EP4673186A1

EP4673186A1 - Air sterilizer system using multi diffracted uvc radiation and a wide-angle hepa filter

Info

Publication number: EP4673186A1
Application number: EP23741762.1A
Authority: EP
Inventors: Georgios Nikolaidis
Original assignee: Elke University Of West Attica
Current assignee: Elke University Of West Attica
Priority date: 2022-06-28
Filing date: 2023-06-07
Publication date: 2026-01-07
Also published as: WO2024003584A1; GR1010502B

Abstract

The present invention discloses a fast air sterilizing apparatus based on a chamber for the circulating air stream sterilization which comprises from a UVC radiation source, which is focused by reflection on a filter grid made out of pure quartz microfibers which is 90% transparent by the UVC radiation, it produces through constructive interference a multi diffraction pattern with points of amplified relative intensity and this multi diffraction pattern irradiates deeply onto a new type of HEPA filter, with the result of destroying and eliminating all of the trapped into the filter pores pathogens such as microbes, fungi (aspergillus, Candida), Clostridium difficile, bacteria and viruses including SARS COV 2.

Description

AIR STERILIZER SYSTEM USING MULTI DIFFRACTED UVC RADIATION AND A WIDE-ANGLE HEPA FILTER.

DESCRIPTION

Technical field

The technical field of the present invention is air sterilizing filters using UVC radiation. The invention refers to an air disinfection apparatus based on the use of UVC radiation focused on a reflector and multiply diffracted on the surface of a novel HEPA filter.

Background

The air sterilization-disinfection of confined spaces has become an essential tool for the public health protection in times of pandemics such as the recent one due to the SARS COV-2 virus.

According to scientific research results, the main reason of contracting the infection is the airborne bio-aerosols emitted by infected people through the respiration, coughing or sneezing process. The bio-aerosol droplets according to their size could remain suspended in the air for long time, be inhaled by the nearby people and thus leading to the contraction of the virus first and perhaps to the development of illness.

Various measures were introduced in order to limit the transmission of i.e. SARS COV 2 which were proposed by contagious diseases control specialists and the World

Health Organization, were worldwide adapted by the most countries. These measures, besides that of the general public vaccination, were based on the scientific fact that the virus is transmitted through airborne bio-aerosols therefore a) a compulsory use of a face surgical mask and b) a compulsory social distance of minimum 2 m were implied.

Unfortunately, as of up today’s experience, there are confined spaces where the congestion of people is unavoidable. Such spaces are the means of public transport (bus, trains, passenger airplanes), teaching rooms, hospitals -health care units etc. In such spaces with high congestion of people, the social distance of the 2 m is very difficult to be kept, while the musk becomes inefficient since there is a high air leakage of the persons exhaling air from the mask’s sides. In such a case the exhaled air from one person is most likely inhaled by the nearby person. The transmission of the SARS COV 2 recently has become even more acute since new mutations of the virus (delta, omicron, omicron 2 ) is found to have a much higher rate of contagiousness even at social distances much larger than that of the 2 m.

In addition, another factor of serious infections is the so called Nosocomial Infections (Health care Associated Infections-HAI), where patients while their treatment in health care units, acquire infections caused by various microbes such as Candida, aspergillus, Clostridium difficile, etc. which exist in health care units, and might lead to serious illness and sometimes to death..

Therefore, according to all the above, it is understood that there is an urgent need to use a system-device which will be able to disinfect-sterilize the air of a closed space in a short period of time. Because of this need, there has been a massive production of a variety of such devices which are available on the market and which offer sterilization of the air of closed spaces. A good air sterilization device should have the following main features:

A) Have a retention system for pathogenic microorganisms-microbes-viruses-micro particles with dimensions greater than 100nm (nanometers).

B) Be able to destroy various micro-organisms - germs, bacteria and viruses on the spot C) Be able to retain organic volatile substances - VOC- Volatile Organic Compounds (e.g. odors)

D) Be able to achieve the cleaning result in a short period of time. That is, there should be such a design in the air flow system so that on one hand will provide a relatively high CADR (Clean Air Delivery Rate) value in cubic meters per hour (m3/h) and on the other hand it will provide a high outlet air velocity (Outlet Air Velocity-OAV) measured in meters per second (m/s). Although a device may have a high CADR, the requirement for a high OAV exit velocity is necessary to create the turbulent air currents necessary to quickly and efficiently recirculate air in closed spaces of big volume. State of the art

Devices available on the market for air sterilization today can be classified into the following categories: i) Those that have only mechanical particle retention filters with particle dimension down to 200-300 nm in combination with an active carbon filter. The mechanical filters used are of high specifications, HEPA type (High Efficiency Particulate Air filter), which can retain in theory up to 99.97% of particles (dust, mold, fungi, pollen)

- microbes - bacteria - viruses, and their pore dimensions are of the order of 300 nm (HEPA 13), although they can capture even smaller particles down to 100 nm(HEPA 14). The material of this filter is made of either polymer or Boron Silicateglass s. The big disadvantage of these devices is that with the saturation of this filter, there is a high probability that the filter itself would become a secondary source of germs, therefore it should be replaced frequently. ii) Devices equipped with electrostatic filters (ESP- Electrostatic Precipitators). Electrostatic filters are based on the principle that air passes through a system of electrostatically charged plates, which create a strong electrostatic electric field. The particles are initially charged upon entry i.e. by the negatively charged metal plates or metal grids and along their way end up being attracted to the positively charged metal plates or positively charged metal grids. There is no need to change these filters. The electrostatic filter can be periodically cleaned by washing.

The disadvantage of these devices is that the above-described charged particles have a high probability of escaping from the positive electrodes due to high kinetic energy, with the result that when inhaled, they not only settle on the mucous membrane of the nose or mouth, but also due to the extra electrostatic force could penetrate it. This most likely would lead to the infection if not to the illness development of the person. iii) Ionization devices-lonizers, where the electrostatic charging of particles- microbes-viruses it occurs through the creation of negative ions. The negatively charged particles-microbes-viruses settle on the surfaces of the confined spaces (i.e. the walls of the premises). The creation of negative ions is done by electric arc techniques, plasma technology or use of ultraviolet radiation. Their disadvantage is that the emitted charged and possibly pathogenic particles are electrostatically attracted not only by the surfaces of a space, but also by the human body (and its mucous membranes) and therefore we will have a similar result described in the above case (ii). iv) Air sterilization devices using ultraviolet radiation of wavelength λ in the C band region with λ=100 nm to λ=300 nm (UVGI- Ultra Violet Germicidal Irradiation).

It has already been known for decades that UV radiation with λ wavelengths in the range of 10Onm -300nm, due to the high energy of its photons, destroys the DNA and RNA of microorganisms, microbes, bacteria and viruses. Systems with ultraviolet mercury radiation lamps with wavelengths λ=185nm and λ=253.7nm were used and are still used to disinfect surfaces in hospital areas without human presence, since this radiation is dangerous for humans. It should also be noted here that in the wavelength range λ < 240 nm the radiation breaks down a percentage of the oxygen (O2) in the air creating ozone (O3), a gas irritating the lungs, which in high concentrations (> 0.1 ppm) it can also be toxic. This production of ozone (ozonizers) is often used to disinfect closed spaces without human presence.

Air sterilizers using UV radiation, directly irradiate the air stream within a closed cavity- sterilization chamber, assuming that this irradiation will destroy fast-moving pathogens-bacteria-viruses. Recently though it has been studied and found that ultraviolet radiation to destroy e.g. the SARS COV 2 virus, must act on it for a period of time from 10 to 40 seconds, with a power of at least 2 mW/cm². This scientific result leads to the conclusion that it is not possible to destroy SARS COV 2, when moving in an air stream even at a low speed, since the UV radiation does not act on it for the required time, due to its speed of movement. In such a device with an emitted optical lamp power of 2mVWcm² even with a low airflow, i.e. of the order of 1m/s, and with a path length of e.g. 1 m into the device, the virus would only be irradiated only for 1 s, not long enough to be destroyed. Similarly, all UV lamp systems that are designed to be placed in air streams (i.e. air outlet of air conditioning ) are not able to inactivate-destroy the virus due to the relatively high airvelocity. . Also, there are devices using UVC radiation in order to destroy - inactivate microbes and viruses as we mentioned above (while they are moving in the air stream), where the UVC sources are LED (Light Emitting Diodes). The disadvantage here is that the power of LEDs is very low (a very large number of LEDs should be used), the wavelength is quite larger than that of the UV C band (λ= 260-300 nm mostly approaching UV B band)) compared to that emitted by mercury lamps (Hg). This results in a lower photon energy, based on the known photon energy relationship E= h c/λ (where h=Plank's constant, c=speed of light, λ= wavelength of radiation).

Another disadvantage of LEDs is that the emission-dispersion angle of their light beam, due to the nature of their construction, is small (< 180^s) since they behave as flat point light source. On the contrary, for mercury lamps, the radiation angle can reach 360 degrees, depending on their support base and their shape (i.e. tube like).

A typical example in this case is the invention [W02022025509A1], where the small droplets of the bio aerosols adhere (adsorption) to a kind of "brush" where they are irradiated with UVC LEDs. Another related invention [WO2022065627A1] for cars, uses similar technology with the difference that it increases the air path (by zigzagging) supposing that there is enough time for the UVC LED radiation to destroy germs and viruses. Again the disadvantage here is that even at very low air speeds, viruses and microbes do not remain for the required time (10-40 seconds) in the irradiated area to be destroyed, taking into account the dimensions of the device (for cars, dimensions « 1 m).

Another invention [WO2019158545A1] refers to a similar device as the aforementioned inventions, which uses UVC radiation to irradiate the passing air stream, uses a HEPA filter which, as the invention describes, removes particles smaller than 0.5 pm (micrometers), a filter of activated carbon which as described removes particles with dimensions smaller than 100 pm, and a filter coated with

TiO2 which as stated removes particles with dimensions smaller than 100 pm as well.

The substance TiC>2 serves for its photocatalytic action, which destroys pathogenic microorganisms and viruses. The disadvantages of this invention are a) in order to destroy the microbes-viruses, the air is irradiated with ultraviolet radiation, which moves at a certain speed, where, as mentioned above, it is impossible to destroy them, because there is no enough time for the radiation to have an effect b) the use of photocatalytic oxidation using TiO2 has as a side effect the creation of unwanted gases such as ozone (O₃), nitrogen oxides (NOx), carbon dioxide (CO2) etc., and c)

The filtering capability of each filter is indicated completely wrong. When we refer to the filtering ability of any air filter with a specific dimension, e.g. 100 pm clearly means that the specific filter captures and removes any particle with dimensions larger than 100 pm. However, in the text of this invention, in the claims, the possibility of filtering is completely wrong, since it is stated that the filters used by the invention do not remove particles larger than their characteristic pore size, but smaller instead.

In the invention [WO2021237172A1], an invention similar to the aforementioned is presented, but differs a) in that multiple reflective surfaces are used in the "sterilization chamber" so that the UVC irradiation is more efficient. Here too, the passing air is irradiated, which for the same reasons as mentioned above, cannot work with the desired results of satisfactory sterilization of the air within such a short time. According to all the above, it has been realized that there is an almost common way of sterilizing the air in all the above inventions that use UVC radiation, expecting to deactivate-destroy the pathogenic microorganisms-bacteria-viruses "in flight" as they pass through the sterilization chamber at a relatively high speed, where there isnot enough time for them to be sufficiently irradiated and destroyed (small dwelt timefor the pathogens). Furthermore in some inventions using the previously mentioned sterilization process of the air stream which contains the pathogens, realizing that the dwelt time of the pathogens while in the sterilizing zone of their apparatus is practically very small in order the pathogens to be deactivated, they tried to overcome this problem by increasing the length of the sterilization zone path by enforcing the air stream (and the contained pathogens) to move through a spiral path. For example in the invention [GB2597361A] it is used an helicoidal -spiral quartz tube in order to increase the flight time path for sterilization of pathogens using a UVC light sourcefor pathogen deactivation. In fact in the abstract of the GB2597361A it is stated that the advantage of the invention is that the air stream passes along a spiral pathway, thus maximising exposure to the light source and decontaminating the air stream. Similar inventions (i.e. CN207055679U, RO 118844B1) have used a similar technique of using a spiral path of the air stream in order to deactivate the pathogens.

Advantageous Effects of Invention

The invention proposed here uses a novel and totally different technology ensuring the complete deactivation-destruction of all contained pathogens and it consists of capturing first the pathogens on the surface of a wide angle HEPA filter and subsequently fully deactivating them through the intense, continuous and multifocused (JVC irradiation. HEPA is a type of pleated mechanical air filter. It is an acronym for "high efficiency particulate air and can theoretically remove any airborne particles with a size of 0.3 microns (pm). The multi focusing of the UVC irradiation on the wide angle HEPA it is achieved by using an optical grating from quartz fibers (quartz fabric) because of which the physics optical phenomena of multi diffraction and optical constructive interference arise. The advantage of this method is that the deactivation of pathogens does not depend on the speed of the air stream carrying the pathogens neither on the dwelt time of pathogens. The continuous and multi focused irradiation of the pathogens which have been immobilised on the surface of the wide angle HEPA is a guarantee of their 100% destruction.

Brief description of the invention More analytically, instead of irradiating the air stream (which contains and carries the pathogenic germs-bacteria-viruses), the surface of a HEPA filter- which consists of material resistant to ultraviolet radiation and is placed at the exit of the sterilization chamber -is irradiated instead, via a multiple focusing manner.

In the invention we are describing here, the method of destruction of pathogenic microorganisms-bacteria-microbes-viruses is based first on their retention by the HEPA filter and secondly on the continuous irradiation of the surface of this filter with ultraviolet radiation of a suitable wavelength, resulting in their destruction. This method is operationally the most successful since, on one hand the HEPA filter retains in theory 99.97% of pathogenic microbes-microorganisms-bacteria-viruses and on the other hand, it eliminates the problem with the "during flight-irradiation" time of the microbes, since they are trapped from the surface of this filter, and thus are constantly exposed to UV radiation.

A major problem of the prior art solved in the disclosed invention is the difficulty of irradiating the entire active filtering surface of the HEPA filters available on the market today due to their geometry. In the disclosed invention the geometry of the HEPA filter used differs radically to the used in the prior art since it has pleats connected in wide angle geometries allowing UVC radiation to fully radiate the surface of the filter and furthermore we use a densely woven fabric-filter-screen made of micro-fibers of pure quartz glass (quartz-fused silica glass) in order to focus the incident ultraviolet radiation on the surface of the aforementioned wide-angle HEPA filter, by means of the natural phenomenon of multiple diffraction of light

A UV-resistant HEPA filter consists of boron glass microfibers. These fibers have been compressed so that the final material appears as a compressed paper with pores measuring approximately 200nm-300nm (nanometers). Due to this fact, its resistance to air flow is quite high. In order to facilitate the air flow through it, the surface of this filter needs to be increased as much as possible. This is achieved by folding the filter into multiple small areas - a ZIQ-ZAQ - accordion type or pleats. The commercially available HEPA filters consist of pleats, which at their top (at the edge) are separated by a distance of 2 mm to 3 mm, while the height of the pleat (or its depth) varies, depending on the device, from 15mm to 50 mm. It is therefore easy to realize that the UV radiation falling on this type of filter will illuminate only the edges of the pleats and not the side surfaces, since the direction of radiation is almost parallel to the side surfaces of the pleats.

To understand the problem of the technical difficulty of irradiating the entire filtering surface of a classic HEPA filter, for example, we make the following calculations:

In a commercially available HEPA filter, the standard distance between the pleats is d=3 mm, with a depth h= 30 mm, with filter dimensions x=300 mm and y=200 mm, where the pleats are parallel in the y direction, the total active surface of the filter will be S= 2-N-S_pl (1)

Where S_pi is the active surface of the one side of a pleat, which is equal to S_pl= h y (2)

N being the total number of pleats. In this example, N=300mm/d = 300mm/3mm = 100.

For the particular filter the total active surface according to relations (1) and (2) will be: S= 2- 100-30-200 mm² = 1 .2 m².

If φ is the angle between the pleats, then tan(φ 2) = 0.5-d/h=1.5/30= 0.05. This leads to a value of the angle φ /2 = 2.82°, hence φ =5.64°.

The radiation of flux, Φ falling on the surface S is given by the relation Φ= l-S-cos(α) (3) where I is the intensity of the incident radiation, S the area of the surface and a the angle formed by the direction of incidence of the radiation with the perpendicular to the surface S. Of course we could replace the cosine of the angle a with the sine of the angle θ (θ=90^º- a). So the relation (3) transforms into

Φ=l-S-sin(θ) (4) Due to geometry, θ=φ 2. Therefore the quantity S-sin(θ) =S-sin(φ /2) is the total active irradiated surface.

For the particular example, the irradiated active surface S_ef will be

S_ef= S-sin(φ /2) = S*0.05,

Where S is the total filtrating surface of the HEPA. If we also take into account the shadowing effects of the deep regions of the pleats, then less than 5% of the available filter surface is irradiated.

Solving this technical problem is part of this invention and is described below. Brief description of the embodiments The present invention concerns a new air sterilizing apparatus comprising a novel air sterilizing filtering system.

This air sterilizer filtering system comprises.

- one or more sources of ultraviolet UVC radiation with a wavelength λ from 180nm to 320nm

- a type HEPA filter with folds/pleats which have an angle φ between 6° to 20°

- a filter-screen made of material with high optical permeability to ultraviolet radiation, placed between the source of ultraviolet UVC radiation. The filter screen is placed in order the UVC radiation from the ultraviolet sources to focus on the surface of the HEPA filter after passing through the filter screen. This allows the focused ultraviolet radiation to destroy the pathogenic microorganisms-bacteria- fungi-viruses that are on the UVC radiated surface of the said wide-angle HEPA filter.

In one embodiment the type HEPA filter is made from Boron silicate glass material and in another embodiment has holes with diameters less that 500nm so it canretain particles with dimensions greater than 500 nm (nanometers). Preferably the porosity of the type HEPA filter is from 0.1 μ (HEPA 14) to 0.3μ (HEPA13)

In a further embodiment the filter screen is made from a fabric comprising quartz or fused silica glass.

In another embodiment the said sources of UVC radiation are two or more low pressure mercury vapor (Hg) lamps having preferably a nominal electrical power of 30 W to 150 W and an emitted radiation power at a distance of 2 cm from the source ranges from 2 mW/cm² to 200 mW/cm² and preferably between 50 mW/cm² to 200 mW/cm². In one embodiment the wavelength of the emitted UVC radiation λ is between 240 and 265 nm. In a further embodiment the pleats of the type of HEPA filter, is larger than 3.5 mm, and preferably may vary between 6 mm to 10 mm, and the height h of the pleat (fold) may vary from 10 mm to 50 mm. Another aspect of the invention is the use of the previously described air sterilizer filtering system in an air sterilizing device. The said device comprises a closed chamber with one opening for air inlet and one opening for air outlet, an air sterilizing filtering system as described before, and an electrically powered fan inside the chamber configured to propel the air from the environment to the chamber from the air inlet and then to return the air to the environment from the air outlet after passing the air through the said air sterilizing filtering system so to be sterilized.

In one embodiment the fan is configured to provide an air supply at the outlet (CADR- clean air delivery rate) greater than 150 m³/h and the air speed at the outlet should be greater than 3m/s.

In a further embodiment a filter is added after the air inlet and before the air sterilizing filtering system with holes of a diameter to retain particles with a dimension greater than 200 pm (micrometers) while in another embodiment an active carbon filter with pleats, is placed after the air inlet and before the air sterilizing filtering system between the textile filter with holes of a diameter to retain particles with a dimension greater than 50 pm (micrometers). When we refer to a filtering system that retains particles of a dimension greater than one size, we mean that it retains particles that their largest diameter is of that size. Furthermore, in one embodiment, an internal lining of a highly reflective material (of the focusing mirror type) preferably of polished aluminum or of TEFLON (polymer of tetrafluoroethylene) was used to isolate and shield the ultraviolet UVC radiation in the chamber. The fan of the device is powered by an electrical supply system either from alternating voltage ( 110 Vac to 240Vac) or from DC voltage (12 Vdc to 110 Vdc) while in one embodiment, an. electronic control system was used to control the fan revolutions per minute and consequently the CADR, and so the supply of m³/h of clean air. In order to reduce the power consumption and to elongate the life of the UVC sources, in one embodiment, the operating time of the (JVC radiation sources is limited to 30 minutes in every hour while the fan is operating. Brief Description of Drawings

Fig. 1 . Schematic representation of the air sterilizing device

Fig 2. Schematic representation of the geometry of the type HEPA filter disclosed in the current invention. Description of the invention - examples

The present invention discloses an air sterilizing device comprising:

A) The total body of the sterilizer consisting (indicatively in FIGURE 1 ) of:

1) a box (made of wood or polymer or metal) which can have a parallelepiped or cylindrical shape, has at least one inlet (1.1.) of the ambient air, at least one outlet

(1.2) of the sterile air, contains (2) a fan with power and geometry depending on the volume of the space to be sterilized, placed either at the air inlet or at the air outlet, the air inlet has (3) a pre-filter capable of retaining particles with a dimension greater than 200 pm (micrometers), which is followed by a special (4) activated carbon filter with pleats and with the ability to retain particles that have a dimension greater than

10 pm (micrometers) and which also retains any volatile organic compounds present in the space (VOC- Volatile Organic Compounds), contains a (14) sterilization chamber which consists of a number (6) of ultraviolet UVC radiation lamps with a wavelength of λ from 200nm to 300nm, and is internally coated with highly reflective material (7) (polished aluminum), where the ultraviolet radiation is focused on (8) a filter-screen made of material with high permeability to ultraviolet radiation (quartz fabric), where the radiation is further focused on a new type of filter (9) - named wide angle HEPA- made of micro boron silicate glass material and preferably of micro boron silicate glass fibers. This filter can retain particles with dimensions greater than 500nm (nanometers). In addition, it contains a system (10) of electrical supply either from alternating voltage or from DC voltage, (11) has a control system of the fan RPM and consequently the supply of clean air per hour (CADR-clean air deliveryrate), it contains (12) a timer to control the operating time of the UVC radiation sources in order to increase the life time of these sources, since an operating time of 15 minutes with a 15-minute pause is more than enough for the degradation and destruction of all pathogenic microorganisms-bacteria- fungi-viruses that are trapped in the wide-angle HEPA filter on the one hand, and on the other hand the life hours of the lamps are doubled. In addition, it is portable (possibility of transport with or without a rolling base), and also it is possible to install it on a ceiling or a wall, while it also contains (13) an air flow sensor, to detect the saturation of the filters.

B) THE AIR-FLOWING STERILIZATION CHAMBER according to (A) consisting of: (indicative in FIGURE 1-14):

B1) a system of two to four (6) low pressure mercury vapor (Hg) lamps, 15 W to 50 W each, emitting UVC ultraviolet radiation. The lamp housing consists of rare earth (Y,Tb) modified quartz glass to cut off and filter all radiation wavelengths shorter than λ= 240 nm (nanometers) to exclude any production of ozone gas ( O₃), so the only emission of ultraviolet radiation occurs at a wavelength of λ=253.7 nm. The light output per two lamps at a distance of 2 cm is at least 50,000 pW/cm2 (microwatts per square centimeter). Also this system contains (13) an air flow detector, so that if the air flow is substantially reduced (i.e. the filters are clogged) the lamps stop working. This is also the indication for replacing the filters of the air sterilizer.

B2) a new type (9) of HEPA air filter, which has a new manufacturing geometry, in order to increase the flux of radiation on the active filtering surface. It is made of boron glass micro fibers and with porosity from 0.1μ (HEPA 14) to 0.3μ (HEPA13), where the angle φ between the pleats (pleats) of the HEPA filter is greater than 6°, and the distance d between the pleats is larger than 3.5 mm, and preferably may vary between 6 mm to 10 mm, and the height h of the pleat (fold) may vary from 10 mm to 50 mm. The value of the tangent of the angle φ/2 , tan(φ 2)= tan (d/2h), can range from 0.07 to 0.17, with preferred values from 0.1 to 0.13. These tangent values correspond to an angle φ with values from 11.4° to 15.2°. We shall name this new filter WIDE ANGLE HEPA. (FIGURE 2).

B3) a special (FIG. 1. 8) densely woven fabric-filter-screen made of micro-fibers of pure quartz glass (quartz-fused silica glass) with which a focusing effect of the incident ultraviolet radiation is achieved on the surface of the aforementioned new wide-angle HEPA filter, by means of the natural phenomenon of multiple diffraction of light.

It is known that unlike boron glass, the transmittance of UV radiation through quartz glass is 80% to 90%. As a result of this fact, in a fabric made of quartz microfibers, which has a dense woven (dense woven), the dimensions of the open holes are of the order of 300 nm to 400 nm. The presence of these holes, which have dimensions of the order of magnitude of the wavelength of the incident ultraviolet radiation λ=253.7 nm, combined with the high permeability of the radiation through the quartz, give the possibility and the conditions for the appearance of the phenomenon of light diffraction (in this case of the UVC radiation). That is, multiple constructive interference fringes are produced in a perpendicular direction on the surface of the fabric and are distributed due to diffraction on the surface of the irradiated filter (wide angle HEPA) along the x and y directions of the woven. This phenomenon results in the almost perfect focus of the ultraviolet radiation on the surface of the wide-angle HEPA filter, and on the other hand it can (and does) enter in the form of fine fringes of relatively high intensity within the material of the said filter, through its micro holes, where the pore diameter is 300 nm. As a result, all the microbial-fungal-bacterial-viral load which is concentrated in these holes would be deactivated. The additional positive results-advantages from this combination of the wide angle HEPA and the quartz filter are two: a) from the continuous irradiation, not only degradation-destruction occurs of the pathogens, but also a large degree of dissolution and sublimation occurs of the organic components of microbes-bacteria- viruses, which leads to a "self-cleaning" process of the filter from organic residues and b) by the penetration of the interference bright fringes into the holes of the wide- angle HEPA filter, the shadowing effect deep enough inside the filter material is avoided. This is not possible to be achieved without the use of the filter- quartz screen, because the boron glass has zero permeability to UVC radiation. It should be emphasized that the shading effects do not help to destroy the microbes- bacteria, since in this case they are not "hit" directly by the ultraviolet radiation.

The advantages of this invention are: For the first time at an international level, an innovation such as this ensures the 100% deactivation-destruction of germs-bacteria-bacteria in closed spaces with air sterilization systems based on the correct, safe and innovative use of UVC radiation. The invention, which is also of low-cost, can be applied not only to portable air sterilization devices, but also to any central ventilation facilities of buildings, tradeconference-exhibition centers, airports, airplanes, ships, etc., using only the principle of operation of the above described sterilization chamber (i.e. only UVC radiation in combination with the quartz screen filter and the wide-angle HEPA) since the air circulation system in this case will be pre-existing. Areas of widespread use of this device can also be Hospital areas (ICUs, operating rooms, nursing wards, patient waiting rooms) to limit nosocomial infections, Health Diagnostic Centers, Pharmacies, Sports centers - gyms, classrooms, hotels, and means of public transport such as trains, city buses, tourist buses, ships, planes and anywhere else needed. In relatively small dimensions, it can be used in passenger cars (private use, taxis, mini-buses, ambulances) as well as in elevators. In addition, the sterilization chamber elements in large dimensions can be used independently in central ventilation-air-conditioning systems of buildings, airports, airplanes, ships, shopping centers and in general central (large or small) ventilation-air-conditioning facilities regardless of size and geometry.

This invention enhances at a high level the security of public health.

The use of this invention can also be done by combining all the sterilization methods mentioned at the beginning of this article as well as by additional cleaning with filters containing oxidizing substances (e.g. Potassium permanganate) or dehumidification filters (perlite, zeolite, etc.).

Any air sterilization device that uses a UVC radiation system with the simultaneous use of either the WIDE ANGLE HEPA filter described here or with (or without) the quartz-fused silica screen described here, regardless of its external shape (parallel or cylindrical), regardless of its electronic and mechanical design and the parts contained, regardless of its dimensions and shape as well as the use of other additional filters of a different type, falls within the purpose of the present invention. EXAMPLES

1. Real time Efficiency measurements of the apparatus in a small student laboratory at the University of West Attica, with a volume of 84 m³

The measurement of microbiological load of the air was made by the Hellenic Pasteur Institute before the use of the UVC ULTRAPURE apparatus carrying the sterilizing system described in this invention and also after its use for 15, 30 and 60 minutes

For bacterial load the results found are the following:

Before use: TSA= 75 cfu/m³.

After its use for 15 minutes, TSA =32 cfu/m³ meaning 57.4 % reduction

After its use for 30 minutes, TSA =23 cfu/m³ meaning 69% reduction After its use for 60 minutes, TSA =18 cfu/m³ meaning 76% reduction

2. Real time Efficiency measurements of the apparatus in a wagon of theAthens Metro-Greece with a volume of 97.75 m³

The measurement of microbiological load of the air was made before the use of the disclosed system carrying the sterilizing system described in this invention and also after its use for 15, 30 and 60minutes.

For bacterial load the results found are the following:

Before use : TSA= 415 cfu/m³.

After its use for 15 minutes, TSA =40 cfu/m³ meaning 90.3 % reduction After its use for 30 minutes, TSA =29 cfu/m³ meaning 93% reduction

After its use for 60 minutes, TSA measurements where in the error bar of the experimental apparatus meaning >95% reduction

However, a recent scientific study, conducted in collaboration with the University of Tokyo and Okayama University of Science, proves that Daikin’s Streamer technology requires at least 3 hours to inactivate coronavirus (SARS- CoV-2) in air under specific laboratory conditions. [https://www.daikin.eu/en_us/daikin-blog/air-purification.html]. In addition , in another published report [https://www.daikin.eu/en_us/press- releases/institut-pasteur-de-lille-validates-effectiveness-of-daikin-s-air-purifiers- against-human-coronavirus.html] there are reported the testing results for a particular air purifiers that were tested by Institute Pasteur de Lille and was found that removes 99.93 % of Influenza A virus subtype H1 N1 in 2.5 minutes running time at ‘turbo’ speed in laboratory conditions (air-tight chamber with inner volume 0.47 m³, no air renewal), while another model of purifier removes 99.98 % of Human Coronavirus HCoV-229E in 2.5 minutes running time at ‘turbo’ speed in laboratory conditions (air-tight chamber with inner volume 1 .4 m³, no air renewal).

It is obvious here when we compare the test results published with our test results of our invention there is no comparison and that our invention is of much better performance and efficiency. It is understood that the elimination of microbes, virus e.t.c. in a human congestion place it has to be done in the shortest possible time, since the transmission of the pathogens is quite rapid.

So it is obvious that in a space the elimination of pathogens load in the time interval of 3 hours is extremely long or for the particular models, the time of 2.5 minutes for a space of volume 0.47 m3 is also very long since for the space of our tests 97.75 m3 would be need it 97.75/0.47 X 2.5 minutes = 520 minutes = more than 8.5 hours.

Claims

1. Air sterilizer filtering system comprising

- one or more sources of ultraviolet UVC radiation with a wavelength λ from 180nm to 320nm (6)

- a type HEPA filter with folds/pleats which have an angle φ between 6° to 20° and preferably from Boron silicate glass material (9)

- a filter-screen (8) made of material with high optical permeability to ultraviolet radiation preferably made from a fabric comprising quartz or fused silica glass, placed between the source of ultraviolet UVC radiation, configured so the UVC radiation from the ultraviolet sources is multi focused on the surface of the HEPA filter after passing through the filter screen configured so that the ultraviolet radiation by means of the appearance of constructive interference fringes and the light diffraction phenomena can destroy pathogenic microorganisms-bacteria- fungi-viruses that are on the UVC radiated surface of the said wide-angle HEPA filter.

2. Air sterilizer filtering system according to claim 1 characterized wherein the sources of UVC radiation are two or more low pressure mercury vapor (Hg) lamps haying preferably a nominal electrical power of 30 W to 150 W and an emitted radiation power at a distance of 2 cm from the source ranges from 2 mW/cm² to 200 mW/cm² and preferably between 50 mW/cm² to 200 mW/cm². . Air sterilizer filtering system according to any of the previous claims, wherein the type HEPA filter has holes with diameters less that 300nm so it canretain particles with dimensions greater than 300 nm (nanometers). . Air sterilizer filtering system according to any of the previous claims wherein the wavelength of the emitted UVC radiation λ is preferably between 240 and 265 nm.

5. Air sterilizer filtering system according to any of the previous claims wherein the type of HEPA filter has a porosity from 0.1 μ (HEPA 14) to 0.3μ (HEPA13). 6. Air sterilizer filtering system according to any of the previous claims wherein the distance d between the pleats of the type of HEPA filter, is larger than 3.5 mm, and preferably may vary between 6 mm to 10 mm, and the height h of the pleat (fold) may vary from 10 mm to 50 mm. 7 Air sterilizing device comprising a closed chamber with one opening for air inlet

(1.1) and one opening for air outlet (1.2) comprising.

- An air sterilizing filtering system according to any of the claims 1 to 6,

- An electrically powered fan (14) inside the chamber configured to propel the air from the environment to the chamber from the air inlet and then to return the air to the environment from the air outlet after passing the air through the said air sterilizing filtering system. Air sterilizing device according to claim 7 wherein, the fan is configured to provide an air supply at the outlet (CADR-clean air delivery rate) greater than 150 m³/h and the air speed at the outlet should be greater than 3m/s. Air sterilizing device according to any of the claims 7 to 8 wherein, the chamber comprises further a textile filter after (3) the air inlet and before the air sterilizing filtering system with holes of a diameter to retain particles witha dimension greater than 200 pm (micrometers). 0 Air sterilizing device according to any of the claims 7 to 9 wherein, the chamber comprises further an active carbon filter with pleats (4), placed afterthe air inlet and before the air sterilizing filtering system between the textile filter with holes of a diameter to retain particles with a dimension greater than 50 pm

(micrometers). 1 Air sterilizing device according to any of the claims 7 to 10 wherein, the chamber is configured to isolate and shield the ultraviolet UVC radiation of the sources of the air sterilizer filtering system by covering the air sterilizer filtering system by an internal lining of a highly reflective material (of the focusing mirror type) preferably of polished aluminum or of TEFLON (polymer of tetrafluoroethylene).

12 Air sterilizing device according to any of the claims 7 to 11 wherein the ultraviolet UVC radiation sources and the fan are configured to be powered an electrical supply system either from alternating voltage (110 Vac to 240Vac) or from DC voltage (12 Vdc to 110 Vdc).

13 Air sterilizing device according to any of the claims 7 to 12 further comprising an electronic control system controlling the fan revolutions per minute and consequently the CADR, and so the supply of m3/h of clean air.

14 Air sterilizing device according to claim 13 configured so that the operating time of the UVC radiation sources is limited to smaller times than the timethe fan is operating.

15 A method of sterilizing the air of an indoor space comprising

- passing the air through an air sterilizing device of any of the claims 7 to 14 by means of a fan

- radiating the nanoparticles retained on the surface of the type HEPA filter with ultraviolet UVC radiation focused by multi diffraction -light interference phenomena on the surface of the type HEPA filter by means of a a filter- screen made of material with high optical permeability to ultraviolet radiation using the air sterilizer filtering system according to any of the claims 1 to 6 and returning the air to the indoor space of the building through the air outlet of the said sterilizing device.

16. The use of the air sterilizing device according to any of the claims 7 to 14 to sterilize the air of an internal space from microbes, fungi (aspergillus, Candida), Clostridium difficile, bacteria and viruses including SARS COV 2.