Determining the efficiency of air filters
Air filters are made of glass fiber, synthetic fiber, felt, cellulose fibers, asbestos, biological enzyme, carbon and similar materials according to the purpose of use.
Filter materials consisting of 100% non-woven polyester fibers bonded together with a flame retardant that creates a high-layered structure with synthetic flexible staple fibers are called synthetic fibers or polyester fibers. It is divided into dry type and adhesive coated type.
In dry type filters, materials such as glass wool, cellulose fibers, wool felt, asbestos and synthetic fibers are used as filter material. Glass fiber filter material is concentrated in densely textured glass fiber layers and has high capture ability. The air side part of the filter supports the material and forms the final filtering stage. All of the glass fiber material, except for dye-retaining fibers, is processed with a non-toxic, non-flammable, odorless binder.
Fibrous filters covered with adhesive material are manufactured in the form of flat plates obtained by squeezing the coarse fibers in the form of sheets at sparse intervals. Filter media are covered with oil or a similar substance. This substance allows the powders to adhere to the fiber surface. It is considered appropriate that the air flow velocity in these filters is between 1.25 m / s and 3.5 m / s. These filters provide high efficiency against coarse dust with low pressure loss. Often they are not able to filter enough for atmospheric air dust. It is generally used for coarse filtering before high efficiency filters. Materials such as glass wool, vegetable fibers, synthetic fibers, metal chip fibers, perforated metal sheets and foils, braided wire, open-pore synthetic sponges, are used as filter media.
Manufacturing methods of adhesive coated fibrous type filters are in the form of flat plates perpendicular to the air flow, as well as in the form of curved zigzags, as well as plates with increasing frequency. In order to keep the filter fibers in the form of sheets, a wire mesh enclosure on both sides and a metal frame containing the outer edges are placed. Filter blanket applications tightly fixed on a curved or zigzag wire cage are also common. The purpose of applying zigzags or folds is to increase the filter surface and minimize the air flow rate.
Bio filters contain the smallest dust particles in the air thanks to the eco filter in their content. With its biological enzyme feature, it neutralizes bacteria, fungi and microbes. Enzymes in the biological enzyme filter destroy the cell walls of bacteria by dissolving them. Bio filter is effective in eliminating the problem of repeated pollution in individual air conditioning devices. Bio filter captures 99% of dust particles smaller than 0.3 microns while eliminating 95% of bacteria.
Carbon media are made of non-woven polyester impregnated with fine activated carbon powders. This filter material can be used in ducted applications such as hoods, air washers, domestic air conditioners or in domestic environments where odor removal is required.
Active granular carbons, on the other hand, can be used to eliminate heavy odors caused by industrial studies.
In the selection of air filters, dust holding efficiency, service life and filter starting resistance criteria are important.
Filter test standards allow the filters to be selected according to their intended use and to be compared with each other. According to the European standard, air filters are classified into two separate groups as EN 779 standard applied for filter groups with G and F efficiency and EN 1822 standard which determines the efficiency of hepa filters.
EN 779: 2012 standard determines and classifies G efficiency coarse filters according to their weight average dust retention values.
The efficiency of medium and fine filters is determined by counting the particles in the 0.2 micron – 3 micron size range at the filter inlet and outlet and proportioning them to each other. Since 0.4 micron, which is the average size of the particles used in the test, is used for classification, the efficiency of the filters with F yield is expressed in terms of the average efficiency of the 0.4 micron particle.
HEPA filters, which means high efficiency particle capture, are tested according to EN 1822 standard and their efficiency is determined. Hepa filters are filters that can remove particles up to 0.3 microns from the air at 85% and above. According to the EN 1822 standard, the efficiency of the filters is determined by the particle size that gives the lowest efficiency value at a given air speed for a given filter paper. The particle size exceeding the particle size that will give minimum yield is called MPSS – Most Penerating Particle Size.
After determining the efficiency of the filter paper, the filter efficiency must first be determined by considering the whole filter construction together with the filter casing and gasket. Then, the whole filter surface area should be determined point by point by scanning. The efficiency value should be calculated using the obtained permeability value.
The filter under test should be scanned using the moving aerosol feeding nozzle and measuring tips. Multiple point efficiency values to be determined here should be entered into the graphic to be added to the test report. In order to make the correct classification regarding the efficiency of the Hepa filter, the point efficiency and the efficiency of the entire filter must comply with the values specified in the standard. Filters that are more sensitive than hepa filters and have a rate of 99.999% are called ulpa filters. Hepa and ULPA filters must be tested during their manufacture and after the filter is installed in accordance with the EN 1822 standard.
Determining the efficiency of air filters by testing them with precise measurements according to the standards during their manufacture and use is of great importance in terms of preserving and increasing the quality of life.
İlker KURAN
Alperen Ltd Şti