[0001] This invention relates to apparatus for providing a clean air zone, for example in
surgical operating theatres, and in clean rooms for pharmaceutical production and
packaging, as well as for micro-electronics' production.
[0002] The natural behaviour of air when it is discharged from an orifice or unidirectional
flow diffuser is such that there is peripheral entrainment, all around the diffuser,
of extraneous contaminants, which not only mix with the discharged clean air, but
are also inwardly dispersed between 10° and 12°. To avoid this, without the need for
restrictive drapes or side panels around the air flow zone, apparatus has been proposed
for grading the rate of discharged airflow from a diffuser such that air is discharged
at a higher velocity from the central area of the diffuser and at successively lower
velocities from the respective areas further outward from that central zone, towards
the periphery of the diffuser. Such apparatus, which was first described in U.K. Patent
Specifications Nos: 1488513 and 1488514, gives rises to a downward and outward pattern
of air flow from a ceiling mounted diffuser and this has proved successful in minimising
contamination in the zone below the diffuser.
[0003] However, the effectiveness of the aforesaid type of graded flow diffusion system
is dependant on three exacting conditions. Firstly, the temperature difference between
the discharged air and the ambient air should not be more than ± 2° C. Secondly, and
as described in later U.K. Patent Specifications Nos: 1555563 and 1555564, there must
be equally distributed air recirculation inlets located around the periphery of the
graded discharge air diffuser in order to provide a negative velocity pressure equal
to that of the positive velocity pressure of the discharged air. Finally, the volume
of climatic control air supplied into the graded airflow unit to mix with its recirculation
air should not exceed 25% of the total volume, otherwise the negative velocity pressure
created at the equally distributed air recirculation inlets is insufficient to induce
the peripheral air outwards.
[0004] The difficulties involved in co-ordinating these three requirements for the effective
operation of such a graded flow system in both summer and winter conditions, when
alternatively cooling and heating are required, are considerable. Where these conditions
are not maintained throughout the year, the outward air flow has been found to change
direction and peripheral entrainment of contaminants has been found to occur. In some
cases air from the central zone simply fails to reach the floor, so the clean zone
is reduced. Of course, these failures are not at all apparent at the time and are
only detected by occurence of contamination following by monitoring of air flows.
[0005] In order to overcome the sensitivity of graded flow systems to the aforesaid influences,
the rate, and thus the total volume, of air supplied may be increased. However, this
causes increased noise and, in operating theatres, also causes unacceptable drying
of wounds, and wound cooling by increased evaporation, which in turn leads to hypothermia
in patients. Moreover, in pharmaceutical applications, where powders must not be disturbed
or flames distorted, such a high air velocity is not acceptable.
[0006] It is an object of the present invention to provide an improved clean air supply
system which is not susceptible to the above-mentioned problems.
[0007] According to the present invention, apparatus for providing a clean air zone comprises
supply means operative to supply clean air to a plenum chamber, and diffuser means,
in the form of one or more perforated plates, arranged adjacent the chamber so that
air supplied to the chamber flows out therethrough, characterised in that the diffuser
means has a substantially planar central area and successive peripheral areas which
are arranged at increasingly greater angles relative to the central area so that each
increasingly deflects the air flow outwardly from the direction of air flow from the
central area.
[0008] In use, the aforesaid apparatus provides a pattern of air flow radiating outwards
from the diffuser means. Inlets distributed around the air discharge diffuser means,
for recirculation of air, are no longer essential since the air flow pattern is now
determined by the angle of the peripheral areas of the diffuser means rather than
by the differential lower velocity of air from these areas. Furthermore the proportion
of climatic control air introduced to the air supply means does not affect the air
flow pattern and temperature differentials between air supplied by the apparatus and
ambient air should have less influence than in the previously known arrangement.
[0009] Advantageously, deflector vanes are located between the successive peripheral areas
of the diffuser means.
[0010] In one form of apparatus in accordance with the invention the successive peripheral
areas of the diffuser means may comprise separate perforated plates, each connected
to a respective imperforate deflector vane. In this way, the angle of each plate may
be independently adjustable either upon installation, or subsequently.
[0011] In an alternative form of apparatus, equally within the scope of the invention, the
successive peripheral areas of the diffuser means and the intervening imperforate
deflector vanes are provided as integral portions of respective profiled panels, which
are arranged around the periphery of the central area of the diffuser means. In practice,
this construction is easier to install, as the relative angles of the perforated areas
are fixed and do not have to be selected at the time of installation. The relative
angles may be chosen beforehand, from a small number of different profile configurations
as those most favourable to the site.
[0012] The invention will be described further, by way of example, with reference to the
accompanying drawings, in which:
Fig. 1 is a diagrammatic, sectional view illustrating a first embodiment of the apparatus
of the invention installed in the ceiling of a room;
Fig. 2 is a perspective view of a second embodiment of the apparatus of the invention
installed on the ceiling of a room;
Fig. 3 is an enlarged side elevation of the second embodiment;
Fig. 4 is an enlarged cross-section at the mid-line of the second embodiment (along
line IV-IV in Fig. 5);
Fig. 5 is a plan view of the second embodiment showing its modular construction;
Fig. 6 is an enlarged plan view of one module of the apparatus shown in Figs. 2 to
5;
Fig. 7 is an enlarged end view of the module shown in Fig. 6, in the direction of
arrow VII in Fig. 6;
Fig. 8 is an underside view of the module shown in Fig. 6;
Fig. 8a is an enlarged detail of the panel end portion encircled at VIII in Fig. 8;
Fig. 9 is a diagonal section of the module shown in Fig. 6, along the line IX-IX in
Fig. 6, the peripheral panel being omitted for the sake of clarity;
Fig. 10 is a cross-section along the line X-X in Fig. 6 with the strip lamp omitted;
and
Fig. 11 is a fragmentary cross-section of a peripheral panel, of the embodiment of
Figs. 2 to 10 along the line XI-XI in Fig. 8a, to a further enlarged scale.
[0013] Apparatus conforming to the invention is suitable for installation in the ceiling
of an operating theatre to provide a clean air zone around a patient undergoing surgery,
or in the ceiling of a pharmaceutical or electronic clean room to provide a clean
air zone around a machine or manufacturing process, or in any other instance where
minimal microbiological contamination is essential. However, instead of being installed
in a ceiling, apparatus in accordance with the invention could be mounted in a mobile
frame, upon a trolley, so that it can be moved from one location to another.
[0014] The general principles of the invention will be explained, first of all, with reference
to Fig. 1, which shown one embodiment of the invention in highly diagrammatic manner.
[0015] Air supply means in the form of electrically operated fans (not shown) are mounted
so as to direct air through a plenum chamber 10 which is provided above the level
of a false ceiling 12, and also immediately above an area which is to be kept substantially
free of microbial or particulate contaminants, for example the area where an operating
table is to be located in a surgical operating theatre. In addition to the fans, air
purifiers, heating means, cooling means and humidifiers may be provided to supply
suitably conditioned, sufficiently clean air to the plenum chamber 10. In the illustrated
example a terminal air filter 14 is also provided across the open lower side of the
chamber 10, substantially level with the false ceiling 12.
[0016] Immediately below the filter 14, diffuser means in the form of a plurality of perforated
plates, designated generally by reference numeral 20, is mounted on the false ?eiling
12. These plates 20 effectively cover the open lower face of the plenum chamber 10
and constitute the outlet for air supplied to the chamber 10 by the fans. The perforated
plates comprise a large square, substantially planar central panel 21, arranged horizontally,
aligned with or parallel to the ceiling 14, and a first group of narrow rectangular
panels 22, which surround the central panel 21 and are disposed at an angle relative
thereto, being inclined upwardly from the plane of the central panel 21 at an angle
of about 20°. A second group of rectangular panels 24 in turn surround the first group
22. This second group 24 incline upwardly relative to the plane of the central panel
21 at a greater angle than the first group 22, for example, an angle of about 40°
in the illustrated example. A third group of rectangular panels 26 in turn surround
the second group 24 and these incline upwardly from the plane of the central panel
21 at an angle of about 60°. The panels 22, 24, 26 are all successively narrower and
they are all perforated.
[0017] Each panel 22, 24, 26 is connected along its inner edge to a respective vane 23,
25, 27, which serves as an air deflector. The panels 22, 24, 26 or their respective
vanes 23, 25, 27 are mounted in pivotally adjustable manner whereby the angles of
inclination of the respective diffuser panels 22, 24 and 26 and the proportion of
air passing therethough can be adjusted An additional deflector vane 29 is mounted
at the outer edge of each outermost panel 26.
[0018] In use, the fans operate to supply clean air through the plenum chamber 10 as indicated
by the arrows A. A suitable rate of air flow is 0.55m/sec. The clean air passes into
the room through the perforated diffuser panels 21, 22, 24, 26, issuing in each case
in a direction perpendicular to the plane of the respective panel. Thus the air flows
directly downwards through the large central panel 21, as indicated by the arrows
B, but is deflected outwards, at increasing angles where it passes through the inclined
panels 22, 24, 26 around the periphery of the diffuser arrangement, as indicated by
the arrows C.
[0019] A gap remains between the outermost deflector vane 29 and the edge of the ceiling
12 defining the open lower face of the plenum chamber 10 and air flowing therethrough
is so deflected by the plate 29 that it flows substantially horizontally immediately
below the ceiling 12, as indicated by the arrow D.
[0020] Overall, an air flow pattern radiating outwards in all directions from the diffuser
panel arrangement is achieved. Provided this air flow is of a suitable velocity, e.g.
0.55m/sec it will sweep down to the floor of the room and outwards, eventually dissipating
via air outlets at the edges of the room, and via the door or doors. Such air flow
pattern is known to be advantageous in minimising aeromicrobiological contamination
in the zone below the diffuser arrangement since unclean ambient air and contaminants
introduced by operatives, including their natural emission of epithelial bacteria,
are swept outwardly of that zone to maintain its sterility. The advantage of the present
apparatus is that this pattern is achieved more reliably than with previous apparatus
which relies on differential air velocities.
[0021] A second practical embodiment, which is shown in much greater detail in Figs. 2 to
11, is also ceiling mounted. This apparatus is substantially rectangular, indeed square,
in plan (Fig. 5) and comprises a housing 30 which includes four dependent side walls
31, 32, 33, 34. Perforated diffuser means, designated generally by reference numeral
40, are mounted within the side walls across the outflow passage from the apparatus.
[0022] The housing 30 is constructed from four modules, A, B, C, D as shown in Figs. 2 to
5, a single module being illustrated in greater detail in Fig. 6 to 10.
[0023] Each module has a metallic outer casing 35 consisting of an upper wall 36, adjacent
side wall portions
a b, and inner walls 37, 38, which are not as high as the side wall portions and which
abut corresponding inner walls of the two adjacent modules when all four are assembled
together. The side wall portions
a,
b each have an air intake grille 39, so there are two in each side wall of the assembled
apparatus. Although such air intake is not necessarily essential to the inventive
concept, it is useful in practice because the apparatus is then self-contained so
that at sites of installations where there are no suitable remote air vents already
provided there is no need to undertake fresh construction of vents. Prefilters 89
are mounted at the inside of the grilles to filter out major particulate contaminents.
[0024] The side wall portins
a,
b connect to narrow inturned lower walls 41, 42, which further connect to upturned
auxiliary walls 43, 44. The latter define an outer compartment to the apparatus. Where
the two side walls
a,
b of each module adjoin, i.e. at each corner of the apparatus, a fan 45 is housed in
this outer compartment. Each fan 45 has an outlet duct 46 extending into the inner
comparment of the apparatus which constitutes a plenum chamber P. Thus, in operation,
the fans 45 draw ambient air into the outer compartment through the grilles 39 (and
optionally from a remote inlet as shown in Fig. 3) and supply it to the plenum chamber
P.
[0025] Intermediate walls 47 are provided substantially parallel to the upper wall 36, across
each corner region so as to direct the air from each fan 45 to the central region
of the plenum chamber P.
[0026] All the walls of each module casing are lined internally with sheets of sound attentuation
material, conveniently in the form of foamed plastics material treated with fire retardant.
Additional sound attentuation panels 48 are located in the outer compartment of each
module. The purpose of all this sound attentuation material is, of course, to deaden
the noise of operation of the fans 45.
[0027] At the corner of each module, between the inner walls 37, 38 (i.e. opposite the fan
45) the casing is formed with a part cylindrical recess 49. When the modules A to
D are assembled together these recesses 49 define a central opening through which
a mounting shaft 50 of theatre lighting 51 extends (Figs. 2 to 4).
[0028] A high efficiency HEPA filter 52 is mounted across the plenum chamber, parallel with
the upper wall 36 and between the auxiliary walls 43, 44 and inner walls 37, 38 of
each module by means of respective fasteners 53. Below this the diffuser means 40
is mounted.
[0029] The diffuser means comprises a planar central area consisting of four substantially
square perforate panels 60, one mounted to each housing module, and successive perforate
peripheral areas, which are provided as respective regions of four elongate angled
panels, 61 to 64, mounted along the four sides of the central area (i.e. extending
between adjacent modules from corner to corner of the inner compartment). In this
respect the respective ends of the four panels 61 to 64 are cut obliquely, as for
a mitre joint, and are mounted, with only a slight gap 83 remaining therebetween,
at the corners (see Fig. 8).
[0030] Each large planar panel 60 is formed with an upturned rim 65 along adjacent edges
which face the side wall portions
a,
b, of the relevant module, and with an upward and inwardly directed flange 66 along
its other two edges which are aligned with the inner walls 37, 38 of the module (see
Fig. 10). Each panel 60 is suspended along one edge only from an inturned lower edge
of an inner wall 37 by means of an elongate mounted strip 67, connected to the flange
66 and by means of pins 68. Its opposing edge is suspended by means of individual
brackets 69, which can be released to allow the panel 60 to swing down, e.g. when
access to the filter 52 is required.
[0031] The elongate peripheral panels 61 to 64 are corrugated, and their special angular
profile is best seen in Figs. 7, 10 and 11. They include spaced, longitudinally extending
perforated regions 71, 72, 73, the latter two of which lie in planes arranged angularly
offset by 10° and 15° respectively from the plane of the region 71. Between the regions
71 and 72 and adjacent the region 73 there are longitudinally extending imperforate
regions 74, 75, 76, which are disposed, in each case, at an oblique angle from adjacent
perforate regions.
[0032] With reference in particular to Fig. 11, it will be seen that a hooked region 77
is formed at the inner edge margin of each panel 61 to 64, which, in use, engages
over the rims 65 of two adjoining central panels 60. Preferably a rubber gasket is
fitted over the rims 65 to provide a more secure connection, without excessive play.
Along the outer edge margin of each panel 61 to 64, there is a substantially flat
edge strip 78 which is bolted onto the underside of the lower walls 41 or 42 of adjoining
housing modules, with a slight gap 79 remaining therebetween. The presence and width
of this gap 79 is ensured by location of washers on the fixing bolts.
[0033] When the central panels 60 and the peripheral panels 61 to 64 are mounted in position,
as illustrated, the central panels 60 are substantially horizontal and the peripheral
perforate region 71 is also substantially horizontal and the other two perforate regions
72, 73 are disposed, in this particular embodiment, respectively, at approximately
10° and 15° from the horizontal. Also in this particular embodiment, as best shown
in Figs. 8
a and 11, the three perforate regions 71, 72 and 73 are provided respectively with
three, five and five rows of elongate perforations.
[0034] Between the outermost imperforate region 76 and the flat edge strip 78, there is
a further longitudinal region 81 which lies at 30° to the horitzontal, and on each
panel 61 to 64 on which a respective strip lamp 80 is mounted. The lamp 80 preferably
has a tapering profile, as shown, so as to minimise disturbance of the air flow pattern
when the equipment is in operation. At each end, beyond the end of the respective
lamp 80, the region 81 of each panel is perforated (see Figs. 8 and 8
a). Disposed on an angle of 60° to the horizontal, between the region 81 for mounting
the lamp 80 and the edge strip 78, is a further narrow region 82 provided with a single
row of perforations.
[0035] In operation, the fans 45 draw ambient air in via the grilles 39 and the prefilters
89 (and optionally from one or more remote inlets, as shown in Fig. 3) and supply
it centrally to the plenum chamber P. From there it passes via the HEPA filter 52,
which should remove all remaining particulate contaminants, and out, as sterile air,
via the respective perforations of the diffuser panels 60 to 64 and the predetermined
gaps 83, 79, as shown by the various arrows in Fig. 11. The air flows vertically downwards
from the central panels 60 and from the first perforated peripheral region 71. Where
the air passes out through the second perforated peripheral region 72 it is deflected
outwardly by about 5°, and where it passes out through the third perforated peripheral
region 73 by about 15°. In this respect, the intervening and adjacent imperforate
regions 74, 75, 76 serve as deflector vanes, helping to guide the air outwards in
the aforesaid pattern. At the corners of the apparatus, air passes out downwardly
through the slight gaps 83 between the adjacent mitre cut edges of the peripheral
panels 61 to 64, and additionally it passes outwardly at about 30° via the additional
perforations beyond the ends of the lamps 80. In this way there is no tendancy for
any influx of contaminated ambient at the corners of the area below the apparatus
and the sterility of this zone is maintained. Further outward air flow at about 60°
occurs via the additional single row of perforations in region 82, outwardly of the
lamp 80, and also virtually horizontally below the housing 30 via the gap 79. The
air flow from the regions 73 and 82 is entrained around the tapering surfaces of the
lamp 80 and then merges, so, again, there is no adverse disturbance which might result
in influx of contaminants to the sterile zone.
[0036] The foregoing is, of course, only illustrative, not limitative of the scope of the
invention and many variations are possible. The strip lights 80 are not essential
and, the theatre lights 51 will of course only be appropriate where the apparatus
is used in a hospital operating theatre. The modular construction is also not essential,
although useful, in practice, to facilitate manufacture and installation. The precise
configuration of and manner of attachment of the peripheral panels can vary in many
ways as will be readily devised by designers in this technical field dependent on
the air flow pattern most suitable to the site of installation. Moreover, the apparatus
need not be ceiling mounted and could alternatively be mounted on a trolley, or on
some other wall structure. Intermediate constructions taking some features of the
embodiment of Fig. 1, and some of the embodiment of Figs. 2 to 11 are also quite possible,
i.e. some peripheral panels with more than one perforate region, and some completely
perforate or with merely one such region, each panel being adjustable in its orientation.
1. Apparatus for providing a clean air zone comprises a housing or canopy (30) having
a plenum chamber(10; P), supply means including fan (45) and filter means (14; 89,
52) operative to supply clean air to the plenum chamber, and diffuser means (20; 40),
in the form of one or more perforated plates (21, 22, 24, 26; 60 to 64) arranged adjacent
the chamber so that air supplied to the chamber flows out therethrough, characterised in that the diffuser means has a substantially planar central area (21; 60) and successive
peripheral areas (22, 24, 26; 72, 73, 81, 82) which are arranged at increasingly greater
angles relative to the central area so that each increasingly deflects the air flow
outwardly from the direction of air flow from the central area.
2. Apparatus as claimed in claim 1 wherein imperforate deflector vanes (23, 25, 27;
74, 75, 76) are located between the successive peripheral areas (22, 24, 26; 72, 73;
81, 82) of the diffuser means.
3. Apparatus as claimed in claim 2 wherein the successive peripheral areas of the
diffuser means comprise separate perforated plates (22, 24, 26) each connected to
a respective imperforate deflector vane (23, 25, 27).
4. Apparatus as claimed in claim 2 wherein the successive peripheral areas (71, 72,
73, 81, 82) of the diffuser means (40) and the intervening imperforate deflector vanes
(74, 75, 76) are provided as integral portions of respective profiled panels (61 to
64), which are arranged around the periphery of the central area (60) of the diffuser
means (40).
5. Apparatus as claimed in claim 4 wherein elongate lamps (80) are mounted upon the
profiled panels (61 to 64) around the periphery of the diffuser means (40).
6. Apparatus as claimed in claim 5 wherein the lamps (80) have a generally tapering
cross-section so as to minimise disturbance of the pattern of air flow from the diffuser
means (40).
7. Apparatus as claimed in any preceding claim wherein a gap (79) is provided around
the outer edge of the peripheral areas (61 to 64) of the diffuser means (40), through
which air can flow outwardly in a direction substantially at right angles to the direction
of air flow from the central area (60) of the diffuser means.
8. Apparatus as claimed in any preceding claim wherein the housing (30) is mounted
in or on a ceiling so that the central area (60) of the diffuser means (40) has a
substantially horizontal disposition, and air flow therefrom is directed downwards.
9. Apparatus as claimed in any of claims 1 to 7 wherein the housing is mounted on
a trolley so as to be capable of being moved to a position above any desired area
or machine.
10. Apparatus as claimed in any preceding claim wherein the housing is constructed
of four substantially identical modules (A, B, C, D).