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
Air
Chemistry
ventilation
emissions
deposition

8. Clean Air Delivery Rate (CADR) of sinks
Filtration
Portables: ~300 cfm
Whole house: (periodic) ~1000 cfm
Ventilation and infiltration
Homes: cfm
Surface deposition
Homes: 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 ft/min (2-10 m/h)
2000 sq ft home
CADR due to surfaces = 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., Effects of room furnishings and air speed on particle deposition rates indoors. Atmospheric Environment 36,

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

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
Describe some of the basic material we have and their appearances, texture

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
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.

31. 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.

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, TX June 5-10