the art.
Now referring to FIGURE 2, the collection assembly generally indicated at 6 comprises a perforated upper plate 20 having spaced perforations 22 therein, a plurality of vertical chambers 24 and a lower perforated plate 26 having spaced perforations 28 therein. As best seen in FIGURE 3, each chamber 24 is sealed with respect to adjacent chambers, but communicates respectively through perforations 22 and 28 with enclosed spaced 4 and collection duct 8. Preferably, the perforated openings, in both top plate 20 and lower plate 26 comprise about 550 of the total area of the plates overlying the chambers. The size of each opening is not critical. However, the size should be uniform and preferably the same for both plates. The area of the opening should also be smaller than the cross-sectional area of the chamber. In this way, a pressure differential between enclosed area 4 and chambers 24 is created across upper plate 20; and a second pressure differential is created in like manner between chambers 24 and collection duct 8 across lower plate 26. Thus, the chambers 24 are maintained at a pressure intermediate to the respective pressures in enclosed space 4 and collection duct 8. The chambers 24 cause the flow of air entering the enclosed space 4 through ceiling 16 to pass substantially vertically downward through openings 22 in plate 20 into chambers 24.
While the mechanism by which chamber 24 accomplishes this columnar flow is not entirely understood, it is thought that each chamber functions as a cushioning device or surge tank resisting changes in the pressure differential which exist respectively between space 4 and chambers 24, and chambers 24 and collection duct 8. Thus, temporary inbalances created by movements of persons or objects, which might otherwise starve air flow through certain openings by redirecting the vertical flow to other openings, are resisted, or compensated for, by the chambers as well as each chamber tending to provide the same output of air to duct 8 despite temporary starvation or reduction of air output flow into the chamber caused by movement. This constant output, in turn, prevents movement in the room or transient air currents from causing complete inbalance of the entire system such as occurred in prior constructions where interruption of air flow at any one opening into the duct could, in turn, effect the pattern of air flow into each and every other opening into the duct causing a change in the drawing power of the duct at any given opening.
It should be noted here that the venturi effect previously discussed is substantially eliminated or at least nullified in accordance with the invention without any conventional dampening devices employed in the floor system.
For example, a clean room 12' x 24 was constructed in accordance with the invention. The entire floor was made as shown in FIGURE 2 by using a 6 thick honeycomb kraft paperboard construction wherein each honeycomb chamber was hexagonal and had a cross-sectional area of about 0.65 square inch. The top and bottom of the honeycomb kraft paperboard was covered with 24 ga. perforated steel plates having A5" uniformly spaced perforations on /4" centers. A conventional porous ceiling was used to admit air into the room and the air was collected from the chambers in a lower duct such as that previously described. Various air flow velocities ranging from 30-120 feet per minute were tested, and smoke patterns in the room indicated that the flow of air remained vertical and uniform through the room.
The novel construction of the invention offers additional advantages to those engineering the construction of such room because the structural support which the construction offers far exceeds that of a single perforated sheet which must be supported at closed intervals or else made thicker thereby increasing the cost. It has been found, for example, that rooms made in accordance with the invention using 24 gauge steel plates separated by chambers having kraft paper walls can easily withstand loadings of 200-300 pounds per square foot with little if any deformation'even when supported on 24-inch centers.
It is to be understood that neither particular crosssectional shape of the chamber nor the material from which it is constructed is critical. The cross-sectional shape could be circular or polygonal or the like. It can be constructed of sheet metal, plastic, kraft paperboard or other suitable materials. The length of the chamber can be varied as well. However, it has been found that the minimum length of the chamber must be at least 4 times the diameter or longitudinal measurement of the opening to provide a suflicient capacity in the chamber relative to the pressure differential across the opening. Likewise, the collection assembly 6 need not occupy the entire floor area of the clean room; modules of collection assemblies can be regularly spaced throughout the room. However, since the invention provides a means for obtaining substantially vertical air flow in a room it is advantageous to space the modules as close together as possible.
It should be noted that the air need not enter solely through the ceiling, but may enter as well through the ducts placed in the wall near the ceiling. However, for maximum utilization of the vertical air current flow made possible by this invention, the entrance ducts should be placed in the ceiling and should be placed as uniformly as possible throughout the entire ceiling.
Although the novel system of the invention has been illustrated in a particular embodiment wherein a single layer of vertical chambers is used, it is to be understood that the invention contemplates the use of one or more layers of vertical chambers separated by perforated plates to cause pressure differentials between the layers of chambers as well.
While the system described is preferably utilized to direct air flow vertically and smoothly into a perforated floor, it is recognized that the system could also be used in the ceiling to more uniformly distribute air into a room. The invention is, therefore, to be limited only by the following claims.
What is claimed is:
1. A controlled environment enclosure having:
(1) a porous ceiling through which air is downwardly directed into said enclosure; and
(2) a porous floor comprising a plurality of longitudinally extending columnar vertical chambers, said chambers being of substantially uniform cross section along their longitudinal axis and in parallel relationship, each being sealed with respect to adjacent chambers and having an upper portion with at least one opening therein in direct communication with said enclosure and a lower portion with at least one opening therein opposed to the opening in said upper portion and communicating directly with an air collection duct, the respective areas of the openings in said upper portions and said lower portions being each less than the cross-sectional area of said chamber, said longitudinally extending columnar vertical chambers acting to direct the flow of air in said enclosure from said porous ceiling downwardly in a substantially nondeviating vertical direction to said chambers.
2. The enclosure of claim 1 wherein the length of said chamber is at least four times the diameter of said open ing into the chamber.
3. The enclosure of claim 1 wherein said porous floor comprises an upper portion which is a perforated metal plate, a spaced lower portion which is a perforated metal plate and a series of vertical chambers therebetween of corrugated material having an upper edge sealed to said upper perforated metal plate and a lower edge sealed to said lower perforated metal plate to prevent the chambers from communicating with one another and to provide physical support beneath said upper perforated plate to mitigate buckling of said upper plate beneath a load.
4. The enclosure of claim 3 wherein said porous floor comprises perforated steel plates having corrugated kraft paperboard therebetween.
5. The enclosure of claim 4 wherein said steel plates having circular openings therein of about Ms" diameter spaced apart on about centers, and said corrugated kraft paperboard forms hexagonal chambers of about 6 inches in length and a cross-sectional area of about 0.65 square inch.
6. A system for vertically directing air flow in a clean room comprising a space formed by:
a ceiling; and
means spaced above said floor portion for admitting .air downwardly into said space;
means in said floor portion for causing the air to flow substantially vertical in said space and for removing air from said space, said means comprising a plurality of regularly spaced longitudinally extending columnar vertical chambers, each having spaced opposed openings, one of which openings communicates directly with said space, each of said chambers being of substantially uniform cross section along its longitudinal axis, said chambers being sealed from each other and forming zones of intermediate pressure between said space and a collection duct beneath said chambers.
7. The system of claim 6 wherein said means for admitting air comprise a porous ceiling and said means in said floor portion are spaced at regular intervals throughout said floor.
8. The system of claim 6 wherein said means in said floor cover substantially the entire floor area.
9. The system of claim 6 wherein said floor portion comprises a perforated metal plate having openings therein communicating with the upper ends of said chambers and a second perforated metal plate below said chambers and having openings forming exit openings from said chambers to a collection duct, said openings forming pressure differentials to maintain said chambers of a 6 pressure intermediate to said space and said collection duct.
10. The system of claim 9 wherein said vertical chambers have a length at least 4 times the diameter of the openings into said chambers.
11. The system of claim 10 wherein said openings in said perforated metal plates comprise 550% of the total area of said plates.
References Cited UNITED STATES PATENTS 2,912,918 11/1959 Mead.
3,148,676 9/1964 Truog et a1. 126-246 3,158,457 11/1964 Whitfield.
3,314,353 4/1967 Knab 9831 FOREIGN PATENTS 1,162,473 4/1958 France.
LLOYD L. KING, Primary Examiner U.S. CI. X.R. 983 3