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Air Distribution
Published in Samuel C. Sugarman, HVAC Fundamentals, 2020
Air filter are typically made from pleated paper (Figure 7-23) or fiberglass to remove solid particulates such as dust, debris, pollen, mold, and bacteria from the mixed air. Some filters have elements with a static electric charge to attract dust. A charcoal filter is used where odors are a concern. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds or ozone. Filters made for cleanrooms or other applications which are more than 99% efficient are known as High Efficiency Particulate Air (HEPA) and Ultra Low Penetration Air (ULPA) filters. H o w often filters need to be change will depend on the type of HVAC and the cleanliness of the environment in which the system is located. In order for filters to function properly they must be installed correctly. To help with this, most filters will have an arrow showing direction of airflow. To help determine when filters need changing, a differential pressure gauge can be installed with measuring points on either side of the filters. This gives a pressure drop across the filters. When the pressure drop reaches a given limit the filters need to be changed. Since airflow capacity decreases and static pressure increases over time filters actually become more efficient as the filter loads. The filter should be changed once it has reached its capacity. The filter frame should be tight against all sides of the filter housing so that no air bypasses the filters.
Gas Filtration Applications in the Pharmaceutical Industry
Published in Maik W. Jornitz, Filtration and Purification in the Biopharmaceutical Industry, 2019
The DOP (dioctylphthalate) aerosol test has seen extensive use in measuring the efficiency of HEPA and ULPA filters used to provide air to clean rooms, and for similar applications. DOP was used when the test was first developed but this has been superseded by other less toxic materials, such as Poly Alpha Olefin (PAO). During the test, the oil is aerosolized to form droplets which have a mean diameter of 0.3 µm. The droplets are then carried at high concentration, in a gas stream to the filter under test. Any droplets which pass through the filter are detected and counted by either a light scattering photometer or laser particle counter, attached to the downstream side of the filter under test, giving a percentage penetration when compared to the upstream concentration. For a filter to be rated as a HEPA filter it must meet or exceed the Military Standard, MIL-STD-2821 [14] and must retain 99.97% of 0.3 µm particles. For a filter to be rated as an ULPA filter it must meet or exceed 99.999% retention of particles at 0.12 µm. The commercially available equipment operates at 4 cubic feet per minute (CFM), and cannot detect fractional penetration by 0.3 μm droplets of 10−6 (0.0001%). Using microbiological terminology, the method, at 4 CFM, is able to measure titer reduction (defined as the ratio of upstream to downstream cfus) of 106. It cannot, for example, distinguish between two filters having respective titer reductions of 108 and 106, nor can it detect a minor defect that could compromise sterility of the gas filtered.
Considerations for Development and Manufacture
Published in Richard J. LaPorte, Hydrophilic Polymer Coatings for Medical Devices, 2017
To remove contaminating particulate from the controlled environment, room air is passed through high-efficiency particulate air (HEPA) filters or ultralow particulate air (ULPA) filters, depending on the degree of cleanliness required for the operation. Filters are characterized by their efficiency at removing particles of a given size from the air entering the cleanroom (Table 4.2). For instance, a type C HEPA filter, appropriate for a class 100,000 cleanroom, is 99.99%) efficient at removing particles that are ≥ 0.3 μm in size, if filter coverage is at least 10% of the total floor space and if airflow through the filters is at least 10 cfm/sq ft. The efficiency of ULPA filters can be as high as 99.9999% or higher for particles 0.12 μm or greater.
Modification of the commercial polyester filter media support with electrospun polyethylene terephthalate fibers and its application for air purification
Published in Science and Technology for the Built Environment, 2022
Wei Lin Ng, Lei Zhou, Abu Bakar Sulong, Eng-Poh Ng, Soon Huat Tan
The primary filter with the lowest efficiency acts to protect the air conditioning equipment and extend the life of the secondary and tertiary filters. Therefore, all the air entering the supply duct will flow through the secondary and tertiary filters. The application of tertiary filters is mainly found in a particular environment, such as cleanrooms, biosafety laboratories, isolation rooms, and hospital operating rooms. In general, high efficiency particulate air (HEPA) filter or ultra-low penetration air (ULPA) filter is used as a tertiary filter.
Medical textiles
Published in Textile Progress, 2020
There are also Ultra-Low Particulate Air (ULPA) filters and whereas HEPA filters are designed to remove up to 99.97% of contaminants of sizes down to 0.3 µm, ULPA filters are designed to remove 99.99% of particles down to 0.12 µm in size which does therefore include virus-sized particles. However, the ULPA filters are much more demanding both in terms of maintenance and operating costs, so they are intended to be reserved for specialist treatment areas.