Fundamentals of Ultraviolet Germicidal Irradiation for Air and Surface Disinfection

1. Fundamentals of Ultraviolet Germicidal Irradiation for Air and Surface Disinfection William P. Bahnfleth, PhD, PE, FASHRAE The Pennsylvania State University Katja Auer, MA, MBA Lumalier Corporation NAFA TECH2010

2. Outline • Introduction • UVGI Fundamentals • Application Issues • UVGI System Types • Upper Air vs. In-Duct Economics • In-duct system performance • Summary NAFA TECH2010

3. Introduction Microorganisms Microbial control alternatives UVGI history Evidence for UVGI effectiveness NAFA TECH2010

4. Indoor Microorganisms-Pathogens • Bacteria • Tuberculosis • Anthrax • MRSA • Virus • Rhinovirus • SARS • Influenza • Sources • Infected humans • Biological warfare/ terrorism • Characteristics • m and sub-m • Carrier particles • Droplet residue • Dust • Transmission • Airborne • Fomite NAFA TECH2010

5. Indoor Microorganisms-Fungi • Cause/aggravate • Allergies • Asthma • Opportunistic infections • Grow in presence of food (organic material) and water • Types • Aspergillus • Stachybotris • Penicillium • Characteristics • Surface growth—mycelium • Spores, O(1-10 m) • VOCs • Mycotoxins • In HVAC systems • Cooling coils • Damp filter media NAFA TECH2010

6. Indoor Microbial Control Approaches • All • Filter • Dilute in air • Clean from surfaces • Inactivate • Pathogens • Limit person to person transmission with good hygiene • Fungi • Control sources of moisture • Treat surfaces that cannot be kept dry NAFA TECH2010

7. Indoor Microbial Control-Filtration • All airborne biological agents are filterable • Ease of filtration depends on particle size—MERV 6 not effective against m-sized particles • HEPA and near-HEPA filters have high pressure drops • Fungi can grow on filter media NAFA TECH2010

8. Indoor Microbial Control-Dilution • Outside air can be used to dilute any airborne indoor contaminant • Conditioning of outside air is a major energy consumer • Large amounts of outside air conditioning in hot/humid climates may lead to moisture control problems NAFA TECH2010

9. Indoor Microbial Control-UVGI • UVC, UVB radiation (~200–320 nm) damages DNA, RNA of microorganisms NAFA TECH2010

10. History • 1880s Finsen uses UVB to treat skin diseases • 1920s Studies of UV effect on microorganisms • 1930s First air treatment applications-Wells, et al. m Multi-year PA school study shows upper room highly effective against measles • 1940s Studies of surface mold disinfection • 1950s Use of UV in A/C described as “standard” application in GE literature • 1980s First cooling coil disinfection Philips UV lamp application guidance • 1990s Growth of commercial UVGI, renewed scientific interest in UVGI • 2005 ASHRAE TG 2.UVAS formed • 2007 TG 2.UVAS becomes TC 2.9 Ultraviolet Air and Surface Treatment • 2008 ASHRAE Handbook-S&E chapter on UV • 2009 ASHRAE Position Document on Airborne Infectious Diseases identifies UVGI as a proven technique for airborne infection control • 2009 NIOSH guidelines for control of tuberculosis with upper room UVGI • 2009 Formation of ISO working group on “UV devices” NAFA TECH2010

11. Recent Evidence of UVGI Efficacy • Major laboratory study documents ability to deactivate microorganisms in moving air (RTI, 2002) • EPA ETV tests of nine commercial products show effectiveness against 3 standard microorganisms • Double blind office building study shows reduction of sick building symptoms and sampled microbial levels (Menzies, et al. Lancet 2003) • More evidence of impact on outcomes is needed NAFA TECH2010

12. ASHRAE Position Document – Airborne Infectious Diseases • Airborne infectious disease transmission can be reduced using UVGI (and other modalities) • Research that shows UVGI can inactivate some disease transmitting organisms and that it can affect disease transmission rates. • Additional research is needed showing clinical efficacy specifically in occupancies with high-risk sources • Top three research priorities are UVGI-related NAFA TECH2010

13. Fundamentals History Microbial response UV sources NAFA TECH2010

14. Microbial response to UVGI • To a first approximation: • S = surviving fraction of initial population • I = UV fluence (µW/cm2) • t = duration of exposure (s) • k = decay rate constant (cm2/µW-s) • Single pass efficiency of UVGI = 1-S NAFA TECH2010

15. Microbial Response to UVGI • k varies widely for different microorganisms • Representative values (cm2/W-s) • Bacillus anthracis 0.000031 • Influenza A 0.0019 • Mycobacterium tuberculosis 0.002132 • Streptococcus pneumoniae 0.006161 • Accurate measurement of k is difficult and a weakness of existing design data NAFA TECH2010

16. UVGI Susceptibility-Spores vs. Bacteria -Filter may be more effective for some microorganisms -Consider multiple modes of air treatment NAFA TECH2010

17. Microbial Response • Multi-Stage • Superimposed exponentials for susceptible and resistant populations NAFA TECH2010

18. Microbial Response • “Shoulder” • Slow no response until threshold dose is reached NAFA TECH2010

19. UVGI Sources • Low-pressure Hg vapor lamps with quartz tubes produce nearly pure 253.7 nm UVC • UVC output ~20-30% of input power • Lifetime depreciation typically15-20% over 9000 hr life, but some lose 50% in 6000 hr life with moderate switching rate NAFA TECH2010

20. UVGI Sources • Variety of sizes and shapes • Output Level • Standard output (425 ma) • High output (800-1200 ma) • High output lamps operate at higher temperature than standard output lamps • Cathode • Hot cathode • Coated filament, thermo-ionic effect • Higher output than cold cathode • Starts affect life • Cold cathode • High voltage potential ionizes gas in lamp • Low power/output • Long life, not affected by starts NAFA TECH2010

21. UVGI Lamp Depreciation and Life Hot Cathode NAFA TECH2010

22. Effect of Ambient Conditions-Cold Spot Temperature Maximum output when cold spot T = 40°C (109°F) NAFA TECH2010

23. Ambient Conditions-Flow and T(standard output lamp, manufacturer’s data, cross flow) 1 m/s = 196 ft/min, 15.6°C = 60°F, 35°C = 95°F NAFA TECH2010

24. Temperature DistributionsConditions: 32.2ºC (90.0ºF), 1.78 m/s (350 ft/min) Center (flow left to right) Socket End (hot spot at cathode) NAFA TECH2010

25. Lamp Performance Map NAFA TECH2010

26. Application Issues Lamp output variation Humidity Safety Material degradation Mixed mode air treatment NAFA TECH2010

27. Lamp Output • Rated capacity measured after 100 hr burn-in under favorable environmental conditions—may not be representative • Depreciation and convective effects are independent, multiplicative • Lamp selection should be based on worst case temperature/velocity combination and end-of-life depreciated lamp output NAFA TECH2010

28. Humidity • Negligible effect on • Lamp output (heat transfer) • Attenuation of UVGI in air • Possibly significant effect on microbial susceptibility to UVGI—may increase or decrease, depending on the organism NAFA TECH2010

29. Material Compatibility • UVC can degrade organic materials commonly found in HVAC systems • Synthetic filter media • Gaskets • Electrical insulation • Plastic pipe • Potential problem for retrofits • Rule of thumb-shield all organic components within 4-5 ft (1.5 m) of UV lamps • ASHRAE 1509-RP, "Study the Degradation of Typical HVAC Materials, Filters and Components Irradiated by UVC Energy” in progress – report due completed Jan 2011 NAFA TECH2010

30. Safety • UVB and UVC cause skin and eye irritation • Overexposure is a concern • Due to leakage from imperfectly sealed devices • Improper maintenance procedures and/or malfunction of safeties • Upper room systems • NIOSH RELs for 253.7 nm UVC • 1 min: 100 W/cm2 • 1 hour: 1.7 W/cm2 • 8 hours: 0.2 W/cm2 • Incorporate safeties in fixed systems • Train maintenance staff • Maintain equipment NAFA TECH2010

31. UVGI, Filters, Ventilation • UVGI is complementary to ventilation and particle filtration • Smaller microorganisms (viruses, bacteria) are generally difficult to filter but relatively easy to deactivate with UVGI • Larger microorganisms (spores) are relatively easy to filter and hard to deactivate. • Moderately high efficiency filtration + UVGI with minimum OA may be optimal NAFA TECH2010

32. System Types Room surface treatment Self-contained air treatment Upper room air treatment In-duct air and air/surface treatment NAFA TECH2010

33. Room Decontamination • Standalone, portable • Surface and air • Small unoccupied rooms • Used in EMS vehicles between patient transports NAFA TECH2010

34. Room Decontamination • Portable • Fully automated • Uses advanced sensor technology to measure reflected UVC surface dose NAFA TECH2010

35. Room Decontamination • Automated and self calibrating system • Remote controlled • Can be set to dose for specific pathogens including MRSA, VRE, C-Diff, Acinetobacter NAFA TECH2010

36. Room Decontamination • High-level disinfection of pathogens in any space • >99.9% reduction of vegetative bacteria within 15 minutes and 99.84% for C.difficilespores within 50 minutes (Rutala, et al. 2010) NAFA TECH2010

37. Self-Contained Air Treatment • Lamps and fan in a module • Combines performance issues of in-duct device and portable air cleaner (i.e., ability to turn over air in treated space) NAFA TECH2010

38. Upper Room • UV above occupied zone irradiates circulating air • Environment for lamps is relatively stable • Standard lamps perform well • Depreciation and burn-out are more serious concerns NAFA TECH2010

39. Upper Room • Long approved for control of disease transmission by CDC/NIOSH • NIOSH (2009): Environmental Control for Tuberculosis: Basic Upper-Room Ultraviolet Germicidal Irradiation Guidelines for Healthcare Settings. NAFA TECH2010

40. In-Duct • Deactivate airborne microorganisms “on the fly” • May do dual coil/ filter cleaning duty • Sizing methods vary greatly among manufacturers—from rules of thumb to simulation based on specific disinfection targets NAFA TECH2010

41. Coil/Filter Bank Disinfection • Irradiate coil or filter surfaces to control growth—upstream/ downstream/both • Most well-accepted HVAC application • GSA standards (P100, 5.9)—downstream of coils, above drain pans • Claimed to improve coil heat transfer and air-side pressure drop and clean dirty coils—proof needed • Wide range of opinions on sizing: • 5 W/cm2 on opposite side of coil • 200- 2000 W/cm2 on irradiated face NAFA TECH2010

42. In-Duct Commercial Downstream coil surface/air installations NAFA TECH2010

43. In-Duct Residential NAFA TECH2010

44. Upper Air vs. In-Duct Economics NAFA TECH2010

45. Upper Room Economics • Common rule of thumb for sizing (Riley, HSPH): 30 W per 200 ft2 • Modern fixtures are 36 W (12 UV W) and cost ~$600 • First cost: $2.50/ft2 • Operating cost: $0.13/ft2-yr for continuous operation @ $0.10/kWh NAFA TECH2010

46. In-Duct Economics • Typical air/coil system • Installed cost per 60W fixture ~$300 • Lamps—$25-35 standard vs. $75-$125 proprietary • Typical sizing: one 60W lamp per 6 ft2 duct cross section, mount within 3 ft of coil surface and allow at least 0.25s exposure time • At 500 fpm, one lamp treats 3000 cfm $0.10/cfm first cost, so ~ $0.10/ft2 for a typical all-air system • At $0.10/kWh, annual cost for continuous operation ~$0.018/cfm-yr, also $0.018/ft2-yr ($52.56/yr per 60W lamp) • Min. clearance for 0.25s exposure @ 500 fpm is ~2 ft • Full flow temperature rise ~0.06°F NAFA TECH2010

47. In-Duct System Performance Analysis Efficiency Energy use Economics NAFA TECH2010

48. Simulation-Based LCC Analysis • Performance simulation • Thermal/energy (whole-building—eQUEST) • IAQ control (components, system—custom MATLAB) • Economic analysis • First cost • Annual labor and equipment cost • Energy cost (direct/indirect) • Benefit? If benefit cannot be quantified with sufficient accuracy, an alternative approach is to compare with cost of alternative methods (e.g., filtration, dilution) to achieve the same level of contaminant control

49. Example-Office Building • New York City • 4 floors @ 2380 m2 (25,600 ft2) • 1 VAV system/floor • 8 m3/s (17,000 cfm) SA, 10°C (50°F) SAT, 2.5 m/s (472 ft/min) face velocity, 1.8 m3/s (3800 CFM) OA • MERV 6 filtration (base)

50. Study Cases • Base HVAC system (minimum OA, MERV 6) + UVGI downstream of cooling coil • Base HVAC system + UVGI upstream of cooling coil • Base HVAC system + filtration equivalent to UVGI(MERV 12)