Estimates of HVAC filtration efficiency for fine and ultrafine particles of outdoor origin

Evaluating the Sensitivity of the Mass-Based Particle Removal Calculations for HVAC Filters in ISO 16890 to Assumptions for Aerosol Distributions

“…The combination of instruments used to measure the distributions reported in Jaenicke (1993) [31] (i.e., EAA and OPC) yielded substantial coverage of number concentrations above 1 µm, and thus the results could be used to accurately identify the large volume peaks in the~5-20 µm size range. Therefore, the volume distributions for the 194 distributions reported in Azimi et al (2014) [29] are only accurate up tõ 2.5 µm. Thus, only the estimates of PM 1 and PM 2.5 concentrations (and ePM 1 and ePM 2.5 ) are accurate for these distributions (i.e., not the PM 10 concentrations and ePM 10 ).…”

“…Regardless, the reliance on static assumptions for historical ambient aerosol distributions from the 1970s or earlier raises questions about the relevance and validity of using the distributions to estimate realistic values for ePM 1 , ePM 2.5 , and ePM 10 today, which this work attempts to address. One of the largest known reviews of ambient aerosol distributions globally is Azimi et al (2014) [29], which identified a total of 194 long-term average ambient distributions (i.e., from one year or more of measurements) primarily from North America (i.e., the US and Canada) and Europe (i.e., Sweden, Finland, Norway, Denmark, Germany, France, Italy, Ireland, England, Netherlands, Switzerland, Lithuania, Hungary, the Czech Republic, and Bulgaria). The article fit trimodal lognormal distributions to each of the 194 distributions found in the literature, and reported geometric means, geometric standard deviations, and total number concentrations for each mode fit.…”

“…The article also estimated PM2.5 concentrations for each distribution, assuming spherical particles and both unit and varying size-dependent density. Azimi et al (2014) [29] also used the 194 ambient distributions to estimate the fractional removal efficiencies for a number of HVAC filters for integral measures of PM2.5 and total ultrafine particles (i.e., UFPs: all particles smaller than 100 nm). The work followed a similar procedure as that described in ISO 16890 and in Section 2 herein, albeit with the following exceptions: (1) 194 long-term average trimodal ambient aerosol distributions from around the world were used, rather than a single static urban or rural bimodal distribution; (2) fractional filter removal efficiency data from laboratory tests that measured down to as small as 30 nm were used (and the remaining data were fit with a model down to just a few nanometers) [35]; and (3) in addition to estimating PM2.5 and UFP removal efficiencies assuming 100% outdoor air delivery, PM2.5 and UFP removal efficiencies for indoor particles of outdoor origin were also Seinfeld and Pandis (2006) [30] reference the urban and rural distributions to Jaenicke (1993) [31], who summarized prototypical aerosol distributions for various ambient environments.…”

“…The use of volume distributions necessitates an underlying assumption of spherical particles and constant unit density for volume-based removal efficiencies that yields an equivalent to mass-based removal efficiencies. While these assumptions are not always valid [22][23][24], they are widely used assumptions [25][26][27][28] that have been shown to have only a minimal impact on estimates of mass-based removal efficiency for HVAC filters [29]. Next, filters that are designed to filter primarily PM 1 and PM 2.5 size fractions are assumed to be characterized using the urban volume distribution function, while filters designed to filter primarily PM 10 are assumed to be characterized using the rural volume distribution function.…”

Measured performance of filtration and ventilation systems for fine and ultrafine particles and ozone in an unoccupied modern California house

“…A high performance filter in the forced air heating and cooling (HAC) system will remove particles when the system operates for thermal control and can be operated on a timer when no conditioning is needed. Filtration effectiveness has been investigated through measurement studies in homes (Batterman et al, 2012;Du et al, 2011;MacNeill et al, 2012;Noris et al, 2013;Spilak et al, 2014;Stephens and Siegel, 2013) and also via simulation studies that tend to focus on population-scale benefits (Azimi et al, 2014;MacIntosh et al, 2010;Zhao et al, 2015).…”