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Ventilation Filters: Do They Clean or Pollute the Air?

Explore the impact of ventilation filters on air quality and learn about engineering solutions for low-polluting filters. Discover the health effects of ambient particles and the importance of indoor air quality in buildings.

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Ventilation Filters: Do They Clean or Pollute the Air?

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  1. Do Ventilation Filters Clean or Pollute the Air? Dr. Gabriel Bekő International Centre for Indoor Environment and Energy Technical University of Denmark

  2. Agenda • Filters as sources of pollution • Cost-benefit analyses • Engineering solutions - Low-polluting filters

  3. What do we inhale during a lifetime? We inhale 10 m3 air per day, 4 000 m3 air per year, 320 000 m3 per lifetime … At a mass concentration of 30 μg/m3 we inhale 10 g of particles in a lifetime = 10 teaspoons!

  4. Ambient Particles and Health • Romans knew that workers in the lead mines became sick • 1700: Ramazzini- “De MorbisArtificumDiatriba” (Workers ill health): “very fine particulas” could be inhaled (stonecutters, carding workers) and cause negative health effects. He describes remedial actions to avoid the exposure • 1760: Linné - mostly women in the church in Orsa; most men died from exposure to airborne stone dust in the mines

  5. • The Big Smoke in London 1952, 5 - 9 December. PM10 up to 4000 mg/m3. More than 4 000 deaths was associated with the elevated air pollution levels. • 70’s - Health effects of particulate air pollution at high levels • 80’s - Health effects at unexpectedly low levels of PM2.5 and PM10 • 90’s - Acute and chronic effects associated with increase in PM2.5 and PM10 (mortality, morbidity)

  6. • European air pollution assessment for Austria, France and Switzerland: – 40 000 deaths per year (6% of total mortality) – 25 000 new cases of chronic bronchitis (adults) – 290 000 episodes of bronchitis (children) – 0.5 million asthma attacks • Mainly sensitive subgroups: children, elderly, people with preexisting pulmonary or cardio-vascular disease No proven threshold concentration below which ambient PM has no effect on health. Künzli et al., 2000

  7. How much time do we spend indoors?

  8. + complaints (eye irritations, headache, ...) and reduced productivity? Potential savings with better protection by buildings 220 – 650 billion USD Health benefits - primary purpose of filtration CAFÉ/MattiJantunen, 2007

  9. The difference is 5 months service …and a lot of chemistry

  10. particles Particle concentration Percentage Dissatisfied

  11. Human requirements to the indoor environment • Indoor environment that is healthy, comfortable and stimulating Engineering interpretation • An indoor environment that is not unhealthy, with a minimum of dissatisfied persons

  12. Measurements of pollution loads directly in offices

  13. ACCEPTABILITY SCALE Clearly acceptable Just acceptable Just not acceptable Clearly not acceptable Nose is the most sensitive detector of chemicals • Air quality: immediate rating of acceptability of air quality upon entering to the office

  14. SBS symptoms: marking visual analogue scales during exposure

  15. Sensory pollution load in olf Sensory pollution strength from a standard person

  16. Most pollution sources can be quantified by olf =

  17. • 20-40% of occupantsfinding the IAQ unacceptable • 20-30% of occupantswith symptoms eventhoughexisting ventilation standards aremet!

  18. Average pollution loads in 56 European office buildings in 9 EU countries EU Audit Project, 1996

  19. Sensory pollution sources in HVAC systems Averagesensory pollution loads (olf/m2) in eight 2-16-year old HVAC systems Pejtersen et al., 1989

  20. After 1 hour Upon entering the room • - Lower acceptability of quality of air & environment • - Higher odor intensity, nose irritation • - Higher occurrence of headache, dizziness • - Lower perceived air quality - Lower perceived freshness of the air - Lower acceptability of the overall environmental conditions After 3 hours still - Lower acceptability of the overall environmental conditions Clausen et al., 2002

  21. Air quality in the office Used filter New filter Alm, 2001

  22. Source strength Alm, 2001

  23. Impact on productivity Intervention study in a call-center with 24 workstations

  24. 6-month old used filter New filter  Synthetic-fiber coarse filter

  25. (8%) (80%)  2.5 L/s person 25 L/s person 34 L/s  344 L/s Total ventilation rate of 430 L/s constant

  26. - Number of calls - Talk-time - Length of pauses Automatically and continuouslyregistered for every 30 minutes for each operatorduring the experimental period

  27. Used filters negatively affect the performance of office work Wargocki et al., 2004

  28. Increasedoutdoor air supply rate throughused filter:Negative effecton performance Wargocki et al., 2004

  29. Time in Use Mass of Particles Surface Area Particles Particle Area/ Filter Face Area 1 month 25 g 50 m2 135 4 months 100 g 200 m2 540 8 months 200 g 400 m2 1075 600 m2 12 months 300 g 1600 Filter Loading (6500ft2) Assumes 0.94 m3/s through filter; 20 g/m3particleconcentration; 50% filter efficiency; 0.37 m2 face area

  30. SVOCs sorbed on particles Oxidized SVOCs

  31. - Ozone removed by polluted filters – oxidation reactions • Oxidation processes diminish by time as reactive compounds on the filter surface are consumed – consistent with sensory pollution

  32. Turning off or reducing the airflow outside working hours increases the sensory pollution from used filters immediately after the ventilation system was turned back on

  33. Sensory evaluation of loaded HVAC filter before & after exposure to ozone

  34. - Fatigue/difficultyconcentrating - Significant associations with lower and upper respiratory symptoms, cough, eye irritation, fatigue, and headache Buchanan et al., Indoor Air Journal, 2008

  35. PTR-MS - Proton Transfer Reaction Mass Spectrometer: on-line monitoring of a variety of organic species with detections limits as low as a few ppt • Response time: < 200 ms • Linearity range: 10 ppt – 5 ppm - SVOCs are difficult to measure and identify

  36. What should we do? - Not to use filters at all ? - Increasing airflow through used filters does NOT help - Change filters more often ? - Use/develop different filtration techniques ? .. ..

  37. Does air filtration pay off? Does it make sense to invest into better filtration?

  38. Cost-Benefit Analysis - Typical office building characteristics: • 1000 occupants • 10 L/s/occupant ventilation air • 14.3 m2/occupant - Single-stage filtration – F7 pocket filters, 12 months lifetime - Annual average PM10 level outdoors – 50µg/m3 indoors without filtration – 35µg/m3 indoor with filtration – 15µg/m3 - Generalized outcomes – 2005 US$/yr(3% discount rate)

  39. Costs Benefits Mortality Initial costs Running costs Morbidity Energy Building cleaning Replacement HVAC cleaning Filter disposal Heat recovery unit efficiency, pressure drop Losses Productivity – decrease due to pollution from used filters (SBS) Heat exchanger efficiency, pressure drop

  40. Costs Running costs Energy - Increases with increasing pressure drop Replacement - Including a set of new filters Filter disposal $ 2,600 /yr = $ 2.6 /yr/occupant

  41. Benefits - Increase in non-accidental mortality for each 10 µg/m3 increase in PM10: 4% (Pope et al. 1995, 2002) Mortality

  42. Increase in mortality for each 10 g/m3increase in fine particles 9% 8% 7% 6% 5% Increase in Mortality 4% 3% 2% 1% 0% All-cause Cardiopulmonary Lung Cancer Jour. Amer. Medical Assn., 2002

  43. $ 2.6/y/o Benefits - Increase in non-accidental mortality for each 10 µg/m3 increase in PM10: 4% (Pope et al. 1995, 2002) - Baseline incidence rates: 20 - 64 yrs age group - Correction through the time spent at work Mortality - WHO GBD, 2002: AMRO A sub-region; Urban Air Pollution risk factor - Value of saved life/years (USEPA BCCAA, 1999): a. $ 4 - 15/y/o a. Human Capital Losses (annual compensation) b. $ 35-160/y/o b. Willingness To Pay - avoid a lost year (VSLY) c. Willingness To Pay - avoid a statistical death (VSL) c. $ 110-490/y/o

  44. $2.6/y/o Benefits Health and welfare endpoints and their values (USEPA BCCAA, 1999): 1. Respiratory hospital admission - Cost Of Illness (COI=medical costs + value of lost productivity) 2. Asthma ER visits - COI 3. Minor restricted activity days - Willingness To Pay 4. Work loss days - Productivity loss (daily compensation) Mortality Morbidity $ 8 - 35/y/o

  45. $2.6/y/o Benefits - Mainly coarse particles on horizontal surfaces - Higher filter efficiency than for PM10 Mortality Morbidity - Building cleaning cost:$ 13 /m2/yr (Kildesø and Schneider, 2001) Building cleaning $ 3.5 - 170/y/o

  46. $2.6/y/o Benefits - HVAC system cleaning neglected - Regulations and standards often missing - Filtration vs. system cleaning ? - Assumption: cleaning every 2 yrs without, every 5 yrs with filtration Mortality Morbidity Building cleaning - Soiling vs. efficiency - Soiling vs. pressure drop - Filtration vs. soiling HVAC cleaning Heat recovery unit efficiency, pressure drop ? ~$ 3.5 - 6.8/y/o ? Heat exchanger efficiency, pressure drop ? ~$ 3.7/y/o ?

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