Penetration of Sub-50 nm Nanoparticles Through Electret HVAC Filters Used in Residence

Abstract

Pleated electret HVAC filters are often used in residence to mitigate the particles that originate both indoors and outdoors. These filters are usually tested with particles larger than 300 nm. However, residential particles can contain a significant amount of nanoparticles with size below 50 nm due to cooking, smoking, cleaning, wood burning, and outdoor infiltration. In order to characterize the nanoparticle removal by electret HVAC filters, penetrations of 3-50 nm silver nanoparticles through five different flat sheet electret media used in commercial residential HVAC filters were tested with face velocities of 0.05, 0.5, and 1.0 m s ¡1. Experimental results showed that all media had significantly high penetrations with 0.35-0.8 at the most penetrating particle sizes (MPPSs) for all three velocities, which were in the sizes of 10-30 nm. A model based on single fiber theory for particle penetration predictions was used and compared with the experimental data. Results showed that the model predicted the nanoparticle penetrations very well for all media and all face velocities tested. According to the model, for enhancing the nanoparticle efficiency of the current commercial HVAC filters, the fiber diameter should be reduced or the number of pleats should be increased. However, by doing these, pressure drop and cost may be largely increased. On the other hand, this study found the existing commercial mechanical HVAC filters were much capable for sub-50 nm nanoparticle removal when their minimum efficiency reporting values (MERVs) were larger than 13 and it is concluded mechanical HVAC filters can do a better job than electret ones. However, the quality factor analysis showed electret filters could be regarded as the best filter media for removing particles smaller than 300 nm.

Capture of Sub-500 nm Particles Using Residential Electret HVAC Filter Media-Experiments and Modeling

“…These media were labeled with #A-#E and their specifications are shown in Table 1. Their fibers were all bipolar charged (Baumgartner et al, 1986) and the charging densities were estimated according to the authors' previous work (Chen et al, 2014;Chang et al, 2015). The value is 75 µC m -2 for media #B, #D, #E and 25 µC m -2 for media #A and #C, respectively.…”

“…where Ku is the Kuwabara hydrodynamic parameter (Chang et al, 2015), C c is the Cunningham slip correction factor, µis the air viscosity (Ns m -2 ), σ is the charge density of the fiber (C m -2 ), q(n) is carried charges by the particle (C), ε f is the fabric dielectric constant (1.5 for the polypropylene of current electret media) and ε 0 is the permittivity of the vacuum (8.85 × 10 -12 …”

“…Here, the KCl particles were generated by an Collision type atomizer (Model 3079, TSI Inc., Shoreview, MN, USA) and classified into 30 to 500 nm monodisperse particles by a long DMA (Model 3081, TSI Inc., Shoreview, MN, USA). The details on the furnace temperature and solution concentration of KCl can be found elsewhere (Chang et al, 2015;Chen et al, 2016). All the particles were brought to Boltzmann equilibrium before entering the filter holder where the round flat sheets of filter media were mounted.…”

“…Therefore, E T is the sum of efficiencies resulting from diffusion (E D ), interception (E R ), interception of diffusing particles (E DR ), impaction (E I ) and electrostatic attraction (E q ). The E T was calculated as (Lathrache et al, 1986;Chen et al, 2014;Chang et al, 2015):…”

“…They were reported to not only pose adverse health effects to people in residential indoor environments (Chang et al, 2015) but also classified as carcinogenic in October of 2013 by the International Agency for Research on Cancer (IARC) as Group 1. As performing a high efficiency while maintaining a low pressure drop, electret HVAC filter media are widely used to remove airborne particles (Romay et al, 1998).…”