| 1. | An air filter assembly comprising: a frame assembly; and a woven filtering medium comprising woven microfilament strands of a substantially constant diameter of at most 30 microns, said strands being spaced apart by at most 20 microns, said filtering medium disposed in the frame assembly, said filtering medium having at least 16% of its surface area open; wherein said filtering medium is non entraining and reduces the passage of pollen and dust particles through said air filter without clogging, while allowing the free passage of air through said air filter. |
| 2. | A window air filter assembly as in claim 1, wherein said filtering medium comprises microfilament strands having a diameter of 15 microns, said strands being spaced apart at 15 microns. |
| 3. | A window air filter assembly as in claim 1, wherein said filtering medium comprises microfilament strands having a diameter of 10 microns, said strands being spaced apart at 7 microns. |
| 4. | A window air filter assembly as in claim 1, wherein said filtering medium comprises microfilament strands having a diameter of 30 microns, said strands being spaced apart at 20 microns. |
| 5. | An air filter assembly for repulsive filtering of particulate matter, said air filter comprising: a laterallyadjustable frame assembly; and a laterallyadjustable woven filtering medium attached to said frame assembly, said filtering medium having at least 16% of its surface area open and comprising woven, smoothsurfaced microfilament strands, said strands having a diameter of at most 30 microns, and being spaced apart at most 20 microns. |
| 6. | A window air filter assembly as in claim 5, wherein said fram assembly comprises a first frame member and a second frame member, said first and second frame members being attached in cooperable and slidable engagement, a first filtering medium anchor being fixedly attached to the first frame member and a second filtering medium anchor being rotatably attached to the second frame member, said filtering medium being attached at respective ends thereof to said first anchor and to said second anchor. |
| 7. | A window air filter assembly as in claim 6, wherein said microfilament strands have a diameter of 15 microns, said strands being spaced apart 15 microns. |
| 8. | A window air filter assembly as in claim 6, wherein said microfilament strands have a diameter of 10 microns, said strands being spaced apart 7 microns. |
| 9. | A window air filter assembly as in claim 6, wherein said microfilament strands have a diameter of 30 microns, said strands being spaced apart 20 microns. |
BACKGROUND OF THE INVENTION The present invention generally relates to air filtering mediums. More particularly, this invention relates to a single-layer, non-entraining, air filtering medium, for small particulate matter, for use in non-forced-air ventilating conditions.
Air filtering systems to remove deleterious particulate matter are important for general health and particularly important for persons having allergies, asthmatic conditions and the like. Ventilation of interior spaces are also important for the removal of dampness and air borne chemicals such as phenols escaping from drapes, furniture, etc.
Air ventilation systems in buildings generally include air filtering means that require the use of mechanical blowers and other large equipment to force air through the filtering media. Air filtering means in forced- air building ventilation systems are generally designed to remove only large dirt and dust particles. There is a need in the art for air filtering means to remove small particulate matter and allergenic pollens. In particular, there is a need in the art for a non-entraining air filtering means for small particulate matter and allergenic pollens that
can be used in non-forced (natural) air ventilating conditions. In the present invention "non forced air natural ventilating" means the movement of air without the use of mechanical blowers or the like. "High efficiency particulate arrestors" (HEPA) units are known in the art, however these units require mechanical forced air in order to push air through the filter medium.
Small particulate matter and allergenic pollens are generally larger than 15 microns in diameter and therefore can be effectively blocked by a filtering medium having smaller openings. For example, pollen from Ambrosia (ragweed) is oblate-spheroid in shape and it size ranges between 22-29 microns by 22- 32 microns. Pollens from the Asteraceae family (herbs and weeds) range between 15-48 microns by 16-40 microns. The many pollens of the Poaceae family (grasses) have a generally spheroid shape ranging in size from 22-122 microns. Loliu (Rye grass ) pollen ranges between 32-45 microns. The tree family pollens include, for examples, Betula (birch) pollen ranging in size from 18-23 micron by 21-30 microns, Alnus (alder) pollen ranging from 19-21 microns by 23-30 microns, Olea (olive) pollen ranging from 22-31 microns by 22-28 microns and Quercus (oak) pollen ranging from 22-36
microns by 19-39 microns. General ventilation systems in buildings do not remove this size range of particulate matter.
Air filter systems specifically designed to remove small particulate matter are known in the art. These systems are usually built up or blown matt filter medium that because of this construction require some type of mechanical forced air blowers and are designed, to function by capturing or collecting the particulate matter on or in the built up matt medium. This results in declining efficiency of the filter as the filtering medium clogs up with particulate matter. Thus air filters of this type must be periodically cleaned or replaced. Where the air is heavily contaminated with particulate matter, such air filters must be cleaned or replaced quite often.
U.S. Patent No. 570,219 to Fletcher, U.S. Patent No. 1,056,722 to Adler, U.S. Patent No. 2,478,097 to Glanzer, and U.S. Patent No. 4,022,596 to Pederson illustrate air filtering systems that function by entraining or collecting small particulate matter. U.S. Patent No. 2,551,175 to Smith, U.S. Patent No. 2,615,477 to Crawley illustrate liquid filtering systems which function by entraining or collecting small particulate matter.
U.S. Patent No. 4,728,349 to Oshitari, U.S. Patent No. 4,904,288 to d'Augereau, and U.S. Patent No. 5,037,445 to Scheineson discloses multilayered air filter mediums which also function by entraining or capturing particulate matter and which must also utilize mechanical forced-air ventilation to pass air across the filtering medium. The Oshitari patent and U.S. patent No. 4,824,451 to Vogt et al. disclose non- woven, blown matt type filtering mediums which also require mechanical forced-air.
The key elements for an air filtering medium to prevent entry of small particulate matter in non forced air ventilating conditions are: (1) the openings in the filtering medium must be sufficiently small to prevent the passage of the particulate matter, and (2) the surface area of the filtering medium must be sufficiently open to develop a pressure differential across the filtering medium that is low enough to permit natural, non-mechanical ventilation.
The present Applicant has discovered that an air filtering medium having more than 16% and more ideally 25% or more of the surface area directly open would have a low enough pressure differential across the filter medium as to provide suitable natural ventilation without the necessity of forced mechanical
means. This structural limitation can be utilized to construct an air filter having openings sufficiently small to prevent the passage of small size particulate matter without collection or adhesion of the particulate matter in or onto the filter media while simultaneously permitting sufficient air flow for natural ventilation. It is further useful if an air filter medium having this characteristic can be provided in a structure that can be selectively disposed in a window frame or other opening.
U.S. Patent No. 3,675,402 to Weed shows a sliding window air filter assembly, utilizing a multilayered filtering medium. The air filter assembly in the Weed disclosure is not selectively adjustable however. The filtering medium must be manually cut down as the frame is shortened, and therefore the frame cannot be subsequently widened after the filtering medium has been cut down.
SUMMARY OF THE INVENTION
The present invention is a portable window air filter assembly generally comprising a selectively adjustable frame assembly and a fixedly single layer, non entraining filtering medium disposed in the frame assembly. In one embodiment of the present invention the filtering medium is formed from smooth-surfaced
microfilament strands having a diameter of at most 30 microns which are spaced apart at most 20 microns which is approximately 500 strands per inch. This construction provides a filtering medium having substantially 16% of its surface area open. In a more preferred embodiment of the present invention, the filtering medium may be formed from smooth surfaced microfilaments having a diameter of 15 microns spaced at 15 microns or 25% directly open or approximately 850 strands per inch. The filtering medium of these embodiments of the present invention has the woven strands spaced sufficiently close to prevent passage of small particulate matter, yet has sufficient direct open surface area (>16%) to permit the development of a low pressure differential across the filtering medium for natural ventilation.
In another embodiment of the present invention, instead of a woven single - layer filter medium in which the openness is contingent on the size and spacing of microfilament strands, the openness could be created by cutting holes, such as by lasers, into a single layer, flat sheet of material. Chemically etching micropores would be another example.
An object of the present invention is to provide air filtering means that prevents the passage
of small size particulate matter without collecting or entraining the particulate matter in or upon the filtering medium.
Another object of this invention is to provide air filtering means that permits natural ventilation, i.e. air flow under low differential pressures without the necessity of forced-air (mechanical) ventilation.
Another object of the present invention to provide an air filter system that is self-cleaning and thereby eliminates or substantially reduces the need for short term replacement or cleaning.
Another object of the present invention is to provide a selectively adjustable frame in which the filter medium can be selectively adjusted to varying size windows or other like openings.
It is also an object of this invention is to provide air filtering means that can be easily transported from one window or like opening to another.
These and other objects and advantages of the present invention will be better understood by those skilled in the art from the following description of a preferred embodiment, claims and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front perspective view of window air filter assembly constructed in accordance with the teachings of the present invention.
FIG. 2 is a cross-sectional view of the window air filter assembly taken along line 2-2 of FIG. 1.
FIG. 3 is an enlarged section of the woven filtering medium of one embodiment of the present invention.
FIG. 4 is an enlarged section of a non - woven filtering medium, another embodiment of the present invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 illustrates in a front perspective view a preferred embodiment of the window air filter assembly 1 of the present invention. Air filter assembly 1 generally comprises a laterally-adjustable frame assembly 2 and a woven filtering medium 3 fixedly disposed in frame assembly 2. In the preferred embodiment shown of air filter assembly 1, frame assembly 2 incudes a first frame member 4 and a second frame member 5 cooperably and slidably engageable. The first and second frame members 4, 5 are formed having a substantially C-shaped configuration. The respective second horizontal legs 5a, 5b of second frame member 5
slidably engage the respective first horizontal legs 4a, 4b of first frame member 4.
As can be seen in the cross-sectional view of the air filter assembly 1 illustrated in FIG. 2, a filtering medium anchor or attachment 6 is centrally disposed and fixedly attached in an interior portion of the vertical leg 4c of the first frame member 4. A filtering medium roller 7 is eccentrically disposed in an interior portion of the second vertical leg 5c of the second frame member 5. Roller 7 is rotatably attached to second frame member 5. Filtering medium 3 is attached at respective ends thereof to anchor 6 and roller 7. Roller 7 automatically takes up slack in filtering medium 3 by spring biasing means (not shown) as the frame assembly 2 is shortened or compressed and automatically lets out the filtering medium 3 as frame assembly 2 is laterally expanded. Filtering medium 3 extends through respective first and second frame member slots 4d, 5d formed in the respective first and second frame members 4, 5. The slidable attachment of first frame member 4 and second frame member 5 and laterally rotatable attachment of filtering medium 3 thereto permits lateral adjustment of the air filter assembly 1 so that it may easily adjust to variously- sized windows or other openings. The frame assembly 2
may be constructed in various shapes and configurations to perform as heretofore described. Frame assembly 2 is preferably formed from a waterproof material, and weatherstripping 13 surrounding frame assembly 2 may also be included.
One embodiment of filtering medium 3, illustrated in FIG. 3 is preferably formed from woven, smooth-surfaced microfilament strands 8,9, for examples, polyester, nylon, polypropylene, carbon, fiberglass, ceramic or metal strands and may be electrostatically treated. The strands 8,9 are fixedly spaced at a predetermined distance. The filtering medium 3 of the present invention is provided to prevent the passage of small particulate matter through the spaces between strands 8, 9, without collecting or entraining the particulate matter therein and simultaneously providing sufficient openings in its surface area to permit natural ventilation. A filtering medium 3 that is woven of continuous monofilament strands (or continuous flat film as in 3b of FIG. 4) has the strength to withstand high pressure fluxuations (wind gusts for example) for construction of a single ply filtering medium. Blown matt type filtering mediums are made of short non-continuous strands generally require a support system to remain
intact. Built up matt type filtering media is designed to be entraining (capturing particles) , while the single layer filtering media of the present invention is designed to be non-entraining.
A filtering medium 3 having microfilament strands 8, 9 spaced apart at approximately 15 microns will prevent the passage of most air-borne pollens. In FIG. 3 the spacing of microfilament strands 8, 9 of filtering medium 3 is represented by the letter " X ". The diameter of the microfilament strands 8, 9, is represented by the letter "Y".
To construct a filtering medium 3 in accordance with the teachings of the present invention, a balance must be struck between the diameter of the microfilament strands 8, 9 "Y" and the spacing between strands 8, 9 X". The strands 8, 9 must be spaced sufficiently close to prevent passage of small particulate matter, but not so close that adequate natural ventilation cannot occur. As noted herein, a filtering medium 3 having substantially 16% or more of its surface area open permits the air exchange by natural ventilation to meet the terms of this invention. Selecting strand sizes and spacing of the strands 8, 9 to meet this critical limitation and the limitations imposed by the size of the particulate
matter that is to be blocked by the filtering medium 3 provides the basis for the construction of the filtering medium 3 of the present invention.
A filtering medium 3 having strands 8,9 more closely spaced for filtering of even smaller particles, for example strands spaced 10 microns apart, would require the use of microfilament strands 8,9 having a smaller diameter for example, strands 8,9 having a diameter of 10 microns to achieve a 25% surface area opening. Presently, the minimum size strands commercially used for weaving is 25 microns. For a filtering medium 3 meeting the requirements of the present invention, 25 micron- strands must be spaced at most 20 microns apart, which is useful for filtering the upper range of small particulate matter. As should be understood, a balance must be struck between the size of the opening between strands, 8, 9 and the diameter of the strands 8, 9. As microfilament weaving [or micropore sheet] technology advances, filtering mediums 3 having progressively smaller openings between the strands 8, 9 can be obtained and natural ventilating filters for even the smallest particulate matter can be constructed utilizing the teachings of the present invention or conversely with with the same
opening size a greater overall openness of the filter medium for an increase of ventilation volume.
The microfilament strands 8,9 of the filtering medium 3 are preferably formed having a smooth outer surface for the purpose of preventing entanglement and entrainment of pollen, dirt and the like in the individual strands 8,9. Smooth surfaced microfilament strands 8, 9 woven to form filtering medium 3 clean the air by reflecting or repelling particulate matter, instead of entraining or collecting the particulate matter in the filtering medium 3. The non-entraining filtering of the present invention extends the useful life of the filtering medium 3 between cleanings, and facilitates self-cleaning of the filtering medium 3.
Substantially perpendicular air flow as illustrated by arrow "10" in FIG. 2 shows small particulate matter 12 being repelled by the filtering medium 3 by virtue of the sizes of the openings in the filter medium 3 being smaller than the particulate matter. Nonetheless, some small particulate matter 12 may become lodged in filtering medium 3. Since natural ventilating air flow (wind) impinges the filtering medium 3 at a variety of angular orientations, substantially lateral air flow as illustrated by arrow
"ll" in FIG. 2 will remove small particulate matter lodged in the filtering medium 3. Reverse pressure fluxuations through filtering medium 3 will also facilitate self -cleaning of the filtering medium 3.
The preferred embodiment described of the present invention has been described as having a woven filtering medium. It should be understood by those skilled in the art that a non woven filtering medium having a plurality of openings formed therein now known or developed in the future, meeting the terms of this invention is within the scope of this invention. For example, FIG. 4 shows such an embodiment in which very small holes 14 are drilled or cut for example by laser through a single layer sheet of material 3b in such a manner and spacing as to conform to the present invention. Chemical etching of micropores would be another example.
Various changes, additions and modifications may be made to the present invention without departing from its spirit and scope. Such changes, additions and modifications within a fair reading of the appending claims are intended as part of the present disclosure.