ASHRAE HVAC APPLICATIONS SI CH 31-2015 VENTILATION OF THE INDUSTRIAL ENVIRONMENT.pdf

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1、31.1CHAPTER 31VENTILATION OF THE INDUSTRIAL ENVIRONMENTVentilation Design Principles . 31.2General Comfort and Dilution Ventilation . 31.2Heat Control 31.5Energy Conservation, Recovery, and Sustainability. 31.6NDUSTRIAL environments require ventilation to reduce expo-Isure to excess heat and contami

2、nants that are generated in theworkplace; in some situations, cooling may also be required. Venti-lation is primarily used to control excess heat, odors, and hazardousparticulate and chemical contaminants. These could affect workershealth and safety or, in some cases, become combustible or flamma-bl

3、e when allowed to accumulate above their minimum explosiveconcentration (MEC) or lower flammable limit (LFL) also calledthe lower explosive limit (LEL) (Cashdollar 2000). Excess heat andcontaminants can best be controlled by using local exhaust systemswhenever possible. Local exhaust systems capture

4、 heated air andcontaminants at their source and may require lower airflows thangeneral (dilution) ventilation. See Chapter 32 for more informationon the selection and design of industrial local exhaust systems.General ventilation can be provided by mechanical (fan) systems,by natural draft, or by a

5、combination of the two. Combination sys-tems could include mechanically driven (fan-driven) supply air withair pressure relief through louvers or other types of vents, andmechanical exhaust with air replacement inlet louvers and/or doors.Mechanical (fan-driven) supply systems provide the best contro

6、land the most comfortable and uniform environment, especially whenthere are extremes in local climatic conditions. The systems typicallyconsist of an inlet section, filtration section, heating and/or coolingequipment, fans, ductwork, and air diffusers for distributing air in theworkplace. When toxic

7、 gases or vapors are not present and there areno aerosol contaminants associated with adverse health effects, aircleaned in the general exhaust system or in packaged air filtrationunits can be recirculated via a return duct. When applied appropri-ately, air recirculation can be a major contributor t

8、o a sustainable in-dustrial ventilation design and may reduce heating and cooling costs.In addition, regardless of the method selected, any positive ven-tilation into an industrial space should be from a source that is essen-tially free of any contaminants under both normal and abnormalconditions in

9、 the surrounding atmosphere. In many cases, this mayrequire a sealed intake stack or ductwork, as opposed to a perimeterwall hood or other air intake device, wherein the source of intakeshould be from a point well above or beyond the veil of the hazard-ous space that may surround a ventilated space.

10、 Where this cannot beachieved, additional action should be undertaken (e.g., providingparticulate or carbon filtration).A general exhaust system, which removes air contaminated bygases, vapors, or particulates not captured by local exhausts, usuallyconsists of one or more fans, plus inlets, ductwork

11、, and air cleanersor filters. After air passes through the filters, it is either dischargedoutdoors, or partially recirculated within the building. The air filtra-tion systems cleaning efficiency should conform to environmentalregulations and depends on factors such as building location, back-ground

12、 contaminant concentrations, type and toxicity of contami-nants, and height and velocity of building exhaust discharge.Many industrial ventilation systems must handle simultaneousexposures to temperature extremes and hazardous substances. Inthese cases, the required ventilation can be provided by a

13、combina-tion of local exhaust, general ventilation air supply, and generalexhaust systems. The ventilation engineer must carefully analyzesupply and exhaust air requirements to determine the worst case. Forexample, air supply makeup for hood exhaust may be insufficient tocontrol heat exposure. It is

14、 also important to consider seasonal cli-matic effects on ventilation system performance, especially for nat-ural ventilation systems. Duct material and its compatibility with theexhaust airstream is also important to consider when ventilating haz-ardous, abrasive, or corrosive substances.Most impor

15、tantly, if the hazardous substances are ignitable gasesor dusts, all electrical components of the ventilation system shouldbe rated for the proper electrical classification in the absence of anyventilation, regardless of their locations in the ventilation system.In specifying acceptable chemical con

16、taminant and heat expo-sure levels, the industrial hygienist or industrial hygiene engineermust consult the appropriate occupational exposure limits thatapply as well as any governing standards and guidelines. The leg-islated limits for the maximum airborne concentration of chemicalsubstances to whi

17、ch a worker may be exposed are listed as (1) max-imum average exposures to which a worker may be exposed over agiven work day (generally assumes an 8 to 10 h work day and a tra-ditional 40 h work week); (2) short-term exposure limits, which arethe maximum average airborne concentration to which a wo

18、rker maybe exposed over any 15 min period; and (3) ceiling limits, which arethe maximum airborne concentration to which a worker may beexposed at any time. However, occupational exposure limits forcold, heat, and contaminants are not lines of demarcation betweensafe and unsafe exposures. Rather, the

19、y represent conditions towhich it is believed nearly all workers may be exposed day afterday without adverse and/or long-term effects. Because a smallpercentage of workers may be affected by occupational exposurebelow the regulated limits, it is prudent to design for control to themost conservative

20、occupational exposure limits (OELs) available.In the case of exposure to hazardous chemicals, the number ofcontaminant sources, their generation rates, and the effectiveness ofexhaust hoods may not be known. Consequently, the ventilationengineer must rely on industrial hygiene engineering practices

21、whendesigning toxic and/or hazardous chemical controls. Close coopera-tion among the industrial hygienist, process engineer, and ventila-tion engineer is required.In the case of exposure to flammable or ignitable chemicals, thespecific gravity of the contaminant source(s), their concentration,and th

22、e rating of all electrical devices in the space, along with anysource or point of excessive heat, must be carefully considered toprevent possible loss of life or severe injury. As with all hazardouschemicals, cooperation of knowledgeable experts, including electri-cal engineers, is required.This cha

23、pter describes principles of ventilation practice andincludes other information on industrial hygiene in the industrialenvironment. Publications from the American Industrial HygieneAssociation (AIHA 2011), British Occupational Hygiene Society(BOHS 2002), U.S. Department of Health and Human Services(

24、DHHS 1986), National Safety Council (2012), and U.S. NationalThe preparation of this chapter is assigned to TC 5.8, Industrial VentilationSystems.31.2 2015 ASHRAE HandbookHVAC Applications (SI)Institute for Occupational Safety and Health (NIOSH 1986) providefurther information on industrial hygiene

25、principles and their appli-cation.1. VENTILATION DESIGN PRINCIPLESSpecial Warning: Certain industrial spaces may contain flam-mable, combustible, and/or toxic concentrations of vapors or dustsunder either normal or abnormal conditions. In spaces such asthese, there are life safety issues that this c

26、hapter may not com-pletely address. Special precautions must be taken in accordancewith requirements of recognized authorities such as the NationalFire Protection Association (NFPA), the Occupational Safety andHealth Administration (OSHA), and the American National Stan-dards Institute (ANSI). In al

27、l situations, engineers, designers, andinstallers who encounter conflicting codes and standards mustdefer to the code or standard that best addresses and safeguards lifesafety.General VentilationGeneral ventilation supplies and/or exhausts air to provide heatrelief, dilute contaminants to an accepta

28、ble level, and replaceexhaust air. Ventilation can be provided by natural or mechanicalsupply and/or exhaust systems. Industrial areas must comply withASHRAE Standard 62.1-2013 and other standards as required (e.g.,by NFPA). Outdoor air is unacceptable for ventilation if it is knownto contain any co

29、ntaminant at a concentration above that given inASHRAE Standard 62.1. If air is thought to contain any contami-nant not listed in the standard, consult relevant federal, state, pro-vincial, or local jurisdictions for acceptable exposure levels. Inaddition to their role in controlling industrial cont

30、aminants, generalventilation rates must be sufficient to dilute the carbon dioxideproduced by occupants to a level acceptable under ASHRAE Stan-dard 62.2.For complex industrial ventilation problems, experimental scalemodels and computational fluid dynamics (CFD) models are oftenused in addition to f

31、ield testing.Makeup AirWhen large volumes of air are exhausted to provide acceptablecomfort and safety for personnel and acceptable conditions for pro-cess operations, this air must be replaced, either through intentionaldesign strategy or through paths of least resistance. A safe and effec-tive ven

32、tilation design should be strategic about the mechanism,locations, and physical parameters by which makeup air enters theoccupied space. Makeup air, consistently provided by good air dis-tribution, allows more effective cooling in the summer and moreefficient and effective heating in the winter. Whe

33、n makeup airdesign is not incorporated into the ventilation design scheme, it maylead to inefficient operation of local exhaust systems and/or com-bustion equipment and cross-drafts that affect occupant comfort andenvironmental control settings. Relying on windows or other airinlets that cannot func

34、tion in year-round weather conditions is dis-couraged. Some factors to consider in designs for makeup airincludeMakeup air must be sufficient to replace air being exhausted orconsumed by combustion processes, local and general exhaustsystems (see Chapter 32), or process equipment. (Large air com-pre

35、ssors can consume a large amount of air and should be consid-ered if air is drawn from within the building.)Makeup air systems should be designed to eliminate uncomfort-able cross-drafts by properly arranging supply air outlets, and toprevent infiltration (through doors, windows, and similar open-in

36、gs) that may make hoods unsafe or ineffective, defeat envi-ronmental control, bring in or stir up dust, or adversely affectprocesses by producing temperature or airflow disturbances. Thedesign engineer needs to consider side drafts and other sources ofair movement close to the capture area of a loca

37、l exhaust hood. Inindustrial applications, it is common to see large fans blowing aironto workers positioned in front of the hood. This can render thelocal exhaust hood ineffective to the point that no protection is pro-vided for the worker: Ahn et al. (2008), Caplan and Knutson(1977, 1978), and Tse

38、ng et al. (2010) found that air movement infront of laboratory hoods can cause contaminants to escape fromthe hood and into the operators breathing zone. Hoods should belocated safe distances from doors and openable windows, supplyair diffusers, and areas of high personnel traffic (AIHA StandardZ9.5

39、; NFPA Standard 45).Makeup air should be obtained from a clean source with no morethan trace amounts of any airborne contaminants or hazardous,ignitable substances. Supply air can be filtered, but infiltration aircannot. For transfer air use, see ASHRAE Standard 62.1.Makeup air for spaces contaminat

40、ed by toxic, ignitable, or com-bustible chemicals may have to be acquired through carefullysealed ductwork from an area know to be free of contaminationand be supplied at sufficient rates, pressures, and mixing efficien-cies to (1) remove all contamination, and (2) prevent infiltrationof similar con

41、taminants from surrounding areas or adjacentspaces.Makeup air should be used to control building pressure and air-flow from space to space to (1) avoid positive or negative pres-sures that make it difficult or unsafe to open doors, (2) minimizedrafts, and (3) prevent infiltration.Makeup air should b

42、e used to reduce contaminant concentration,to control temperature and humidity, and minimize undesirableair movement.Makeup air systems should be designed to recover heat and con-serve energy (see the section on Energy Conservation, Recovery,and Sustainability).For more information on potential adve

43、rse conditions caused byspecific negative pressure levels in buildings, see ACGIH (2013)and Chapter 28 in the 2012 ASHRAE HandbookHVAC Systemsand Equipment.2. GENERAL COMFORT AND DILUTION VENTILATIONEffective air diffusion in ventilated rooms and the proper quan-tity of conditioned air are essential

44、 for creating an acceptable work-ing environment, removing contaminants, and reducing installationand operating costs of a ventilation system. Ventilation systemsmust supply air at the proper velocity and temperature, with result-ing contaminant concentrations within permissible occupationalexposure

45、 limits (OELs). For the industrial environment, the mostcommon objective is to provide tolerable (acceptable) working con-ditions rather than comfort (optimal) conditions.General ventilation system design is based on the assumptionthat local exhaust ventilation, radiation shielding, and equipmentins

46、ulation and encapsulation have been selected to minimize bothheat load and contamination in the workplace (see the section onHeat Control). When work operations are generally restricted,such as with equipment operating stations or control booths, spotconditioning of the work environment with clean c

47、onditioned air(see the section on Makeup Air) may further reduce the reliance ongeneral ventilation for conditioning or contaminant dilution. Incold climates, infiltration and heat loss through the building enve-lope may need to be minimized by pressurizing buildings.For more information on dilution

48、 ventilation, see ACGIH (2013).Quantity of Supplied AirSufficient air must be supplied to replace air exhausted by processventilation and local exhausts, dilute contaminants (gases, vapors, orVentilation of the Industrial Environment 31.3airborne particles) not captured by local exhausts, prevent th

49、e entryof contaminants or hazardous (ignitable) substances from any sur-rounding atmosphere during ingress or egress, and provide therequired thermal environment. The amount of supplied air should bethe largest of the amounts needed for temperature control, dilution,and replacement.Air Supply MethodsAir supply to industrial spaces can be by natural or mechanicalventilation systems. Although natural ventilation systems driven bygravity forces and/or wind effect are still widely used in industrialspaces (especially in hot premises in cold and moderate climates),they are inefficient in lar