EP0183709A1 - Portable clean air space system - Google Patents

Abstract

A system for producing a clean air space having a clean air core at a relatively low velocity surrounded by a continuous concentric curtain of clean air at a relatively high velocity using a single plenum (16). The single plenum (16) sends air, through a high efficiency particulate air filter (24), to an air distribution plate (26) which produces the core and to a passage (36) completely surrounding the plate (26) which produces the curtain of clean air. A return air port (22) draws air from the clean air space and recirculates it through the system for insulation. Air is propelled through the system by blowers (12).

Description

PORTABLE CLEAN AIR SPACE SYSTEM

This is a continuation-in-part of application Serial No. 588,385, filed March 12, 1984 and entitled "Portable Clean Air Space System."

Background of the Invention

A. Field of the Invention.

This invention relates to apparatus for the creation of a clean air space and particularly to a portable clean air space surrounded by an air curtain.

B. Background Art.

In many endeavors today, there is a need for exclusion of contaminants. Contaminants are destructive in many manufacturing processes in which they may lead to inferior product quality. Additionally, in many biologic and chemical experiments contaminants may lead to inaccurate results. Extensive effort is there¬ fore being expended to produce contaminant-free assembly areas and experimentation areas. Conventionally, this is done by continuously supplying pressurized clean air to a space, usually enclosed, referred to as the "clean air space." Prom medical terminology the clean air space is said to be "reverse isolated"; that is, any¬ thing within the space is protected from contamination from outside the space.

In addition to preventing contaminants from coming in contact with the work areas, thereby protec¬ ting these work areas, there is a further problem of contaminants from the work areas entering the environ¬ ment outside the work areas. For example, laboratory animals shedding flakes and hair may sensitize labora¬ tory workers if these contaminants are permitted to^' enter the laboratory environment. Recapture of the air supplied to the clean air space is a known method of preventing such environmental contamination, thus produ- cing what is referred to herein as "isolation."

The general problem of cleanliness has been commonly addressed by the provision of "clean rooms" whereby a room is pressurized with filtered air. Clean rooms may include an air distribution ceiling for dis- tributing and delivering pressurized clean air downward¬ ly into the room. One type of air distribution ceiling for this purpose is taught in U.S. Patent No. 4,060,025 - Pelosi, Jr. According to the Pelosi *025 patent, uniform air delivery, referred to as laminar flow, is achieved by allowing pressurized, clean air in a primary plenum above the ceiling to pass successively through pluralities of holes in the upper and lower panels of a secondary plenum, the lower panel of which forms the room ceiling.

Clean rooms are extremely expensive to construct and maintain. They are particularly inefficient and/or ineffective when the work area desired requires only a portion of a room and when isolation for individuals who must work in the clean air space is desired.

To counter these problems, systems have been developed to form a localized clean air space within a room. See, for example, Patent 3,151,929 - Potapenko. Potapenko teaches a clean air supply encompassing a hospital bed and supplied from a plenum within a canopy above the bed. While this device is effective for preventing contamination of a patient in the hospital bed, no provision is made for isolation, except by complete reversal of the system (column 5, lines 39- 56).

It is a known to enhance the isolation of a localized clean air space by surrounding it with a barrier such as a vinyl curtain or other penetrable enclosure. The effectiveness of such barriers is sub¬ stantially impaired when one reaches into the work space while otherwise maintaining clean conditions.

Air curtains have also been used to surround such clean air spaces. An air curtain is a flowing stream of air used to separate the spaces on either side thereof. Air curtains are commonly used in conjunction with doorways. See, for example, U. S. Patent No. 3,886,851 - Berner and U. S. Patent No. 3,023,688 - Kramer, Jr.

Providing a relatively low velocity laminar flow of filtered air as a clean air space core, surrounded by a relatively higher velocity air curtain to further isolate the core area, is disclosed in U. S. Patent No. 3,626,837 - Pelosi, Jr. and U. S. Patent No. 3,726,204 - Lindestrom. In the devices taught in each of these patents, the air is distributed through a dual plenum, one plenum comprising a first air distribution chamber and outlet for the low velocity core, and a second plenum comprising a second air distribution chamber and outlet for the relatively higher velocity directional- ized air flow forming the air curtain which surrounds the core. U. S. Patent No. 3,776,121 - Truhan teaches the use of a single plenum to provide a localized clean air space comprising a column of treated air with progres¬ sively increasing air flow volume from the center of the column outwardly. However, Truhan's apparatus does not teach a continuous discrete "air curtain" surrounding the clean air core. Instead, Truhan specifically avoids formation of such an "air curtain" (see column 5, lines 43-53).

While some recapture of the downwardly flowing clean air is provided both in Truhan and Pelosi '837, the recapture inlet in both cases is outboard of the horizontally defined clean air space, thus seemingly inadvertently impairing whatever isolation effect might otherwise be present.

Other patents, found in a search at the U. S. Patent and Trademark Office directed to the the present invention, but which are felt to be less relevant than those discussed above are: U. S. Patent No. 3,385,036, ^• in which is described a portable apparatus for the production of a column of clean air, surrounded by an air curtain, using a plurality of plenums; U. S. Patent No. 3,803,995 which teaches a ventilated zone parti¬ tioned by an air curtain wherein the ventilated zone and the air curtain are also produced by distinct plenums; and U. S. Patent Nos. 2,074,317; 3,721,067; 4,202,676; and 4,267,769 which generally teach the production of clean air spaces. Another portable clean air space generating apparatus with an air curtain surrouning a low velocity core, but with a double plenum and no air recirculation, is seen in the sales literature submitted herewith and entitled, "VECO International Kleenedge Vertical Laminar Flow Filter Modules."

Additionally, a commercial installation built by the assignee of the present invention prior to the present invention may also be of interest. In this installation, a clean air space is provided in a hos¬ pital operating room. This space comprises a core of low velocity downwardly flowing air surrounded by an air curtain. No air recapture is provided. The core and air curtain are fed from a common overhead plenum, the central portion of the lower wall of which is a per¬ forated plate. Surrounding the perforated plate, the air curtain forming means comprises a multiplicity of narrow channel elements each including a plurality of vertically oriented louvers.

Notwithstanding all of these prior designs and efforts to provide efficient, effective clean air space generating units or systems, there remains a need for such a unit of still further improved design and, par- ticularly, for such a unit which is portable and which provides effective isolation and reverse isolation. It is therefore the general object of this in¬ vention to provide a system meeting this need.

Summary of the Invention

The clean air space, produced.by a system con- tructed in accordance with the present invention, in¬ cludes a relatively low velocity clean air core sur¬ rounded by a continuous, relatively high velocity con¬ centric clean air curtain. The system for producing this clean air space includes a ducted support frame having a vertical outer surface defining a portion of the-periphery of the clean air space and an air return opening at the bottom of this surface. Also included is an air plenum extending horizontally from the ducted support frame and in air flow communication with this frame. The plenum has a bottom for distributing air flow into the plenum to form the clean air core and the clean air curtain. The bottom of the plenum includes a perforated plate for forming the clean air core and a substantially continuous passage surrounding the per- forated plate and extending along the outer surface of the ducted support frame for forming the clean air cur¬ tain. The system also includes means for developing air flow through the ducted support frame and out of the air plenum through the bottom of the air plenum into the clean air space and back into the ducted support frame through the air return opening. Filtering means are provided for capturing particulate matter entrapped in the air flow. The filtering means are positioned in the air flow path through the ducted support frame and the air plenum.

Brief Description of the Figures

Figure 1 is a perspective view of the portable clean air space system of the present invention.

Figure 2 is a sectional view of the system of Figure 1, taken in the plane 2-2 of Figure 1.

Figure 3 is a sectional view in the plane 3-3 of Figure 2.

Figure 4 is an expanded view of Area 4 of Figure 3.

Figure 5 shows an alternate embodiment of the structure of Figure 4.

Figure 6 shows a bottom view of the upper struc¬ ture of the apparatus shown in Figure 1.

Figure 7 is a perspective view of another em- bodiment of the unit which forms the clean air curtain.

Figure 8 is a sectional view showing the Figure 7 unit in place in the system of the present invention. Detailed Description of the Invention

Figure 1 shows portable clean air space genera¬ ting system 10 having a portably mounted ducted frame 15 and a unitary air supply plenum 16 supplied with air by two blowers 12. The sides of plenum 16 are formed by plenum enclosure 17. The top of plenum 16 is formed by high efficiency particulate air (HEPA) filter 24. A portion of the clean air which has passed through HEPA filter 24 passes downward through perforated air distri- bution plate 26, to form a laminar flow core of rela¬ tively low velocity clean air. A second portion of air from filter 24 passes around the perimeter of perforated plate 26 and through slot 36 (described in more detail below) to.produce a relatively higher velocity concen- trie clean air curtain bounding the core. The clean air forced downward from plenum 16 is recaptured through an air return inlet 22 and is conducted by upright duct 18 through prefilter 20 to blowers 12. Portable clean air space system 10 is provided with a stand composed of horizontal members 28 and locking casters 30 to allow mobility. System 10 may thus be rolled up to a work area and plenum 16 may extend above said work area. In its preferred form, system 10 has a height of approxi¬ mately eight feet six inches, a width of approximately seven feet, and a depth of approximately four feet. Figure 2 is a side view of portable clean air space system 10 and shows schematically the air currents created thereby. By proper selection of mechanical design features, approximately 90% to 95% of the air supplied from plenum 16 downward may be recaptured through inlet 22 and recirculated. The disposition of inlet 22 within the horizontally defined area of the clean air space, produced as described, greatly enhances the efficiency of recapture. System 10 thus provides isolation, preventing particulate contamination within the work space from spreading to the environment outside the clean air zone. Upright duct 18, having a depth of approximately ten inches, serves as a conduit for recir¬ culating recaptured air upward toward blowers 12. While passing through upright duct 18, air is passed through prefilter 20. Prefilter 20 is a conventional filter which removes approximately 30% of the contaminants thereby prolonging the life of HEPA filter 24.

Air drawn up through upright duct 18 by blowers 12 is shown passing into an upper chamber above unitary plenum 16. HEPA filter 24 securely seals the chamber above plenum 16 thereby forcing all air supplied by blower 12 to be forced through filter 24. The large pressure loss through filter 24 causes all of the air forced through filter 24 to have a substantially uniform linear velocity. HEPA filter 24 is effective to remove particu¬ late contaminants to provide Class 100 air under Federal Standard 209(b) which requires fewer than 100 particles of .5 microns and larger per cubic foot. In the pre- ferred form of the invention, as described herein, Class 100 air is provided to the work space horizontally de¬ fined the by area of plate 26.

Filter 24 is secured to support bars 38 using suspension rods 32. There are eight suspension rods 32 around the periphery of filter 24, two on each of its four sides.

Air which has passed through filter 24 must pass either through the free areas of perforated plate 26 or across the perimeter of plate 26 in a direction per- pendicular to plate 26 and therefrom through slot 36. The free area of perforated plate 26 is created by one-eighth inch holes with staggered centers separated by approximately twenty-one-thirty-seconds inch. This arrangement of perforations is effective to produce laminar flow in the core area of the clean air space. Slot 36 is a continuous slot defined by spaced apart, vertically oriented, channel defining means, described more fully below. Slot 36 completely surrounds plate 26. Air forced from plenum 16 through slot 36 forms a concentric air curtain completely surrounding the clean air core. By providing an appropriate relationship between the amount of free area of plate 26 and the width of slot 36 it is possible to eliminate the need for two separate plenums or a multiplicity of curtain forming, air directing louvers (as has been required heretofore) to supply the low velocity core and the high velocity curtain. The surface area of plate 26 is approximately 18 square feet. Of this amount, approximately 3.3%, or .594 square feet, is free area. Slot 36, is approxi- mately one-quarter inch wide. With the unitary plenum of this invention, these dimensions allow production of •a core of air with a linear velocity of approximately 33 feet per minute surrounded by a concentric air curtain with a linear velocity of approximately 1000 feet per minute.

In Fig. 3, blowers 12 are seen at the rear of the chamber above plenum 16. Plenum 16 comprises a single air source for the core and the curtain. Suspension bars 32, which secure HEPA filter 24 to support member 38, continue downwardly and are bolted to support angle 34. Support angle 34 completely encircles and supports perforated plate 26. Slot 36 is formed between an upwardly extending strip of support angle 34 and a facing upwardly extending wall of plenum enclosure 17 dependant from ducted frame 15. Perforated plate 26 is tack welded to support angle 34 and all gaps between plate 26 and angle 34 are sealed with an appropriate sealant such as Selastic manufactured by Dow Chemical. This prevents random air motion caused by air leaking between the plate and the support means which is a common problem in clean air rooms where the ceiling panels are removable.

As seen in the enlarged view of Figure 4, each suspension rod 32 is a stainless steel threaded bar with a diameter of approximately five-sixteenths inch.

Because suspension rods 32 are not in the air flow of the air curtain, they do not cause any discontinuities. HEPA frame 52 is conventionally manufactured as part of a HEPA filter assembly and may be formed from wood, metal or plastic. Filter frame 52 rests on eight 2" x 1-1/4" right angle filter supports 53 which may be rotated ninety degrees to allow removal of filter 24. Each support 53 is secured to a rod 32 by a pair of rod nuts 32.

Horizontal support member 38 is, in turn, secured to support member 44 which is dependant from ducted frame 15 (not seen in Figure 4) . Suspension rod 32 is bolted to angle support 34 through perforated plate 26 to secure plate 26 at a level above the bottom 50 of wall 42. Slot 36, between support angle 34 and the wall 42, is approximately one-quarter inch wide. It is through this slot that an air curtain with a velocity of approximately 1000 feet per minute is formed in the preferred form of the present invention. Both the horizontal and vertical portions of support angle 34 are approximately one inch wide.

Fig. 5 shows an alternate embodiment of the plate support structure of Fig. 4. In this embodiment suspension rod 32 does not extend beyond the length necessary to secure filter 24. The function of the portion of suspension rod 32 which extended downward to support perforated plate 26 is now performed by fastener 46. Fastener 46 is secured to wall 42 by pop rivets 48. Fastener 46 is approximately one-eighth inch thick and one inch wide. Support angle 34, sealed to perforated plate 26 as in the previous embodiment, is bolted to fastener 46. In this embodiment, the upper horizontal portion of fastener 46 serves as a spacer to maintain a distance of approximtely one-quarter inch between sup¬ port angle 34 and wall 42.

As seen in Figure 6, the bottom view of the air supply portion of portable clean air space system 10, perforated plate 26, which supplies the low velocity clean air core, is located centrally in apparatus 10. Support angle 34 completely surrounds perforated plate 26. Eight suspension rods 32 are attached to support angle 34, two on each of its four sides. Slot 36, which produces the concentric air curtain with a linear veloc¬ ity of approximately 1000 feet per minute is formed around support angle 34.

Eight spacers 52, two on each of the four sides, assist in maintaining the proper spacing of approxi¬ mately one-quarter inch for slot 36. Spacers 52 occlude only approximately .9% of the total length of slot 36. Therefore, any discontinuities caused by spacers 52 are quickly "healed" as the air curtain travels downwardly beyond spacers 52. The extension of wall 42 below the ends of spacers 52 assists in this "healing" because the air tends to follow the surface- of the wall 52.

Referring again to Figure 2, a further function¬ al feature of the present invention comprises a hinged attachment of the upper distribution chamber assembly to the lower part of ducted frame 15 by means of hinge 60. Welded strap halves 62 A and 62 B fastened to the upper assembly and lower frame segment, respectively, are secured by a single outer strap 64 and bolts 66. For ease of transport and movement, removal of bolts 66 permits the upper distribution chamber assembly to be folded, at hinge 60, downwardly and against the front of the lower segment of ducted frame 15. Figures 7 and 8 show another arrangement for forming the clean air curtain. This arrangement differs from the apparatus illustrated in Figures 2-6 by the use of a pair of concentric openings 70 and 72 to form the clean air curtain instead of a single concentric open¬ ing. By dividing concentric slot 36 of Figures 2-6 into two concentric slots 70 and 72, with each, for example, 1/8" wide and 1" high, the velocity of the flow of the air curtain drops off at a lower rate than with a single slot. This is believed to result from each slot pro¬ ducing a narrower, laminar flow of air which reduces the turbulence of the air flow and, therefore, reduces the aspiration of the surrounding air by the air curtain. Reduced aspiration results in a smaller mass of air movement with the final result that the reduction in velocity of the clean air curtain is less than for an air curtain produced by a single slot. A 1:8 ratio of slot width to slot height has been found to produce the desired results.

Concentric slots 70 and 72 are formed by a rec¬ tangular frame composed of four sections 74, 76, 78 and 80. Each frame section has three spaced vertical walls 82, 84 and 86 which define slots 70 and 72. Walls 82 and 86 of frame sections 76, 78 and 80 have horizontally extending flanges 88 and 90. Flanges 88 extend inward of walls 82 and flanges 90 extend outward of walls 86. Only inner wall 82 of frame section 74 has a flange 88. Outer wall 86 of.frame section 74 has no flange which extends outward of the frame. This permits placement of frame section 74 against the outside surface 91 of the ducted support frame with slots 70 and 72 close to this surface. In this way, the clean air curtain is formed along surface 91, rather than being spaced from this surface.

The frame sections are assembled from com¬ ponents, as illustrated, which are joined together by suitable means, such as weld joints 92. The frame sec- tions, in turn, are joined together at their ends by suitable means, such as weld joints 94.

• The frame of Figure 7 is mounted in place, by attachment to the air plenum. This can be accomplished by a plurality of screws extending through outer flanges 90, running along three edges of the frame, and the walls of the air plenum. A suitable gasket material 96 is placed between frame section 74 and surface 91 and between flanges 90 and the walls of the air plenum to seal these joints.

With the frame in place, perforated plate 98, which forms the clean air core, is placed within the frame and rests on inner flanges 88. This is shown in Figure 8. While this invention has been described with reference to specific embodiments thereof, it is not considered to be limited thereto. Accordingly, the appended claims are intended to be construed to encom- pass not only those forms and embodiments of the inven¬ tions specifically described or generally referred to herein but to such other embodiments and forms of the invention as may be devised by those skilled in the art without departing from the true spirit and scope of the present invention.

Claims

Claims :

1. A system for producing a defined clean air space, said clean air space having a relatively low velocity clean air core surrounded by a continuous, relatively high velocity concentric clean air curtain, said system comprising:

a ducted support frame having a vertical outer surface defining a portion of the periphery of said clean air space and an air return opening at the bottom of said surface;

an air plenum extending horizontally from said ducted support frame and in air flow communication with said frame, said plenum having a bottom for distributing air flow into said plenum to form said clean air core and said clean air curtain, said bottom including a per- forated plate for forming said clean air core and a sub¬ stantially continuous passage surrounding said plate and extending along said outer surface of said ducted support frame for forming said clean air curtain;

air circulation means for developing air flow through said ducted support frame and out of said air plenum through said bottom into said clean air space and back into said ducted support frame through said air return opening; and filtering means, positioned in the air flow path through said ducted support frame and said air plenum, for capturing particulate matter entrapped in said air flow.

2. A system according to claim 1 wherein the free area of said perforated plate is much less than the obstructed area of said perforated plate.

3. A system according to claim 2 wherein said passage is a single opening surrounding said perforated plate.

4. A system according to claim 3 wherein said single opening is formed by the vertical walls of said air plenum and the vertical walls of angle supports which extend around said perforated plate.

5. A system according to claim 4 wherein said single opening is approximately 1/4" wide.

6. A system according to claim 2 wherein said passage is a pair of concentric openings surrounding said perforated plate.

7. A system according to claim 6 wherein said bottom of said air plenum includes a frame having three spaced vertical walls which form said pair of concentric openings.

8. A system according to claim 7 wherein each opening is approximately 1/8" wide and 1" high.

9. A system according to claim 7 wherein said frame is rectangular.

10. A system according to claim 9 wherein said innermost walls of said frame have horizontal flanges extending inward of said innermost walls and said per¬ forated plate rests on said horizontal flanges.

11. A system according to claim 10 wherein the outermost walls of three sides of said frame have hori¬ zontal flanges extending outward of said outermost walls and the outermost wall of the fourth side of said frame is positioned against said vertical outer surface of said ducted support frame.

12. A system according to claim 3 wherein said filtering means include a first filter positioned in said ducted support frame and a second filter positioned in said air plenum.

13. A system according to claim 12 wherein said air circulation means include at least one air blower.

14. A system according to claim 13 further including a stand upon which said ducted support frame is mounted and having casters for moving said system.

15. A system according to claim 6 wherein said filtering means include a first filter positioned in said ducted support frame and a second filter positioned in said air plenum.

16. A system according to claim 15 wherein said air circulation means include at least one air blower.

17. A system according to claim 16 further including a stand upon which said ducted support frame is mounted and having casters for moving said system.

18. A system according to claim 7 wherein the ratio of the width of each opening to the height of each opening is 1:8.

19. Apparatus for forming an air curtain comprising:

an air curtain forming unit having three spaced walls forming a pair of extended slots through which air flows;

and means for developing an air flow through said slots and across a space downstream from said slots.

20. Apparatus according to claim 19 wherein the ratio of the width of each slot to the air flow path through each slot is approximately 1:8.

21. Apparatus according to claim 20 wherein said width of each slot is approximately 1/8" and said air flow path through each slot is approximately 1".

22. Apparatus according to claim 19 wherein said means include an air return at the downstream end of said space, a duct and circulation means for circulating air through said duct and said slots, across said space and back into said duct through said air return.

23. Apparatus according to claim 22 further including means, positioned in the path of said air flow, for conditioning said air flow.

24. A system for producing a defined clean air space, said clean air space having a relatively low velocity clean air core and a relatively high velocity clean air curtain, said system comprising:

a source of clean air;

an air plenum in air flow communication with said source of clean air and having a bottom for distributing air flow into said plenum to form said clean air core and said clean air curtain, said bottom including (a) a perforated plate having a free area which is much less than its obstructed area and through which air from said plenum flows to form said clean air core, and (b) an elongated passage outward of said perforated plate and through which air from said plenum flows to form said clean air curtain;

and means for developing air flow from said source of clean air, through said plenum and out through said perforated plate and said elongated passage.

25. A system according to claim 24 wherein said passage is a single opening.

26. A system according to claim 25 wherein said single opening is formed by the vertical walls of said air plenum and vertical walls extending along the periphery of said perforated plate.

27. A system according to claim 24 wherein said passage is a pair of concentric openings.

28. A system according to claim 27 wherein said pair of concentric openings are formed by three spaced walls extending along the periphery of said perforated plate.

29. A system according to claim 24 wherein said source of clean air includes filtering means upstream of said air plenum.

30. A system according to claim 29 wherein said source of clean air further includes a duct extending along said clean air space and having a return opening through which air flow through said clean air space enters said duct.

31. A system according to claim 30 wherein said filtering means include a filter positioned in said duct.

32. A system according to claim 31 further including a second filter which defines the top of said air plenum.