Ultraviolet Germicidal Irradiation for Reducing Disease Transmission and Energy Use

1
Ultraviolet Germicidal Irradiation for Reducing
Disease Transmission and Energy Use

• Shelly L . Miller
• Associate Professor, Mechanical Engineering
  Environmental Engineering ProgramUniversity of
  Colorado, Boulder

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Objectives

• Since 1997, our research group has studied the
  efficacy of ultraviolet germicidal irradiation
  (UVGI) for inactivating airborne bacteria,
  viruses, and fungal spores
• Investigated temperature, relative humidity, and
  photoreactivation affects, as well as UV
  radiation distribution, air mixing, and lamp type
• Funded by CDC, NIOSH, Gilbert Foundation, NSF,
  and Industry partners
• Experimental paradigms include
• Multi-pass
• Intrinsic
• Upper-room air
• UV-HEPA air cleaners
• Single-pass
• In-duct
• Small-scale personal devices
• CFD Modeling

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UVGI as an Engineering Control

• The use of ultraviolet germicidal irradiation
  (UVGI) for the sterilization of microorganisms
  has been studied since the 1930s, mostly surface
  and water effects
• Microbes are uniquely vulnerable to radiation at
  wavelengths at or near 260 nm due to the
  resonance of this wavelength with molecular
  structures
• This wavelength is not naturally observed at
  the earths surface it is absorbed in the
  stratosphere by ozone

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UVGI Lamps

• mercury vapor lamps are most commonly used in
  applications, providing 254 nm radiation
• Mercury toxicity is a concern in some
  applications
• Non-toxic sources are not yet commercially
  available
• We are assessing prototype diodes and xenon lamps
  
• Xenon produces peak radiation at 242 nm

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UV Irradiation and DNA
Formation of dimers between adjacent thymine
nucleotides promotes cellular inactivation
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Guidelines for Preventing the Transmission of M.
tuberculosis in Health-Care Settings

• Environmental controls are the second line of
  defense in the TB infection control program,
  after administrative controls
• Environmental controls include technologies for
  the removal or inactivation of airborne M.
  tuberculosis
• These technologies include local exhaust
  ventilation, general ventilation, HEPA
  filtration, and UVGI
• (MMWR December 30, 2005 / 54(RR17)1-141)

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Multi-pass

• IntrinsicUpper-room air
• UV-HEPA air cleaners

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Building applications

• Crowded environments where unsuspected infectious
  persons may be present (e.g. jails, homeless
  shelters, hospital waiting rooms)
• Rooms in which infectious aerosol may be
  generated (e.g. hospital treatment and isolation
  rooms, rooms in a home, indoor pool facilities)
  and additional control is needed
• Rooms in which HVAC retrofits are difficult to do
  but additional air changes are needed to reduce
  risk of infections (e.g. hospital treatment and
  isolation rooms)

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Measles in Schools

• Wall-mounted UV lamps installed in three NY
  schools showed no difference in measles
  incidence, but the UV lamps did modify the
  spread of the disease in the school with the
  most lamps, the outbreak occurred over 4 months,
  compared to over 1 month in the school with no
  lamps
• (Perkins et al., 1947)

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CU Larson Laboratory

• T and RH control
• 87 m3
• Full-scale computer controlled HVAC system
  provides ventilation air, both outdoor and
  recirc, at 2-8 ACH

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Z Value

• First order reaction rate coefficient IRUV
  (sec-1) normalized by average UV fluence rate (?W
  cm-2)
• Z-value is directly proportional to UVGI
  inactivation rate
• a higher Z-value indicates a lower resistance of
  the microorganism to inactivation by UV radiation
  and vice versa
• Adopted from medical community (Riley et al.
  1976 Riley, 1988, Riley and Nardell 1989)

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Z value for Aspergillus versicolor is order of
magnitude smaller than the Z value for M.
parafortuitum

• (Kujundzic et al., 2005)

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The upper-room air inactivation rate provided by
our 5 fixture 216 W system for A. versicolor is
0.4 h-1 (Kujundzic et al., 2005) compared to 16
h-1 for M. parafortuitum
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Photoreactivation may be an important factor95
RH, 25 C, 0 ACH ventilation Effects observed
in intrinsic configuration, but not at full-scale
M. parafortuitum
no sunlight
sunlight

• (Peccia and Hernandez 2001) (Xu et al., 2005)

Light-activated enzymatic repair of thymine
dimers may decrease airborne UV-induced
inactivation rate (Gillis, 1972)
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Increasing UV fluence rate does not increase
inactivation rate linearly (Xu et al., 2005)
Z value for M. para
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M. parafortuitum
Inactivation Rate (1/h)
Increasing RH from 50 to 90 decreased the
inactivation rate by half (Xu et al., 2005)
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M. parafortuitum
Inactivation Rate (1/h)
Unevenly distributed UV radiation results in 30
lower inactivation rates (Xu et al., 2005)
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Effectiveness (E)

• Quantifies improvement in indoor air quality that
  is associated with the technologys use

E ranges between 0 and 1E 1 ideal
performanceE 0 complete lack of improvement
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Effectiveness
M. bovis BCG
M. parafortuitum
B. subtilis

• UVGI reduces culturable concentrations by 40-95
• Effectiveness depends on microorganism (Xu et
  al., 2003)

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M. parafortuitum
At 6 ACH and wintertime ventilation conditions
UVGI effectiveness decreased from 89 to 12
when the mixing fans were off(Xu et al.,
2005).
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HEPA-UV Air Cleaners In an Indoor Therapy Pool
Building
(Kujundzic et al. 2005)
Pool Air (1,100 m3)
Outside Air
Pool Water (208 m3) Residence Time 6 h T33oC
12 UV Units
6 Sand Filters
Addition of H2O2
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Culturable Bacteria
(Kujundzic et al., 2005)
69 (Y1) and 80 (Y2) REDUCTION
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Single-pass

• In-ductSmall-scale personal devices

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Building applications

• Irradiation of cooling coils an drip pans
• Limited scientific studies to assess impact of
  this application
• Anecdotally it seems to work well
• Two scientific studies recently completed showed
  no effect
• Irradiation of recirculation air within HVAC
  system

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HVAC Guinea Pig Study

• Guinea pigs exposed simultaneously in 2 separate
  chambers, one receiving unchanged air from a TB
  ward, and the other, ward air that was irradiated
  with UV-C. A total of 63 guinea pigs contracted
  TB over a 2-year period, and all were breathing
  unirradiated air from ward
• (Riley et al. 1962)

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Residential Asthma

• Study of 19 asthmatic children in homes with
  central AC systems in which UV lamps were
  installed showed a statistical improvement in
  PEFR variability in subjects with UV lamps
  compared to no UV lamps
• (Bernstein et al. 2006)

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Impact of in-duct UV on office workers

• Double-blind cross over study of 771 participants
• 3 office sealed air-conditioned buildings
• UV was alternately off for 12 weeks, on for 4
  weeks, and repeated 3 times
• Operation of UVGI reduced surface microbial
  contamination by 99
• Use of UVGI was associated with significantly
  fewer work-related symptoms overall, as well as
  respiratory and mucosal symptoms than was non-use
• (Menzies et al. 2003)

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Impact of in-duct UV on office workers
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In-Duct UVGI

• Bacteria continuously aerosolized outside near
  HVAC supply intake
• High wattage UVGI in recirculation duct
• Sample upstream, downstream

• Single-pass efficiency determined by comparing
  upstream and downstream concentrations

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In-Duct UVGI Single Pass Efficiency
91
80
75
Duct velocity 2.2 m/s No inactivation at
velocity of 5.1 m/s(kujundzic et al., 2006)
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Small-Scale Personal Device

• Requirements
• High flow rate
• Non-toxic UVGI source
• Coated to enhance reflectance

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UV Source

• LEDs
• solid state, expensive, low UV efficiency
  (0.3), 45-65 mW UV array
• Mercury
• Cheap, efficient (10), toxic, peak at 254 nm, 1
  W bulb
• Xenon
• Not commercially avail, efficient (10),
  nontoxic, peak at 270 nm, prototype built for
  project

UV fluence rate predictionin tube with coating
UV spectrum for Xenon lamp
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CU Experimental Test Facility
UV Radiation Exposure tube
UV source
Sampling upstream and downstream of UV tube
Equilibration chamber and aerosolization system
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B. Subtilis Hg uncoated tube
Coating enhanced inactivation by 25-28
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Energy Implications

• Mostly anecdotal evidence
• One MS thesis presents economic analysis
• More research needed

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Anecdotal Evidence

• Tacoma Jail
• Installed UV lights in HVAC VAV box/cooling
  coils, went from 100 outside air to 70 OA and
  30 recirc
• Saved 34,100 therms of natural gas/yr
• Review of utility bill confirms they saved gt
  70,000/yr in natural gas, overall saved 55,000
  after accounting for parts/labor

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Anecdotal Evidence

• Florida Hospital
• Installed UV lights in one 6000 cfm unit, near
  cooling coils where visible mold and clogging of
  coil apparent
• Within weeks of installation, static pressure
  over coil decreased from 1.8 in wg to 0.7 in wg
• Air velocity doubled from 230 fpm to 520 pfm
• 4900 in savings - 2000 installation cost
  2900
• Also observed less mold build up in duct work,
  reducing maintenance costs

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Anecdotal Evidence

• Boston Museum of Fine Arts
• Noticed a mold problem in humidifiers
• Had to drain and clean humidifiered almost daily
• Installed UVGI devices above humidifier sump and
  downstream of chilled water coils
• Standing water much clearer, huge reduction in
  maintenance and cleaning procedures
• American Electric Power, Dallas
• Installed UVGI in air handlers
• Eliminated cleaning programs
• Saw significant drop in pressure across coil,
  translating into energy savings of 139,000 over
  two-yr period

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Dreiling 2008, An Evaluation of UVGI Technology
in Health Care Facilities

• Compared three systems to a baseline 3900 cfm
  HVAC system
• Upper-room UVGI system
• HVAC system with increased ACH
• UVGI system in an AHU

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Dreiling 2008, Economic Evaluation Summary

• Upper-room UVGI
• increased predicted time for 99 disinfection
  from 46 minutes to 18 minutes
• Increased ACH to 15.2 from 6 ACH
• 62 increase in total cost
• HVAC system with increased ACH
• Similar to upper room UVGI, in both cost and
  increased ACH
• UVGI in AHU
• Room still at 6 ACH
• Cooling coils cleaned
• More focused on the fan energy consumption

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Acknowledgements

• CDC, NIOSH, NSF, Gilbert Foundation, Industry
  Sponsors
• Students at CU Elmira Kujundzic ,Fatimah
  Matalkah, Cody Howard, Jordan Peccia, Peng Xu
• Colleagues Mark Hernandez, Millie Shafer, Kevin
  Fennelly, Byron Jones, DTU faculty,
• Joint Center for Energy Management

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References

• Dreiling J. (2008). An Evaluation Of Ultraviolet
  Germicidal Irradiation (UVGI) Technology In
  Health Care Facilities, MS Thesis, Kansas State
  University.
• Bernstein JA. (2006). Health effects of
  ultraviolet irradiation in asthmatic childrens
  homes, J Asthma 43255-262.
• Jamriska M et al. (2000). Effect of ventilation
  and Filtration on Submicrometer Particles in an
  Indoor Environment Indoor Air 10(1)19-26
• Kujundzic E et al. (2007). Ultraviolet germicidal
  irradiation inactivation of airborne fungal
  spores and bacteria in upper-room air and in-duct
  configurations, JEES 61-9.
• Kujundzic E et al. (2006). Air cleaners and
  upper-room air UV germicidal irradiation for
  controlling airborne bacteria and fungal spores,
  JOEH 3536-546.
• Kujundzic E et al. (2005). Effects of
  ceiling-mounted HEPA-UV air filters on airborne
  bacteria concentrations in an indoor therapy pool
  building, JAWM 55210-218.
• Mendell MJ et al. (2002). Indoor particles and
  symptoms among office workers results from a
  double-blind cross-over study, Epidemiology
  13296-304.
• Menzies D et al. (2003). Effect of ultraviolet
  germicidal lights installed in office ventilation
  systems on workers health and wellbeing
  double-blind multiple cross-over trial, The
  Lancet 3621785-1791.
• Perkins et al. (1947). Effect of ultra-violet
  irradiation of classrooms on spread of measles in
  large rural central schools, Amer J Public Health
  73529-537.
• Riley et al. (1962). Infectiousness of air from a
  tuberculosis ward, Amer Rev Respir Disease
  85511-525.
• Xu P et al. (2005). Impact of environmental
  factors on efficacy of upper-room air ultraviolet
  germicidal irradiation for inactivating airborne
  Mycobacteria, ES T, 399656-9664.
• Xu P et al. (2003). Efficacy of ultraviolet
  germicidal irradiation of upper-room air in
  inactivating bacterial spores and Mycobacteria in
  full-scale studies, Atmos Environ 37405-419.
• Peccia, J. and Hernandez, M. (2001).
  Photoreactivation in Airborne Mycobacterium
  parafortuitum. Appl. Environ. Microbiol.
  674225-4232.