SE541085C2 - Controlled deposition of airborne particles indoors using structured electrostatic forces - Google Patents

Abstract

SummaryThe airborne bioload (concentration of biologically active particles) has become a major health issue affecting the pregnant woman, the growing child and the elderly.The present invention relates to a method and apparatus for the reduction of airborne fine particulate matter. More particularly, the invention relates to a method and apparatus for reducing the level of air borne particles in a micro-environment using an electrostatic field generated by an active electron repulsing emitter avoiding the creation of negatively charged surrounding structures allowing the generation of a surface current on a high resistivity surface and thereby the maintenance of said electrostatic field. The term micro-environment as used herein is intended to define a localized volume of air to be cleaned according to the invention. The micro-environment may be a large, contained environment such as a room of varying size.

Description

CONTROLLED DEPOSITION OF AIRBORNE PARTICLES INDOORS USING STRUCTURED ELECTROSTATIC FORCES The airborne bioload (concentration of biologically active particles) has become a major health issue affecting the pregnant woman, the growing child and the elderly.

The present invention relates to a method and apparatus for the reduction of airborne fine particulate matter. More particularly, the invention relates to a method and apparatus for the reduction of the level of air borne particles in a micro-environment using an electrostatic field generated by an active electron repulsing emitter avoiding the creation of negatively charged surrounding structures allowing the generation of a surface current on a high resistivity surface and thereby the maintenance of said electrostatic field. The term micro-environment as used herein is intended to define a localized volume of air to be cleaned according to the invention. The micro-environment may be a large, contained environment such as a room of varying size.

“The state of the art” in relation to the current application is defined from UK patent ”Reduction of airborne contaminants” (GB 2304576) and PCT application WO201 3/089610A1 “A technique including a method and arrangements to improve animal’s biological and/or physical performance by reducing the bioload, defined as biologically active particles in the stable air or within transporter vehicles”, The current application should be regarded as a progression of knowledge and experience earned from extensive field tests.

The bioburden of the air Airborne infections Microorganisms (bacteria and moulds) and viruses are transmitted by the air we breathe. At the same time as we may be exposed to viruses, we will also contaminate the air ourselves. A person who is infected will transmit viruses 24h before there are any clear symptoms. Apart from coughing and sneezing, influenza viruses will appear in the exhaled air.

The influenza virus may only survive in the air in form of a virus-carrying small drop of water. These drops of water containing an infectious influenza virus particle are 0.3 - 1 um large. This means that the infectious virus may stay airborne for a considerable amount of time. 50% of particle of 1 um size will stay airborne for more than 10 hours and if the particle is only 0.3 - 0.4 um in size less than 10% would have settled after 10 hours. This means that the air may be contaminated many hours after an infected person have visited the room.

What is then the possibility to reduce airborne contamination and the infection rate? Fine and electrically charged airborne particles are required to allow the formation of droplets (achieved as water molecules cluster around a fine particle), a substantial reduction in the number of fine airborne particles should reduce the likelihood of virus particles surviving the hostile environment of the clean air. It would seem logical to test the hypothesis that less fine particles indoors would also reduce infection rates among young children exposed to frequent upper airway infections from attending day care centres.

Daycare centres with numerous young children attending are known for their high viral infection rates influencing health costs<1>, productivity and quality of life for the child and its family. In a daycare centre, the child’s immune system has to handle respirable particulates generated by the activity in the room as well as those generated by the surrounding environment and as a consequence the ability to manage an infection may be affected. There is limited documentation on efficient methods to improve the situation. Own research<2>has shown that room operated electrostatic air cleaners (EAC) reduce the concentration of activity generated particles by 60% and the sickness rate from viral infections among pre-school children by 55% as well. Apart from capturing the virus particles, the purified air may reduce the level of immunological stress, enhancing the capacity of the child to withstand a viral infection. Furthermore, to maintain its viability, a virus needs to protect itself from reactive oxygen. This is done by being part of a cluster of vapour, forming around a small particle. If there are fewer particles it may not be so easy for the reduced number of air borne viruses to hide and avoiding evaporation. The electrostatic field is generated through the release of electrons that will combine with oxygen and vapour generating hydrogen peroxide (H2O2), another deterring mechanism for the viruses further reducing the bioload of the indoor air. This is the most likely explanation to a recent experimental observation of ionizer killing a multitude of viruses<3>.

Regarding bacteria, we have observed a 60% reduction in air borne colony forming units in a hospital ward exposed to an electrostatic field generated by the liberation of electrons into the indoor air. <1>de Hoog, M. L., Venekamp, R. P., van der Ent, C. K., Schilder, A., Sanders, E. A., Damoiseaux, R. A., ... & Bruijning-Verhagen, P. (2014). Impact of early daycare on healthcare resource use related to upper respiratory tract infections during childhood: prospective WHISTLER cohort study. BMC medicine, 12(1), 107. <2>Rosén KG, Richardson G. Would removing indoor air particulates in children's environment reduce rate of absenteeism - a hypothesis. Sci Total Environ. 1999, 234.: 87-93. <3>Ilagbom, M., Nordgren, I, Nybom, R., Hedlund, K. ()., Wigzell, II., & Svensson, L. (2015). Ionizing air affects influenza virus infectivity and prevents airborne-transmission. Scientific reports, 5.

Article number: 11431 doi:10.1038/srepl 1431.

The mould issue Mould is part of our natural environment outdoors but once it starts to accumulate in the indoor air there may be a problem both for humans and animals. The problem may increase markedly in case the mould starts to fight for its own existence by starting a warfare using mycotoxins. There are about 400 different toxins found indoors with the most well-known aflatoxin and penicillin<4>. These become airborne as very fine particles<5>and once inhaled are known to cause a multitude of problems from the mucosal membranes of the airways to general fatigue and neurological symptoms<6,7>.

Improving the activity of the immune system The obvious problem is that most of us are forced to live under circumstances that are less favourable with regard to the fine and very fine respirable particles that have been shown to reduce quality of life and even life expectancy<8>. The reason seems to be that as the particles gets down the respiratory tract, they are trapped and has to be handled by the immune system generating something called “oxidative stress” like we see with an inflammatory reaction. This stress may become so marked that it occupies the immune system resources and causes a cascade of events leading to alterations in the functioning of other cells and organs including our ability to manage our own bacteria. This may be an important mechanism behind the maintained and increased post-operative infection rates in elderly patients living in polluted areas are exposed to major surgery.

However, it seems as if we are able to recover once the bioload of the air is reduced. Our own research in Swedish day-care centres published in 1999<2>using electrostatic air cleaning principles operating in the microenvironment was, to our knowledge, the first to identify the impact of electrostatic air cleaning reducing particulate matter of the indoor air and substantially improving the attendance rates due to less upper air way infections among children aged one to six years of age. These infections are viral in origin and the outcome of <4>Bloom E Mycoloxins in Indoor Environments - Determination using Mass Spectrometry, Thesis December 2008, Dept of Microbiology, Univ of Lund, Sweden <5>Bloom E, Nyman E, Must A, Pehrson C, I.arsson L. Molds and mycotoxins in indoor environments— a survey in water-damaged buildings. J Occup Environ Hyg. 20y09 Nov;6(ll):671-8. <6>Straus DC (2009) Molds, mycoloxins, and sick building syndrome. Toxicology and Industrial Health 25: 617 635. <7>Kilbum KH (2009), Neurobehavioral and pulmonary impairment in 105 adults with indoor exposure to molds compared to 100 exposed to chemicals. Toxicology and Industrial Health 25: 681-692 <8>WHO. Burden of disease from household air pollution for 2012. Geneva: WHO, 2014. http://www.who.int/phe/health_topics/outdoorair/databases/FINAL_HAP_AAP_BoD_24March2014.pdf the study verified the hypothesis that ambient air cleaned from fine particles reduces the rate of airborne contamination.

The impact of particle reduction measures have been studied in healthy elderly<9>. The study used HEPA filters to clean the indoor air and looked at the function of the vascular bed and the blood flow to the hand. Surprisingly, the Danish study found that already after 48 hours a significant improvement occurred. Thus, it appears as if short periods of air cleaning would reduce the environmental stress caused by fine particles in the air.

HEPA filters may have additional electrostatic air cleaning mechanisms incorporated.

However they will only clean the air that passes through the fan operated system and have negative side effects through their size, noise and energy consumption as well as cost of maintenance. Furthermore, a high flow of air may cause problems from particulate matters becoming airborne.

Very fine particulate matter with a size of < 1.0 micrometer (?m), generated by the combustion engine, particularly the diesel engine, is a major health problem even indoors because it is virtually impossible to prevent particles of this size from entering normal buildings. In addition, activity within the building itself creates particulate matter of a similar size. All these small particles may affect lung function and activate the immune system.

It is worth noting that, during an eight hour working day, we breathe some 3,000 1 of air which, in average inner city air, contains some 150,000 particles per litre of air with a particle size of > 0.3 ?m.

Furthermore, the crust of the earth and the floors and walls our indoor environments have naturally occurring positive electrostatic charges. This means that particulates in the air also become positively charged. The repellent force will enhance their ability to stay airborne. From this follows that altering the electrostatic forces within the room would provide a suitable means for reducing the very fine particles in the air we breathe and in view of the health issues raised may be considered as an important task. <9>Bräuner E.V., Forchhammer L., M0ller P., Barregard L., Gunnarsen Afshari A et al. Indoor particles affect vascular function in the aged - an air filtration-based intervention study. Am J Respir Crit Care Med 2008;177:419 425.

Electrostatic Air Cleaning (EAC) as presented in previously publicized patents<10>has been designed to create an electrostatic field within the room, using a high voltage technique utilising carbon fibre emitting technology. The intention of the prior art has been to optimize the release of electrons from the free-ending carbon fibres by using an electron emitting structure based on a methodology in which the electrons and ionized air are directionally concentrated within the micro-environment by reflecting them from a capacitor located adjacent the electron generator (claim 7<10>). An apparatus built according to the claim would contain an electrically conducting material -preferably a metal that would be fully isolated from zero potential and thus passively over time obtain a negative potential. Furthermore, this capacitor plate was mounted on an electrically insulating surround which was bounded by a metal frame connected to zero potential via a mega ohm resistor. Such a construction would serve its purpose in theory but due to the accumulation of dirt over time and the high voltage used, the surface of the insulating surround would serve as a conductor and charges would be lost to the grounded frame eliminating the function of the basal plate to serve as an electron reflecting mirror.

A means to achieve the electron mirror function is disclosed in reference<11>. Basically, instead of having an electron mirror function that is built over time from a passively generated negatively charged capacitor, we now generate the electron reflecting function actively by having the whole structure charged with a high voltage (active electron mirror). Thus, the emitting structure preferably consists of electrically conductive polymer bands on which carbon fibres are connected and extended in the air. Such multi stranded carbon fibres consist of >100 filaments, each serving as a point of release of electrons into the air (coronal points). These bands are connected to a high voltage generator delivering a minimum of -6 kV at low amperage (less than 1.0 mA). The free-ending carbon fibre filaments will emit electrons which are repelled from the negatively charged surface of the conducting polymer band surface, generating an electrostatic field to capture the particles and at the same time the oxygen molecules will become charged with an extra electron generating a superoxide molecule adding to the oxidative capacity of the ambient air. As indicated in ref.<11>, in a stable <10>Swedish patent (Metod och anordning att reducera halten luftburna föroreningar i ett mikroområde; SH521 662) and UK patent ”Reduction of airborne contaminants” GB 2304576. <11>KG Rosén A technique including a method and arrangements to improve animal’s biological and/or physical performance by reducing the bioload, defined as biologically active particles in the stable air or within transporter vehicles, PCT application WO2013/089610A1 there is no need to control the deposition of particulates whereas this has to be handled differently indoors where humans reside.

As a function of this air cleaning ability, we will have a potential problem with the deposition of particulate matter, not letting it contaminate the surfaces of the room. To illustrate the matter, a standard room of 30 m<3>with a basal air exchange rate of 0.5 air changes per hour and a particulate matter concentration (PMio) of 30 ?g per ft<3>will have approximately 300g of black sooth deposited on the surfaces a year assuming a 70% air cleaning rate.

In the previous invention, the grounded frame located within a short distance (centimetres) from the “capacitor plate” was used for dirt deposition purpose. This grounded frame was located a short distance from the negatively charged capacitor operating back plate. This has been found to be an inadequate technology as particles would settle not only on the grounded frame but also on the non-conductive structure located between the negatively charged capacitor and the grounded frame. These particles would accumulate over time and serve as a conductive media causing the loss of the negative charge and thus the ability to increase the kinetic energy of the electrons released from the free ending carbon fibres.

With the experience earned, we may now look at the prerequisites of a method and apparatus to optimise the following items: 1. Achieve an electrostatic field from the release of electrons without the risk of generating ozone. 2. Generate an air cleaning compartment of sufficient size within the micro environment. 3. Controlled deposition of particulates on easy-to-clean surfaces by providing a method for a controlled loss of electrons from said electron exposed surfaces as well as other adjacent structures.

Item 1: The risk of ozone production is related to the electrical charge at the coronal point of electron release into the air. The non-oxidizing property of carbon fibres enables a steady and high electrical charge without the risk of ozone production. The addition of a positively charged surface within a short distance (3 - 20 cm) from the negatively charged emitter will increase the difference in potential and serve to focus and at the same time strengthen the electrostatic field.

Item 2.

The size of the air cleaning, electron enriched compartment has to be related to the size of the micro environment and the bioburden within said environment. A minimum of 100 coronal points covering an area of at least 150 cm<2>is required to reduce and control the bioload in a 30 m<3>single occupancy bed room. In a room with many occupants, this air cleaning capacity has to increase markedly often covering an area of >1 m<2>allowing several cubic meters of the room air to be included in the electron enriched compartment. From this follows that said compartment has to be extended using the walls or windows for fixation of a suitable apparatus consisting of 1. an electrostatic field generator 2. an electrostatic field enhancement and focus function 3. a suitable particle deposition surface.

Item 3.

As illustrated above, the air borne bioload indoors may be considerable and the particulates has to be captured on an easy-to-clean surface located on the vertical surfaces such as a wall or a window. Furthermore, an efficient air purification process requires the maintenance of the electrostatic field and the prevention of a build-up of charged surfaces apart from those involved in the electron emitting structure. Thus, an important part of the current invention is to allow for a surface current to be generated.

Figure 1 illustrates how the concentration of course (>2.5 ?m) particulates in a 60 m<2>class room alters when the air is exposed to electrons initially (Friday - Monday afternoon) without the power supply (12V AC/DC converter) being connected to earth.

Although there was no activity within the room over the weekend, the particulates accumulated to >600 particles L<-1>during the night whereas the norm would be <20 particles of a size >2.5 ?m (activity generated particles). When the power supply was connected to earth (A), the air was purified with particulates reaching low levels.

Thus, it appears there is a risk in using an active electron emitting function where the kinetic energy of the electrons are enhanced by an electron repulsing mechanism as not only may the air cleaning properties be lost but the massive electron release may create an uncontrolled electrostatic field and a dominant negative charge within the room adding to the kinetic energy of the particulates making them less affected by gravitation and the sedimentation process being counteracted by the electrostatic forces making the particulates to accumulate over time.

Another example is when said electro emitting structure with its power supply properly connected to earth, is positioned in front of a surface, conductive or non-conductive, that is used to deposit the particulates and where said surface is not connected to zero potential (earth). Within some minutes a negative charge will be created on said surface equalizing the difference in electrical potential between said electron emitting structure and said surface hereby weakening the electrostatic field to the extent that it will disappear.

These two observations illustrate the need to combine the high electron emitting capacity obtained from a multitude of free ending carbon fibres connected to high voltage at low amperage and fixed on an electron reflecting negatively charged conductive polymer and an adjacent positively charged structure serving to direct the electrostatic field with a mechanism to control and maintain the flow of electrons generating the electrostatic field enabling said electrostatic field to be maintained over time. This is achieved by having both the power supply unit and surface where the particle are deposited connected to zero potential allowing an unidirectional surface current to be generated avoiding the build-up of a negatively charged structure near said electron emitter.

The novelty of the current embodiment is the control of an extended electrostatic field within the microenvironment, said control reflecting on its ability to capture airborne particulates on an easy-to clean surface avoiding the build-up of adversely charged structures located near, within centimetres of the electron emitting unit. This is achieved by having both the power supply and the particle collecting site connected to earth.

Furthermore, in case said surface is made from a clean electrically non-conductive material of high surface resistivity such as glass or acrylic sheets (resistivity > 10<13>ohms); the particle deposition should be enhanced by adding a positive charge onto said surface. This is achieved by having said adjacent positively charged structure connected to said non-conductive surface.

It is an object of the invention to purify the indoor air, where the particulate load and especially the biologically-active load or “bioload” can be reduced by creating a hostile environment for micro-organisms in a highly contaminated and large environment such as a school or a hospital ward.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which: Fig. 2 is a side view of the principles of the electrostatic field generating and particulate capturing apparatus.

Fig 3 provides a schematic presentation of the power supply and the connections to earth required to avoid the generation of an electrostatic field of uncontrolled direction together with the components depicted in Fig. 2.

Fig 4 provides a schematic side view of electrode emitting and particle collecting components.

In Figure 2 the design of the emitter band is shown in a side view of the electrostatic field generating arrangement consisting of a semi-conductive polymer band 3 designed with a base 2 having a width of 10 to 25 mm, preferably 15 mm and on which a multitude of carbon fibre filaments 1 are attached. Located at a distance of 3-5 centimetres is the positively charged structure 4 that has a contact 5 with the easy-to-clean surface 6 that is in contact to earth.

Figure 3 depicts the connections to earth 8 for both the power supply (AC/DC converter) 7 and the particle collecting surface 6 via the special lead 9. The figure also depicts the high voltage generator 10 connecting 11 to the electron emitter delivering a negative electrical charge and also connecting 12 to the positively charged structure 4 delivering a positive charge.

Figure 4 illustrates an embodiment of the apparatus with the electron emitting electrical field generating unit consisting of the semi-conductive polymer 3 on which the free ending multitude of carbon fibres 1 are attached. Said band mounted on holders made from a nonconductive polymer 13.

The length of said unit will vary depending on the size of the room and the bioload generated both from the ambient outdoor air and from the activity within the room.

To purify the indoor air corresponding to an air exchange of 1.5 air exchanges of particle free air per hour in a room of 190 m<3>size requires an EAC unit consisting of a semi-conductive polymer of three meter with carbon fibres attached with a minimum distance of 9 centimetres. The basic conductive structure is charged with >6 kV minus. Positioned in parallel to this emitting structure is another band 4 of similar structure but connected to a positive charge of >500 V plus. In connection with this positively charged band of semi-conductive polymer is the easy-to-clean surface, preferably made from acrylic glass and positioned on a wall exposing the electrostatic field to the indoor air. The distance between the two bands 3 and 4 should be between 3 and 10 centimetres, preferably five centimetres.

The basic conductive structure 3and 1 is negatively charged with >6 kV minus. This charge will enable the release of electrons from the free ending carbon fibre filaments 1 with one end attached to the conductive emitter band 3 and the other extending out into the air and as the surface of the conductive band 3 is negatively charged it will enhance the electron emitting function to generate an enhanced electrostatic field, thus serving as an active electron mirror.

The positively charged band 4 is charged with >500 V plus and serves to focus the electrostatic field towards the particle collecting surface 6. This surface could be made from a conductive as well as a non-conductive material that is connected to earth.

Even an electrically non-conductive high resistivity surface made from glass or acrylic sheets will become a suitable easy-to-clean recipient of the electrostatic field and the particulates due to the mixture of airborne particulates (dirt) and moisture located on its surface providing sufficient contact with earth enabling a surface current towards ground and prohibiting the build-up of unwanted negatively charged structures. In case of a non-conductive surface, the deposition of particulates is enhanced by securing a positive charge on said surface generated by the high voltage generator 10.

The air purification capacity, i.e. the clean air delivery rate (CADR) can be tested in a so called smoke test according to Nordtest method NT VVS 106. Such tests using a 70 centimetre emitter band mounted on a window glass have documented a CADR of 96 m<3>h<1>when assessing particulates of 100 - 125 nm size and allowing the air to circulate in the room.

Other field tests in a school corridor of 210 m<3>with no ventilation have shown a CADR value for particles >2.5 ?m corresponding to 1.7 air exchanges h<-1>using the embodiment presented in Fig.4 mounted on the wall of the 30 m long corridor as two 3 meter long electrostatic air cleaning units.

Claims (4)

Claims

1. Method for the reduction of airborne particulate matter, which may be fine or ultrafine, characterized in the generation of high voltage generator ( 10) generated enhanced electrostatic field that is focused onto a particle collecting surface (6) through the positioning of positively charged structure (4) between an emitter (3) and the particle collecting surface, avoiding the creation of surrounding negatively charged structures by having the particle collecting surface (6) and the power supply (7) connected to earth (8), allowing a surface current on said surfaces of said structures (4) to be generated.

2. Arrangement for the reduction of airborne particulate matter, which may be fine or ultra-fine, characterized in the generation of a high voltage generator (10) generated enhanced electrostatic field, that is focused onto a conductive particle collecting surface (6) comprising a positively charged structure (4) positioned between an emitter (3) and a particle collecting surface (6) and means (9) for connecting the particle collecting surface (6) to earth (8).

3. Arrangement for the reduction of airborne particulate matter, which may be fine or ultra-fine, characterized in the generation of a high voltage generator (10) generated enhanced electrostatic field, that is focused onto a high-resistivity particle collecting surface (6) comprising a positively charged structure (4) positioned between an emitter (3) and a particle collecting surface (6) and means (9) for connecting the particle collecting surface (6) to earth (8).

4. Arrangement according to claim 3, characterized in means for connecting the high resistivity surface to the positively charged structure (4).