1、17.1CHAPTER 17ULTRAVIOLET LAMP SYSTEMSTerminology 17.1UVGI Fundamentals . 17.2Lamps and Ballasts . 17.3Maintenance 17.6Safety . 17.6Unit Conversions. 17.9V energy is electromagnetic radiation with a wavelengthUshorter than that of visible light, but longer than soft x-rays. AllUV ranges and bands ar
2、e invisible to the human eye. The UV spec-trum can be subdivided into following bands: UV-A (long-wave; 400 to 315 nm): the most abundant in sunlight,responsible for skin tanning and wrinklesUV-B (medium-wave; 315 to 280 nm): primarily responsible forskin reddening and skin cancerUV-C (short-wave; 2
3、80 to 200 nm): the most effective wave-lengths for germicidal control; Radiation 200 nm is also calledvacuum UV and produces ozone (O3) in airUse of ultraviolet (UV) lamps and lamp systems to disinfectroom air and airstreams dates to about 1900; see Riley (1988) andSchechmeister (1991) for extensive
4、 reviews of UV disinfection.Early work established that the most effective UV wavelength rangefor inactivation of microorganisms was between 220 to 300 nm,with peak effectiveness near 265 nm.UV-C energy disrupts the DNA of a wide range of microorgan-isms, rendering them harmless (Brickner 2003; CIE
5、2003). Figure 1shows the relative effectiveness of UV-C energy at various wave-lengths to cause DNA damage. Most, if not all, commercial UV-Clamps are low-pressure mercury lamps that emit UV energy at 253.7nm, very close to the optimal wavelength.Ultraviolet germicidal irradiation (UVGI) in the UV-C
6、 band hasbeen used in air ducts for some time, and its use is becomingincreasingly frequent as concern about indoor air quality increases.UVGI is being used as an engineering control to interrupt the trans-mission of pathogenic organisms, such as Mycobacterium tubercu-losis (TB), influenza viruses,
7、mold, and possible bioterrorismagents (Brickner 2003; CDC 2002, 2005; General Services Admin-istration 2003).This chapter includes a review of the fundamentals of UV-Cenergys impact on microorganisms; how UV-C lamps generate ger-micidal radiant energy; various components that comprise UV-Cdevices an
8、d systems; and a review of human safety and maintenanceissues.TERMINOLOGYBurn-in time. Period of time that UV lamps are powered onbefore being put into service, typically 100 h.Droplet nuclei. Microscopic particles produced when a personcoughs, sneezes, shouts, or sings. The particles can remain sus
9、pendedfor prolonged periods and can be carried on normal air currents in aroom and beyond to adjacent spaces or areas receiving exhaust air.Erythema (actinic). Reddening of the skin, with or withoutinflammation, caused by the actinic effect of solar radiation or arti-ficial optical radiation. See CI
10、E (1987) for details. (Nonactinic ery-thema can be caused by various chemical or physical agents.)Exposure. Being subjected to something (e.g., infectious agents,irradiation, particulates, chemicals) that could have harmful effects.For example, a person exposed to M. tuberculosis does not neces-sari
11、ly become infected.Exposure dose. Radiant exposure (J/m2, unweighted) incidenton biologically relevant surface.Fluence. Radiant flux passing from all directions through a unitarea in J/m2or J/cm2; includes backscatter.Germicidal radiation. Optical radiation able to kill pathogenicmicroorganisms.Irra
12、diance. Power of electromagnetic radiation incident on asurface per unit surface area, typically reported in microwatts persquare centimeter (W/cm2). See CIE (1987) for details.Mycobacterium tuberculosis. The namesake member of M.tuberculosis complex of microorganisms, and the most commoncause of tu
13、berculosis (TB) in humans. In some instances, the speciesname refers to the entire M. tuberculosis complex, which includesM. bovis, M. africanum, M. microti, M. canettii, M. caprae, and M.pinnipedii.Optical radiation. Electromagnetic radiation at wavelengthsbetween x-rays ( 1 nm) and radio waves ( 1
14、 mm). See CIE(1987) for details.Permissible exposure time (PET). Calculated time period thathumans, with unprotected eyes and skin, can be exposed to a givenlevel of UV irradiance without exceeding the NIOSH recommendedexposure limit (REL) or ACGIH Threshold Limit Value(TLV)for UV radiation.Personal
15、 protective equipment (PPE). Protective clothing, hel-mets, goggles, respirators, or other gear designed to protect thewearer from injury from a given hazard, typically used for occupa-tional safety and health purposes.The preparation of this chapter is assigned to TC 2.9, Ultraviolet Air andSurface
16、 Treatment.Fig. 1 Relative UV-C Germicidal Efficiency17.2 2012 ASHRAE HandbookHVAC Systems and Equipment (SI)Photokeratitis. Defined by CIE (1993) as corneal inflammationafter overexposure to ultraviolet radiation.Photoconjunctivitis. Defined by CIE (1993) as a painful con-junctival inflammation tha
17、t may occur after exposure of the eye toultraviolet radiation.Photokeratoconjunctivitis. Inflammation of cornea and con-junctiva after exposure to UV radiation. Wavelengths shorter than320 nm are most effective in causing this condition. The peak of theaction spectrum is approximately at 270 nm. See
18、 CIE (1993) fordetails. Note: Different action spectra have been published for pho-tokeratitis and photoconjuctivitis (CIE 1993); however, the lateststudies support the use of a single action spectrum for both oculareffects.Threshold Limit Value(TLV). An exposure level underwhich most people can wor
19、k consistently for 8 h a day, day after day,without adverse effects. Used by the ACGIH to designate degree ofexposure to contaminants. TLVs can be expressed as approximatemilligrams of particulate per cubic meter of air (mg/m3). TLVs arelisted either for 8 h as a time-weighted average (TWA) or for 1
20、5 minas a short-term exposure limit (STEL).Ultraviolet radiation. Optical radiation with a wavelengthshorter than that of visible radiation. See CIE (1987) for details.The range between 100 and 400 nm is commonly subdivided intoUV-A 315 to 400 nmUV-B 280 to 315 nmUV-C 100 to 280 nmUltraviolet germic
21、idal irradiation (UVGI). Use of ultravioletradiation to kill or inactivate microorganisms. UVGI is generated byUV-C lamps that kill or inactivate microorganisms by emittingultraviolet radiation, predominantly at a wavelength of 253.7 nm.UV dose. Product of UV irradiance and exposure time on a givenm
22、icroorganism or surface, typically reported in millijoules persquare centimetre (mJ/cm2).Wavelength. Distance between repeating units of a wave pat-tern, commonly designated by the Greek letter lambda ().UVGI FUNDAMENTALSMicrobial Dose ResponseLamp manufacturers have published design guidance docume
23、ntsfor in-duct use (Philips Lighting 1992; Sylvania 1982; Westing-house 1982). Bahnfleth and Kowalski (2004) and Scheir and Fencl(1996) summarized the literature and discussed in-duct applica-tions. These and other recent papers were based on case studies andpreviously published performance data. Th
24、e Air-Conditioning andRefrigeration Technology Institute (ARTI) funded a research projectto evaluate UV lamps capability to inactivate microbial aerosols inventilation equipment, using established bioaerosol control deviceperformance measures (VanOsdell and Foarde 2002). The data indi-cated that UV-
25、C systems can be used to inactivate a substantial frac-tion of environmental bioaerosols in a single pass.For constant and uniform irradiance, the disinfection effect ofUVGI on a single microorganism population can be expressed asfollows (Phillips Lighting 1992):Nt/N0= exp(kEfft) = exp(k Dose) (1)wh
26、ereN0= initial number of microorganismsNt= number of microorganisms after any time tNt/N0 = fraction of microorganisms survivingk = microorganism-dependent rate constant, cm2/(Ws)Eff= effective (germicidal) irradiance received by microorganism, W/cm2Dose = Eff t, (Ws)/cm2The units shown are common,
27、but others are used as well, includ-ing irradiance in W/m2 and dosein J/m2.Equation (1) describes an exponential decay in the number of liv-ing organisms as a constant level of UVGI exposure continues. Thesame type of equation is used to describe the effect of disinfectantson a population of microor
28、ganisms, with the dose in that case beinga concentration-time product. The fractional kill after time t is(1 Nt/N0). In an air duct, the use of Equation (1) is complicated bythe movement of the target microorganisms in the airstream and thefact that the UVGI irradiance is not constant within the duc
29、t. Inaddition, the physical parameters of the duct, duct airflow, and UVinstallation have the potential to affect both the irradiance and themicroorganisms response to it. As is the case with upper-room UVinstallation design, the design parameters for UVGI in in-duct appli-cations are not simple bec
30、ause of some uncertainty in the data avail-able to analyze them, and because of secondary effects.A key difference between surface decontamination and airborneinactivation of organisms is exposure time. Residence time in in-duct devices is on the order of seconds or fractions of seconds. In amoving
31、airstream, exposure time is limited by the effective distancein which the average irradiance was calculated; for instance, at2.54 m/s, 0.3 m of distance takes 0.12 s. Therefore, neutralizationmethods against an airborne threat must be effective in seconds orfractions of a second, depending on the de
32、vices characteristics, andhigh UV intensity is generally required. Conversely, when irradiat-ing surfaces in an HVAC system, exposure time is often continuous,so much lower levels of UV intensity may be required. Susceptibility of Microorganisms to UV EnergyOrganisms differ in their susceptibility t
33、o UV inactivation; Figure2 shows the general ranking of susceptibility by organism groups.Viruses are a separate case and are not included in Figure 2, because,as a group, their susceptibility to inactivation is even broader thanbacteria or fungi. A few examples of familiar pathogenic organismsare i
34、ncluded in each group for information (see Table 1). Note that itis impossible to list all of the organisms of interest in each group.Depending on the application, a public health or medical profes-sional, microbiologist, or other individual with knowledge of thethreat or organisms of concern should
35、 be consulted.As shown in Figure 2, the vegetative bacteria are the most sus-ceptible, followed by the Mycobacteria, bacterial spores, and,finally, fungal spores, which are the most resistant. Within eachgroup, an individual species may be significantly more resistant orsusceptible than others, so c
36、are should be taken, using this rankingonly as a guideline. Note that spore-forming bacteria and fungi alsoFig. 2 General Ranking of Susceptibility to UV-C Inactivation of Microorganisms by GroupUltraviolet Lamp Systems 17.3have vegetative forms, which are markedly more susceptible toinactivation th
37、an the spore forms. Using Equation (1), it is clear thatlarger values of k represent more susceptible microorganisms andsmaller values represent less susceptible ones. Units of k are theinverse of the units used for dose.Using k values to design HVAC duct systems can be challeng-ing. Values of k var
38、y over several orders of magnitude, dependingon organism susceptibility, and values reported in the literaturefor the same microorganism sometimes differ greatly. For exam-ple, Luckiesh (1946) reported a k for Staphylococcus aureus of0.9602 m2/J 0.009602 cm2 /(Ws) and 0.00344 m2/J for Aspergil-lus a
39、mstelodami spores. However, k values for S. aureus as small as0.419 m2/J were reported by Abshire and Dunton (1981). The widevariation for a single species is the result of a number of factors, themost important of which is differences in the conditions underwhich measurements were conducted (in air
40、, in water, on plates).Especially for many of the vegetative organisms, the amount of pro-tection offered by organic matter, humidity, and components ofambient air can significantly affect their susceptibility to UVGI(VanOsdell and Foarde (2002). Kowalski (2002) has an extensivecompilation of publis
41、hed k values, and research to obtain more reli-able design values is ongoing. Take care when using published val-ues, and obtain the original papers to evaluate the relevance of the kvalue of any particular organism to a specific application.LAMPS AND BALLASTSTypes of UV-C LampsAlthough other option
42、s exist, the most efficient UV-C lamps arebased on a low-pressure mercury discharge. These lamps containmercury, which vaporizes when the lamp is lighted. The mercuryatoms accelerate because of the electrical field in the discharge col-liding with the noble gas, and reach an excited stage. The excit
43、edmercury atoms emit almost 85% of their energy at 253.7 nm wave-length. The remaining energy is emitted at various wavelengths inthe UV region (mainly 185 nm); very little is emitted in the visibleregion.UV lamps exist in different shapes, which are mostly based ongeneral lighting fluorescent lamps
44、:Cylindrical lamps may be any length or diameter. Like fluores-cent lamps, most UV lamps have electrical connectors at bothends, but single-ended versions also exist. Typical diameters are38 mm T12, 28 mm T8, 20 mm T6, and 16 mm T5.Biaxial lamps are essentially two cylindrical lamps that are inter-c
45、onnected at the outer end. These lamps have an electrical con-nector at only one end.U-tube lamps are similar to biaxial lamps having the electricalconnector at one end. They have a continuously curved bend atthe outer end.UV lamps can be grouped into the following three output types:Standard-output
46、 lamps operate typically at 425 mA.High-output lamps have hot cathode filaments sized to operatefrom 800 up to 1200 mA. Gas mixture and pressure are opti-mized to deliver a much higher UV-C output while maintaininglong lamp life, in the same lamp dimensions as standard-outputlamps.Amalgam lamps have
47、 hot cathode filaments sized to operate at1200 mA or higher. The gas mixture, pressure, and sometimeslamp diameter have been optimized for delivering an even higherUV without deteriorating lamp life.As shown in Figure 3, UV lamps use electrodes between whichthe electrical discharge runs and are fill
48、ed with a noble gas such asargon, neon, or a mix thereof. A small amount of mercury is presentin the envelope.The electrodes are very important for the lamp behavior. Thereare two major types:A cold-cathode lamp usually contains a pair of cathodes parallelto one another. The cathodes are not heated
49、in order to excite theelectrons. A high voltage potential is needed to ionize the gas inthe tube and to cause current flow in an ambient temperature.Cold-cathode lamps offer instant starting, and life is not affectedby on/off cycles. Cold-cathode UV lamps provide less UVGIoutput than hot-cathode UV lamps, but consume less energy andlast several thousand hours longer, thus requiring less costlymaintenance.A hot cathode emits electrons through thermo-ionic emission.The electrode consists of an electrical filament coated with a spe-cial material (emitter) t
