Hoover SilentAir vs. HEPA

Hoover SilentAir vs. HEPA - Comparisons

SilentAir Index

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Hoover SilentAir Purifier SA2000

Hoover SilentAir Dielectric Technology vs. HEPA Filtration:

TEST PERFORMED BY:
Hauser Chemical Research, Inc.
Engineering Services Department
Test Report No. L2-09095
2100 Central Ave, Suite 100
Boulder, CO 80301

CLIENT:
SilentAir Corporation
1660 17th Street, Suite 120
Denver, CO 80202

Fig. 1
HEPA Filter - New

PURPOSE:
The purpose of this project was to evaluate the performance of two different air cleaners, one using a HEPA filter vs. another using a dielectric collection sheet. The evaluation was focused on examining the size range of particles captured by both the HEPA model and Hoover™ SilentAir® Purifier to compare the effectiveness of the different filter media.

MATERIALS:
Hoover™ SilentAir®TM Purifier using an electrostatic, sheet-type particle collecting medium, and a leading brand portable air cleaner utilizing HEPA filtering medium, supplied new, in unopened packages.

TESTS
Operation of both air cleaners continuously in a laboratory environment for 168 hours to collect airborne particles. Both units were operated at maximum settings, following the manufacturer's instructions. Subsequent particle evaluation was conducted on each type of filtering medium using Scanning Electron Microscopy (SEM). Visual particle counting was used to establish the particle size distribution present in a 0.1 mm x 0.1 mm viewing area of each medium.

Fig. 2
HEPA Filter - after 168 hours of use

Results: HEPA Filter Medium Evaluation
Figures 1 through 4 on the following pages are actual photographs of SEM images used for the analyses.

Figure 1 shows the clean HEPA filter fibers at 500X magnification prior to the operation of the air cleaner. Note the, more or less, random orientation of the fibers and the openings in the medium allowing very small particles to blow through the filter.

After 168 hours of operation, the HEPA filter assembly was removed from the machine housing and a section was taken at the outside edge of the filter, facing the airflow, which was believed to be the area with the highest amount of particles collected.

Figure 2 shows two large and several small particles entrapped in the HEPA filter medium photographed at 500X magnification.

Results: Hoover SilentAir Dielectric Sheet Evaluation
Operation of both air cleaners continuously in a laboratory environment for 168 hours to collect airborne particles.

Figure 3 shows the dielectric collection sheet used in Hoover™ SilentAir® Purifier at 500X magnification prior to operation. Note the significantly larger fibers utilized in the dielectric collection sheet since airflow through the sheet is not required. The fibers are very clean and tightly arranged without the through holes that were evident in the HEPA filter medium.

After 168 hours of operation, the SilentAir® dielectric collection sheet was removed from the machine and a section was taken that had been directly over the charged strip, believed to be the area where the highest number of particles were collected.

Figure 4 shows several large and numerous small particles entrapped in the dielectric collection sheet medium photographed at 500X magnification. Note that a significant number of particles collected are those of smaller sizes.

Fig. 3
Hoover SilentAir Dielectric Collection Sheet - New

Fig. 4
Hoover SilentAir Dielectric Collection Sheet - After 168 hours of use

Conclusions:

The construction of the dielectric collection sheet used in Hoover™ SilentAir® Purifier was quite different than that of the HEPA filter.
No through holes were observed in the dielectric collection sheet, while many openings were present in the HEPA filter which allow very small particles to pass through without capture.
As shown in the table below, the fanless, electrostatic attraction provided by Hoover™ SilentAir® Purifier resulted in a significantly larger number of particles less than 0.3 microns collected when compared with the HEPA filter. The relatively low number of particles present on the HEPA filter sample after 168 hours of operation did not permit a statistically significant evaluation.
Data developed indicate that the SilentAir® dielectric collection sheet, however, does capture a higher percentage of particles smaller than 0.3 microns than does the HEPA filter unit. Smoke, viruses, dust, and bacteria are mainly in this size range.