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Secondary HVAC Systems
Published in Moncef Krarti, Energy Audit of Building Systems, 2020
The efficiency of an air filter to remove particulates from air streams can be measured using standard testing procedures such as ASHRAE Standard 52.1. Table 7.3 outlines typical efficiencies and rated air flow velocities for commonly available air filters. The flat filters are the least efficient and the least expensive. The HEPA (high-efficiency particulate air) filters are the most efficient but are generally expensive. For general HVAC applications such as office buildings and schools, pleated filters are typically used. Bag filters are suitable for most hospital spaces. HEPA filters are appropriate for clean-room applications. To extend the life of the more expensive filters, it is a common practice to add inexpensive prefilters, which are placed upstream of the more expensive and effective filters in order to reduce dirt loading.
Industrial ventilation
Published in Sue Reed, Dino Pisaniello, Geza Benke, Principles of Occupational Health & Hygiene, 2020
David Bromwich, Elaine Lindars, Kate Cole
Often all that is required to reduce the dust is for an appropriate vacuum cleaner to be connected to the tool. This can reduce inhalable dust by up to 98 per cent, although with very fine respirable particles the method is less effective. Respirable dust is invisible to the naked eye and tends to deposit not in the nose or throat, but in the lungs. Some domestic vacuum cleaners may have high-efficiency particulate air (HEPA) filters, but they are not designed to meet industrial standards and have been found to pass up to 50 per cent of particles 0.35 µm in diameter (Trakumas et al., 2001). HEPA filters remove 99.97 per cent of particulates 0.3 µm or larger. Toxic dusts collected by a vacuum cleaner can also become a source of air contamination when they are re-suspended inside the cleaner, particularly with cyclonic and wet vacuum cleaners.
Mechanisms of Particle Removal from Air and Other Gases
Published in Maik W. Jornitz, Theodore H. Meltzer, Sterile Filtration, 2020
Maik W. Jornitz, Theodore H. Meltzer
Air filters find use in every biopharmaceutical facility in several applications and system configurations. The most commonly known air filters are HEPA (high efficiency particulate air) filters, which are used within HVAC (heat-venting-air conditioning) systems. All clean room ceilings are outfitted with HEPA filters. ULPA (ultralow particulate air) filters are commonly used in the electronics industry. These filters have a tighter retention rating than HEPA filters and are required to satisfy the ultraclean standards within the electronics industry, where even very small particles can become “killer particles,” bridging electronic circuits and destroying the element. Both ULPA and HEPA types are depth filters. They are composed of polypropylene or glass fiber. The glass fiber filters usually have a heat-stabilized polypropylene layer on the downstream side to contain any fiber shedding. Glass fiber is highly adsorptive and is therefore the preferred choice for removing smaller particles. Nevertheless, such filters require stipulated process conditions for their best performance.
Integrating IAQ control strategies to reduce the risk of asymptomatic SARS CoV-2 infections in classrooms and open plan offices
Published in Science and Technology for the Built Environment, 2020
Air cleaning strategies involve applying air filtration or purification in the outdoor supply, recirculated or mixed air duct, locally in a room or a cubical, and at personal level (e.g., properly worn masks). To be effective, high efficiency filters and sufficient airflow through them are necessary. At the building level, high efficiency particulate (HEPA) filters in the recirculated or mixed air duct can reduce the cross contamination between rooms and increase the total clean air delivery rate (outdoor plus filtered air) for diluting the virus concentration in the ventilated space. HEPA filters have a minimum efficiency of 99.97% for 0.3 to 10 µm particles. MERV 14 or higher rating filters have a minimum efficiency of 75% − 84% for 0.3 − 1.0 µm, and 90% or greater for 1.0 − 3.0 µm particles. Assuming that 80% of the air is recirculated, use of MERV 14 or HEPA filters to treat the recirculated air can further dilute the pollutant concentration by a factor of 4 or 5, respectively. The benefit of having the filters on the recirculated air reduces as the percent of outdoor air increases as expected. The updated ASHRAE Position Document on Infectious Aerosols (ASHRAE 2020) recommends the use of ventilation in combination with air filtration to reduce the risk of infection.
Measuring airflow through the portable high-efficiency air filtration (PHEAF) device to assess reliability of instrument and sample location
Published in Journal of the Air & Waste Management Association, 2019
Derek A. Newcomer, Peter LaPuma, Robert Brandys, Amanda Northcross, Abhijit Dasgupta
The NSF International Standard/American National Standards Institute 49: Biosafety Cabinetry: Design, Construction, Performance, and Field Certification protocol is referenced for testing biological safety cabinets (NSF International Standard/American National Standards Institute 2014). Testing is performed by injecting a homogenous concentration of aerosol upstream of the HEPA filter and measuring the percentage of aerosol penetrating through the filtration system. The baseline is determined by calibrating the photometer to the upstream aerosol challenge concentration. A homogenous upstream mixture is obtained by introducing the aerosol at the location identified by the manufacturer of the HEPA system (Institute of Environmental Sciences and Technology 2016).
Wildfire and prescribed burning impacts on air quality in the United States
Published in Journal of the Air & Waste Management Association, 2020
Samuel L. Altshuler, Qi Zhang, Michael T. Kleinman, Fernando Garcia-Menendez, Charles Thomas (Tom) Moore, Merlyn L. Hough, Eric D. Stevenson, Judith C. Chow, Daniel A. Jaffe, John G. Watson
Sheltering-in-place is promoted to reduce exposure to outdoor air contaminants, but if the sheltering locations have indoor emissions, often the case within homes, exposures may also be high. In homes with combustion sources (e.g., gas stove tops, fire places, wood stoves, candles, etc.), there is a potential for poor air quality. High efficiency HEPA air filters, HVAC filters with ratings >13, and indoor air cleaners can mitigate indoor air pollution as well as smoke intrusions. Use of solvents or strong cleaners (containing bleach) indoors should also be avoided. Use of N-95 masks outdoors should also reduce PM exposures.