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  • William P. Bahnfleth, PhD, PE, FASHRAE Department of Architectural Engineering

    The Pennsylvania State University

    1KC ASHRAE Tech 2008 Seminar 4/17/2008

  • Bacteria ◦ Tuberculosis ◦ Anthrax Virus ◦ Rhinovirus ◦ SARS Sources ◦ Infected humans ◦ Biological warfare/

    terrorism

    Characteristics ◦ μm and sub-μm ◦ Carrier particles

    Droplet residue Dust

    Transmission ◦ Airborne ◦ Fomite

    2KC ASHRAE Tech 2008 Seminar 4/17/2008

  • 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 μm) ◦ VOCs ◦ Mycotoxins In HVAC systems ◦ Cooling coils ◦ Damp filter media

    3KC ASHRAE Tech 2008 Seminar 4/17/2008

  • Pathogens ◦ Remove from air ◦ Remove from surfaces ◦ Limit person to person transmission with good

    hygiene ◦ Deactivate/destroy in air or on surfaces Fungi ◦ Control sources of moisture ◦ Treat surfaces that cannot be kept dry ◦ Remove spores from air ◦ Deactivate/destroy in air or on surfaces

    4KC ASHRAE Tech 2008 Seminar 4/17/2008

  • All airborne biological agents are filterable Ease of filtration depends on particle size—MERV 6 not effective against μm-sized particles HEPA and near-HEPA filters have high pressure drops Fungi can grow on filter media

    5KC ASHRAE Tech 2008 Seminar 4/17/2008

  • 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

    6KC ASHRAE Tech 2008 Seminar 4/17/2008

  • UVC, UVB radiation (~200–320 nm) damages DNA, RNA of microorganisms

    7KC ASHRAE Tech 2008 Seminar 4/17/2008

  • 1880s Finsen uses UVB to treat skin diseases 1920s Studies of UV effect on microorganisms 1930s First air treatment applications 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 2008 ASHRAE Handbook-S&E chapter on UV

    8KC ASHRAE Tech 2008 Seminar 4/17/2008

  • Major laboratory study documents ability to deactivate microorganisms in moving air (RTI, 2002) Double blind office building study shows reduction of sick building symptoms and sampled microbial levels (Menzies, et al. Lancet 2003) EPA ETV tests of nine commercial products show effectiveness against 3 standard microorganisms But…much more is needed

    9KC ASHRAE Tech 2008 Seminar 4/17/2008

  • 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

    10

    ( )expS kIt= −

    KC ASHRAE Tech 2008 Seminar 4/17/2008

  • k varies widely for different microorganisms Representative values (cm2/μW-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

    11KC ASHRAE Tech 2008 Seminar 4/17/2008

  • 12

    -Filter may be more effective for some microorganisms -Consider multiple modes of air treatment

    KC ASHRAE Tech 2008 Seminar 4/17/2008

  • 13

    Multi-Stage ◦ Superimposed

    exponentials for susceptible and resistant populations

    ItkItk feefS 21)1( −− +−=

    0.00001

    0.0001

    0.001

    0.01

    0.1

    1

    0 20 40 60 80 100 120

    Time, min Su

    rv iv

    al F

    ra ct

    io n

    ItkItk feefS 21)1( −− +−=

  • 14

    “Shoulder” ◦ Slow no response

    until threshold dose is reached

    0.1

    1

    0 5 10 15 20 25 30

    Time, min

    Su rv

    iv al

    F ra

    ct io

    n

    0.000001

    0.00001

    0.0001

    0.001

    0.01

    0.1

    1

    0 5 10 15 20 25 30 35 40

    Time, min

    Su rv

    iv al

    F ra

    ct io

    n

  • 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

    15KC ASHRAE Tech 2008 Seminar 4/17/2008

  • 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

    4/17/2008KC ASHRAE Tech 2008 Seminar 16

  • 80

    85

    90

    95

    100

    0 2000 4000 6000 8000 Hour

    O ut

    pu t (

    % )

    0

    50

    100

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    0.1 1 10 Switching rate (#/3hr)

    % o

    f r at

    ed li

    fe

    0.3 3

    17KC ASHRAE Tech 2008 Seminar 4/17/2008

    Hot Cathode

  • 18

    0

    20

    40

    60

    80

    100

    0 20 40 60 80 Lamp Surface Temperature [οC]

    U V

    O ut

    pu t [

    % ]

    Maximum output when cold spot T = 40°C (109°F)

    KC ASHRAE Tech 2008 Seminar 4/17/2008

  • 19

    1 m/s = 196 ft/min, 15.6°C = 60°F, 35°C = 95°F

    KC ASHRAE Tech 2008 Seminar 4/17/2008

    0

    20

    40

    60

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    0 20 40 60 80 Lamp Surface Temperature [οC]

    U V

    O ut

    pu t [

    % ]

  • Effects are independent, multiplicative Implies that lamp selection should be based on worst ambient conditions and lamp output just before changeout Rated capacity typically measured after 100 hr burn-in under favorable environmental conditions

    4/17/2008KC ASHRAE Tech 2008 Seminar 20

  • Temperature-controlled variable flow lamp test duct

    Philips TUV 25W – G25T8 in cross-flow test

    4/17/2008KC ASHRAE Tech 2008 Seminar 21

  • Must correlate lamp output with surface cold spot temperature Use quantitative infrared thermography Feasible because quartz lamp tubes are ~opaque to infrared

    4/17/2008KC ASHRAE Tech 2008 Seminar 22

  • Center (flow left to right) Socket End (hot spot at cathode)

    4/17/2008KC ASHRAE Tech 2008 Seminar 23

  • Raw Data Output Contours

    4/17/2008KC ASHRAE Tech 2008 Seminar 24

  • 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

    4/17/2008KC ASHRAE Tech 2008 Seminar 25

  • Number and configuration of lamps Reflectivity of enclosure Air flow conditions ◦ Impact on lamp output ◦ Impact on dose distribution

    4/17/2008KC ASHRAE Tech 2008 Seminar 26

  • 27

    UV above occupied zone irradiates circulating air Common rule of thumb for sizing (Riley, HSPS): 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

    KC ASHRAE Tech 2008 Seminar 4/17/2008

  • Environment for lamps is relatively stable Standard lamps perform well Depreciation and failure are more serious concerns

    4/17/2008KC ASHRAE Tech 2008 Seminar 28

  • 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 Installed cost per 60W fixture ~$300 Replacement lamps—$25- 35 standard vs. $75-$125 proprietary

    29KC ASHRAE Tech 2008 Seminar 4/17/2008

  • Typical recommendation: 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) Minimum clearance for 0.25s exposure @ 500 fpm is ~2 ft Full flow temperature rise ~0.06°F

    4/17/2008KC ASHRAE Tech 2008 Seminar 30

  • Cooling effects on standard output lamps in- duct applications can be severe Use of high output lamps (“windchill compensated) improves output relative to maximum but does not eliminate output variation as conditions change

    4/17/2008KC ASHRAE Tech 2008 Seminar 31

  • 4/17/2008KC ASHRAE Tech 2008 Seminar 32

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