GB2304576A

GB2304576A - Reduction of airborne contaminants

Info

Publication number: GB2304576A
Application number: GB9518207A
Authority: GB
Inventors: George Richardson; Karl Gustav Rosen
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-09-07
Filing date: 1995-09-07
Publication date: 1997-03-26
Anticipated expiration: 2015-09-07
Also published as: GB2304576B; GB9518207D0

Abstract

Airborne contaminants in a micro-environment (e.g. localised volume of air to be cleaned) are reduced by subjecting them to negatively charged ionised air (e.g. containing superoxide ions) and water vapour. Electrostatic forces may assist in causing the resulting immuno-chemical products (e.g. hydrogen peroxide) and reactive oxygen species to become dissipated within the micro-environment. The ionised air may be produced by generating electrons and the electrons and ionised air may be directionally concentrated within the micro-environment by reflecting them from a capacitor, thereby enabling the apparatus to be located away from the direct air pathway.

Description

REDUCTION OF AIRBORNE CONTAMINANTS The present invention relates to means for the reduction of airborne contaminants. More particularly, the invention relates to means for the reduction of the level of contaminants in a micro-environment.

The term micro-environment as used herein is intended to define a localised volume of air to be cleaned according to the invention. The micro-environment may be a large, contained environment such as a building or a room or a smaller environment which may or may not be contained, such as an air shower.

In general, a modern indoor environment is highly contaminated with both naturally occurring particulate matter, for example mould spores, pollen and dust mite droppings, and those generated by other means, all of which are relatively harmless but do constitute allergens which can be irritating and possibly damaging to some people, particularly to those who are asthmatic or who suffer from allergenic rhinitis (hay fever or similar allergies). Indoor environments which are air-conditioned sometimes have air-conditioning systems including filters or air-scrubbers which remove particulate material from the air taken from outside. However, such a system will only filter particles above a certain size and does not allow for the removal of particulate material generated inside a building, brought in by the occupants or entering through an open window or other outdoor airvent.

Potentially more serious is the fact that the conditions generally found in modern buildings allow the spread of infections, which may range from the common cold and so called childhood diseases such as rubella and chickenpox to serious and potentially life-threatening diseases such as tuberculosis (TB) and Legionnaire's disease, causing ill-health for the occupants of the building and loss of man-hours to industry.

It is worth noting that clean outdoor air generally has a concentration of small negatively charged air-ions of about 1,600 per cm3of air, whereas indoor air typically has about 200 negative ions/cm3 of air. It is generally considered that a high concentration of negative ions is healthy and invigorating. Accordingly, one object of the present invention is to provide a significantly higher ion concentration indoors at least comparable to that found outdoors.

The creation of cleaner indoor air is desirable both to reduce the levels of allergenic materials and to reduce at least the spread of microbes. It is even more desirable to create an indoor environment which is hostile to microbes, preferably to the extent that their growth rate is reduced. The latter is particularly suited to places where high proportions of people susceptible to infection are found, for example in hospitals, children's nurseries and homes for the elderly.

An ever increasing number of people visit and/or work in public buildings. Statistics show that we spend on average 85-90% of our time indoors. People carry with them dirt material and shed skin particles which may become airborne allergens with a size that can penetrate to the finest part of the lung.

Very fine particulate matter with a size of < 1.0 micrometre (pom), generated by the combustion engine, particularly the diesel engine, is becoming a major health problem 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, if average inner city air, contains some 150,000 particles per litre of air with a particle size of > 0.3 wn.

It is another object of the invention to provide cleaner indoor air, where the particulate load and especially the biologically-active load or "bioload" can be reduced by some 50 - 70% for the small airborne particles and aerosols, and to create a hostile environment for microorganisms.

The scope of the present invention is set out in the appended claims.

Field studies have shown the objects to be realised by installing high voltage, low current air cleaning devices, based on carbon fibre electron emitting systems in the indoor environment. The present invention seeks to achieve the following air cleaning principles: 1. to generate a large number of negatively charged oxygen molecules (superoxides), often referred to as ionised air, and free electrons, with the minimal generation of ozone ( < 0.1 ppm), causing particles to cluster and thereby precipitate due to gravitational forces; 2. to cause negatively charged ionised air to come into contact with water vapour such that immunochemical products are produced, and to introduce such products into the micro-environment, whereby at least the growth and spread of micro organisms is reduced; 3. to cause ionised air and free electrons to come into contact with contaminated air in the micro-environment, and to allow the electrons, the ionised air and the contaminated air to react, in such quantities and with such kinetic energy whereby a minimum of ozone is generated; 4. to cause controlled electrostatic interactions with the contaminated air, whereby the mobility of particulate airborne contaminants is reduced and reactive oxygen species are generated, thereby reducing the levels of chemical airborne contaminants by enhanced oxidation; 5. to increase the levels of superoxides to scavenge chemical contaminants, including ozone, and thereby remove them from the micro-environment, according to the following equations: e +Oi 2 2' 2 + 0 -,202 202 + 6. to generate a directional- and strength-controlled electrostatic field in the main air-stream of the room, thereby capturing the positively charged small particles entering the room, or being produced in the room, by electrostatic forces. The negatively charged electrostatic field should have sufficient strength throughout a large volume of air, herein referred to as the "air cleaning compartment", in order to efficiently reduce the number of airborne particulates/aerosols.

The following principal formula applies to the invention: 2 0 2-- + 2H+= 20H +[20 ] = H202 + 02, where H 20 2 has anti-microbial properties.

Apparatus for carrying out the method of the invention to reduce the level of airborne contaminants in a microenvironment includes means for generating electrons, thereby producing ionised air, and means for facilitating the electrons and the electrostatic field to come into contact with contaminated air in the micro-environment, optionally including means for detecting the level of ions and/or H2O2in the micro-environment, and means to control the output of the electrons and ionised air in response to signals received from the detector means.

The detector means may comprise a simple diode and capacitor arrangement whereby a small lamp is lit if high levels of ions are present. Alternatively, a complex detector/control system may be installed as part of a complete air conditioning system in, for example, a building.

Preferably, to allow for high ion production, a nonoxidising carbon fibre thread is used to generate the electrons. The main advantage of this thread is its ability to generate very large numbers of electrons around its entire circumference, without hindrance from its design or method of application. Such a thread has a very high coeffecient of wear coupled with a low maintenance requirement Although the above mentioned principles reduce the number of airborne particles, it would be desirable to position air cleaning apparatus away from the direct main air-flow pathway of the room, to avoid interference with the airflow per se. Furthermore, an effective air cleaning system used to handle particulate matter creates a dirt deposition problem if placed in the main air-flow pathway.Preferably, therefore, in the method and apparatus according to the invention and in order to ensure that sufficient number of superoxide molecules reach the air stream without the emitting system being located in the forced air flow, the kinetic energy of the superoxide molecules is increased by providing an electrically insulated back plate at a distance, for example of 2 - 4 cm, away from the high voltage emitting thread. Such a back plate would then serve as a capacitor, itself becoming negatively charged over time, thereby reflecting the negative charged oxygen molecules and emitted electrons. The back plate is constructed from a conductive material, for example a metal or a conductive plastics material, and is fully isolated from zero potential.Experiments have shown that this design produces a three-fold increase in the concentration of superoxide molecules and electrons at a distance of two metres in front of the apparatus, thus serving as an electron/superoxide reflector/mirror.

Naturally, any flow of air within the superoxide-enriched "air cleaning compartment" will distribute the superoxide molecules for further reduction of particulate matter by clustering, as described above.

The electron/superoxide reflector/mirror allows the emitting system to be brought into the room away from the direct air pathway and allows the construction of appropriate apparatus to efficiently trap small airborne particulate matter within a large volume of air, say sum3.

There is a risk that electron emitters, with their accompanying electrostatic field, will deposit particulate material on surrounding surfaces such as walls and ceilings. However, suppressing these electrostatic fields reduces the air cleaning capacity.

Therefore, it is desirable to divert the generated electrostatic field away from these surfaces. This is achieved in the present invention by locating a conductive material/surface with zero potential at a distance of, for example, approximately 20 cm from the high voltage, electron emitting carbon fibre thread. Such a surface at zero potential will not only prevent deposition of particulate material on the surrounding surfaces, but it will also serve as a collector of some of the particulate matter flowing past the electron emitter.

By positioning two such electron reflectors/mirrors opposite each other, an air cleaning compartment is created which achieves the combined effects of optimal superoxide and negative electrostatic field generation, thereby ensuring an optimal reduction of airborne particulate matter.

A complementary technique of securing deposition of particulate matter on a dedicated surface is to have such a surface positively charged (approximately + 3 kV) and to locate the surface some metres away from the electron emitting system. The latter may include means, such as a fan, to enhance the flow of contaminated air within the air-cleaning compartment. Once cleaned during this initial passage, the air will become saturated with superoxide molecules and spread into the room thereby decreasing the airborne bio-burden.

In one embodiment of the invention the negatively charged ionised air is produced by generating a high output of electrons from an ioniser. The ioniser is preferably run at very high voltages in order to maximise the kinetic energy of the ions produced. Preferably, the ionising chamber of the ioniser comprises carbon in the form of individual filaments made up into a special material such as threads of fibres. The negatively charged ionised air thus produced is introduced to water vapour; the water vapour may be provided by a water-holding chamber, a humidifier or simply the ambient atmospheric moisture.

Free electrons from the negatively charged ionised air react with the water vapour to produce immunochemical products, for example hydrogen peroxide, in low concentrations, for example from 15 - 25 parts per million (ppm). Hydrogen peroxide levels of this order are sufficiently high to have anti-microbial activity without causing problems associated with higher levels of hydrogen peroxide such as skin irritation.

According to another aspect of the invention, electrons are generated by an ioniser to generate ionised air. The ionised air reacts with chemical contaminants, for example hair spray, such that the reaction products are non-irritant substances. Additionally, the ionised air will cause electrostatic interactions to occur with particulate material, such as microbes, pollen, dust and dander. Because like charged particulate matter repels other such matter, dust as an example tends to remain airborne because walls, floors and ceilings are generally positively charged. Introducing equipment according to the invention will force the particles to follow the direction of the negatively charged electrostatic field and settle on grounded or positively charged surfaces.

Depending on the construction of the wall or other surface, these may become negatively charged thereby diverting the air pollution particles to settle on more appropriate surfaces. Thus the airborne particulate material is removed from the air. In this manner, the likelihood of inhalation of and hence irritation by particulate airborne contamination is greatly reduced.

The means for causing the ionised air to come into contact with the contaminated air in the micro environment could be a fan positioned either up- or downstream of the ionising elements. Alternatively, the ions could be generated at such a level as to cause a draught or so called ionic wind and thus convey the ionised air to the contaminated air without assistance.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which Fig. 1 is a plan view of electron-emitting apparatus; Fig. 2 is a side view of the apparatus of Figure 1; Fig. 3 shows two sets of such apparatus suspended from a ceiling; and Fig. 4 illustrates the air-cleaning principles of the arrangement of Figure 3.

Referring to Figures 1 and 2, the component parts of the apparatus are a carbon fibre electron emitting thread 1 having radially-disposed filament ends extending outwardly around the circumference, and a capacitor 2 as a back plate to the thread 1. The thread is mounted in spaced-apart relationship to the capacitor via electrically-insulating studs 3; the capacitor plate 2 is mounted on an electrically-insulating surround 4 which is bounded by a metal frame 5 connected to zero potential via a megaohm resistor 6. A high voltage generator 7 is connected to the thread 1 by a cable 8 insulated from the capacitor 2.

With reference to Figure 3, two sets of apparatus as illustrated in Figures 1 and 2, are shown suspended from the ceiling of a room. The capacitor plates 2 act as electron mirrors and enable the air in the room to be effectively cleaned, as illustrated in Figure 4, despite the apparatus being located away from the direct air pathway.

Claims

1. A method for reducing the level of airborne contaminants in a micro-environment, the method comprising generating negatively charged ionised air in the micro-environment and contacting the ionised air with water vapour to produce immuno-chemical products and reactive oxygen species, whereby airborne micro-organisms in the micro-environment are killed or are prevented from increasing.

2. A method according to Claim 1, further including generation of electrostatic forces to cause the immunochemical products and reactive oxygen species to dissipate within the micro-environment.

3. A method according to Claim 1 or Claim 2, in which the reactive oxygen species include superoxide and/or hydrogen peroxide.

4. A method according to any preceding claim, in which electrons are generated to produce the ionised air, the ionised air, electrons and reactive oxygen species are reacted with the contaminants to reduce the level thereof, the electrons and ionised air being produced in such quantities and with such kinetic energy that generation of ozone is maintained at a minimum and electrostatic interaction with the contaminants is caused to occur, whereby mobility of the contaminants is reduced.

5. A method according to any preceding claim, in which the airborne contaminants include combustion particles, allergens, spores, pollen, dander and micro-organisms.

6. A method according to any preceding claim, in which the contaminants are caused to form clusters.

7. A method according to any of Claims 4 to 6, in which the electrons and ionised air are directionally concentrated within the micro-environment by reflecting them from a capacitor located adjacent the electron generator.

8. Apparatus for carrying out the method of any of Claims 1 to 6, the apparatus comprising means for generation of negatively charged ionised air, said means utilizing a high voltage and a low current, and means for contacting the ionised air with water vapour.

9. Apparatus according to Claim 8, in which the means for generation of ionised air comprises means for generation of electrons.

10. Apparatus according to Claim 9, further including means to detect the level of ions in the microenvironment and means to control the output of electrons and ionised air in response to signals received from the detector means.

11. Apparatus according to any of Claims 8 to 10, in which the generator means comprises a non-oxidising carbon filament thread including free filament ends substantially radially extending from the circumference of the thread.

12. Apparatus according to any of Claims 9 to 11, further including a charged or chargeable capacitor means disposed so as to reflect electrons generated by the generator means to concentrate said electrons at a desired location within the micro-environment.

13. Apparatus according to Claim 12, in which the capacitor means comprises an electrically insulated conductive plate disposed adjacent said generator means, whereby the plate can passively retain a negative charge from said generator means.

14. Apparatus according to Claim 12, in which the said desired location is positively chargeable. Amendments to the claims have been filed as follows CLAIMS 1. A method for reducing the level of airborne contaminants in a micro-environment, the method comprising generating negatively charged ionised air in the micro-environment and contacting the ionised air with water vapour to produce immuno-chemical products and reactive oxygen species, whereby airborne micro-organisms in the micro-environment are killed or are prevented from increasing.

11. Apparatus according to any of Claims 8 to 10, in which the generator means comprises a non-oxidising carbon filament thread.

12. Apparatus according to Claim 11, in which the thread includes free filament ends substantially radially extending from the circumference of the thread.

13. Apparatus according to any of Claims 9 to 11, further including a charged or chargeable capacitor means disposed so as to reflect electrons generated by the generator means to concentrate said electrons at a desired location within the micro-environment.

14. Apparatus according to Claim 13, in which the capacitor means comprises an electrically insulated conductive plate disposed adjacent said generator means, whereby the plate can passively retain a negative charge from said generator means.

15. Apparatus according to Claim 13, in which the said desired location is positively chargeable.

16. A method for reducing the level of airborne contaminants substantially as herein described.

17. Apparatus for reducing the level of airborne contaminants substantially as herein described with reference to and as illustrated in the accompanying drawings.