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Buildings and their indoor surfaces as passive filters

This study explores the potential of buildings and their indoor surfaces to act as passive filters for pollutants. It examines various pollutant sources and sinks, such as outdoor sources, indoor sources, and people. The study also investigates the filtration and deposition of pollutants on surfaces, and the role of air chemistry in this process. The findings suggest that buildings can be designed to effectively filter and remove pollutants from indoor air, improving indoor air quality.

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Buildings and their indoor surfaces as passive filters

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  1. Buildings and their indoor surfaces as passive filters Glenn Morrison Civil, Architectural and Environmental Engineering Missouri University of Science & Technology

  2. Pollutant sources and sinks • Outdoor sources • ventilation and infiltration • smog, pollen, diesel soot, air toxics • Indoor sources • Combustion, off-gassing, cleaning, solvent use, industrial operations • People: infectious disease • Sinks • Filtration • Air chemistry • Deposition and removal at surfaces

  3. Clean indoor air: indoor surfaces

  4. Buildings are “reactors”

  5. Buildings are “reactors”

  6. Models: good approximations Mathematical model estimate Ozone emitted from ion “air cleaners”

  7. Major elements of IAQ models • Sources • Sinks filtration ventilation ventilation Air Chemistry emissions deposition

  8. Clean Air Delivery Rate (CADR) of sinks • Filtration • Portables: ~300 cfm • Whole house: (periodic) ~1000 cfm • Ventilation and infiltration • Homes: 50-500 cfm • Surface deposition • Homes: 0 - 5000 cfm !! • Continuous! Air cleaner efficiency, h Flowrate, Q CADR=hQ

  9. Surfaces as sinks GASES SMALL PARTICLES bounce Sticks until re-suspended or cleaned stick or react

  10. Driving forces: gradients Net flux concentration

  11. Deposition velocity, vd • Not a real “velocity” but identical math wall filter deposition velocity air velocity vd u •CADR = vd x surface area •CADR = u x filter area (100% efficiency)

  12. Deposition velocity CADR • CADR = vd x surface area • Residence surface area ~5 ft2/sq ft • Maximum CADR • Max vd 0.1-0.5 ft/min (2-10 m/h) • 2000 sq ft home • CADR due to surfaces = 1000-5000 cfm

  13. Surface CADR dependences • Air: mixing, velocities • Surfaces • Composition and “fleeciness” • Coatings and chemistry • Gaseous pollutants • Chemistry: reactions at surface • “Stickiness” (pesticides very sticky) • Particles • Size and charge • Other: temperature, humidity

  14. Particle deposition and CADR 2000 200 CADR (cfm) 20 Thatcher, T. L., Lai, A. C. K., Moreno-Jackson, R., Sextro, R. G., Nazaroff, W. W., 2002. Effects of room furnishings and air speed on particle deposition rates indoors. Atmospheric Environment 36, 1811-1819

  15. Filtration of large particles National Academy of Sciences, Clearing the Air: Asthma and indoor exposures Committee on the assessment of asthma and indoor air. Washington DC. 2000.

  16. Gases vd and CADR

  17. Controls: passive systems • CADR depends on • Air mixing • Surface characteristics • Pollutant characteristics • Temperature, humidity • Identify surface-pollutant pairs • Identify effective air mixing-surface combinations    

  18. Possible applications

  19. Target pollutant: ozone • Smog: ozone, acids, aerosols, … • Ozone increases mortality, respiratory illness • Ozone reacts with some indoor surfaces • generates formaldehyde & strong irritants • Opportunity to reduce population smog exposure through passive controls

  20. Your home and ozone Undesirable reaction byproducts

  21. You as passive filter…and source Ozone concentration Rim et al., Indoor Air, 2009

  22. Drywall and activated carbon • Collaboration: Missouri S&T, U Texas, Austin • Place materials in room-sized chamber and evaluate vd estimate CADR

  23. CADR of AC and wallboard activated carbon CADR ~ 2000 cfm CADR ~ 1200 cfm unpainted gypsum board

  24. Fun with A.C. • AC on fan blades: CADR ~ 100 cfm • Average 33% decrease in indoor ozone • Negligible by-product formation + reduction in products from other reactions UT master’s student Donna putting AC sleeves on fan blades

  25. Green building materials • Collaboration: Missouri S&T and UT Austin (US Green Building Council) • Criteria for materials • Green by some measure • Covers lots of area • Goals • Test methods for ozone removal capability • Also test for undesirable byproducts

  26. Green furnishings tested • Ceiling • Armstrong Ceiling Tile • Certainteed Ceiling Tile • Chicago Metallic Eurostone Ceiling Tile • Flooring • American Olean Clay Tile • Marmoleum Forbo Floor Tile • Interface Carpet • Shaw Carpet • Smith & Fong Plyboo Flooring • Armstrong Sustainable Floor Tile • Rubber Products Rubber Tile • Wall • American Clay Wall Plaster • Enjarre Clay Paint • Bio Shield Clay Paint • Carnegie Fabrics Acoustic Tiling • Benjamin Moore Ecospec Paint • Ecotrend Paint • EcoByDesign Cork Wallboard • Carnegie Fabrics Xorel Rayon Wall Paper

  27. Cork wall covering Clay Tile Rubber Tile Clay wall coating Carpet Floor Tile

  28. Students hard at work

  29. CADR matters more than vd

  30. Deposition Velocities & Yields Undesirable Product Yields Clay coating Carpet Ceiling tile Rubber tile Wall fabric Floor tile Cork tile Paint 1 Paint 2 Linoleum Clay tile

  31. Ranking materials for LEED credit Byproducts

  32. Personal exposure in a home

  33. Building surfaces are opportunities! • First find out what works (don’t reinvent the wheel) • Then consider design • Easy: ozone, acids, photochemical smog • Difficult: particles, VOCs, formaldehyde

  34. Acknowledgements • Seth Lamble, Sarah Shell • University of Texas Crew: Donna Kunkel, Donghyun Rim, Rich Corsi, Atila Novoselac, Jeff Siegel • US Green Building Council • Jim Rosenthal • NAFA!

  35. Shameless promotion: Indoor Air 2011, Austin, TXJune 5-10

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