Leaving speech at the ISO/TC 142 plenary meeting

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Looking for the minimum efficiency of fibrous air filters during their service life

Electret fibrous filter media achieve high efficiencies while maintaining low air flow resistance by incorporating electrostatic charges on their fibers. However, captured ultrafine particles reduce electrostatic effects. Existing test methods specify preconditioning to detect the minimum efficiency by eliminating electrostatic effects. ASHRAE 52.2 exposes media to nanoparticle KCl aerosols. ISO/TS21220 and EN779 immerse media in isopropyl alcohol (IPA). These approaches have some problems: - Nanoparticle generation is fairly complicated and needs to be kept under control; - The structure of some media may be changed by liquid immersion; - Soaking full scale air filters requires large amounts of IPA. A new procedure, exposure to IPA vapor, has been shown to be effective. We summarize these studies and ISO/TC142 activities related to the

New method to measure the mechanical collection mechanisms of full-scale air filters

Air filters are chosen for the minimum particle-capture efficiency they can provide in a specific application. Some media can achieve high efficiencies at low resistance to air flow by adding electrostatic charges on fairly coarse fibers. However, prolonged filter exposure to fine particles reduces the electrostatic enhancement effect. The filter efficiency must then rely mainly on mechanical collection mechanisms, and can fall well below the initial value. It is useful to test filter media when the effect of electrostatic charges is eliminated. To estimate the efficiency drop that may occur, air filter test standards include filter conditioning procedures to inhibit the effect of electrostatic charges. These treatments should leave only particle capture effects from mechanical collection mechanisms such as sieving, aerodynamics and diffusion, but not reduce or enhance these effects. EN779:2012 and ISO 21220:2009 describe such a conditioning treatment for filter media, and ASHRAE 52.2-2012 describes one for full-scale filters. The ASHRAE 52.2-2012 optional treatment suggests that air filters be exposed to a potassium chloride aerosol having approximately 35 nm count mean diameter. Following the charge-elimination treatment, procedures measuring efficiency as a function particle size are performed. In ISO/TS 21220:2009 and EN779:2012 the discharging treatment is also mandatory, but is performed on samples of the media used to manufacture the filter. This treatment requires a 2 minute soak in essentially pure isopropyl alcohol (IPA), after which the media samples are dried for 24 hours before further tests. This method presents problems, namely, that soaking in a liquid may alter the mechanical efficiency of media, and that samples of media may not be representative of the media used in the full-scale filter. A new approach, developed by T. Hayashi in Japan, eliminated electrostatic effects in electret-enhanced media sheets by exposure to IPA vapor for 16 hours or longer. This procedure was successfully duplicated by J. Cai in China, and at the Politecnico di Torino. ISO/TC142/WG9 in 2010 ran an inter-laboratory comparison to assess this procedure, and in 2011 organized another comparison which extended the method to full-scale filters. The full-scale tests have included three different types of air filters, comparing the results with the other approaches previously mentioned. These results will be useful for revising the current ISO 29461-1 test method and also for developing the new ISO 16890 series for general ventilation applications. Here we summarize the data obtained at the Politecnico di Torino, and describe the new test protocol that could be adopted by future international filter test standards

Looking for the minimum efficiency of fibrous air filters during their service life

Electret fibrous filter media achieve high efficiencies while maintaining low air flow resistance by incorporating electrostatic charges on their fibers. However, captured ultrafine particles reduce electrostatic effects. Existing test methods specify preconditioning to detect the minimum efficiency by eliminating electrostatic effects. ASHRAE 52.2 exposes media to nanoparticle KCl aerosols. ISO/TS21220 and EN779 immerse media in isopropyl alcohol (IPA). These approaches have some problems: - Nanoparticle generation is fairly complicated and needs to be kept under control; - The structure of some media may be changed by liquid immersion; - Soaking full scale air filters requires large amounts of IPA. A new procedure, exposure to IPA vapor, has been shown to be effective. We summarize these studies and ISO/TC142 activities related to them

Procedures for realistic models of fibrous gas filtration media

The behavior of most HVAC system components has been quantified with accuracy sufficient to allow meaningful minimization of both economic and energy system costs. For one component - air filters - performance and cost predictions are still highly approximate, hence designers have difficulty including their contribution to capital, operating, and energy costs

Ultrafine particles: A review about their health effects, presence, generation, and measurement in indoor environments

Human exposure to aerosols has been associated with diseases and death, reducing the population's life expectancy up to a few years. Indoor particulate matter is predominant in determining human exposure to PM because people spend most of their time indoors. Ultrafine particles (UFP) impact the human body differently from PM2.5 or PM10 fractions. Therefore, scientists cannot apply the same approach to assess the effects of UFP and PM on human health. This work summarizes the health effects, generation, and measurement of ultrafine particles in indoor environments through a literature review. When indoor particle generation is low, particle concentration indoors depends strongly on outdoor aerosols, with an indoor-to-outdoor ratio below 1. In buildings with a high indoor particle generation, the average indoor-to-outdoor UFP concentration ratio can reach 14. Combustion, electric heating, and house cleaning are the main generators of UFP indoors. Current standards for UFP assessments do not provide a solid ground for accurate and reliable measurements. Moreover, the lowest detection limit of instruments used to measure UFP concentration can be significantly different while also showing poor repeatability even among instruments with the same manufacturer and model. Consequently, data supplied by studies on UFP health effects are insufficient and inconclusive. Using ultrafine portable monitors would allow determining properly human exposure to PM0.1, but such instruments are expensive for wide use. Since there is a good correlation between UFP and NOX data, low-cost NOX sensors are good candidates to create a dense and accurate monitoring network of UFP, including indoor environments

Developing parameters for local multimode ambient aerosol models including nanometer mode

The particle count, surface and mass in an occupied space can be modeled when the outdoor and recirculation airflows are known, along with the particle-size distribution for outdoor air, internal generation rates as a function of particle size, and the efficiency of the filter system as a function of particle size. Data on outdoor air particle-size distribution is rarely available, but two measures of particle mass concentration, PM2.5 and PM10, are often available for both urban and rural locations. Many studies have shown that outdoor air aerosol size distributions are well modelled by sums of two or three log-normal distributions, with essentially all the mass contained in the two larger modes, the accumulation mode and the coarse mode. Other studies have also shown that the geometric mean diameter and standard deviations of the accumulation and coarse modes are, in general, related by simple functions. This paper shows how these relationships can be combined with the known characteristics of PM2.5 and PM10 samplers to create reasonable models of outdoor air aerosol-size distributions, and thus allow calculation of aerosol mass effects in occupied spaces. Means of estimating the parameters of aerosol modes with mean sizes below 100 nm and the efficiencies of filters in that range are described. These estimates allow extension of indoor-air modeling to include aerosol surface, which is predominately due to particles with diameters below 100 nm. Sources of the necessary data for all size ranges are examined