1. OZONE INTERACTIONS WITH HVAC FILTERS
Ping Zhao, Jeffrey Siegel, Richard Corsi
The University of Texas at Austin

2. Motivation Mendell and Smith, American Journal of Public Health ,1990
Indoor air pollution: greatest health risks (EPA)
People spend more than 90% inside
Robinson and Nelson, EPA, 1995
HVAC: more sick-building syndrome symptoms
Mendell and Smith, American Journal of Public Health ,1990

3. Central Question
Why are HVAC systems implicated in sick building syndrome?
Hypothesis: Ozone reactions on HVAC filters are part of the answer

4. Ozone Chemistry Ozone reacts with carbon-carbon double bonds
Products: ketones, hydroxyl radicals, aldehydes, and carboxylic acids

5. Evidence Aldehydes, organic acids, other carbonyls
Weschler et al., Environmental Science & Technology, 1992
Commercial: 8 to 26% ozone consumption
Hyttinen et al., Indoor and Built Environment, 2003
90% dissatisfied with air downstream of filters after exposure to ozone
Regeneration of ozone removal
Halás and Beko, Masters Thesis, DTU, 2003
Emission of formaldehyde, acetaldehyde and acetone
Schleibinger and Rüden, Atmospheric Environment, 1999

6. Ozone/Filter Interaction
CO3(up)
CO3(down) O3
Byproducts O3
Regeneration

7. Experimental System Pump O3 Generator Mixing Fan Top Chamber
O3 Analyzer
HVAC Filter
Bottom Chamber
Flow Controller
Bubble Flow Meter

8. Experimental System

9. Experiments Filters: 8 residential and 7 commercial
In field: weeks
MERV rating: 4 or < 4

10. 1. Clean
2. Residential
3. Commercial
4. Residential

11. Results to Date: Clean

12. Results to Date: Residential

13. Results to Date: Commercial

14. Ozone Removal Efficiency

15. Summary Ozone is removed by HVAC filters
Removal: reaction with particles
Removal: commercial > residential
Regeneration during periods of low ozone

16. So What? Do we have a problem? Ozone reduction is good
Production of byproducts
Dissatisfied occupants
Irony: Remove pollutants and then introduce all air for building across those pollutants

17. Strategies to Minimize Ozone Reactions
1) Change filters frequently
Obvious cost consequences
Even lightly soiled filters can react

18. Strategies to Minimize Ozone Reactions
2) Expose and vent filters to high levels of ozone
Technique called passivation
Some byproducts can persist for a long time
Possibility of secondary reactions
Continuous particle deposition
New ability to react with ozone

19. Strategies to Minimize Ozone Reactions
3) Scrub ozone from incoming air
Can be done with activated carbon
Removes other pollutants
Expensive, particularly to get complete removal

20. Strategies to Minimize Ozone Reactions
4) Scrub VOCs after filter
Can be done with activated carbon
Removes other pollutants
Expensive, particularly to get complete removal
Potentially more complex than ozone removal

21. Proposed Strategies Filter industry has a challenge
Opportunity for innovation
Ideas include
Embedding activated carbon (or other sorbent) in filters
Coating filters with reactant that causes benign byproducts
Line ducts with disposable liner
Strongly advocate more research on nature and extent of problem

22. Research Questions What by-products are emitted from HVAC filters?
What are the impacts of ozone concentration, relative humidity, and air flow rate?
How to model ozone removal process?
What are HVAC filter impacts on occupant exposure to ozone and byproducts?
What is effect of varying ozone exposure?
What is effect of continuous particle deposition?
What is influence of particle composition?
To what degree do HVAC filters lower indoor concentrations of O3 in residential and commercial buildings?
What species and quantity of by-products are emitted from HVAC filters during and after exposure to O3?
To what degree do O3 concentration, relative humidity, and air flow rate affect O3 removal and production of reaction products?
How to model ozone removal process?

23. Questions?