Abstract
ABSTRACTElectret HVAC filter are widely used to remove airborne particles in residential or commercial indoor environments. Based on the International Commission on Radiological Protection (ICRP) deposition model, sub-500 nm particles have enhanced depositions in the tracheobronchial region and the alveolar region than particles larger than 500 nm. In this study, filtration efficiencies of five residential electret HVAC filters against monodisperse silver (Ag) and potassium chloride (KCl) particles with 3–500 nm diameters at face velocities ranging 0.05–1.5 m s–1 were investigated. For further understanding the effect of fiber charges on particle collections, electret media were discharged and the efficiencies acquired from pure mechanical mechanisms were compared with that of electret media. The figure of merit (FOM) of the five electret filter media was also investigated to further understand the effect of charge density on filtration performance. A theoretical model without parametric fittings used in literature was adopted and further modified by considering the polarization forces for charged particles. The modified model predicted the particle penetrations very well at low face velocities for all tested media and also well at high face velocities for the media with low charges. The discrepancy occurred for the media with high charges at higher face velocities was due to the nonuniform particle concentration distribution in the media layers. The validated model is able to be applied to improve the design for electret media for nanoparticle removal.
Highlights
Particulate matters, PM, which can be originated from many residential activities (Wallace et al, 2004; Afshari et al, 2005; Wallace, 2006; Lunden et al, 2015) or transported from outdoor air into indoor environment through make air system and infiltration (McAuley et al, 2010; Rim et al, 2010; Stephens and Siegel, 2012)
The HVAC filter media are usually evaluated only with particles larger than 200 or 300 nm according to ASHRAE 52.2 and EN 779, it is important to obtain their efficiencies against smaller nanoparticles since the majority of ambient particles, e.g., PM2.5, in number reside in these size ranges
This indicates at high face velocity and in the large particle size, the deposition is the electrostatic force dominant for high charged filter while it is mechanical effects dominant for the medium charged filters
Summary
Particulate matters, PM, which can be originated from many residential activities (Wallace et al, 2004; Afshari et al, 2005; Wallace, 2006; Lunden et al, 2015) or transported from outdoor air into indoor environment through make air system and infiltration (McAuley et al, 2010; Rim et al, 2010; Stephens and Siegel, 2012) They were reported to pose adverse health effects to people in residential indoor environments (Chang et al, 2015) and classified as carcinogenic in October of 2013 by the International Agency for Research on Cancer (IARC) as Group 1. Whereas the charges can be shielded or neutralized gradually by the incoming particles, which cause a reduced in-use efficiency of the electret based filters. It is necessary to remove the charge on the fiber to know the ‘worst’ performance of the electret filter and to compare the data obtained before and after discharging to learn about the performance elevation brought by different level of charge, which can provide useful references for improving the filter design
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