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Air Cleaners for Particulate Contaminants

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Air Cleaners for Particulate Contaminants CHAPTER 29 AIR CLEANERS FOR PARTICULATE CONTAMINANTS Terminology ............................................................................. 29.1 Air Cleaner Test Methods ........................................................ 29.4 Atmospheric Aerosols .............................................................. 29.2 Types of Air Cleaners ............................................................... 29.6 Aerosol Characteristics ........................................................... 29.2 Filter Types and Performance ................................................. 29.6 Air-Cleaning Applications ....................................................... 29.2 Selection and Maintenance ...................................................... 29.9 Mechanisms of Particle Collection .......................................... 29.3 Air Cleaner Installation ......................................................... 29.11 Evaluating Air Cleaners .......................................................... 29.3 Safety Considerations ............................................................. 29.12 HIS chapter discusses removal of contaminants from both DEHS. Di-ethyl-hexyl-sebacate. Tventilation and recirculated air used for conditioning building DHC. Dust-holding capacity. interiors. Complete air cleaning may require removing of airborne DOP. Dioctyl phthalate. particles, microorganisms, and gaseous contaminants, but this EN. European norm (European standard). chapter only covers removal of airborne particles and briefly dis- EPA. Environmental Protection Agency. cusses bioaerosols. Chapter 47 of the 2019 ASHRAE Handbook— EB. Existing buildings. HVAC Applications covers the removal of gaseous contaminants. ETS. Environmental tobacco smoke. The total suspended particulate concentration in applications dis- HEPA. High-efficiency particulate air. 3 cussed in this chapter seldom exceeds 2 mg/m and is usually less IEST. Institute of Environmental Sciences and Technology. 3 than 0.2 mg/m of air (Chapter 11 of the 2018 ASHRAE Handbook— IPA. Isopropyl alcohol. Refrigeration). This is in contrast to flue gas or exhaust gas from pro- ISO. International Organization for Standardization. cesses, where dust concentrations typically range from 200 to 3 LCC. Life-cycle cost. 40 000 mg/m . Chapter 26 discusses exhaust gas control. LEED. Leadership in Energy and Environmental Design. Most air cleaners discussed in this chapter are not used in exhaust MERV. Minimum efficiency reporting value. gas streams because of the extreme dust concentration, large particle MIL-STD. U.S. Military standard. size, high temperature, high humidity, and high airflow rate require- MPPS. Most penetrating particle size. ments that may be encountered in process exhaust. However, the air MSHA. Mine Safety and Health Administration. cleaners discussed here are used extensively in supplying makeup air with low particulate concentration to industrial processes. NAFA. National Air Filtration Association. NC. New construction. 1. TERMINOLOGY NIOSH. National Institute for Occupational Safety and Health. NIST. National Institute of Standards and Technology. Definitions PAO. Polyalphaolefin. Aerodynamic Diameter. The diameter of a spherical particle PM. Particulate matter. with a density of 1000 kg/m3 and the same settling velocity as the PSE. Particle size removal efficiency. irregular particle of interest. PSL. Polystyrene latex. Arrestance. A measure of the ability of an air-cleaning device UL. Underwriters Laboratory. with efficiencies less than 20% in the size range of 3.0 to 10.0 µm to ULPA. Ultra-low particulate air. remove loading dust from the air passing through the device. VAV. Variable air volume. Dust Holding Capacity. The total weight of synthetic loading dust captured by an air-cleaning device over all of the incremental 2. ATMOSPHERIC AEROSOLS dust loading steps. Atmospheric dust is a complex mixture of smokes, mists, fumes, Particle Size Removal Efficiency. The fraction or percentage of dry granular particles, bioaerosols, and natural and synthetic fibers. particles retained by an air cleaner for a given particle-size range. When suspended in a gas such as air, this mixture is called an aero- Particulate Matter (PM). Solid and/or liquid particles of vari- sol. A sample of atmospheric aerosol usually contains soot and ous sizes suspended in ambient air. smoke, silica, clay, decayed animal and vegetable matter, organic Penetration. The fraction or percentage of particles that pass materials in the form of lint and plant fibers, and metallic fragments. through an air cleaner for a given particle-size range. It may also contain living organisms, such as mold spores, bacteria, Resistance to Airflow. Difference in absolute (static) pressure and plant pollens, which may cause diseases or allergic responses. between two points in a system. This parameter is often called pres- (Chapter 11 of the 2017 ASHRAE Handbook—Fundamentals con- sure drop. tains further information on atmospheric contaminants.) A sample Acronyms of atmospheric aerosol gathered at any point generally contains materials common to that locality, together with other components AFI. Air Filter Institute. that originated at a distance but were transported by air currents or AHRI. Air-Conditioning, Heating, and Refrigeration Institute. diffusion. These components and their concentrations vary with the ASME. American Society of Mechanical Engineers. geography of the locality (urban or rural), season of the year, BI/BO. Bag-in/bag-out. weather, direction and strength of the wind, and proximity of dust CEN. Comité Européen de Normalisation. sources. Aerosol sizes range from 0.01 µm and smaller for freshly formed The preparation of this chapter is assigned to TC 2.4, Particulate Air Con- combustion particles and radon progeny; to 0.1 µm for aged cooking taminants and Particulate Contaminant Removal Equipment. and cigarette smokes; and 0.1 to 10 µm for airborne dust, microor- 29.1 29.2 2019 ASHRAE Handbook—HVAC Applications (SI) ganisms, and allergens; and up to 100 µm and larger for airborne Table 1 U.S. EPA Standards for Particulate Matter in soil, pollens, and allergens. Outdoor Air Concentrations of atmospheric aerosols generally peak at sub- Time Period micrometre sizes and decrease rapidly as the particulate size in- Type of Standard Applicable PM , μg/m3 PM , μg/m3 creases above 1 µm. For a given size, the concentration can vary by 10 2.5 Primary 24 h 150 35 several orders of magnitude over time and by location, particularly 1 yr — 12 near an aerosol source, such as human activities, equipment, fur- Secondary 24 h 150 35 nishings, and pets (McCrone et al. 1967). This wide range of partic- 1 yr — 15 ulate size and concentration makes it impossible to design one Source: EPA (2015). cleaner for all applications. dards intended to protect against adverse environmental effects. The 3. AEROSOL CHARACTERISTICS limits presently in place (Federal Register 2013) are shown in Table 1. There is no filtration requirement for areas of noncompliance. The characteristics of aerosols that most affect air filter perfor- mance include particle size and shape, mass, concentration, and Bioaerosols are a diverse class of particles of biological origin. electrical properties. The most important of these is particle size. They include bacteria, fungal spores, fungal fragments, pollen Figure 3 in Chapter 11 of the 2017 ASHRAE Handbook—Funda- grains, subpollen particles, viruses, pet- and pest-associated aller- mentals gives data on the sizes and characteristics of a wide range of gens, and plant debris (Fröhlich-Nowoisky et al. 2016). They are of airborne particles that may be encountered. particular concern in indoor air because of their association with Particle size in this discussion refers to aerodynamic particle size. allergies and asthma and their ability to cause disease. Chapters 10 Particles less than 0.1 µm in diameter are generally referred to as and 11 of the 2017 ASHRAE Handbook—Fundamentals contain ultrafine-mode or nanoparticles, those between 0.1 and 2.5 µm are more detailed descriptions of these contaminants. termed fine mode, and those larger than 2.5 µm as coarse mode. Bioaerosols range in size from 0.01 to 100 µm. Single bacterial Whereas ultrafine- and fine-mode particles may be formed together, cells are approximately 1 µm or less in aerodynamic diameter; how- fine- and coarse-mode particles typically originate by separate ever, they are often transported as larger bacterial cell agglomerates mechanisms, are transformed separately, have different chemical (~2 to 5 µm) or attached to other biological and abiotic particles. compositions, and require different control strategies. Vehicle ex- Unicellular fungal spores are generally 2 to 5 µm in aerodynamic haust is a major source of ultrafine particles. Ultrafines are mini- diameter and multicellular fungal spores are larger than 10 µm mally affected by gravitational settling and can remain suspended (Després et al. 2012, Qian et al. 2012). Fungal fragments are typi- for days at a time. Fine-mode particles generally originate from con- cally less than 1 µm in size (Mensah-Attipoe et al. 2016). Pollen densation or are directly emitted as combustion products. Many mi- grains range in size from 10 to 100 µm (Després et al. 2012), croorganisms (bacteria and fungi) either are in this size range or whereas subpollen particles span ~0.01 µm to several micrometers produce components this size. These particles are less likely to be re- in size (Taylor et al.
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