CA2020114A1 - Dust precipitation from air by negative ionization - Google Patents

Abstract

"DUST PRECIPITATION FROM AIR BY NEGATIVE IONIZATION"
ABSTRACT OF THE DISCLOSURE
A system of precipitating dust includes providing a screen arrangement either in the form of a ceiling with walls or in the form of a canopy with the screen being penetrable by air. Inside the screen and particularly adjacent edges of the screen or the canopy there are provided negative ion emitters positioned in rows so as to generate a curtain of ions precipitating the dust from the air onto the ground for collection. Within the screen can be defined either a clean zone or the screen can be used to confine a dust producing process so as to precipitate the dust immediately adjacent the process to prevent it spreading to other areas. Emitters are provided in the form of a carbon fiber yarn which projects outwardly through openings in a channel member with the yarn being doubled back upon itself in some cases to provide a highly directional emission.

Description

DUST PRECIPITATION FROM AIR BY NEGATIVE IONIZATION
BACKGROUND OF THE INVENTION
This invention relates to a system for dust precipitation from air using negative ionization of the air.
The concept and pcospective commercialization of negative ionization techniques has been around for decades with very little progress due to the lack of credibility arising fcom inappropciate, largely unsuccessful applications and clouded by exaggerated unsubstantiated claims.
At the same time the effectiveness of the technique suffered because the equipment to generate and distribute the required volumes of negative ions was initially bulky, expensive, cequiring constant maintenance and was generally unreliable. These circumstances meant that the effectiveness of applications deteriocated rapidly and became totally suspect in operation.
The increasing employment of the technology is being brought about by some basic trends:
- the development of equipment utilizing electronics and new materials which provide a ~afe, reliable, inexpensive, and non polluting soucce of negative ions and their distribution.
- an increasing need to impcove the air quality ~ . .

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in enclosed enviconments which have been designed to minimize enecgy costs foc heating, ventilating and aic conditioning installations.
- highec standards of safety and health in the wockplace in cegacd to the control of micronic and submicconic pollutants identified as a health hazacd.
- zero defect objectives in manufacturing opecations requicing moce effective means to contcol the migcation of fine dust and pollutants.
- hacd evidence of the effectiveness of industcial applications and incceasing supportive scientific evidence as cegacds pcoper electro climate conditions for human comfoct and wocking efficiency.
Off-shoce countcies, pacticulacly Iscael have maintained a faicly high level of reseacch and development effoct into pursuing the effectiveness of negative ionization techniques in a wide range of applications with considecable success.
Pcogress in Nocth America in this cespect, industrially at least, has been limited to the elimination of static electricity, but with stcong indications of a cecent revival of aic tceatment by modulac, fan assisted negative ion dispecsal units.

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Conventional systems to obtain super clean air with filtcation efficiencies in the micronic and sub-micronic ranges are capital intensive and expensive to run in terms of energy consumption and maintenance costs.
At the same time the systems while fully effective on the air circulated can have little influence to prevent small pacticulants and pollutants ociginating in the working plennum producing pcoblems, apact fcom the inherent dilution cefreshening pcocess allowed by the cycle of aic change~ supplied to the acea. An investigation into further pcioc act suggests that while the use of negative ionization techniques to improve air quality and contain dust pollution in a general way is gaining gcound, thece is little doubt that the level of technology available is relatively crude.
Ions are created in natuce by sunlight, cosmic and tercestcial cadiation and the friction of moving aic and watec that causes electcons to leave hydrogen, nitrogen and othec molecules and to attach themselves to oxygen molecules.
Molecules with extca electcons from negative ions and have a positive effect on the enviconment. They neutralize odours and contribute to the cleac air and the fc~sh smell we find in non-industcial, sparsely populated areas and at the seaside oc healthy holiday cesocts.

2~11J1 In the Pcairie cegions of Canada, the phenomenon best manifests itself by the invigoration experienced after a summer storm with lightning, which relieves the heavy depressing conditions which gradually build up periodically in such areas ducing the summer.
Positive ions are produced by car and factory exhausts, cigacette smoke, dust, soot, fumes from new processes and other domestic and industcial pollutants.
In the wide open spaces these pollutants are attcacted to the negative ground and ace harmlessly dischacged.
But in the enclosed enviconments of modern society - metals, cacs, builings lined and fucbished with synethetic matecials, etc., these pollutions cannot be dischacged to eacth.
At the same time the enveloping car bodies and building structures that keep the positive ions in, also keep the beneficial negative ions out because theic electrical chacges ace absocbed by steel and conccete, bricks and siding material.
A controlled output of negative ions can be produced by electronic means/corona discharge and this source is an appcoved altecnative foc the Polonium Ionizecs withdcawn fcom the macket by 3M in Febcuacy 1988. The soucce generation of ozone is so low as to be almost immeasucable and well below ~ ) 2 ~ 4 the FDA maximum of 0.05 ppm.
SWMMARY OF THE INYENTION
It is one object of the pcesent invention to pcovide an impcoved method for cleaning aic within a building using the negative ionization principles in a unique manner to obtain aic which is cleaned to a hiqh degree with low capital and maintenance costs.
According to a ficst aspect of the invention, thecefore, thece i9 pcovided a method of pcecipitating pacticles fcom aic within a building compcising defining a zone within the building at least pactly pactitioned fcom a cemaining part of the building, sepacating the zone from the building by a scceen which is pecfocated to allow transmission thecethcough of aic and light, and mounting within the zone a plurality of emittecs of negatively charged aic ions.
Accocding to a second aspect of the invention, therefore, there is provided an emitter of negatively chacged aic ions for use in pcecipitating particleq from aic within a building compcising an elongate membec defining a channel thecealong and having a closed fcont sucface, a conductoc mounted in the channel member, means defining a plucality of openings in front sucface through which poctions of the conductor project, and connectoc means on the channel membec .~ :

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foc connecting a high voltage to the conductoc such that the exposed portions of the conductoc generate ions in aic exposed to the conductoc focwacdly of the fcont face.
The pcovision of the elongate multiple emittec enables a high very degree of flexibility to be used in the location and mounting of the emitters for the negative ionization tceatment so that the units can be installed vecy quickly and at low capital cost.
The use of the screen to sepacate the zone to be cleaned fcom the remainder of the building enables a system to be used known as a "clean-zone" or as an altecnative a "revecse clean-zone" in which the majoc dust emitting pcocess is mounted within the zone and the negative ionization tceatment used to extcact the dust fcom the aic prioc to its celease to the cemaindec of the building.
The scceen is pcefecably focmed of a matecial which is pecmeable to aic and light so that the zone can be mounted within the building without regacd to the location of the ventilation units and pcovision of lighting. In many cases, thecefoce, the zone can be developed at an acea leaving the ventilation systems and lighting systems outside of the zone so that thece is no interference whatevec with the existing utilities within the building. The light and aic movement necessacy foc ventilation can then take place thcough the scceen with the scceen and the negative ionization system coopecating to extcact the dust and to prevent its penetcation thcough the scceen.
The system as installed, const~ntly and efficiently will precipitate about 99% of the fine dust pacticles and pollutants in a work acea defined and isolated by specially constcucted barciec screens.
With the coccectly calculated and distcibuted negative ion density within the zone, all fucthec migcation of the pcecipitation micconic and submicconic pacticles will be ef~ectively and continuously pcevented, as a result of the electco-climate cceated and maintained in the "Clean Zone"
area.
The emittecs ace prefecably sepacated fcom any aic flow genecating systems such as fans oc aic duct outlets so that the ions ace fceely emitted into the area to be cleaned wihtout passage of the ions oc any aic stceam caccying the ions through a filtec. Thus the particles ace sepacated fcom the aic by a pcecipitation technique which causes the pacticles to fall to the floor foc collection by conventional house cleaning techniques.
The enclosuce which acts as a cage to isolate and . ' ~

define the acea/volume cequiced fof the application, is considered to be a basic and essential featuce of the "clean zone" concept. The design, constcuction and matecials employed, all contcibute to ensucing the effectiveness of the system.
Installation of the "Clean Zone" enclosuce is simple and flexible and easily fitted cetco-actively with the minimum difficulty to accomodate existing equipment.
The light open natuce of the enclosuce gives little sense of restciction to employees inside the zone and it is generally unnecessary to upgrade lighting levels in the area aftec the installation of the zone.
The effectiveness of the system is ceadily measurable and can be demonstcated by the simple action of enecgizing and deenecgizing the AC powec input.
The cesults in regard to the contcol of fine dust, and ceduction of inclusions are fully substantiated in practical cost effective tecms by satisifed industcial end usecs in cegard to:

- ceduced level of cejections due to inclusions;
- incceased productivity - impcoved wocking enviconment inside and outside the zone.

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Accocding to a thicd aspect of the invention, there iq provided a method of cleaning particles from air within an acea of a building comprising mounting emitters of negatively charged ions in the area of the building separate from any aic flow accangements for causing air flow within the acea, causing the ions to engage particles in the area and to precipitate the particleq downwacdly onto a floor of the acea and collecting the particles fcom the flooc.
Pceferably the method includes a canopy which assists in dicecting the pacticles away from a source of the particles e.g. a dust producing machine towards sides of the machine for precipitation on the floor.
With the foregoing in view, and othec advantages as will become apparent to those skilled in the art to which this invention celates ai this specification proceeds, the invention is herein desccibed by reference to the accompanying dcawings forming a part hereof, which includes a description of the best mode known to the applicant and of the prefecred typical embodiment of the pcinciples of the present invention, in which:
DESCRIPTION OF THE DRAWINGS
~igure 1 is an isometcic view showing a scceen system defining a zone for separation from the cemaindec of building and including ionization generating elements mounted within the zone.
Figure 2 is a top plan view of the zone of Figure 1 showing the location of the ion emittecs.
Figuce 3 is a ccoss-sectional view showing a modified acrangement of scceen assembly defining a zone within a building.
Figure 4 is a ccoss-sectional view through an emittec element of a type shown schematically in Figures 1 and 2.
Figure 5 i3 an isometcic view of the emittec element of Figure 4, Figuce 6 is a cross-sectional view through a second emittec element of the type illustcated schematically in Figuce 1.
Figuce 7 is an isometcic view of the emittec of Figure 6.
In the dcawings like chacactecs of cefecence indicate corcesponding parts in the diffecent figuces.
DETAILED DESCRIPTION
In Figuces 1 and 2 is illustcated a zone defined by a sucrounding wall structure genecally indicated at 10 within which is mounted a machine 11 which is illustcated 2 ~ 2 ~ ~ ~ L~

schematically and is wholly enveloped by the succounding wall stcuctuce defining the zone.
The wall structure comprises two side walls 12 and 13 together with end walls 14 and 15 each of which includes an opening 16 and a slidable closing dooc 17. Accoss the top of the walls is provided a ceiling 19. The height of the walls is arranged to be approximately equal to the minimum wocking height of the ocdec of eight feet and up to a maximum of the ocder of ten feet so that the ceiling 19 is genecally positioned beneath the coof oc ceiling stcuctuce of the building and is sepacate fcom the lighting, duct wock and othec utilities which ace often provided in structural buildings of an industrial type.
This critical acea oc zone is enclosed using a slotted metal structuce as the main suppoctive fcamewock, housing panels coveced with perfocated scceen material of a type which is pecmeable to aic and light but is cesistant to teh passage of dust oc othec fine pacticles. One example of material which can be used is known as TAK Barrier Scceening.
The TAK Bacciec Scceening is a fine gauge fabcic, tceated with a special tacky cesin. This Bacciec scceening is electconically compatible with negative ion pcesence and wocks harmoniously to create a dust fcee enclosuce, tcapping lacge particles, yet allowing the zone to bceathe without any inccease in air speeds across the fabric.
The enclosuce which acts as a cage to isolate and define the acea/volume required for the application is considered to be a basic and essential featuce of the "clean zone" concept. The design, construction and materials employed, all contcibute to ensucing the effectiveness of the 3ystem.
Installation is simple and flexible and easily 10fitted cetroactively with the minimum difficulty to accommodate existing equipment.
The light open nature of the enclosuce gives little sense of restriction to employees inside the zone and it is genecally unnecessary to upgcade lighting levels in the acea after the installation of the scceens.
Strategically located emitters at ceiling level within the enclosure produces a bombardment of negative ions to pcecipitate particles inside the zone. At the same time a high density is created within the confines of the enclo~uce which 20will not allow particles to penetrate the screens, in either direction.
All openings into the zone cequired foc access are protected by a cuctain of ions which comprises a peciphecal ~?.~

distcibution of emi~ters to focm an high density concentration of directed negative ions to pcecipitate any dust which might otherwise migrate into the area. Altogethec a total screened, "cage" effect is pcoduced with a fully isolated Clean Zone sepacate and distinct from the general wocking area of the facility.
On completion of a Clean Zone, and activation of the ion generation system, an ultra Clean Zone will be established foc process within 24 houcs. This pcotection will be available as long as the system is in opecation with the necessary negative ions densities being maintained automatically at the pcopec levels.
The slotted steel frame wock is indicated at 20 and is of a conventional nature available for ceceiving wall panels and foc bug screens. A solid panel is indicated at 21 and the screen material i3 indicated at 22.
The ceiling is formed in the same stcuctuce employing wholly the scceen material 22. The enclosure can thus be focmed relatively simply by the assembly of the frame work following which the panels ace simply flipped into place to define the completed zone. In Figures 1 and 2 there is provided a plurality of emitters of negative ions including two separate types of emitters indicated at 25 and 26 respectively.

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The details of the emitters 25 are shown in Figuces 6 and 7 and the details of the emitters 26 are shown in Figuces 4 and 5.
Turning therefore to the emitters 25 shown in Figuces 6 and 7, this emitter comprises an elongate channel member 30 formed in two halves 31 and 32 which a~e snap fit together along a joining line 33 to focm an enclosed elongate tubular member. End caps 34 are pcovided of a type shown in Figure 4 which compcise a press fit into the end of the tubular member thus forming a complete enclosure. The emitter 26 as shown in Figuce~ 4 and 5 comprise~ the same basic housing tructuce. The length of the housing can be selected according to requirements as shown in Figures 4 and 5 the emitter is of a celatively short length whereas in Figure 6 and 7 the emitter 25 can be significantly longec.
Each of the housings includes a connectoc 36 of a type including a body 37 which has an outec screw thread 38 and an end cap 39. The body can thus be attached thcough an opening in the housing simply by clamping into place by one oc moce nuts 40 and 41. In the arrangement shown in Figuce 6 there are two nuts provided each on a respective side o~ a wall of the housing so as to space the end cap 39 away from the wall. In the arrangement shown in Figure 4, the end cap is clamped against the end face of the housing by the nut 40 on 2 ~

the opposed side of the wall of the housing. The housing includes a centcal bore which caccies a conductoc 42 and a volume of the sleeve which projects outwacdly beyond the inner end of the body to connect to a conductoc 43 pcovided within the housing. The tubulac connector 42 is thus of a type which can ceceive simply a single pole connectoc by which high voltage feom a genecator 45 (Figuce 2) can be connected to the emittec with a plucality of emittecs arcanged in secies by connection of a wice fcom each to the next.

The conductoc 43 is focmed of a yacn of a conductive fibce matecial foc example cacbon fibces which ace cut into staple fibces and then spun and twisted to focm a multi fold yacn. The housing is focmed of vecy suitable insulating plastics matecial so that the conductoc yacn can simply be thceaded into the housing and can cest against the housing without focming a shoct ciccuit.
In Figuces 4 and 5, a fcont face of the emittec which is defined by the uppec face of the uppec pact 31 has a plucality of openings 48 substantially equidistantly spaced along the front face in a single line accos~ the centce of the fcont face. The yacn is then thceaded simply in a stitch pattecn so that poctions of the yacn ace exposed on the outec side of the fcont face and poctions of the yarn ace maintained ?~2~ Ll on the innef side of t~e ffont ~ace that is within the housing as indicated at 49 and 50 respectively.
This focm of emittec is substantially multidicectional so that when a high voltage of the ocder of 6000 volts is applied to the conductor 43 the exposed poctions 49 of the yarn generate a corona effect causing the creation of ions in the area of the cocona effect with those ions tending to escape fcom the exposed poftion of the yarn 49 in all dicections away fcom the front surface. The ions thus tend to spcead away fcom the emitter in all dicections and to attach to pacticleq within the aic. A~ the pacticleq ace heaviec than aic the particles tend toward the ground surface and in view of the generally positive charge on the ground surface, the negatively chacged pacticles are attracted to the gcound surface and fall to the ground surface foc collection on the gcound sucface both in view of gravity and in view of the electrostatic attraction.
As shown in Figure 2, the emitters 26 are arcanged in arcay acound the centre of the zone. In the example shown thece are fouc rows of the emittefA accanged substantially equadistantly spaced across the width of the zone. In this way the full area of the intefioc of the zone is bombarded with the ions which ace spcead equally throughout the 2~2~

centcal acea of the zone. As shown in Figure 1 the emitters 26 are mounted at the ceiling area on suitable suppocts (not shown). This place~ the height of the emitters generally at the height of the ceiling which would be in the order of eight to ten feet from the ground which has been found to be particularly effective since the ions ace thus prevented from dissipation to othec aceas of the building befoce they can caccy out theic function of attachment to particles and tcansporting those particles to the ground surface.
The e~i~ter 25 shown in ~igures 6 and 7 i3 modified celative ~o the emi~tec 26 in that the conductoc 43 i3 confined into shoct poctions which project outwacdly fcom the fcont face of the channel membec 31. Thus the fcont face 31 includes foc each poction a pair of holes 55 and 56 which ace closely positioned togethec with only a naccow separating portion 57. The conductor is then thceaded thcough the holes 55 and 56 and passes thcough a collar membec 58 succounding the holes and supporting the outerly pcojecting portion of the conductoc 43 a~ indicated at 59. The collar member 58 can be bonded to the front sucface of the channel member or can compcise a separately manufactuced product which insects fcom an undecside of the upper surface of the channel membec through a single hole in the wall 31 and provides by itself the pcopec - ~ ~ 2 Y~

suppoct foc the projecting poction 59.
The pcojecting portion 59 is confined to a short length of the fcont face of the channel membec is caused to turn back upon itself at a sharp angle. This tends to cause individual ones of the staple fibces 60 to pcoject outwardly from the yarn at the point where it is tucned sharply thus focming a plurality of spikes which pcoject outwardly from the sharply tucned portion of the conductoc 43. These spikes have been found to generate ions in a highly dicectional mannec in that the ion~ are pcefecentially generated at the apex of the fibre spike and thus tend to be emitted in a direction generally at right angles to the front face.
The emitter 25 is therefore much more directional than the emittecs 26. In view of this propecty, the emittecs 25 ace thus arcanged to generate a curtain of ions lying in a plane longitudinal of the emittec 25 and at right angles to the front face.
Turning therefoce to Figure 1 the emitters 25 are mounted acound the opening 16 along the sides of the opening and along the top of the opening with the emitters facing inwardly to generate a cuctain across the plane of the opening of a high concentcation of ions. This cuctain acts to "attack"

any dust particles attempting to pass through the opening so 1, . .

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that those particles are acted upon quickly and tend quickly to fall to the ground at the acea of the opening. As a back up foc the emitters 25 at the opening, one oc more cows of further emitters 25 can be positioned inwardly of the opening. Thus in Figure 2 there ace two further rows of emitters one positioned just inside the opening and the next behind the first thus forming three curtains of ions acting specifically on the dust tending to move through the opening carried by persons or equipment passing through that opening oc by air movement thcough the opening.
The cuctain of ions thus act at the openings in the zone and in addition the genecal level of ions within the zone acts in coopecation with the permeable tacky scceen to cause dust and othec particles to be collected at the screen rather than to pass through the scceen. It has been noted that the ions have a tendancy to act upon the dust just outside of the scceen so that lacge quantities of pacticles fall to be collected on ground oc othec horizontal sucfaces just outside the screen thus preventing the dust fcom passing through the screen.
As shown in Figure 3 there ls provided a modified arrangement including a floor surface 70, a machine 71, a screen 72, an uppec ceiling 73 of the building and utilities , . . . :

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including duct wock 74 and lighting 75.
In this case the screen is modified in that it comprises simply a canopy suppocted fccm the ceiling or coof on support wireq 76. The canopy includes a ceiling 77 formed in panels similac to the ceiling 19 togethec with four side wall portions 78 which hang down fcom the side edges of the ceiling.
The details of the constcuction are not shown but are similar to that ~hown in Figure 1. This of course leaves the side walls of the zone open for passage of persons or equipment but generates enough of a 9eparation of the zone from the building to enable the cleaning of dust from around the machine 71.
Figuce 3 also illustrates the arrangement in which the zone is separated from the ventilation systems including the duct work 74 and from the lighting systems which are maintained without modification in the building. The light into the zone is thus provided by the conventional lighting of the building. The ventilation or air movement within the zone is provided by the conventional building ventilation systems including the duct work 74 and a nozzle 80 which projects aic to move downwardly through the scceen and into the zone.
In the arrangement of Figuce 3, the dust iq prevented f~om passing into the intecior of the zone through the open side walls by the generation of a cuctain of ions , ~2~

similac to that at the opening 16. Thus the emittecs 25 aee po3itioned so as to generate a cuctain pcojecting downwacdly at the open side walls and this can be backed up by one or moce fucthec cows of emittecs 25 positioned inwafdly of the side walls. Also similar to the construction shown in Figures 1 and 2, intecioc emittecs can be of the type illustrated at 26 to genecate a moce even spcead of ions thcoughout the zone.
In Figures 1 and 2 the machine 11 illustcated schematically compcises a machine foc caccying out an indu9trial pcocess of a type which requires vecy clean air for example a paint spcaying machine oc part molding machine so that this machine is maintained within a clean zone in which the dust in the cemaindec of the building is kept outside of the zone and is pcevented from entering the zone and from remaining within the zone once it has enteced. The clean zone must of course be backed up with good housingkeeping pcactices which will not be explained in detail here.
In the accangement shown in Figuce 3, the zone is effectively a "ceverse clean zone" in which the machine 71 is of a type which generatea high levels of dust, foc example a paper cutting machine or a textile spinning machine. In this case the machine itself is succounded by a zone which pcotects the cemaindec of the building fcom ceceiving the high `` 2~

quantities of dust generated by the machine itself. In this way instead of maintaining the w~ole of the building cleaned, it is only necessary to clean the acea sucrounding the machine concecned so that the dust fcom that machine is prevented from escaping to the remain~er of the building and is also contained within that acea by ~he action of the negative ions on the dust particles and the tendency to pcecipitate and thus to collect on the gcound su;cfaces fcom which they can be readily removed by nocmal housekeeping systems.
The emitte~ are enticely free fcom any focced air effect so that neithec the ions noc any pacticle laden air passes thcough a filter. Thus the negatively chacged ions collect onto the pacticles causing them to conglomerate and to pcecipitate onto the flooc. The flooc thus acts as a collectoc foc the particles and thi~ can be ceadily cleaned by conventional housekeeping practices. In addition, the tendancy of the pacticles at the acea above the machine is to rise so that the bombacdment of the pacticles in the aic space of the canopy with ~he ions causes the pacticles to tend to flow outwacds of the machine and to pcecipitate out onto the flooc at the sides of the machine.
The details of the electcical equipment genecating the high voltage ace not shown as these ace well 2 ~ 2 ~

known to one skilled in the act. In addition the wicing connections and the necessary conduit are not shown.
As an altecnative arrangement for use in some building structures, the emittec 25 can be used at the exit nozzle of the ventilation duct wock so that the ions are dicected into the aic stream which passes thcough the nozzle as the air emecges fcom the nozzle and is communicated into the building. The u~e of the emitters in the elongate or stcip form enables the emittecs to be tailoced to the 3pecific nozzles concerned by simply cutting to length oc selection fcom a numbec of available lengths and attachment at the nozzle.
Since various modifications can be made in my invention as heceinabove described, and many apparently widely diffecent embodiments of same made within the spicit and scope of the claims without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustcative only and not in a limiting sense.

Claims

(1) A method of precipitating particles from air within a building comprising defining a zone within the building at least partly partitioned from a remaining part of the building, separating the zone from the building by a screen which is perforated to allow transmission therethrough of air and light, and mounting within the zone a plurality of emitters of negatively charged air ions.
(2) The invention according to Claim 1 wherein the emitters are mounted in an array within the zone, at least some of the emitters being separated from any air movement devices.
(3) The invention according to Claim 1 wherein the building includes ventilation systems for introduction of air into the building, the ventilation system being separate from the emitters.
(4) The invention according to Claim 3 wherein the ventilation system is positioned outside of the zone so that air movement within the zone is obtained by passage of air through the screen.
(5) The invention according to Claim 1 wherein the screen has at least one opening therein to allow passage therethrough of persons and/or equipment and wherein there is provided a plurality of emitters arranged in a cow at the opening so as to generate a curtain of ions.
(6) The invention according to Claim 5 including a second cow of emitters parallel to the row at the opening so as to define a second curtain of ions.
(7) The invention according to Claim 5 or 6 wherein the emitters at the opening are shaped to generate ions in a preferred direction with the direction being arranged so as to define the ions into a curtain.
(8) The invention according to Claim 7 wherein the array of emitters includes a plurality of further emitters mounted within the zone at a position spaced from the opening with the further emitters being shaped to be less directional than the emitters at the opening.
(9) The invention according to Claim 1 wherein the zone is arranged to surround an industrial process which constitutes a source of particles which is higher than that in the remainder of the building.
(10) The invention according to Claim 1 wherein the zone is arranged to surround an industrial process which requires a particle concentration in the air which is less than that of the remaining part of the building.
(11) The invention according to Claim 1 wherein the screen is arranged to define a ceiling and a plurality of walls spaced from the ceiling and walls respectively of the building so as to substantially fully surround the zone and partition the zone from the remainder of the building.
(12) The invention according to Claim 1 wherein the screen comprises substantially a canopy including a ceiling portion so as to overlie the zone leaving walls of the zone open and wherein there is provided a plurality of highly directional emitters arranged around the edge of the canopy so as to define a curtain of ions around the edge of the canopy.
(13) The invention according to Claim 1 wherein the emitters are positioned so as to emit ions in a generally downward direction so as to precipitate the particles downwardly for collection on the floor.
(14) The invention according to Claim 1 wherein at least one of the emitters comprises an elongate member defining a channel therealong and having a closed front surface, a conductor mounted in the channel member, means defining a plurality of openings in front surface through which portions of the conductor project, and connector means on the channel member for connecting a high voltage to the conductor such that the exposed portions of the conductor generate ions in air exposed to the conductor forwardly of the front face.

(15) The invention according to Claim 14 wherein the conductor comprises a yarn formed from a conductive fibrous material.
(16) The invention according to Claim 14 wherein the conductor portions form a plurality of loops projecting outwardly from the channel member.
(17) The invention according to Claim 16 wherein each loop comprises a portion of yarn which is sharply angled back upon itself to define a sharp turn in the yarn leaving a plurality of fibres exposed at the sharp turn.
(18) The invention according to Claim 17 including a collar member surrounding the loop of yarn and supporting it so as to project outwardly from the front surface of the channel member.
(19) An emitter of negatively charged air ions for use in precipitating particles from air within a building comprising an elongate member defining a channel therealong and having a closed front surface, a conductor mounted in the channel member, means defining a plurality of openings in front surface through which portions of the conductor project, and connector means on the channel member for connecting a high voltage to the conductor such that the exposed portions of the conductor generate ions in air exposed to the conductor forwardly of the front face.
(20) The invention according to Claim 19 wherein the conductor comprises a yarn formed from a conductive fibrous material.
(21) The invention according to Claim 19 wherein the conductor portions form a plurality of loops projecting outwardly from the channel member.
(22) The invention according to Claim 21 wherein each loop comprises a portion of yarn which is sharply angled back upon itself to define a sharp turn. in the yarn leaving a plurality of fibres exposed at the sharp turn.
(23) The invention according to Claim 17 including a collar member surrounding the loop of yarn and supporting it so as to project outwardly from the front surface of the channel member.
(24) A method of precipitating particles from air within an area of a building comprising mounting emitters of negatively charged ions in the area of the building separate from any air flow arrangements for causing air flow within the area, causing the ions to engage particles in the area and to precipitate the particles downwardly onto a floor of the area and collecting the particles from the floor.
(25) A method according to Claim 24 including forming a canopy over the area having a ceiling portion and depending wall sections at edges of the ceiling portion with lower edges of the wall sections having spaced from the floor, positioning the emitters adjacent the wall sections and at the ceiling portion so as to emit ions into the air space defined within the canopy, locating a source of particles to be cleaned underneath the canopy so that the particles tend to rise into the canopy and causing the ions to precipitate the particles to sides of the source for collection on the floor adjacent the source.
(26) A method according to Claim 25 including mounting emitters on the lower edge of the wall sections and directing the ions directionally downwardly therefrom.