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”

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 Chemistry ventilation emissions deposition

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

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

Driving forces: gradients Net flux concentration

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)

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

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 Air mixing Surface characteristics Pollutant characteristics 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

You as passive filter… and source Ozone concentration 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 CADR ~ 2000 cfm CADR ~ 1200 cfm unpainted gypsum board

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 EcoByDesign Cork Wallboard Carnegie Fabrics Xorel Rayon Wall Paper

Cork wall covering Clay Tile Rubber Tile Clay wall coating Carpet Floor Tile Describe some of the basic material we have and their appearances, texture

Students hard at work

CADR matters more than vd

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 Graphs of deposition velocity and yields have been placed side by side with the bars arranged in descending order by deposition velocity. American Clay showing great promise has a very high deposition velocity while a almost negligible yield. While carpet as previous studies have shown has a high deposition velocity but a moderate yield, including nonenal, which is to be expected. Rubber Tile has a moderate deposition velocity but a very high yield, the other 2 with high yields being Corkboard, that is wood based and C6 and C10 Aldehydes are common with wood products and Marmoleum which is made with Linseed oil has a high yield of Nonenal also.

Ranking materials for LEED credit High   •Rubber Tile •Marmoleum •Interface Carpet •Corkboard •Wall Fabric •Eurostone •EcoTrend •EcoSpec Low •Clay Tile •American Clay Ozone Removal Potential Byproducts A simple graph of the materials tested thus far, that the deposition velocities and yields are both known. On the right is yield, whether the yield could be considered low or high, along the bottom is the ozone removal potential that also travels from low to high. Materials were generally classified on where they would fall, with materials like American Clay and Eurostone having both high removal potential and low yields, while the three in the upper right are materials with low removal potential and high yields. A few of the other materials have both low yield and low removal potential while carpet has both high yield and high removal potential. From the beginning the materials that we would classify as GOOD would fall in the green zone. Orange is not necessarily BAD but not good, and the other two are simply neutral. Other materials left off because I do not have the aldehyde yields for them yet.

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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