Buildings and their indoor surfaces as passive filters

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

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

Clean indoor air: indoor surfaces

Buildings are “reactors”

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

Major elements of IAQ models • Sources • Sinks filtration ventilation Air ry t mis Che emissions ventilation deposition

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

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

concentration Driving forces: gradients Net flux

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

Deposition velocity CADR • CADR = vd x surface area • Residence surface area ~5 ft 2/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

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

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

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.

Gases vd and CADR

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

Possible applications

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

Your home and ozone Undesirable reaction byproducts

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

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

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

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

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

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 – Eco. By. Design Cork Wallboard – Carnegie Fabrics Xorel Rayon Wall Paper

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

Students hard at work

CADR matters more than vd

Deposition Velocities & Yields Undesirable Product Yields Deposition Velocities (m/hr) 0 Clay coating American. Clay Carpet Ceiling tile Eurostone Rubber tile Rubber Tile Wall fabric Wall Fabric Floor tile Tile Cork tile Cork. Board Paint 1 Eco. Trend Paint 2 Eco. Spec Marmoleum Linoleum Clay Tile Clay tile Empty 1 2 3 4 5 0 0. 2 0. 4 0. 6 C 5 C 6 C 7 C 8 C 9 C 10 C 11 C 12

Ranking materials for LEED credit High • Rubber Tile Byproducts • Marmoleum • Corkboard • Wall Fabric • Eurostone • Eco. Trend • Eco. Spec • American Clay Low • Clay Tile • Interface Carpet Low High Ozone Removal Potential

Personal exposure in a home

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

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!

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