Table 3.
Filtration air cleaning technology. Filtration is a mechanical or physical operation which is used for the removal of particles by physical separation from air by interposing a medium through which only the air can pass.
| Papers | Results by the authors | Research type/test procedure | Target pollutants/concentration | Airflow rate, air velocity, or residence time | CADR (m3 h−1)/efficiency (%) | By-product tested or not and results |
|---|---|---|---|---|---|---|
| Batterman et al. (2005) | Filter decreased PM concentrations in field tests (ETS) by 30–70%, depending on size fraction and occupant activities, and significantly reduced the half-life of PM 0.3–1. No evidence of VOC removal. | Field test, homes. Decay and modeling. Stand alone HEPA, with activated carbon prefilter, max airflow 745 m3 h−1. |
−1: 110000–340000 counts L−1; PM1–5: 450–2400 counts L−1; Toluene: 26–33 μg m−3; 2–5 dimethyl furan (2–5 DMF): 0.60–1.09 μg m−3. | – | CADR is 374 m3 h−1 at airflow of about 700 m3 h−1 for PM 0.3–1. | No. |
| Bekö et al. (2008) | Bag filters in combination with activated carbon downstream of the particle filter can remove particles odor, and part of ozone. | Laboratory/field test, Sensory assessment. EU5, EU7 and combination of EU7 and activated carbon. | Odor. | 0.2 m s−1 for sensory assessment. 2.0 m s−1 during soiling period (5 months, outdoor air). | – | Yes. By sensory assessment. |
| Bekö et al. (2009) | Filters containing activated carbon downstream can remove particles odors and part of ozone (more with more AC). | Laboratory test, Sensory assessment. F7 filter and F7 with activated carbon. | O3: 15–25 ppbv, odor. | 0.2 m s−1 for sensory assessment, 2.0 m s−1 for soiling (3 and 6 months, outdoor air). | – | Yes. By sensory assessment. |
| Bekö et al. (2006) | Oxidation by O3 of organic compounds adsorbed on filters resulted in increased odor. | Laboratory; Single-pass test. EU7. | O3: 75 ppbv. | 0.125 m s−1. | 5–10% (ozone). | No. |
| Cheng et al. (1998) | HEPA filters reduced particle (fungal spores and pollens) concentration by 80% of which settling accounts for 50% at an air change rate of 1–1.2 ach. At a low air change rate no difference, as the particles settle rapidly. | Field test, home, Portable HEPA filter (404 m3 h−1). | Pollens and fungal spores. | – | – | No. |
| Davis et al. (1994) | The experimental data significantly deviated from model predictions. No significant difference in filtration efficiency between different types of filters (standard, electret, electrostatically enhanced). | Laboratory test, of 11 ducted commercial residential filters, including standard mechanical, electret, and electrostatically enhanced filters. Single-pass, validation modeling. | PM 0.5–4. | 2.3–3.8 m s−1. | PM 0.5: 0–32%; PM 4: 35–86%. | No. |
| Kujundzic et al. (2005) | HEPA-UV air filter can reduce the concentration of culturable and total bacteria, but not of airborne endotoxin. | Field and laboratory test. | Mycobacterium parafortuitum cells. | – | 12–76%. | No. |
| Lee et al. (2004) | Unipolar ion emission produced by corona discharge can be efficient in controlling indoor particles. | Laboratory; Chamber test. | Fine and ultrafine particles. | – | PM 0.1: 97%; PM 1: 95% (in 30 min). Strong ion source! Particles settle on surfaces including humans. | No. |
| Lorimier et al. (2008) | Fiber arrangement has an impact on filtration efficiency: the more homogeneous the better; many layers of media can give high efficiency. | Laboratory; Single-pass test; activated carbon. | PM 0.1–2.5: 2500 particles cm−3. | 0.37–0.50 m s−1. | 52–86%. | No. |
| Miller-Leiden et al. (1996) | Filtration was effective in reducing airborne particle (droplet nuclei) concentration. The degree of protection provided by in room air filtration may not be sufficient for tuberculosis infection control. | Field test, 4 portable, and three mounted air cleaners, 5 with HEPA filters. Max airflow 250–1175 m3 h−1. | Chemical and Bacterial particles with an aerodynamic diameter of 0.7 μm and 1.3 μm. | – | 30–90%. | No. |
| Offermann et al. (1985) | Panel filters were largely ineffective at removing ETS. Extended surface filters and electrostatic precipitators had a high efficiency. | Field test, commercial product/decay; 4 panel filters, 2 extended surface filters (one with HEPA), 2 electrostatic precipitators, 2 ion generators. | Cigarette smoke particles: 1–2×105 particles cm−3. | – | Panel filters 0–12 m3 h−1; extended surface filters 97–306 m3 h−1 (HEPA); electrostatic precipitators 197–207 m3 h−1; ion generators, residential type 2 m3 h−1, commercial type 51 m3 h−1. | No. |
| Offermann et al. (1992) | Extended surface filters, (one HEPA) and electrostatic precipitators were more effective than single panel filters. For HEPA filters, the measured efficiency (73%) was significantly lower than according to the manufacturers’ data (99.97%, of DOP particles). | Field test of 6 ducted air cleaners, 2 panel filters, 2 extended surface filters, and 2 electrostatic precipitators. | Cigarette smoke particles: 1–2×105 particles cm−3. | – | Panel filters 2–3%; Extended surface filters 71–73%, electrostatic precipitators, 4% (two stage foam filters), 69% (two stage flat plate collector). | No. |
| Schleibinger and Rüden (1999) | A test of VOC emissions from used and unused (cellulose fiber) filters. Formaldehyde and acetone were the main products from dust loaded filters. The emission of acetaldehyde was higher from new filters. Chemical reactions or microbial activity may be the cause. | Field test; Filter class EU6, EU7. | Carbonyl compounds (14 aldehydes and two ketones). | Normal velocity in HVAC ducts. | – | Yes. Formaldehyde, acetaldehyde, acetone. |
| Waring et al. (2008) | The pollutant removal benefits of ozone-generating air cleaners may be outweighed by the generation of indoor pollution. | Laboratory; Chamber test. Commercial products. | Particles with sizes 12.6–514 nm diameter. | – | CADRs: HEPA:188–324 m3 h−1; Electrostatic precipitator 284 m3 h−1; Ion generators 35–41 m3 h−1. | Yes. Ozone. |
| Zhao et al. (2007) | Ozone can to some extent be removed by common HVAC filters. Loaded filters are more effective than new. | Laboratory test/single-pass; 21 MERV 4 and one MERV 8 filters. | O3:80 ppbv. | Face velocity: 0.004 m s. | Ozone removal, 0–9% for new filters, 10–41% for loaded particle filters. | No. |
Formaldehyde and acetone were the main by-products from dust loaded filters. Emission of VOC from the filter material should be very low. However, there were unknown oxidation products due to reactions between O3 and adsorbed organic compounds.