FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2006
COMPLETE
Specification
(See Section 10 and Rule 13)
AIR PURIFICATION SYSTEM
THERMAX LIMITED
an Indian Company
of D-13, MIDC Industrial Area,
R.D. Aga Road, Chinchwad,
Pune-411 019,
Maharashtra; India
Inventors:
1. BHANDARKAR VISHWANATH
2. MISAL SHRIRAJ
The following specification particularly describes the invention and the manner in which it is to be
performed.

FIELD OF DISCLOSURE
The present disclosure relates to a sequential air purification system, more particularly, the present disclosure relates to an indoor sequential air purification system for removing particulates, dust/smoke, chemical contaminants, microorganisms/bacteria, mold, odor, pollen, pathogens, and the like.
BACKGROUND
Air contamination and pollution is a long-standing problem. The air pollution levels continue to rise, with the contaminants like dust, mold, pollen and bacteria being prevalent. Other major contaminants are gaseous chemical contaminants including volatile organic compounds (VOC's), such as formaldehyde, ammonia, and other common contaminants, which are released from indoor sources like building materials, adhesives, pesticides, cleaning agents, etc. Further, carbon monoxide is released from fireplaces, gas stoves and smoking. Apart from the indoor sources, gaseous chemicals from outdoors such as vehicular emissions, smog, etc., can affect the indoor air quality. This problem is aggravated by inadequate ventilation in the newer "tight" construction buildings.
The inhalation of such contaminated air can cause serious health risks, mostly for people suffering from dust/pollen allergies, asthma, emphysema and other respiratory illnesses. Filters have long been used to remove contaminants like particulate contaminants, mold, pollen and dust/smoke. The filters, however, are designed only to remove contaminants up to a specific size.
Many devices use activated charcoal filters and high efficiency particulate arrester (HEPA) filters to remove the air contaminants. However, activated charcoal filters and HEPA filters are fairly expensive and tend to lose their

effectiveness progressively with use. HEPA filters in particular are extremely expensive and are generally not practical when used to sterilize the air, since they only gather bacteria and do not kill them, and viruses are too small to be trapped by HEPA filters.
A plethora of indoor air purification devices that are currently available use mechanical filters in conjunction with electronic air cleaners or ion generators for providing purified indoor air. The negatively charged ions have the effect of purifying the atmosphere. A typical indoor area has an increased ratio of positive ions to negative ions, due to household activities like smoking, cooking or dusting or even due to the static electricity generated by synthetic fibers, which is not conducive to preservation of negative ions. However, these devices are not able to completely remove contaminants like gaseous chemicals and bacteria/viruses.
Purification of polluted air by removing gaseous chemicals has also been accomplished through the use of adsorbents or catalysts. Effective clean-up of air requires several beds of different types of adsorbents. Though catalysts can continuously remove harmful gaseous chemicals, catalysts typically operate only at high temperatures, due to which their use is limited in air purifying devices. In many applications, ozone is used to destroy viruses, bacteria, mold spores, pathogens and also remove odors and harmful gases. Ozone itself is toxic beyond a certain threshold level. It has been proved that long exposure to ozone might influence a critical step in the development of lung cancer by increasing the frequency of early, precancerous changes in cells.
There have also been attempts to use ultra violet or UV lamps to destroy bacteria on a variety of surfaces, including filter surfaces. It is known that UV-C light is an effective germicidal, capable of destroying microorganisms in the air.

As contaminated air passes through intense UV-C light, bacteria, viruses and other organic compounds get destroyed. Passing air through UV light creates activated oxygen atoms, i.e., ozone (O3). However, the UV-C also creates harmful radiations. Further, the UV-C intensity for the destruction of different micro- organisms is different. A high intensity UV-C radiation means more power consumption.
Photo-catalytic Oxidation (PCO) is the current state of the art technology used for air purification. PCO is achieved by combining UV light rays with a titanium oxide (TiO2) coated filter. The process creates hydroxyl radicals and super-oxide ions, which are highly reactive electrons. These highly reactive electrons aggressively combine with other elements in the air, such as bacteria and VOC's. Once bound together, a chemical reaction takes place between the super-charged ion and the pollutant, effectively oxidizing (or burning) the pollutant and breaking it down into harmless carbon dioxide and water molecules, thereby purifying the air. Single or multiple PCO filters coated with titanium dioxide (with and without dopant) coated on different supports, including non-woven fabric, have been used. A HEPA filter can be provided upstream of the PCO filter to capture some of the microorganisms.
A number of different air purification devices using the photo-catalytic oxidation technology for providing purified indoor air have been developed in the past.
EP Patent No. 1433515 discloses an air purifier where the main body allows air to pass through it. A replaceable filter is inserted into the main body and it is replaceable on the basis of the environmental properties of the space to be purified. Further, the air purifier includes a dust collecting unit to charge dust particles electrically and to collect the dust particles by electrostatic attraction.

In addition, a metal filter collects the dust particles charged in the dust collecting unit, and a HEPA filter is used to collect micro-contaminants. The metal filter is positioned in front of the HEPA filter.
US Patent No. 8328917 discloses an air filtration system comprising a particulate filter operably coupled to a substrate, where the substrate is powder coated with a solvent-free and heat-cured binary photocatalyst-resin mixture of titanium dioxide and polymer resins; wherein the binary photocatalyst-resin mixture is electrically charged and sprayed onto the substrate, and the binary photocatalyst-resin mixture is cured by heating onto the substrate to form a photocatalyst powder coated-substrate. A UV light source is provided for irradiating UV light on the photocatalyst powder-coated substrate to remove contaminants from the surface of the photocatalyst powder coated-substrate once the contaminants bind to the photocatalyst powder coated-substrate.
US Patent Application No. 20030019738 discloses a photocatalytic air purifier including filter structures coated with a catalytic material such as titanium dioxide. One or more UV lamps are interposed between the filter structures. The catalytic layer reacts with airborne VOCs and bioaerosols when activated by the UV lamps to oxidize the VOCs and destroy the bioaerosols. The photocatalytic air purifier further includes a control system.
US Patent Application No. 20110033346 discloses an air cleaner comprising: an air channel in the air cleaner, an air moving unit configured to create an airflow in the air channel, a photo-catalytic oxidation (PCO) element disposed in the airflow, and an Ultraviolet A (UV-A) Light Emitting Diode (LED) to illuminate the PCO element. The PCO element can be a substrate comprising: a first coating comprising a VOC decomposing catalyst; a second coating comprising

an ozone decomposing catalyst; and a third coating comprising titanium dioxide.
US Application No. 20050069464 discloses an air purification system in which a photocatalytic coating oxidizes volatile organic compounds, which get adsorbed onto the coating, into water, carbon dioxide, and other substances. When photons of ultraviolet light are absorbed by the coating, reactive hydroxyl radicals are formed. When a contaminant is adsorbed onto the coating, the hydroxyl radical oxidizes the contaminant to produce water, carbon dioxide, and other substances. Water adsorbs strongly on the coating, and water and contaminants compete for adsorption sites on the coating. A magnetron emits microwaves of a desired wavelength. The microwaves are only absorbed by the adsorbed water, desorbing the water from the photocatalytic coating, thereby creating additional photooxidation sites for the contaminants.
Indian Application No. 524/MUMNP/2012 discloses a fluid disinfection device having a substrate in optical communication with a photon source. The photon source may provide UV-A and UV-B light. The substrate may include photocatalytic particles on its surface and the photocatalytic particles may include Ti02, Bi203, W03, ZnO, FeO, SnO, or SiO2. Further, the substrate may be a filter or may include a series of filters. The filter in turn includes fibers, which may be composed of cotton, wool, polymers, metals, metal oxides, or carbon fibers. The filter is positioned within the path of the fluid thereby allowing the fluid to move over fibers as it passes though the filter. While passing through the fibers, the contaminants in the fluid come in contact with the photocatalytic particles and are thus destroyed.

Traditionally, when multiple PCO filters were used, all the filters generally had the same coating composition, thereby limiting filter efficiency when more than one contaminant was pre-dominant. This also resulted in over-working of the HEPA filters, which if present, captured most of the micro-organisms, resulting in their choking and thereby requiring frequent replacements. In conducive environments, there is a possibility of further microbial growth on the upstream face of the HEPA filter. Therefore, there has been a long felt but unmet need for a more effective purification unit that combines the bacteria destroying effects of UV radiation with effective purification of other contaminant by filtering in a more efficient and effective manner and simultaneously killing bacteria/viruses in the air stream and on the filtering medium.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Accordingly, an object of the present disclosure is to provide an air purification system that can be used to purify the indoor circulating air in residential and commercial settings; which is a simple, structured and sequential combination filter that includes high purification efficiency to remove particulates, dust/smoke, chemical contaminants, microorganisms/bacteria, mold, odor, pollen, pathogens, and the like, in a modular, replaceable and disposable unit; which is capable of being easily installed; which can be easily changed or extended according to the specific needs and conditions of the space to be purified, and also in which the modular units that are no longer needed, due to a

change in the environmental conditions, can be withdrawn without dismantling the system.
Another object of the present disclosure is to enhance the life of the HEPA filter by in-situ cleaning.
Yet another object of the present disclosure is to provide an air purification system which is aesthetically appealing.
Still another object of the present disclosure is to provide the enhanced area of filtration by unique way of manufacturing the pleated catalytic filter.
An additional object of the present disclosure is to provide an air purification system which can be used as a standalone unit or with an air handling unit in a centralized HVAC (Heating, Ventilating and Air Conditioning) system.
Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.
SUMMARY
In accordance with the present disclosure, there is provided a sequential air purification system comprising:
a housing having an air intake end for receiving the air to be purified and an air outflow end for discharging the purified air flow;
a combination of system components for providing said purified air flow, said system components are positioned sequentially from said air intake end to said air outflow end, said system components comprising:

a primary purification unit including at least one filter selected from the group of filters consisting of a pre-fllter and a minimum-efficiency reporting value (MERV) filter;
a secondary purification unit including at least one stage of at least one photo-catalytic oxidation (PCO) filter coated with a catalyst and a dopant provided in operative communication with one or more ultra-violet lamps, said PCO filter is adapted to substantially encompass said lamp; and
a tertiary purification unit including at least one filter selected from the group of filters consisting of a high-efficiency particulate air (HEPA) filter and an activated carbon filter; and
a fan positioned at said air outflow end for directing said purified air flow.
Typically, in accordance with the present disclosure, said catalyst is nano titania. Preferably, two or more PCO filters having different coating compositions are provided. More preferably, said filters are made of fabric and are bound to a frame made of a material selected from plastic, metal, and the like.
Preferably, in accordance with the present disclosure, spacers are provided between each of said system components and said system components are removably positioned in said housing. The said spacers are corrugated spacers made of a material selected from aluminum and anodized material.
In accordance with the present disclosure, said PCO filter is optimally spaced from said ultra-violet lamp.
Alternatively, in accordance with the present disclosure, said coating on said PCO filter may be supported on a fabric.

Typically, in accordance with the present disclosure, said air purification system comprises embedded controls with a printed circuit board. The system further comprises sensors for monitoring the pollution level, and is configured to automatically change the purification level based on the pollution level. Further, said system is adapted to detect any fault in the operation and provide an indication in at least one situation selected from lamp failure and requirement for filter replacement.
In accordance with the present disclosure, there is provided a method for purifying the indoor circulating air, said method comprising the following steps:
receiving the air to be purified at an air intake end of a housing;
purifying said air by passing through a combination of system components, said system components are positioned sequentially from said air intake end to an air outflow end, said system components comprising:
a primary purification unit including at least one filter selected from the group of filters consisting of a pre-filter and a minimum-efficiency reporting value (MERV) filter;
a secondary purification unit including at least one stage of at least one photo-catalytic oxidation (PCO) filter coated with a catalyst and a dopant provided in operative communication with one or more ultra-violet lamps, said PCO filter is adapted to substantially encompass said lamp; and
a tertiary purification unit including at least one filter selected from the group of filters consisting of a high-efficiency particulate air (HEPA) filter and an activated carbon filter; and
discharging the purified air flow at said air outflow end via a fan.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The disclosure will now be explained in relation to the non-limiting accompanying drawings, in which,
Figure 1 illustrates a schematic of a preferred embodiment of the air purification system of the present disclosure;
Figure 2 illustrates a schematic of another preferred embodiment of the air purification system of the present disclosure; and
Figure 3 illustrates a schematic of the pleated sheet and the filter assembly in accordance with the present disclosure.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The disclosure will now be described with reference to the accompanying drawings which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The present invention envisages a sequential air purification system for clean
room application, purifying indoor circulating air in residential and commercial
settings. The system can be used in variety of industries, not limited to, but
including pharmaceuticals, food, semiconductors, or in residences, offices, or
hospitals. The system can be used as a standalone unit or along with an air
handling unit in centralized heating, ventilation and air conditioning (HVAC)
systems. The system of the present disclosure is a simple, structured and
sequential combination filter that includes high purification efficiency to
remove particulates, dust/smoke, chemical contaminants,
microorganisms/bacteria, mold, odor, pollen, pathogens, and the like. Further, the system has modular, replaceable and disposable units capable of being easily installed and which can be easily changed or extended according to the specific needs and conditions of the space to be purified. Also, when the modular units are no longer needed, they can be easily withdrawn without dismantling the system.
The air purification system of the present disclosure comprises a housing having an air intake end for receiving the air to be purified and an air outflow end for discharging the purified air flow. The system comprises a combination of system components for purifying the air flow. The system components are positioned between the air intake end and the air outflow end, in a sequential manner. The system components comprise a primary purification unit including at least one filter selected from the group of filters consisting of a pre-filter and a minimum-efficiency reporting value (MERV) filter; a secondary purification unit including at least one stage of at least one photo-catalytic oxidation (PCO) filter coated with a catalyst and a dopant provided in operative communication with one or more ultra-violet lamps, the PCO filter is adapted to substantially encompass the lamp; and a tertiary purification unit including at least one filter selected from the group of filters consisting of a high-efficiency particulate air

(HEPA) filter and an activated carbon filter. The purified air from the system components is discharged via a fan.
The air intake end and the air outflow end are provided with means for creating a uniform air flow distribution across the filters at minimal pressure resistance. The system components are each separated by spacers and are removably placed in the housing. The spacers are corrugated spacers made of a material selected from aluminum and anodized material. A flip arrangement may be provided for removal of the filters. The fan blade may be provided with an anti-microbial coating.
The primary purification unit is adapted to remove particulate matter and dust. The pre-filter may be provided with an anti-microbial coating to capture the microbes. The pre-filter and the MERV filter are the primary stages of filtration for removal of dust from the air. This also safeguards the secondary and the tertiary purification units provided downstream of the primary purification unit, whose performances would otherwise deteriorate due to blockage of catalyst sites or filter fibers.
The secondary purification unit comprises at least one PCO filter coated with photo-catalytic oxidation (PCO) catalyst and dopant. Two or more PCO filters can be used and optimized to treat various contaminants. Based on the application, for principle contaminant removal (VOC's or micro-organisms), multiple PCO filters can be coated with the same or different optimum concentrations of nano-titania and dopant. The filters are made of fabric and are bound to a frame made of a material selected from plastic, metal, and the like. The PCO filters are provided in communication with an ultra-violet lamp to receive UV radiations, typically UV-A radiations, where two PCO filters can be provided with a single UV lamp placed in-between or a single PCO filter can be

provided with multiple UV lamps. The PCO filter substantially encompasses the UV lamp, with an optimal space between the PCO filter and the UV lamp, for maximizing the realized photo-catalytic reaction at the catalyst surface.
Multiple stages of photo-catalytic oxidation, in series, ensure effective treatment of the air-borne contaminants. Placement of the ultraviolet light source in-between the PCO filtration stages ensure energy-efficient and effective use of the available photon energy, thereby reducing the power consumption. The catalytic filter may have a pleated non-woven fabric which is coated on both sides with nano-titania dioxide and dopant.
The tertiary purification unit typically comprises a HEPA filter and an activated carbon filter. Traces of remnant contaminants, if any, are captured by the HEPA filter, which is used downstream to the PCO filtration stages. HEPA filter's useful life, when used with upstream PCO filters, is much more than when used in isolation. Hydroxyl and super-oxide radicals produced by the UV-PCO action, help in keeping the HEPA surface area clean by continuous destruction of the micro-organisms, thereby providing improved filtering efficiency. For tertiary treatment of VOC's, an activated carbon filter is used in the last stage of air purification.
The filters are typically made of corrugated aluminum sheet and have a pleated structure which provides higher catalytic surface area in a given filter size. This aids in faster destruction rate for contaminants and low pressure drops. Furthermore, the layout and the disposition of the filtration stages enable a larger contact surface area with the turbulent contaminant currents, yielding enhanced purification and decontamination performance. The activated carbon filter also has a pleated structure, which provides a good adsorption area. The

filter surface is coated with an anti-microbial coat to prevent deposition of microbes.
The system further comprises embedded controls with multilayer printed circuit board (PCB). The system may be provided with a detachable electrical cabinet for easy access. The system may be provided with a remote having an auto-mode feature. Further, a soft touch start button may be provided on a swoosh design front panel for either switching on/off or for changing modes. The system uses an android based application for the air purifier control and data logging. The system further comprises a remote locator key on the front panel and a real time clock for setting the time. The system further comprises sensors such as an optical dust sensor and a VOC sensor for monitoring the pollution level and is configured to automatically change the purification level based on the pollution level. Further, the system is adapted to detect any fault in the operation and provides an indication in a situation such as lamp failure and requirement for filter replacement. Various components of the system may be composed of plastic, sheet metal and composites, to reduce the cost.
FIGURE 1 of the accompanying drawings illustrates a preferred embodiment of the air purification system. The system is generally referenced by the numeral 100 in Figure 1. The system 100 comprises a primary purification unit including a pre-filter 102 and a MERV filter 104; a secondary purification unit including two PCO filters 106 & 110 coated with a catalyst and a dopant of different composition provided in operative communication with an ultra-violet lamp 108, the PCO filters 106 & 110 substantially encompassing the lamp 108; a tertiary purification unit including a HEPA filter 112 and an activated carbon filter 114; and a fan 116 for directing the purified air flow. The PCO filters 106 & 110 are spaced by a distance 118 from the UV lamp 108. The positioning of the HEPA filter 112 subsequent to the PCO filters 106 & 110 helps in reducing

the load on the HEPA filter 112, thereby increasing the efficiency. The MERV filter 104 is a MERV 8 grade with 85% efficiency in removing particles >20μ., the PCO filters 106 & 110 through the photocatalytic oxidation remove greater than 90% of the microbes in a single pass, the activated carbon filter 114 adsorbs the VOC and traps greater than 90% particles >10μ., and the HEPA filter 112 provides 99.997% removal of particles > 0.3μ.
The working of the system 100 was checked both as a standalone unit and as a duct mounted unit for treating an uncountable microbe inlet load (i.e. > 500 CFU) in a single-pass filtration process. A filtration efficiency of 99.997% was achieved at removing microbes, gaseous chemicals and dust.
FIGURE 2 of the accompanying drawings illustrates another preferred embodiment of the air purification system. The system is generally referenced by the numeral 200 in Figure 2. The system 200 comprises a primary purification unit including a pre-filter 202 and a MERV filter 204, a secondary purification unit including two UV lamps 206 & 210, one on each side of a PCO filter 208 which is coated with a catalyst and a dopant, and provided in operative communication with the ultra-violet lamps 206 & 210, a tertiary purification unit including a HEPA filter 212, an activated carbon filter 214, and a fan 216 for directing the purified air flow. The PCO filter 208 is spaced by a distance 218 from the UV lamps 206 & 210. The positioning of the HEPA filter 212 subsequent to the PCO filter 208 helps in reducing the load on the HEPA filter 212, thereby increasing the efficiency. The MERV filter 204 is a MERV 8 grade with 85%o efficiency in removing particles >20μ, the PCO filters 208 through the photocatalytic oxidation remove greater than 90% of the microbes in a single pass, the activated carbon filter 214 adsorbs the VOC and traps greater than 90% particles >10μ, and the HEPA filter 212 provides 99.997% removal of particles > 0.3μ.

FIGURE 3 of the accompanying drawings illustrates the pleated sheet and the filter assembly, generally referenced by the numeral 300. The filter assembly is constructed by providing a frame defining an opening; a pleated sheet extends across the opening, having a plurality of pleats, each pleat defining a fold line, a plurality of fold lines parallel to each other. The pleated sheet comprises corrugations 302 and punched slits 304. The expanded view 320 of the pleated sheet shows a corrugated aluminum sheet 306 with a nano titania coated cloth 308 and a press bend 310, compacted by pressing in the direction 318. The compacted view 322 is shown in the filter assembly which also illustrates bent clips 312, a plastic frame 314 and a side frame 316.
TECHNICAL ADVANTAGES
The air purification system in accordance with the present disclosure described
herein above has several technical advantages including but not limited to the
realization of: the air purification system can be used to purify indoor
circulating air in residential and commercial settings; it is a simple, structured
and sequential combination filter that includes high purification efficiency to
remove particulates, dust/smoke, chemical contaminants,
microorganisms/bacteria, mold, odor, pollen, pathogens, and the like, in a modular, replaceable and disposable unit capable of being easily installed; it can be easily changed or extended according to the specific needs and conditions of the space to be purified, and the modular units that are no longer needed, due to a change in the environmental conditions, can be withdrawn without dismantling the system. Further, the life of the HEPA filter is enhanced by in-situ cleaning. Additionally, the air purification system is aesthetically appealing. Still further, the air purification system can be used as a standalone unit or with an air handling unit in a centralized HVAC system. The air purification system uses a unique pleated catalytic filter which provides an enhanced filtration area.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be

understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

We Claim;
1. A sequential air purification system comprising:
a housing having an air intake end for receiving the air to be purified and an air outflow end for discharging the purified air flow;
a combination of sequentially arranged system components for providing said purified air flow, said system components being positioned sequentially from said air intake end to said air outflow end, said system components comprising:
a primary purification unit including at least one filter selected from the group of filters consisting of a pre-filter and a minimum-efficiency reporting value (MERV) filter;
a secondary purification unit including at least one stage of at least one photo-catalytic oxidation (PCO) filter coated with a catalyst and a dopant provided in operative communication with one or more ultra-violet lamps, said PCO filter is adapted to substantially encompass said lamp; and
a tertiary purification unit including at least one filter selected from the group of filters consisting of a high-efficiency particulate air (HEPA) filter and an activated carbon filter; and
a fan positioned at said air outflow end for directing said purified air flow.
2. The air purification system as claimed in claim 1, wherein said catalyst is nano titania.
3. The air purification system as claimed in claim 1, wherein two or more PCO filters having different coating compositions are provided.

4. The air purification system as claimed in claim 1, wherein said filters are made of fabric and are bound to a frame made of a material selected from plastic, metal, and the like.
5. The air purification system as claimed in claim 1, wherein said filters have a pleated structure.
6. The air purification system as claimed in claim 1, wherein spacers are provided between each of said system components, said spacers are corrugated spacers made of a material selected from aluminum and anodized material.
7. The air purification system as claimed in claim 1, wherein said system components are removably positioned in said housing.
8. The air purification system as claimed in claim I, wherein said PCO filter is optimally spaced from said ultra-violet lamp.
9. The air purification system as claimed in claim 1, wherein said coating on said PCO filter is supported on a fabric.
10. The air purification system as claimed in claim 1, wherein said air purification system further comprises embedded controls with a printed circuit board.
11. The air purification system as claimed in claim 10, wherein sensors are provided for monitoring the pollution level, and the system is configured to automatically change the purification level based on the pollution level.
12. The air purification system as claimed in claim 10, wherein said system is adapted to detect any fault in the operation and provide an indication in at least one situation selected from lamp failure and requirement for filter replacement.
13. A method for purifying the indoor circulating air, said method comprising the following steps:
receiving the air to be purified at an air intake end of a housing;

purifying said air by passing it through a combination of system components, said system components being positioned sequentially from said air intake end to an air outflow end, said system components comprising:
a primary purification unit including at least one filter selected from the group of filters consisting of a pre-filter and a minimum-efficiency reporting value (MERV) filter;
a secondary purification unit including at least one stage of at least one photo-catalytic oxidation (PCO) filter coated with a catalyst and a dopant provided in operative communication with one or more ultra-violet lamps, said PCO filter is adapted to substantially encompass said lamp; and
a tertiary purification unit including at least one filter selected from the group of filters consisting of a high-efficiency particulate air (HEPA) filter and an activated carbon filter; and
discharging the purified air flow at said air outflow end via a fan.