1、60.1CHAPTER 60 ULTRAVIOLET AIR AND SURFACE TREATMENTFundamentals. 60.1Terminology . 60.3UVGI Air Treatment Systems . 60.5HVAC System Surface Treatment. 60.8Energy and Economic Considerations. 60.9Room Surface Treatment 60.10Safety 60.11Installation, Start-Up, and Commissioning . 60.12Maintenance. 60
2、.13LTRAVIOLET germicidal irradiation (UVGI) uses short-waveUultraviolet (UVC) energy to inactivate viral, bacterial, and fun-gal organisms so they are unable to replicate and potentially causedisease. UVC energy disrupts the deoxyribonucleic acid (DNA) of awide range of microorganisms, rendering the
3、m harmless (Brickneret al. 2003; CIE 2003). Early work established that the most effectiveUV wavelength range for inactivation of microorganisms wasbetween 220 and 280 nm, with peak effectiveness near 265 nm. Thestandard source of UVC in commercial systems is low-pressure mer-cury vapor lamps, which
4、 emit mainly near-optimal 253.7 nm UVC.Use of germicidal ultraviolet (UV) lamps and lamp systems to dis-infect room air and air streams dates to about 1900 (Reed 2010).Riley (1988) and Shechmeister (1991) wrote extensive reviews ofUVC disinfection. Application of UVC is becoming increasinglyfrequent
5、 as concerns about indoor air quality increase. UVC is nowused as an engineering control to interrupt the transmission of patho-genic organisms, such as Mycobacterium tuberculosis (TB), influ-enza viruses, mold, and potential bioterrorism agents (Brickner et al.2003; CDC 2002, 2005; GSA 2010; McDeVi
6、tt et al. 2008; Rudnicket al. 2009).UVC lamp devices and systems are placed in air-handling sys-tems and in room settings for the purpose of air and surface disin-fection (Figure 1). Control of bioaerosols using UVC can improveindoor air quality (IAQ) and thus enhance occupant health, comfort,and pr
7、oductivity (ASHRAE 2009; Menzies et al. 2003). Detaileddescriptions of UVGI components and systems are given in Chapter17 of the 2012 ASHRAE HandbookHVAC Systems and Equip-ment. Upper-air (also commonly called upper-room) devices areinstalled in occupied spaces to control bioaerosols (suspendedvirus
8、es, bacteria, and fungi contained in droplet nuclei and othercarrier particles) in the space. In-duct systems are installed in air-handling units to control bioaerosols in recirculated air that may becollected from many spaces, and to control microbial growth oncooling coils and other surfaces. Keep
9、ing the coils free of biofilmbuildup can help reduce pressure drop across the coils and improveheat exchanger efficiency (and therefore the energy required to moveand condition the air), and eliminates one potential air contamina-tion source that could degrade indoor air quality. UVC is typicallycom
10、bined with conventional air quality control methods, includingdilution ventilation and particulate filtration, to optimize their costand energy use (Ko et al. 2001).This chapter discusses these common approaches to the applica-tion of UVC products. It also surveys the most recent UVC designguideline
11、s, standards, and practices and discusses energy use andeconomic considerations that arise when applying UVC systems.Other UV-based HVAC applications, such as photocatalytic oxida-tion (PCO), are not discussed in this chapter.1. FUNDAMENTALSUltraviolet energy is electromagnetic radiation with a wave
12、lengthshorter than that of visible light and longer than x-rays (Figure 2).The International Commission on Illumination (CIE 2003) definesthe UV portion of the electromagnetic spectrum as radiation havingwavelengths between 100 and 400 nm. The UV spectrum is furtherdivided into UVA (wavelengths of 4
13、00 to 315 nm), UVB (315 to280 nm), UVC (280 to 200 nm), and vacuum UV (VUV; 200 to 100)(IESNA 2000). The optimal wavelength for inactivating microor-ganisms is 265 nm (Figure 3), and the germicidal effect decreasesrapidly if the wavelength is not optimal.UV Dose and Microbial ResponseThis section is
14、 based on Martin et al. (2008).UVGI inactivates microorganisms by damaging the structure ofnucleic acids and proteins at the molecular level, making them inca-pable of reproducing. The most important of these is DNA, which isresponsible for cell replication (Harm 1980). The nucleotide bases(pyrimidi
15、ne derivatives thymine and cytosine, and purine derivativesguanine and adenine) absorb most of the UV energy responsible forcell inactivation (Diffey 1991; Setlow 1966). Absorbed UV photonscan damage DNA in a variety of ways, but the most significant dam-age event is the creation of pyrimidine dimer
16、s, where two adjacentthymine or cytosine bases bond with each other, instead of across thedouble helix as usual (Diffey 1991). In general, the DNA moleculewith pyrimidine dimers is unable to function properly, resulting inthe organisms inability to replicate or even its death (Diffey 1991;Miller et
17、al. 1999; Setlow 1997; Setlow and Setlow 1962). An organ-ism that cannot reproduce is no longer capable of causing disease.UVGI effectiveness depends primarily on the UV dose (DUV,J/cm2) delivered to the microorganisms:DUV = It (1)where I is the average irradiance in W/cm2, and t is the exposuretime
18、 in seconds (note that 1 J = 1 W/s). Although Equation (1)appears quite simple, its application can be complex (e.g., when cal-culating the dose received by a microorganism following a tortuouspath through a device with spatial variability in irradiance). The doseis generally interpreted as that occ
19、urring on a single pass through thedevice or system. Although the effect of repeated UV exposure onmicroorganisms entrained in recirculated air may be cumulative, thiseffect has not been quantified and it is conservative to neglect it.The survival fraction S of a microbial population exposed to UVCe
20、nergy is an exponential function of dose:S = ekDUV(2)where k is a species-dependent inactivation rate constant, in cm2/J.The resulting single-pass inactivation rate is the complement of S: = 1 S (3)The preparation of this chapter is assigned to TC 2.9, Ultraviolet Air andSurface Treatment.60.2 2015
21、ASHRAE HandbookHVAC Applications (SI)and is a commonly used indicator of overall UVC effectiveness, rep-resenting the percentage of the microbial population inactivatedafter one pass through the irradiance field(s).Inactivation rate constants (k-values) are species-dependent andrelate the susceptibi
22、lity of a given microorganism population to UVradiation (Hollaender 1943; Jensen 1964; Sharp 1939, 1940). Mea-sured k-values for many species of viruses, bacteria, and fungi havebeen published in the scientific literature and previously summa-rized (Brickner et al. 2003; Kowalski 2009; Philips 2006)
23、. As shownin Figure 4, bacteria are generally more susceptible to UVC energythan fungi, but this is not always the case (see Chapter 17 of the2012 ASHRAE HandbookHVAC Systems and Equipment). It ismore difficult to generalize when it comes to viruses. Reported k-values for different species of microo
24、rganisms vary over severalorders of magnitude. Consequently, choosing which k-value to usefor UVC system design is often difficult and confusing. The varia-tion in reported k-values makes generalizing the use of Equation (2)particularly complicated for heterogeneous microbial populations.Even accura
25、tely determining S for one specific microorganism canbe difficult, because the reported k-values for the same speciessometimes differ significantly.Variations in published k-values may relate to differences in con-ditions under which the UV irradiance of the microbial populationwas conducted (in air
26、, in water, or on surfaces), the methods used tomeasure the irradiance level, and errors related to the microbiolog-ical culture-based measurements of microbial survival (Martin et al.2008). Because no standard methods are currently available for thedetermination of inactivation rate constants, care
27、 is necessary whenapplying values reported in the literature to applications under dif-ferent environmental conditions.Fig. 1 Potential Applications of UVC to Control Microorganisms in Air and on Surfaces(ASHRAE 2009)Ultraviolet Air and Surface Treatment 60.3UV Inactivation of Biological Contaminant
28、sThe focus of this chapter is application of UVC energy to inac-tivate microorganisms, specifically bacteria, fungi, and viruses onsurfaces and in air streams. The application of UVC for upper-airtreatment generally applies to pathogenic bacteria and viruses.Under some circumstances, these pathogens
29、 have the potential to betransmitted throughout the HVAC system.As shown in Table 1, infectious diseases can be transmitted by avariety of means. UVC is effective against microorganisms in the airthat flows through the UVC irradiation field and on irradiated sur-faces.As shown in Table 2 and Figure
30、4, viruses and vegetative bacte-ria are the generally most susceptible to UV inactivation, followedby Mycobacteria, bacterial spores, and finally fungal spores.Within each group, an individual species may be significantly moreresistant or susceptible, so this ranking should be used only as ageneral
31、guideline. Note that the spore-forming bacteria and fungialso have vegetative forms, which are markedly more susceptible toinactivation than are the spore forms. Viruses are a separate case.As a group, their susceptibility to inactivation is even broader thanfor the bacteria or fungi.2. TERMINOLOGYJ
32、ust as it is customary to express the size of aerosols in microm-eters and electrical equipments power consumption in watts, regard-less of the prevailing unit system, it is also customary to express totalUVC output, UVC irradiance and fluence, and UVC dose using SIunits.Burn-in time. Period of time
33、 that UV lamps are powered onbefore being put into service, typically 100 h.Fig. 2 Electromagnetic Spectrum(IESNA 2000)Fig. 3 Standardized Germicidal Response FunctionsMultiply I-P By To Obtain SIBtu/ft2(International Table) 1135.65 J/cm2Btu/hft2315.46 W/cm2To Obtain I-P By Divide SIFig. 4 General R
34、anking of Susceptibility to UVC Inactivation of Microorganisms by Group60.4 2015 ASHRAE HandbookHVAC Applications (SI)Cutaneous damage. Any damage to the skin, particularly thatcaused by exposure to UVC energy.Disinfection. Compared to sterilization, a less lethal process ofinactivating microorganis
35、ms.Droplet nuclei. Residual viable microorganisms in air, followingevaporation of surrounding moisture. These microscopic particlesare produced when an infected person coughs, sneezes, shouts, orsings. The particles can remain suspended for prolonged periodsand can be carried on normal air currents
36、in a room and beyond toadjacent spaces or areas receiving exhaust air.Erythema (actinic). Reddening of the skin, with or without in-flammation, caused by the actinic effect of solar radiation or arti-ficial optical radiation. See CIE (1987) for details. (Nonactinicerythema can be caused by various c
37、hemical or physical agents.)Exposure. Being subjected to infectious agents, irradiation, par-ticulates, or chemicals that could have harmful effects.Fluence. Radiant flux passing from all directions through a unitarea, often expressed as J/m2, J/cm2, or (Ws)/cm2.Irradiance. Power of electromagnetic
38、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 the M.tuberculosis complex of microorganisms, and the most commoncause of tuberculosis (TB) in humans. In
39、 some instances, the speciesname refers to the entire M. tuberculosis complex, which includesM. bovis, M. africanum, M. microti, M. canettii, M. caprae, M. pin-nipedii, and others.Ocular damage. Any damage to the eye, particularly that causedby exposure to UV energy.Permissible exposure time (PET).
40、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 protective equipment (PPE). Protective clothing, hel-mets, goggl
41、es, respirators, or other gear designed to protect thewearer from injury from a given hazard, typically used for occupa-tional safety and health purposes.Photokeratitis. Defined by CIE (1993) as corneal inflammationafter overexposure to ultraviolet radiation.Photokeratoconjunctivitis. Inflammation o
42、f cornea and con-junctiva after exposure to UV radiation. Exposure to wavelengthsshorter than 320 nm is most effective in causing this condition. Thepeak of the action spectrum is approximately 270 nm. See CIE(1993) for details. Note that different action spectra have been pub-lished for photokerati
43、tis and photoconjuctivitis (CIE 1993); how-ever, the latest studies support the use of a single action spectrum forboth ocular effects.Radiometer. An instrument used to measure radiometric quanti-ties, particularly UV irradiance or fluence.Threshold Limit Value(TLV). An exposure level underwhich mos
44、t people can work 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 averag
45、e (TWA) or for 15 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 intoUVA: 315 to 400 nmUVB: 280 to 315 nmUVC: 200 to 280 nmVa
46、cuum UV 100 to 200 nmUltraviolet germicidal irradiation (UVGI). Ultraviolet radiationthat inactivates microorganisms. UVC energy is generated by ger-micidal lamps that kill or inactivate microorganisms by emittingradiation predominantly at a wavelength of 253.7 nm.UV dose. Product of UV irradiance a
47、nd specific exposure timeon a given microorganism or surface, typically reported in milli-joules per square centimeter (mJ/cm2).Wavelength. Distance between repeating units of a wave pattern,commonly designated by the Greek letter lambda ().Table 1 Modes of Disease TransmissionExposure ExamplesDirec
48、t contact with an infected individualTouching, kissing, sexual contact, contact with oral secretions, or contact with open body lesionsUsually occurs between members of the same household/close friends/familyIndirect contact with a contaminated surface (fomite)Doorknobs, handrails, furniture, washro
49、om surfaces, dishes, keyboards, pens, phones, office supplies, childrens toysDroplet contact Infected droplets contact surfaces of eye, nose, or mouthDroplets containing microorganisms generated when an infected person coughs, sneezes, or talksDroplets are too large to be airborne for long periods of time, and quickly settle out of airAirborne droplet nuclei (residue from evaporated droplets) or other particles containing microorganisms 5 mSize allows them to remain airborne for long periods of timeOrganisms generally hardy (capable of surviving for long per
