AIR PURIFICATION SYSTEM FOR AIR HANDLING UNITS

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an air purification system for air handling units to enhance the indoor air quality.

BACKGROND OF THE INVENTION

Enclosed spaces including commercial buildings such as mails, offices, hotels, interior spaces of buildings etc. are typically supplied with conditioned air, heated or cooled, as necessary, using centralized air conditioning system such as HVAC. The centralized air conditioning system circulates the same air within the building. Typically, air flows through the air handling unit (AHU) by an air blower therein and a network of ducts or conduits, and indoor, return air (RA) also flows back from the enclosed space to the AHU through separate ducts or channels, where it is reconditioned and circulate back to the enclosed space. As the air is recirculated through the AHU, the AHUs become breeding ground for mold, fungus and bacteria leading poor indoor air quality. Further, it is also observed that in order to save power/electricity, people limit the supply of fresh air into an air-conditioned space as this increases the cooling load. Therefore, there is limited fresh air to dilute the air borne pathogens brought in. This leads accumulation and cross contamination of pollutants in different zones within the building. Further, harmful VOC’s (volatile organic compounds), emitted by chemical cleaning agents, paints, varnish, and aerosols used daily in the enclosed spaces also contribute to poor indoor air quality. This poor indoor air quality in the said enclosed spaces has become a growing concern these days, as several studies have revealed that indoor air pollution is 2-5 times worse than outdoor air pollution. Therefore, individuals spending time in the enclosed spaces, for example people working approximately 8-10 hours a day in the offices, are exposed to dangerous indoor air pollutants such as bacteria, mold, viruses, carcinogenic VOC’s (volatile organic compounds) generated within that leads to sick building syndrome where occupants experience headaches, fatigue and drowsiness, eye, nose, and throat irritation leading to loss of productivity and absenteeism.

The most common device used for the air purification is a mechanical filter that is disposed within the unit cabinet structure in the path of air being forced there through on its way back to the conditioned space served by the unit. However, the mechanical filter only traps the virus and bacteria and do not effectively kill them thereby fails to solve the abovementioned problem.

Further, it is observed that biofilm forms over the surface of cooling coil of Air Handling unit over the time. Presently, UVGI System is used for surface decontamination by elimination of biofilm over the cooling coil of Ah Handling unit, however it has been observed there is lot of by-pass of microbial organism as air is travelling at speeds of 400-500 FPM. Moreover, UVGI System does not take care of dangerous carcinogenic VOC’s and Odour.

Hence, there is a need of a purification system for air handling units that at least solve one of the above discussed problem.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a purification system for air handling units (AHU) having a primary air filter and cooling coil, said purification system comprising a photocatalytic reactor designed to allow air to pass through with a substantially minimum pressure drop; and an Ultra Violet Germicidal Irradiation (UVGI) system having one or more UV-C emitters emitting UV rays. According to the present invention, the said UVGI is adapted between the photocatalytic reactor and the cooling coil of the AHU in such a way that the UV-C emitters covers surface of the cooling coil of the AHU at one side of the UVGI system for eliminating formation of biofilm on the cooling coil and surface of the photocatalytic reactor at other side of the UVGI system for oxidizing carcinogenic VOC’s, bacteria, virus and pathogens present in air into harmless by-products such as carbon dioxide and water vapor. According to an embodiment of the present invention, the photocatalytic reactors is dimensioned to provide a surface area of the photocatalytic reactor 25-40 times greater than the face area of cooling coil of the AHU.

According to another embodiment of the present invention, the photocatalytic reactor is also designed to prevent the UVC rays from irradiating through the photocatalytic reactor. Advantageously, the pressure drop across the photocatalytic reactor is less than lOmmHg.

According to further embodiment of the invention, the photocatalytic reactor comprises an array of aluminium strips with parabolic design arranged vertically or horizontally allowing only to pass air without a substantial pressure drop. The array is coated electrostatically with photocatalyst material. The photocatalyst material includes nano Ti0 _2, KMn0 ₄ and the like.

According to the present invention, the UV-C emitters emit UV rays of 254 NanoMeters to deliver dosage of 400-4000 pW/cm ² depending on the applications such as hospitals, offices airports, manufacturing industries or commercial buildings.

According to preferred embodiment of the present invention, the UVGI system is adapted on a sliding mechanism for adjusting the UV-C emitters between the cooling coil and photocatalytic reactor so that adequate amount of UV-C irradiation covers both the cooling coil surface, as well as the photocatalytic reactor to facilitate effective dosage of UV-C.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

Figure 1 shows a schematic of an air purification system for AHU according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

Referring Figure 1 shows a purification system (100) fitted in an AHU (200) between a cooling coil (210) and a primary air filter (220) of the AHU (200) according to the preferable embodiment of the present invention. The purification system encapsulates a photocatalytic reactor (110), an Ultra Violet Germicidal Irradiation (UVGI) system (120) having one or more UV emitters emitting UV rays, spaced apart from the photocatalytic reactor (110) in a modular frame (not shown).

The system has an integrated microprocessor controller which monitors critical performance parameters like UVC 254 nm intensity, emitter and ballast run hours and life. The system integrates with the BMS and interlocks with the access panel for safety of service personnel. All parameters are logged and displayed on the LCD screen of controller to monitor system functionality, diagnostics and generate alarms in the event of failure. The system has a means to transfer the data through a communication port for remote monitoring to ensure that the system performs as per design. The functions of the controller include performance parameters like UV intensity in pW/cm ² , Kill rate %, Real Time clock (RTC) to facilitate monitoring of individual run hours /starts/stops for each emitter and run hours for each individual ballast.

According to the present invention, the photocatalytic reactor (110) is designed to allow only air to pass through the reactor with a substantially minimum pressure drop and prevents the UVC rays from irradiating through the photocatalytic reactor thereby protecting the personnel in the AHU room as well as the air filters from dangerous UV radiation. Further, according to the present invention, the photocatalytic reactor is also dimensioned in such a way that it provides a surface area of the photocatalytic reactor in the range between 25-40 preferably 30 times greater than that of face area of cooling coil maximizing contact period for air passing through the photocatalytic reactor. According to the inventor of the present application, the surface area of the photocatalytic reactor 30 times greater than that of face area of cooling coil is preferable. According to the present invention the photocatalytic reactor is also designed in such a way that the preferable pressure drop across the photocatalytic reactor is less than lOmmHg. However, it is apparent to the person skilled in the art the minimum pressure drop is only preferable and not limiting invention to the said numeral as the pressure drop will keep increase over the time and depends upon the design of the photocatalytic reactor.

In preferable embodiment, the photocatalytic reactor (110) comprises an array of aluminium strips (not shown) with a parabolic design arranged vertically or horizontally allowing only to pass air without a substantial pressure drop so that it provides maximum contact surface to the air passing through it. The array is coated electrostatically with photocatalyst material. The photocatalytic reactor does not allow dangerous UV rays to pass through it.

According to the present invention, any material capable of catalysing photocatalytic oxidation when illuminated with a source of UV is suitable for use as a photocatalyst material in the present invention. Such materials are readily available. However, as per the inventor, nano Ti0 ₂ (Titanium dioxide) is preferable. Alternatively, photocatalyst material such as KMn0 ₄ and the like can be used. Further, any material doped with noble metals or other metals may be employed.

According to an embodiment of the present invention the UV-C emitter irradiates in the range between 200-280 nanometer producing germicidal UV rays that destroys the DNA of harmful micro-organisms such as Bacteria, Mold Spores, Virus and Pathogens present on the cooling coil surface as well as in the air passing through the AHU and eliminates the formation of biofilm on the cooling coil. Advantageously, the UV-C emitter irradiates at 254 nanometer with dosage range of 400-4000 pW/cm ² .

According to the present invention, the UVGI system is mounted on a sliding mechanism which allows the UVGI system to move forward and backward as shown in Figure 1 by arrows‘X’ in order to increase and/or decrease intensity of the UV rays falling on the photocatalytic reactor and cooling coils based on the applications such as hospitals, offices airports, manufacturing industries or commercial buildings.

In operation, the indoor air return to the AHU may comprise carcinogenic VOC’s, bacteria, virus and pathogens passes through the filter. When returned air comes in the contact with the surface of the photocatalytic reactor of air purification system of the present invention wherein UV-C rays irradiates onto coated with nano-particles of titanium dioxide of the photocatalytic reactor results in release of hydroxyl radicals and super oxides, which react with present in return and/or fresh air and converts them into harmless by-products such as carbon dioxide and water vapor. The treated air then passes through the cooling coil of which surface is also covered by the UV-C rays wherein it gets cooled to the predetermined temperature and directed to the indoor places though the ducts of the AHU. The UV-C rays falling on the surface of the cooling coil decontaminates the cooling coil by elimination of growth of biofilm on the cooling coil surface. Accordingly, the air purification system of the present invention ensures effective air decontamination by elimination of all kinds of micro-organisms, dangerous carcinogenic VOC’s and odour thereby enhancing the Indoor air quality.

The purification system provides decontamination of cooling coil surface and the decontamination of air passing through the AHU resulting in dual decontamination. The purification system of the present invention is retrofittable with a pre-wired plug and play design to ease on-site installation and commissioning. The supply, installation, testing and commissioning of purification system is easy for integration with AHU. The purification system is capable of eliminating the pollutants such as microbial organisms, virus and bacteria, VOCs, and prevent the formation of mold and fungus growth on the cooling coil to sustain the as built design condition thereby preventing deration of the heat exchanger i.e. cooling coil resulting in energy savings.

The following example further illustrate the present invention and is not to be construed as limiting the scope thereof.

Example 1 A testing facility was set up in a 2000 Sq. Ft. sterilized room with a closed-circuit air-conditioning system, with ducted supply and return air flow (Figure 3. & 4.). All openings were properly sealed to ensure that there were no leakages and no infiltration of outside air into the test area. The temperature was maintained at 24 deg. C and RH at 55 % to simulate a commercial building environment.

A) Determining the efficacy of the system for micro-organisms

A mixture containing a consortium of 5 species of micro-organisms was prepared by using 24 hours old broth culture for the bacteria, Presley sub cultured Candida Albicans for Yeast, and Spore Suspension for Mold to simulate commonly prevalent airborne micro-organisms. The concentrated mixture of micro-organisms was spray coated onto two test plates and placed inside the AHU. For carrying test, the blower was started and regulated to air velocity of 500 FPM across the coil. The AHU operated with air purification system of the present invention and with UVGI alone.

To monitor the reduction in colony forming units (CFU) of micro-organisms over a specified time interval, swab samples from test plates were collected and spread over selective culture media (agar plates) to capture specific micro-organism counts and determine the kill rates for each species. The samples were collected at intervals of 0 hour to get the initial baseline count and further samples are collected after 15 minutes and 180 minutes. Similarly, to monitor the reduction in CFU in air, air samples are collected with an Anderson sampler as well as manual Gravimetric method, with the same selective culture media plates used above. The air sampling was not done at 0 hour since it would take a few minutes for the micro-organisms to get airborne. Air sampling was started after 15 and 180 minutes.

Result:

From test as shown in Table 1, concluded that the kill rates with the air purification system of the present invention was clearly far more efficient than without air purification system i.e. with only UVGI as seen in the surface sampling test, with the reduction of CFU (colony forming units) counts reducing to 0 within the first 15 minutes of exposure. The UVGI by itself was not able to reduce the fungal count to zero for one species even after 3 hours of exposure. The air sampling also clearly establishes that 100 % air decontamination is successfully carried out due to the efficient design of the photocatalytic reactor. The air samples collected after 15 minutes show that the micro-organisms were airborne after being blown off by the high air velocity in the AHU but after 3 hours the CFU counts reduced to 0. This substantiates the fact that there is minimal bypass due to the unique design of the reactor and that all the air circulated within the air-conditioned space is effectively decontaminated.

TABLE 1 B) Determining the efficacy of the system for TVOC’s.

The same test facility was fumigated, sterilized and used to determine the efficacy for TVOC’s. Measured quantities of Paint thinner, Varnish, Adhesives, Cleaning Chemicals, Insect repellant, Sanitary Deodorizer & Aerosols were introduced into the air-conditioned space, to represent the commonly prevalent TVOC’s present in commercial buildings. To test the efficiency of the system, TVOC counts above Toxic Limits were simulated. Graywolf IAQ Sensors were setup for monitoring and when the reading on the TVOC sensor was stable at 31500 pgm/m ³ , the data logger was started to record the TVOC count and monitor TVOC reduction with the IAQ system running, in real time. Data logging was stopped when the VOC count reached the permissible count of 500 pgm/m ³ . The process was repeated for the same timeframe without the Air purification system of the present invention to determine the TVOC reduction count and establish the efficacy of the system of the present invention.

Result:

The rapid decomposition rate of the TVOC’s was observed when the air was circulated in the test area with the air purification system of the present invention, and the TVOC count reduced from a Toxic level of 31,500 pgm/m ³ to the acceptable count of 500 pgm/m ³ within 23 hours. However, when the test procedure was repeated without the air purification system of the present invention, the decomposition was slow and the TVOC count reduced to 6184 pgm/m ³ for the same timeframe. The combination of TVOC concentration. This test clearly establishes the efficacy of the system and proves the effectiveness of the photocatalytic reactor in rapid decomposition of VOC’ s. Refer Figure 2

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SU BSTITUTE SH EETS (RU LE 26) Example 2

The air purification system of the present invention was installed in five indoor places spread for test purpose. The units were installed on AHU's with varying sizes and capacities ranging from 12,000 to 24,000 CFM. Swab samples were collected from the cooling coils before installing the air purification system and spread over culture media to establish the micro-organism counts in CFU's. This test was repeated 30 days post installation of the air purification system and the results clearly show the effective reduction of microorganisms. Refer Table 2:

Table 2

The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended

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SU BSTITUTE SH EETS (RU LE 26) to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.

The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.

It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.