industrial ventilation cap

P1: GPB Final pages Qu: 00, 00, 00, 00Encyclopedia of Physical Science and Technology En017B-808 August 2, 2001 17:39

Ventilation, IndustrialHoward D. GoodfellowUniversity of Toronto and Stantec Global Technologies Ltd.

I. Ventilation Design MethodologyII. Ventilation EquipmentIII. Design Equations for Industrial VentilationIV. Ventilation Modeling Using ComputersV. Ventilation Modeling Using Fluid Dynamics

VI. Solving Ventilation Problems for Existing Plants

GLOSSARY

Canopy Structure or enclosure located above a contam-inant source to capture the rising contaminant into aducted system.

CFD Computational Fluid Dynamics.Dust Small particles created by the breaking of larger

particles by mechanical action.Face velocity Air velocity at the hood opening.Froude number Dimensionless number that is the ratio

of inertial forces to buoyancy forces.Fume Small solid particles formed by the condensation

of vapors of solid materials.Hood Structure designed to enclose or partially enclose

a contaminant-generating operation.Industrial air technologies Air flow control technolo-

gies to control workplace indoor environment andemissions.

Mist Small droplet of materials that are ordinarily liquidat normal temperature and pressure.

Neutral zone or plane of neutral pressure Elevationwithin a building at which neither the outside air tends

to move into the building nor the inside air tends tomove out.

Reynolds number Dimensionless number that is the ra-tio of inertial to viscous forces.

Target levels Acceptable design levels for contaminantsin an industrial environment.

Threshold limit values Airborne concentrations of sub-stances for conditions under which it is believed thatnearly all workers may be repeatedly exposed day afterday without adverse effect.

THE FIELD OF INDUSTRIAL ventilation, or the moregeneral, Industrial Air Technology (IAT) is a challengingfield, which has been neglected by the scientific commu-nity until the last decade.

In all ventilation, the condition of the indoor environ-ment called Indoor Air Quality (IAQ) and the exposuresfor the occupants are important. In industrial facilities, thecontaminant emission rates may be 10100 times higherthan in nonindustrial facilities, but for many contaminants,the IAQ levels may be the same. From a design point of

435

P1: GPB Final pagesEncyclopedia of Physical Science and Technology En017B-808 August 2, 2001 17:39

436 Ventilation, Industrial

view, the first priority is to consider the process, but otherimportant issues, such as occupants, energy, environment,corporate image, etc., must also be considered.

The benefits of advanced industrial ventilation with im-proved IAQ are Improved health of workers and reduced absenteeism Improved work satisfaction, higher productivity, and

reduced production failures Reduction in maintenance costs for the building

fabrics, machinery, and products Reduction in energy consumption Opportunity to select new energy-efficient systems in

ventilation design Environmental pollution is reduced by lower energy

usage and lower emissions to the surroundings Embraces Clean Plant Design Concept Improve life cycle

Figure 1 is a schematic representation of the principlesof industrial ventilation.

It is typical for industrial premises to have, in one space,zones with different target levels. The target levels may bedetermined for the whole area or locally. Often only a partof the space requires controlling of the indoor environmentparameters. In addition to the main controlled zone, theremay be one or more local controlled zones with differenttarget levels than the main controlled zone.

Industrial air technology field is a more general descrip-tion than industrial ventilation and includes measures toprevent harmful emissions from industrial processes to bedischarged outdoors, conveying and cleaning technolo-gies, and controlled discharge of exhaust air to outdoors.Industrial air technology systems include drying, processventilation, and safety air systems.

The scope of the IAT field includes industrial processbuildings, as well as hospitals, underground car parks,mining, railroad and vehicle tunnels, livestock buildings,and other similar premises and processes.

FIGURE 1 Zoning and IAT systems.

The more general IAT system category can be classifiedinto three categories: (1) industrial ventilation, (2) processair technology, and (3) safety systems.

A more detailed breakdown of these systems is as fol-lows.

INDUSTRIAL VENTILATION Air conditioning systems

Air conditioning systems include control of air qualityand thermal environment for both human occupancyand processes

General ventilation systemsIn general ventilation systems, some indoor airparameters are controlled only partially. Target levelsare usually lower than for air conditioning.

Local ventilation systemsThese are used for local controlled zones. Thesesystems are based on local capture of contaminants.

Process ventilation systemsIn process ventilation, the target is to maintain definedconditions to ensure process performance, e.g., papermachine hoods.

PROCESS AIR TECHNOLOGY Cleaning systems

Cleaning systems are used to remove contaminants,clean the resulting fluid flows and collect materialsbefore discharging the exhaust air.

Pneumatic conveying systemsConveying systems are used to transport capturedpollutants from processes to a collection point.

Drying systemsDrying systems are used to remove moisture, gases,and vapors from the product

SAFETY AIR TECHNOLOGY SYSTEMS Designs to ensure safety from explosions

Typically, industrial premises will have, in one space,zones with different activities, which require different tar-get levels for indoor environment and its control. Thesetarget levels may be determined for the whole area or lo-cally. Also, often only a part of the space needs to be con-trolled. In addition to the main controlled zone, there maybe one or more local controlled zones with different targetsthan in the main controlled zone. For example, machinesequipped with electrical components require very cleanand accurately controlled indoor environment, while the


Ventilation, Industrial 437

unoccupied zone by the ceiling needs only a less stringentcontrolled protection against structural damages.

In industrial premises, the target levels of IAQ, as wellas other targets, e.g., emissions, shall be specified zone byzone.

Controlled zone is a zone in which the thermal and airpurity (quality) conditions are controlled to their specifiedlevels. The two categories of controlled zones are

Main controlled zone is normally a large area, which isoften the same as occupied zone

Local controlled zone, an area where the air iscontrolled locally, the control requirements may be forworker protection and comfort, for process control, orfor production protection

Uncontrolled zone is a zone in which source emissionswill be captured by source capturing system, and where thecapture efficiency is determined and shall be maintainedover the working period. From the pollutant concentra-tion point of view, the capture zone is uncontrolled (e.g.,workers shall not enter a capture zone without additionalprotection).

Room air conditioning systems are used for controllingthe main controlled zone. Systems can be divided intosubsystems:

Air handling systems Air distribution systems (ductwork) Room air distribution systems Ventilation systems Room heating and cooling systems Main exhaust systems Discharge systems: stacks, environmental dispersion

Note: Air distribution systems are not ventilation or airconditioning systems. For example, mixing airdistribution or displacement air distribution aremethods to bring the supply air to the treated space.

Discharge systems are used to discharge exhaust air tooutdoors in such a way that harmful spreading of pollutantsto environment and back to indoors is avoided.

Local ventilation systems are used for local controlledzones. These systems are based on local exhaust ventila-tion for local protection. Primarily local protection shouldbe made using process methods such as encapsulation,process modification, source capturing, etc.

Local ventilation systems can be divided into the fol-lowing subsystems:

Local exhaust Local supply, including air curtains, i.e., control of air

flow using jets

Combined local supply and exhausts

Fans, ducts, and filters are subsystems of local exhaustventilation.

Methods for Room AirConditioningBasic StrategiesTable I summarizes the strategies for room air condition-ing. This table includes a description of the four strategies,main characteristics, and typical applications.

Industrial ventilation refers to the control of the en-vironment with airflow as it applies to processing andmanufacturing operations. The design methodology forventilation systems is described on the basis of the devel-opment of ventilation system design as an integral part ofthe project planning and design activities. Procedures tobe implemented for the development of technical specifi-cations for louvers and roof exhausters are presented. Thetheoretical development of the design equations for heatrelease calculations, air set in motion, gravity or poweredventilators, and dilution ventilation is covered. Ventilationmodeling is described for both computer applications andfluid dynamic techniques. Techniques for solving ventila-tion problems for existing plants are summarized.

I. VENTILATION DESIGN METHODOLOGY

A. BackgroundMost industrial ventilation problems are complex. The de-velopment of cost-effective solutions requires an experi-enced and qualified ventilation engineer working with anindustrial hygienist. Experience has shown that the foursolutions to be considered for a ventilation problem, inorder of priority, are as follows:

1. Process modifications to eliminate the contaminantproblem can range from a total to a partial processchange. For some operations, a change in thematerials handling system may be required (e.g., typeof system, frequency of operation, change in materialcomposition or temperature).

2. If no acceptable process changes are possible, theapplication of local exhaust ventilation should beconsidered. Local exhaust ventilation usually requiresducted systems with hoods and covers. Figure 2 is aschematic of a local exhaust ventilation system. Thesesystems are commonly referred to as dust control,fume control, and mist control systems. For localexhaust ventilation systems, the concentration ofcontaminant in the exhaust duct is significantly higherthan in the general room area.



TABLE I Ideal Room Air Conditioning Strategies

Air conditioningstrategy Piston Stratification Zoning Mixing

Description To create unidirectional To support flow field created To control air conditions To provide uniformair flow field over the by density differences by within the selected zone conditions throughoutroom area by supply air. replacing the airflow out in the room by the supply the ventilated space

from the room area with air and allow stratificationsupply air of heat and contaminants

in the other room areasRoom dimension

SU

EX

T, C, x

Room dimension

SU

EX

T, C, x

Room dimension

SU

EX

T, C, x

Room dimension

SU

EX

T, C, x

Heat, Humidity andContaminantDistribution(Pictures)

X-axis: C,mg/m3, %RH

Y:axis: Room dim.(e.g. height)

SU = supply,EX = exhaust

Main characteristics: Room air flow patterns Room air flow patterns Room air flow patterns Room air flow patternscontrolled by low controlled mainly controlled partly by supply controlled typicallymomentum by boyancy; supply air and partly by boyancy by high momentumunidirectional distribution with low supply air flowsupply air flow, momentumstrong enough toovercome disturbances

Ideal Contaminant- 1and Heat Removal Efficiency

Typical application(An example ofa general roomair distributionmethod)

3. For applications where local exhaust ventilation is notfeasible, process building or general work areaventilation must be employed. For these systems,contaminated air is exhausted to the outdoors andlarge volumes of makeup air are introduced to diluteplant air contaminants to acceptable concentrations.For these industrial ventilation applications, theconcentration of contaminant in the exhaust duct isnot significantly higher than the contaminantconcentration in the general room air. Figure 3 is aschematic of a general work area ventilationsystem.

FIGURE 2 Schematic of local exhaust ventilation system.

For any specific industrial ventilation problem, thecontaminated air can be exhausted by naturalventilation (taking advantage of buoyancy-drivenforces arising from heat sources) or forced ventilation(using fans or roof exhausters). Design equations aredeveloped in Section III for natural or forcedventilation systems for the control of heat, dust, and

FIGURE 3 Schematic of general work area ventilation system.



fume for large industrial process buildings. Designequations are also developed for dilution ventilationapplications as they apply to gases and volatile vapors.

4. Personal protection equipment, such as respirators,should only be considered for solving ventilationproblems as an emergency or an interim maintenancerequirement.

B. Design MethodologyOn a global basis, significant progress has been madesince 1990 in developing a systematic design procedurefor industrial ventilation systems. The initial research anddevelopment effort was started in Finland in 1991 withthe launch of the INVENT program and an investment ofmore than $20 million U.S. dollars. In 1995, a decisionwas made at a workshop in Zurich to start preparation ofan international guidebook for industrial ventilation. Ananalysis of the current state-of-the-art identified the fol-lowing issues:

1. No scientific basis for many design applications2. No harmonization of design equations from different

countries or researchers3. Gaps in technical literature not defined and no

roadmap identified for future technologicaldevelopments

4. Many ventilation books are out of data5. No longer acceptable to overdesign ventilation

systems6. No handbook in the industrial ventilation field7. No accepted design methodology based on a

rigorous scientific approach8. Ventilation field fragmented on a global basis so

need collaboration by a team of international experts9. Excellent opportunity to collate worldwide research

and development efforts into a single handbook10. INVENT program started in Finland has generated

momentum and a critical mass to make projectsuccessful

The design of a ventilation system must be incorpo-rated into the plant design and layout at the earliest con-ceptual stage of the project. The ventilation engineer mustwork closely with the project design team at all stages ofthe project since the ventilation system can have a ma-jor impact on the type of process to be used, the plotplan, the building profile, and equipment layout within theplant.

In many applications, the ideal ventilation scheme maybe in conflict with other environmental design criteria suchas noise control and fume control. For example, ideal ven-tilation schemes may be based on the concept of a wide-

open building to enhance natural ventilation: this is inconflict with noise control considerations that require theplant to be enclosed as much as possible to reduce neigh-borhood noise. Another example of this conflict is the useof canopies for remote fume capture. Canopies performbest if the building is totally enclosed to prevent crossdrafts from disturbing the rising plume and causing it tomiss the fume control system. Cost-effective ventilationsystems can only be developed if the ventilation systemdesign is an integral part of the project planning and designactivities from the preliminary conceptual stage.

Figure 4 is an outline of the systematic design method-ology procedure for industrial ventilation. This designmethodology has been developed over many years of inter-national collaboration and represents input from numerousengineers, researchers, scientists, and practitioners in theindustrial ventilation field. A brief description of the differ-ent design steps follows below. (More details can be foundin the Handbook of Industrial Ventilation edited by H.D.Goodfellow and E. Tahti, listed in the bibliography.)

C. Target LevelsIt is difficult to achieve a good indoor environment inan industrial facility because of the lack of a scientific

FIGURE 4 Outline of the systematic design methodology proce-dure for industrial ventilation.



FIGURE 5 Design methodology for industrial ventilation systems.

basis for defining acceptable design levels for contami-nants in an industrial setting. A detailed database for ex-isting contaminant exposure is available from the FinnishInstitute of Occupational Hygiene (FIOH). Figure 5 showsa recommended approach for assessing target levels of in-dustrial air quality.

Target concentrations of air contaminants can be devel-oped based on both human risk assessment and technol-ogy. Health risk estimates at low concentrations (e.g., be-low one-tenth of the current occupational exposure limits)are, in general, inaccurate and rather unreliable. Conse-quently, technology-based approaches for the assessmentof target concentrations have been emphasized. The con-trol technology approach is based on information on cur-rent concentrations achieved by standard practices andbenchmark concentrations achieved by the advancedventilation and production technologies.

Existing contaminant exposure data banks, such asavailable from FIOH and other international health andsafety bodies, can be utilized for assessing concentrationlevels that are achievable. The benchmark air quality hasbeen determined by measuring concentrations in factoriesequipped with the advanced technologies. This informa-tion on the benchmark air quality, the current concentra-tion levels, and the health and comfort effects form the

foundation for setting target levels for industrial air quality.This target level becomes the design input for establishingthe industrial ventilation system design parameters. A de-tailed description of the use of target levels of air qualityas a valuable design tool is presented in a Handbook ofIndustrial Ventilation by H.D. Goodfellow and E. Tahti.Details of a case history of the application of target leveland design methodology for paper machine room ventila-tion are also included.

Step 1: Given data

Identify and collect data that are site specific (i.e.,climatic conditions, site elevation, etc.)

Literature search to obtain published ventilation designdata

Step 2: Process description

Understand the industrial process and identifysubprocesses

Identify possible emission sources, occupational areas,effects of environmental parameters on production,needs for enclosure, and ventilation equipment

Divide process in such parts that their inputs andoutputs to the environment can be defined

Step 3: Building layout and structures

Collect properties of building layout, structures andbuilding envelope, and openings

Complete zoning of building based on division of theprocess and building layout

Identify layout requirements and structures requiredfor ventilation systems

Develop isometric of building showing all openings

Step 4: Target-level assessment

Define target levels for indoor (zones) and outdoor(exhaust) conditions based on human risk assessmentand technology

Specific design conditions for which the target levelsfor ventilation system based on reliability, energyconsumption, investment, and life cycle costs, etc.

Step 5: Source description

Identify emission sources by type (chemical andphysical properties)

Complete typical data sheet to be used to develop acatalog of emission sources (Fig. 6) reviewrequirements for heat load calculations



FIGURE 6 Catalog of emission sources data sheet.

Step 6: Local protection

Calculate heat loads from individual sources (seeSection III)

Use emission data or calculation models Calculate total volume of air set in motion Heat and flow balances

Step 7: Local protection

Examine feasibility of local source control Calculate working conditions for different options Compare to target levels of local zone

Step 8: Calculation of total building loads

Calculate total loads (heat, humidity, contaminants)from different subprocesses and building for specificzones of the building

Account for time dependency of emissions Evaluate system performance and establish if target

levels or building layout and structures need to berevised

Step 9: Selection of the system

Select acceptable systems based on target levels Identify feasibility of different options selected Select the most effective ventilation system

Step 10: Selection of equipment

Identify system specifications Select acceptable equipment based on performance

characteristics Equipment recommendations Prepare a technical specification for selected

equipment

Step 11: Detailed design

Calculate dimensioning requirements for selectedsystems

Detailed layout ventilation systems Design control system Consider special issues such as thermal insulation,

condensation risks, fire protection, sound and vibrationdamping, maintenance, etc.

Develop construction and commissioning plan

II. VENTILATION EQUIPMENT

A. BackgroundFor industrial ventilation systems, the major equipmentcomponents are louvers and roof ventilators (gravity orpowered). This equipment should only be purchased af-ter the system design has been completed and propertechnical specifications have been prepared by a quali-fied and experienced ventilation engineer. The technicalspecifications must clearly and concisely communicatethe users requirements or criteria to the bidders. Someimportant guidelines that will assist the engineer in thepreparation of better technical specifications include thefollowing.



1. Do your homework. The engineer preparingspecifications must have an in-depth technicalknowledge of the specified components.

2. Clearly define the scope of work. that is, what isincluded and excluded.

3. Strive for clarity and conciseness. Avoid ambiguousphrases, legalese, and repetition.

4. Discuss your requirements with suppliers first. Whatis available?

5. Define performance criteria and the requiredwarranty. The basis of performance criteria must bewell developed and must include details of testingprocedures.

6. Aim for performance specifications. Avoid highlyrestrictive ones.

7. Do not reinvent the wheel. Modify standardspecifications.

8. Supply pertinent process data, test results,information on operating conditions, and samples ofcontaminants.

9. Be specific. Minimize reference to general standards.10. Attach a technical questionnaire to be completed by

all bidders and used during bid analysis.

B. Louvers

In industrial buildings, the prime purpose of louvers is tocontrol the location and flow of incoming air. Some designguidelines for industrial louvers follow.

1. The velocity of the incoming air must be low enoughto prevent uncomfortable drafts on personnel(0.5 m/sec).

2. Louvers must be located to account for windpatterns.

3. Any openings for louvers must minimize thepenetration of rain or snow.

4. Airflow requirements must be reduced during thewinter.

5. Louvers must be of rugged design and able tooperate in hot, dusty environments as well as underfreezing conditions.

6. Resistance to airflow must be minimized.7. Louver designs must be architecturally pleasing.8. A special screen design may be required to keep out

insects or birds.9. Acoustic treatment may be required.

10. Design must be flexible to accommodate theaddition of heat to the incoming air.

11. Louver elevation must be high enough to avoiddamage from snow removal or other equipment.

12. Louver elevation must be low enough to supply airwithout the occurrence of dead zones.

FIGURE 7 Typical ventilation equipment: (a) louvers, (b) roof gra-vity ventilators, (c) square or rectangular powered roof exhausters.

Louvers are available in a great variety of types, bladeprofiles, materials, and finishes. A typical industrial lou-ver profile is shown in Fig. 7. Louver types can be fixed oroperating, coordinated louvers, or custom special louvers.The operating types can be manual with a push bar springand chain, gear box and shafting, pneumatic, or electric.Louvers come in a wide range of standard materials andfinishes (e.g., galvanized, aluminum) as well as customdesign louvers (e.g., stainless steel). Louvers may be lo-cated in a row around the perimeter of the building or maybe stacked vertically in banks with proper support steel.

In the design of louvers for a ventilation system, thecritical design features involve the air pressure drop at thespecific velocity of the air (either expressed as a face ve-locity or velocity through the free area), as well as theweather penetration at this velocity. The specified air-flow into the building through louvers is established onthe basis of ventilation design calculations. For a specificapplication, the engineer, in consultation with the louversuppliers, can select the type of louver, material of con-struction, blade profile, and actual location of louvers. Forguidance, selection should follow the design guidelineslisted earlier.



With the known flow rate and a recommended louverface velocity, the louver size can be determined. Foreach type of louver, information is available from thelouver supplier that relates pressure drop in millimetersof water to air velocities through the free area of thelouver expressed in meters per second. The percent freearea of the louver can be calculated from informationsupplied by the louver manufacturer. The actual velocityof air through the blades is calculated by dividing theflow rate by the louver free area. For this velocity throughthe blades, the pressure drop can be determined from atypical curve based on test work for the specific louver.The velocity usually selected is about 1.25 m/sec.

C. Roof Ventilators (Gravity or Powered)Roof ventilators are widely used in industrial buildingsand are the workhorses of the industry. Roof ventilatorsare devices designed either to introduce outdoor air intobuildings or to exhaust air from them. Supply systemsmay bring outside air into specific work areas to con-trol the in-plant environment, or they may supply makeupair to balance exhaust requirements. These supply unitsmay be equipped with filters or humidifying sections toproduce cleaned or conditioned air. Some supply unitsmay be designed to recover heat or to add heat by meansof hot water or steam coils to reduce the space-heatingload. The primary function of a roof exhauster is the di-rect exhaust of heat, moisture, and contaminants, such asfume, smoke, noxious gases, or mists, from the workplaceenvironment.

Ventilators may be gravity or powered. Gravity venti-lators depend on thermal driving forces. with the hot airrising and being exhausted through the roof. Power ven-tilators or powered roof ventilators (PRVs) have motor-driven fans. They may be designed to exhaust air, tobring in outdoor air, or to operate in either mode asrequired.

Gravity ventilators are available in many different stylesand materials of construction. Figure 7 shows a typi-cal profile of a gravity ventilator. Gravity ventilators aresometimes referred to as monitors, streamline monitors,or guided-flow or sawtooth roof monitors.

Powered roof ventilators come in three basic configu-rations: round, dome, and square or rectangular. Figure 7shows a schematic of a square or rectangular powered roofexhauster.

For almost all applications. both types of ventilatorsshould be considered at the conceptual stage. A selectionshould only be made after proper technical and economicanalyses have been completed. Some general guidelinesfor selecting either gravity or powered ventilators includethe following.

1. The initial total cost will be much higher for gravityventilators.

2. Operating costs for powered ventilators will be higher(power, maintenance).

3. Community noise is often a problem with poweredroof exhausters.

4. Powered exhausters provide more flexible and bettercontrol. They can be located directly above the hotsource, can operate in an on/off mode or with atwo-speed fan, and can be turned off in winter.

5. A good feature of gravity ventilators is that they areself-regulating. The ventilation rate through a sectionwill increase if the heat release from a source belowincreases.

6. Powered ventilators have higher discharge rates thathelp reduce ground-level concentrations and reducethe effect of wind.

7. Gravity ventilator designs can be used to complementthe architectural features of industrial buildings.

The important design parameter for gravity ventilatorsis the throat area or flow area required for a given flowrate. Exhaust capacities must account for heat, height, andwind factors. It is also known that special building pressureconditions, air supply locations, equipment or structuralobstructions, and the transient nature of heat releases allaffect ventilation rates. For specific conditions, it may benecessary to perform modeling tests or a more rigorouscalculation approach, as described in Section III.

Powered ventilators must be sized to handle the requiredflow at a static pressure by using tables available from theequipment suppliers. In many plants, poor flow conditionsat either the inlet or outlet of the powered roof exhaustershave a very significant effect on the ventilation rate. Ifa ventilation problem exists in a plant with powered roofexhausters, the first step in problem solving should alwaysbe to measure actual flow rates in the field.

III. DESIGN EQUATIONS FORINDUSTRIAL VENTILATION

A. Heat Release CalculationsDetailed calculations can be carried out to establish heatreleases from the different operations within the processbuilding. Heat is released from surfaces by convectiveforces that cause thermal updrafts, thus making up theprimary ventilation flows, and by radiant transfer. Radiantheat that is not ultimately converted into convective heatdoes not affect the primary ventilation flow. This wouldinclude radiant heat that is absorbed by the roof and wallsand subsequently lost to the outside atmosphere. However,



radiant heat absorbed within the building and convertedto convective heat does affect the primary ventilation flowrate. Both the steady and the intermittent heat releases arecalculated. For design purposes, it is recommended that anaverage heat release be established to be somewhat higherthan the steady heat release.

For convective heat losses, the heat release from equip-ment surfaces is calculated with the equation

qc = hc A(Ts Ta)where qc is convective heat loss (kcal/sec), hc the nat-ural convective heat transfer coefficient in kilocalories(kcal/m2 C sec), A the surface area of hot source (m2), Tsthe surface temperature (C), Ta the surrounding air tem-perature (C). The convective heat transfer coefficient hccan be readily estimated from well-established formulasthat can be found in standard heat transfer reference books.

For radiant heat losses, the heat release from equipmentsurfaces is calculated by

qr = F A(T 4s T 4a

)where qr is radiant heat loss (kcal/sec), Stefan-Boltzmann constant (kcal/m2 sec K4), emissivityof substance (blackbody coefficient of the radiatingsurface), F view factor (usually assumed equal to 1),A surface area of hot source (m2), Ts absolute surfacetemperature (K), Ta absolute surrounding air temperature(K). Emissivities for various surfaces are available instandard references.

The total heat release from the equipment surface isthe sum of the convection and the radiation heat losses.The heat loss calculations provide the necessary datafor the ventilation heat balance and total building heatbalance.

B. Air Set-in-Motion CalculationsAir set-in-motion calculations account for major air andfume vertical flows that are produced by the total con-vective portion (may include some radiant heat loss that isconverted to convective heat) of heat release from hot pro-cesses. This hot air is heated by contact with the surfacesof the hot equipment and rises due to thermal buoyancy.The size and velocity of this hot air column is a function ofthe heat release rate and the distance between the sourceand the roof level. The roof ventilators must accommo-date the total flow of hot air delivered to them in order toensure that the hot contaminated air does not recirculateto the lower working areas. It is imperative that the totalvolumes of air set in motion be calculated and comparedto the exhaust rates of roof ventilators.

The heated air stream originating from the surfaces ofhot bodies mixes turbulently with the surrounding air as

it moves upward. An air stream at a hot body source mayhave a flow of 0.5 m3/sec. After some vertical travel, thishot air stream may set in motion, and become mixed with(i.e., entrained in), an additional flow of 50 m3/sec ofsurrounding air. To avoid recirculation, roof ventilatorsshould, as a minimum, accommodate this total flow arriv-ing at the roof level.

The following plume flow rate equations for pointplumes (first equation) and line plumes (second) can beused to calculate air set in motion at different elevations:

Q = (6/5)(18F/5 )1/3z5/3

Q = 2(F/)1/3zwhere Q is the plume flow rate at elevation z (m3/sec)(for a line plume, Q is plume flow rate per unit length ofsource), entrainment constant (point plume 0.093, lineplume 0.156), z vertical distance from plume origin to rooftruss in meters, and F buoyancy flux (m4/s3)

F = qgc/CpT00where q is source heat flux (kcal/sec), gc accelerationdue to gravity (9.81 m/sec2), Cp ambient air specific heat(kcal/kg K), T0 absolute ambient temperature (K), and 0ambient air density (kg/m3).

C. Gravity or Powered VentilationIn a classical technical paper in the ventilation field, pub-lished in 1926, Emswiler defined the concept of a neutralzone or plane of neutral pressure as the elevation withina building at which neither the outside air tends to moveinto the building nor the inside air tends to move out.Emswiler developed two theorems that apply to industrialventilation and form the basis for design.

Theorem 1. The sum of flow rates into the buildingbelow the neutral zone must equal the sum of the flowrates out of the building above the neutral zone.

ni=1

Aivi +n

j=1Q j = 0

where Ai is the area of opening (m2), vi the velocitythrough the opening (m/sec), Q j the powered ventilationflow rates (m3/sec).

Theorem 2. The driving force at each opening is re-lated to the vertical distance between the opening and theneutral zone and the temperature difference between theopening and the neutral zone:

QN = AN

Lnztnz/(RT )where QN is the flow rate (m3/sec), AN the area of theopening (m2), Lnz the distance from center line of the



opening to the neutral zone (m), tnz the temperature dif-ference between the opening and the neutral zone (K), Rthe resistance of the opening, and T the absolute temper-ature of the air at the opening (K).

The resistance of the opening R is given by

R = 1/2gcC2

where gc is acceleration due to gravity (9.81 m/sec2) andC the loss coefficient for the opening. Substituting for Rin the preceding equation, the flow rate is given by

QN = 4.43CAN

Lnztnz/T (m3/sec)For C = 0.65,

QN = (2.88/

T )AN

Lnztnz (m3/sec)Figure 8 shows the plane of neutral pressure for a hot

process building. The elevation of the neutral zone is de-termined by trial and error using the preceding equations.

The temperature rise through a hot process building isa function of the amount of heat released in the buildingand the ventilation flow rate. The heat balance equationcan be written as

t = q/Cp Qwhere t is the temperature rise through the building (C),q the heat release rate (kcal/sec), the air density (kg/m3),Cp the heat capacity of air (kcal/kg C), and Q the venti-lation flow rate (m3/sec).

Baturin has developed four equations that describe theventilation process. These equations can be used to calcu-late air changes in single-span and multispan (commonlycalled multibay) process buildings.

FIGURE 8 The plane of neutral pressure as defined by Emswiler.

The rate at which air flows through an opening of areaA, with a pressure difference P between the pressureindoors and outdoors, is given by

G = CF A

2gcP

where G is the mass flow rate (kg/sec), CF the dischargecoefficient of flow (dimensionless), A the area of the open-ing (m2), gc acceleration due to gravity (9.81 m/sec2), the density of the air in the initial state (kg/m3), and Pthe difference between the inside and the outside pressureat a given opening (kg/m2).

From the continuity equations for the steady state, theamount of air coming into the shop per unit of time (inkilograms per second) is equal to the amount of air leavingthe shop in the same time period. Thus the air balanceequation is given by

G in =

GoutFor the heat balance equation, the quantity of heat re-

moved from the shop must equal the sum of the heatbrought into the shop by the outdoor air plus the surplusheat given off in the shop in the same unit of time.

G = q/[Cp(tout tamb)]where G is the mass flow rate of air leaving the shop(kg/sec), q the quantity of heat removed from the shop(kcal/sec), Cp the heat capacity of air (kcal/kg C), toutthe outlet air temperature (C), tamb the ambient airtemperature (C).

For natural ventilation, wind has a significant effect onbuilding ventilation rates. The effect of wind on a buildingmanifests itself as an increase in pressure on its windwardside and as suction on the leeward size. The pressure at anyarbitrary plane on a building is a magnitude of pressure in



excess of ambient pressure. This ratio is called the pres-sure coefficient and is dimensionless. Experiments haveshown that pressure coefficients remain constant on ge-ometrically similar buildings. Thus, pressure coefficientsfor buildings are found by wind-tunnel tests on geomet-rically similar models. The wind pressures are obtainedby multiplying the pressure coefficient for the points con-cerned by the velocity pressure of the wind as

p = kw(v2 /2gc)where p is the wind pressure (kg/m2), kw the wind pressurecoefficient (dimensionless), the air density (kg/m3), vthe velocity (m/sec), and gc the acceleration due to gravity(9.81 m/sec2).

The preceding equations allow the amount of ventila-tion air required to meet allowable contaminant concen-trations to be determined. The equations also allow theareas of the vents in the walls and roof to be calculated.For systems with mechanical ventilation as well as naturalventilation, the quantity of air that is supplied or removedby mechanical ventilation is written into the air balanceequation on the inlet or outlet side.

D. Dilution VentilationStarting with a fundamental differential material balance,dilution ventilation requirements can be related to the gen-eration and removal rates of a contaminant as

V dCrate of

accumulation

= G dtrate of

generation

Q C dtrate of

removal

where V is the volume of the room or enclosure (m3), C theconcentration of gas or vapor at time t (ppm), G the rateof generation of contaminant (m3/sec), t the time (sec),Q = Q /K the effective rate of ventilation corrected forincomplete mixing (m3/sec), and K the design distributionconstant or mixing factor, allowing for incomplete mixing.

Before solving the dilution ventilation equation for dif-ferent cases, it is important to establish a procedure forestimating K , the mixing factor. Ventilation of contam-inated air in a space would be simple if the outside aircould enter the room in a laminar fashion without turbu-lence and remove the contaminated air in a piston fashion.For this condition, one air change would be required tocompletely remove the contaminated air (K = 1). In prac-tice, however, the introduction of the fresh air results inturbulent mixing with the contaminated air, and after oneair change, the room still contains a dilution mixture offresh and contaminated air. For most industrial ventila-tion applications, K varies from 3 to 10. Factors that mustbe considered by an experienced industrial hygienist orventilation engineer in selecting the K value include

1. Contaminant toxicity2. Location and number of points of generation of

contaminant in the room or work area3. Location of air inlets and outlets4. Duration of the process, operational cycle, and normal

location of workers relative to sources ofcontamination

5. Geometry of enclosures or room6. Reduction in operating efficiency of mechanical air

moving devices7. Seasonal changes in the amount of natural ventilation

The dilution ventilation equation will be solved for thefollowing three cases: (1) case A, rate of contaminant con-centration buildup, (2) case B, maintenance of acceptableconcentrations at steady state, and (3) case C, rate of purg-ing. Figure 9 is a graphical representation of these caseson a plot of concentration versus time.

1. Case A: Rate of ContaminantConcentration Buildup

Rearranging the dilution ventilation equation and integrat-ing,

C2C1

dCG QC =

1V

t2t1

dt

ln(

G QC2G QC1

)= Q

V(t2 t1)

For the case of C1 = 0 at t1 = 0, this can be simplified to

t = VQ ln[ (G QC)

G

]

2. Case B: Maintaining AcceptableConcentrations at Steady State

At steady state, dC = 0 and the preceding equation be-comes

G dt = QC dt

FIGURE 9 Contaminant concentration versus time for differentdilution ventilation conditions.



For a uniform generation rate and a constant concentration

G t2

t1

dt = Q C t2

t1

dt

G(t2 t1) = Q C(t2 t1)

Q = K GC

The preceding equation can be used to calculate theflow rate of uncontaminated dilution air required to re-duce the ambient concentration of a hazardous materialto an acceptable level. For liquid solvents, equations canbe developed based on the steady state to determine theventilation volume requirements for specific weights orvolumes of solvent evaporated. In metric units, the equa-tions are

cubic meters per liter of solvent evaporated

= 24.1 specific gravity of liquid 106 K

molecular weight of liquid TLVcubic meters per kilogram of solvent evaporated

= 24.1 106 K

molecular weight of liquid TLVwhere TLV is the threshold limit value.

3. Case C: Rate of PurgingTo calculate the rate of decrease of concentration of con-taminant over a period of time for the case where a volumeof air is contaminated and the contaminant generation pro-cess ceases (i.e., G dt = 0), the dilution ventilation equa-tion is integrated as C2

C1

dCC

= Q

V

t2t1

dt

ln C2C1

= Q

V(t2 t1)

or

t2 = VQ ln C2C1

For any specific contaminant, the design criteria may bebased on regulated limits, comfort limits, or odor thresh-old concentrations. For many industrial solvents, the moststringent design criterion for a dilution ventilation systemis based on the odor threshold concentration.

Ventilation by displacement is a concept developed andtested in laboratories in Norway and is based on idealunidirectional flow (plug flow). For this situation, as shownin Fig. 10, no short circuiting takes place and the residencetime for the room air is exactly the transit time (idealcase). A stratification takes place between the clean supply

FIGURE 10 Displacement ventilation in workshops.

air and the contaminated air. Systems can be designed toutilize thermal or density stratification to create a tendencyto unidirectional flow, that is, to create displacement flow.

The benefits of displacement flow are that it improvesthe air renewal and contaminant removal speed and thatit assists in maintaining favorable concentration gradientsof the contaminants generated in the room. Calculationprocedures based on mathematical two-zone models havebeen established.

IV. VENTILATION MODELINGUSING COMPUTERS

A mathematical model for building ventilation has beendeveloped based on modifying Baturins four ventilationequations. Except for the simplest cases, the solution pro-cedure is iterative. For a building with many ventila-tion openings, the calculation procedure can become verytime-consuming. Computer programs are available thatcan be applied for solving industrial ventilation problems.Figure 11, a flow diagram of the computer ventilationmodel, shows a typical input, the initialization and iter-ation loop, and the output. Further details are available inthe book by Goodfellow, Advanced Design of VentilationSystems for Contaminant Control.

The computer model has been verified by using datafrom six independent surveys. Five of the surveys werecarried out on three different days in a three-aisle processbuilding approximately 275 m in length. The sixth sur-vey was conducted in a multiple-aisle, high-production,BOF ingot teeming building with several hundred buildingopenings. Results of the verification are shown in Table II.

With prevailing winds accounted for, the predicted andmeasured results are all within 20% of each other. Table IIalso gives the calculated flow rates for the no-wind condi-tion. Results for calm conditions underestimate the totalflow rate by 1520%. The agreement between predictedmodel flows and measured flows for individual openings



FIGURE 11 Computer ventilation model flow diagram.

has also been studied. Scatter of individual points doesoccur because of wind gustiness during measurement,nonuniform distribution of heat sources, and pressure dis-turbances due to local building features. However, theoverall agreement is shown to be good.

Once correct modeling of observed ventilation flowrates is established, the computer program can be usedto study the effects of different atmospheric conditions(summer/winter, wind direction and speed, etc.) on theventilation characteristics for the shop. It is also a very



TABLE II Verification of Ventilation Computer Model

Wind Model total flowHeat MeasuredSurvey Speed release total flow Wind No windnumber Direction (km/hr) (Mcal/sec) (m3/sec) (m3/sec) (m3/sec)

1 NNE 2.7 1.5 260 285 2822 S 9.0 2.7 429 364 3343 S 12.0 2.4 331 371 3264 NNE 3.6 2.0 364 310 3055 NNE 15.5 2.9 492 397 3446 NE 16.2 20.0 5660 5190 4300

useful tool in the evaluation of proposed ventilation im-provement schemes. Different ventilation schemes can beanalyzed, and cost-effective solutions developed and im-plemented to solve the ventilation problems.

From the preceding discussions, it is apparent that thecomputer ventilation model can reliably predict the grossventilation rates for complex process buildings. The use ofhigh-speed computers provides the designer with the ca-pability of examining the impact of architectural changes,wind conditions, or process changes on the performanceof the proposed ventilation scheme. Problems such as con-tamination due to cross drafts or high temperatures in thework environment can be identified quickly and correctivemeasures taken.

The limitations of computer modeling are apparent assoon as predictions are required on the microenvironmentsinside the building. The steady-state and intermittent recy-cle flows caused by process or other heat releases conveycontaminants from one area to another. These details ofthe internal flow fields are required by the designer to en-sure an acceptable work environment for a new facilityor to improve the work environment in an existing facil-ity. Typical ventilation questions that may arise duringthe planning and design of ventilation systems includethese.

1. What are the internal flow patterns under differentlayout and operating conditions?

2. What are the effects of intermittent peak heat releaseson ventilation flow characteristics?

3. Can the flow fields be represented satisfactorily as atwo-dimensional flow?

4. What happens to contaminated plume that misses ahood?

5. What effect do cross drafts have on the workplaceenvironment?

6. Where does the fresh air enter the building?7. What are the predicted contaminant concentrations in

the breathing zone?8. What is the source of contamination in a specific area?

For more complex ventilation and contaminant control,computational fluid dynamics (CFD) can be used. Gov-erning equations similar to the ones presented earlier canbe developed for the three-dimensional non-steady-statecase. These equations represent the laws of conservationof mass, momentum, energy, and related entities, and theirindependent variables are allowed to vary in 1, 2, or 3 spacedimensions and in time. The advent of high speed com-puters and the creation of general computer code systemsallow the practical development of solutions to the type ofinternal flow questions listed above.

A number of items have been identified requiring furtherstudy in order to increase reliability of CFD simulationsin large industrial premises. These are

Identifying a turbulence model that provides asufficient degree of reliability in the prediction of lowReynolds number regimes, near wall effects, andrecirculating flows

Understanding the relative importance of long andshort wave radiation in an industrial setting todetermine if a long-wave radiation can be omitted fromsimulations

Identifying heat transfer correlations for natural,forced, and mixed convection that accurately predictthe heat transfer off a surface

Testing methods to provide for jets from diffusers in aventilated room in order to accurately model thepenetration length without resorting to fine grids

Identifying the role of magnitude of the effect thatpotential errors in boundary condition specificationmight play on the final solution.

A technique that is well developed for quantifying in-ternal flow fields is the use of fluid dynamic models. Usinga small-scale replica of the building and the proper lawsof similarity, the actual flow rates and velocities for thefull-scale building can be predicted from measurementsof the small-scale replica. The fluid dynamic modelingapproach is described in Section V.



V. VENTILATION MODELING USINGFLUID DYNAMICS

The technique of small-scale modeling for fluid flowproblems (i.e., fluid dynamic modeling) has been usedextensively for a wide variety of industrial ventilationapplications. The application of fluid dynamic modelshas the advantage of enabling numerous different testconditions to be examined. The costs for performingmodeling tests are usually much less than the cost forperforming a full-scale field test. A typical range of costsfor modeling studies is $20,000$100,000, dependingon the scope and complexity of the model and testingmethodology. For new facilities, the designer does nothave the option of field testing. Hence, fluid modelscan provide useful design data at the conceptual andpreliminary engineering stages of a project.

The applications of fluid dynamic modeling techniquesinclude the following:

1. External flow fields (e.g., to model pressuredistribution, uncontrolled building emissions, stackdischarge)

2. Internal flow fields (e.g., to model movement of largeair masses far from enclosing walls, flow from onebay to another, flow around obstacles such as cranes)

3. Individual sources of heat and contaminants (e.g., toestablish minimum capture volume for sources).

The general theory behind the use of scale models iswell covered in numerous textbooks on fluid mechanicsand in the technical literature. Therefore, only an outlineof the approach used in fluid modeling for ventilation ap-plications follows.

Data measured in the model flow may be related quan-titatively to the full-scale prototype flow by establishingdynamic similarity between the model and the prototype.The two conditions necessary to establish dynamic sim-ilarity are (1) exact geometric similarity, which requiresthat the linear dimensions of the model are in the sameproportion as the corresponding dimensions of the proto-type, and (2) kinematic similarity which requires that theflow regimes be the same for model and prototype.

Kinematic similarity is achieved by matching govern-ing dimensionless groups that describe the flow regime.For modeling ventilation systems, the governing dimen-sionless groups for scaling model (m) to prototype (p)are the Reynolds number and the Froude number. TheReynolds number similarity criterion is not a critical scal-ing parameter because prototype flows are almost alwaysfully turbulent due to large Reynolds number. Flow pat-terns are similar in the different geometric scales as longas the important flow fields are fully turbulent. Therefore,

the Reynolds number similarity criterion is met by ensur-ing that the flow in the model is fully turbulent. For pro-cesses involving hot gases (i.e., buoyancy-driving forces),the Froude number similarity criterion can be applied tothe model and the prototype.

The flow required in the prototype is given by

Qp = Qm(S)5/3(qp/qm)1/3

where Q is the volumetric flow rate (cubic meters persecond), q the heat flow rate (kilocalories per second), Sthe model scale (e.g., for a 1: 10 scale model, S = 10), pthe subscript identifying prototype parameter, and m thesubscript identifying model parameter.

Figure 12 is a typical flow chart of activities required fora ventilation modeling study. The first step is to define thecontaminant and the source characteristics. Parameters tobe defined are the size of the process building and detailsof the source flux (i.e., heat and contaminant release rates,etc.). Information is required on the major sources of heatin order to calculate heat balances and volumes of air set

FIGURE 12 Typical flow chart for ventilation modeling study.



in motion. Data are required on the external and internalflow conditions for the prototype. Information may be re-quired on site conditions such as wind, speed, direction,and frequency.

The design of the model system requires an examinationof the scaling parameters and the type of fluid medium tobe used. The common fluids used are air or water, but theworking or buoyancy-driven fluids for models can varywidely. Fluid systems that have been used include air andheated air, water and saltwater, water and carbon tetrachlo-ride, and mercury and carbon tetrachloride. Air models areusually the simplest and least expensive models to buildand test. The use of air may require a large model to ensurefully turbulent flow. Because water has a smaller kinematicviscosity than air, a smaller model is required to ensurea high Reynolds number and turbulent flow. Flow visu-alization is also easier with water-based models becausevelocities are lower than in air. A detailed analysis of thescaling parameters and possible fluid systems is requiredin order to select the best modeling technique for the spe-cific ventilation problem. The measuring technique for thecontaminant of concern must also be considered since itmay have a significant impact on the level of accuracy andthe cost of the testing program.

Testing programs for many modeling studies are briefcompared to the time required to design and construct themodel system. For example, it is not uncommon to require810 weeks to design and construct a model. 12 weeksto commission and calibrate the model, and 12 days toperform actual tests and develop solutions for the venti-lation problem. For any model testing program, extensiveuse should be made of photographic and video recordingequipment. The photographs and films will be invaluablein analyzing the test results and for subsequent presenta-tion of solutions to management.

The fluid dynamic modeling technique is a cost-effective, flexible, and powerful tool for the design ofventilation systems for a greenfield plant and for the elim-ination of ventilation problems in existing plants. Someof the applications of scale modeling include

1. Finalizing building ventilation rates and schemes2. Examining internal flow patterns and contaminant

concentrations at any location3. Examining external flow patterns, including

quantitative measurements of downwash andtransport of contaminants to other buildings

4. Establishing the effectiveness of source hoods.

For new process buildings, the recommended sequenceis to use the mathematical models and equations to de-velop the overall ventilation concepts and architecturalconstraints. At this stage, the project design team can

continue with the design of the structural steel while thesmall-scale model is being constructed and tested. Theresults of the small-scale modeling are used to refine theventilation concept and to finalize all requirements.

For an existing plant, the fluid dynamic model is a valu-able tool in modeling the problem and developing alter-native cost-effective solutions.

VI. SOLVING VENTILATION PROBLEMSFOR EXISTING PLANTS

Ventilation flows and design parameters are unique foreach specific process building. For most complex ventila-tion problems, it is recommended that both analytical cal-culations and a field measurement program be carried out

TABLE III Major Activities for a Ventilation Field TestingProgram

Activity Specific items

1. Information gathering Obtain drawings, reports, operatingprocedures

Define problem (summer, winter,heat, supply, exhaust)

Review existing data and studiesVisit site

2. Data on ventilation Isometric drawings: plans, sectionsopenings Schedule of openings

3. Plant questionnaire Identifies factors specific for eachplant

Identifies significant heat sourcesin building

Identifies typical operating practiceIdentifies gaps in data to be filled

in by field testing program4. Develop details of field General considerations

testing program Building ventilationIn-plant flowsField data log sheets for ventilation

measurements, weather conditions,plant operating records

5. Field testing program Field measurements (volume,temperature, etc.)

6. Plant ventilation flow Summary table of flowsbalance and in-plant Sketches to show in-plant flowsflow patterns

7. Meltshop heat balance Total plant heat balance calculationVentilation heat balance calculation

8. Volumes of air set in Based on surface temperature andmotion convective heat release

9. Computer simulation of Calibrate using field test dataventilation flows(natural ventilation)

10. Field testing report Summarize test conditions and testresults



in order to develop a sound, cost-effective solution to theventilation problem. Experience has shown that the fieldsampling program must be developed in detail and mustbe tailormade for each specific ventilation problem. How-ever, there are many elements of the field testing programthat are common for any problem. Although there may beminor variations for any specific ventilation project, the 10activities listed in Table III represent the major activitiesfor a field testing program and the sequence for perform-ing this work. A brief description of the scope of workrequired for each activity is included.

As a starting point, for the field testing program, obtainall pertinent reports and drawings on the plant for reviewand study. Specific information is required on the currentoperating practice, as well as information on the natureof the in-plant dust and heat stress problems. A visit to

FIGURE 13 Walk-through ventilation survey data sheet.

the site should include a walk-through ventilation surveyusing a data sheet as shown in Fig. 13.

It is necessary to develop the details of a field testingprogram and all necessary field data log sheets prior tothe actual field testing. The development of a proper fieldtesting program is the most important step in ensuring asuccessful ventilation study. This program should be re-viewed and approved by plant operating personnel prior tocommencement. Because the ventilation flow in large pro-cess buildings is usually complex, an inexperienced sam-pling team will often collect insufficient data for subse-quent analytical calculations or will spend a considerableamount of effort collecting field data that are irrelevant. Agood approach is to perform preliminary calculations onall sources and then to clearly identify where informationgaps exist and what essential data must be collected.



The measurement of air velocities through all the open-ings must recognize the need to have a representativevelocity for the survey. It is not acceptable to be on thesafe side by rounding readings to a higher value. Gustywind conditions will cause velocity readings to fluctuate.Sufficient time must be allowed to elapse to enable theindividual monitoring the instrument to arrive at a repre-sentative velocity by integrating the observed values inhis or her mind.

A temperature measurement is required for each veloc-ity measurement. For air entering the building, this wouldgenerally be the ambient temperature. The ambient tem-perature should be recorded on an hourly basis. It willchange during the course of the day and could be higherin the wake of the building. Do not expose the thermome-ter or temperature probe to sunlight or radiant heat fromhot objects. The temperature of air leaving the meltshopwill vary considerably. For heat balance calculations, goodtemperature readings are important.

Temperatures associated with in-plant flow patternsmust also be recorded. Sufficient temperature data must beavailable to allow evaluation of the air density distributionwithin the shop.

Mean surface temperatures of hot surfaces must berecorded for subsequent heat release and air-set-in-motioncalculations. The location of the equipment on the floorplan and equipment surface temperature should be reco-rded on a separate sheet.

Weather data should be measured at the site and ob-tained from the nearest airport or meteorological stationas well. Data to be recorded include ambient temperature,relative humidity, and wind speed and direction. Duringthe test period, this information should be recorded on atleast an hourly basis.

A record of plant activities during the testing programis required. Data to be included are the status of operationof all major process and environmental equipment, as wellas production levels.

An in-plant survey will be required to establish param-eters such as dust levels and heat stress. These measure-ments would be concurrent with the ventilation survey.An industrial hygienist would work with the ventilationengineer to establish the scope and extent of the industrialhygiene sampling program.

For any ventilation field testing program, it is essen-tial to prepare a proper engineering report, which includesall the field data, calculations, and test results. Using the

FIGURE 14

results of this field testing program, an experienced ven-tilation engineer can develop cost-effective solutions forany plant ventilation problem.

Computer models based on computational fluid dynam-ics (CFD) can be used to predict the velocity vectors andconcentration of contaminants as a function of positionand time. Figure 14 shows an industrial CFD case studywith momentum sources. For this case, outputs from theCFD program can be used to establish airflow patterns forsummer and winter conditions and for different processoperating scenarios. Data from the computer models canbe validated from the field measurement program.

SEE ALSO THE FOLLOWING ARTICLES

ENERGY FLOWS IN ECOLOGY AND IN THE ECONOMY ENVIRONMENTAL TOXICOLOGY FLUID DYNAMICS(CHEMICAL ENGINEERING) HEAT TRANSFER MACHINEDESIGN POLLUTION, AIR

BIBLIOGRAPHY

American Conference of Government Industrial Hygienists (1998). In-dustrial Ventilation: A Manual of Recommended Practice, 23rd ed.,ACGIH, Cincinnati, Ohio.

Baturin, V. V. (1972). Fundamentals of Industrial Ventilation, 3rd ed.,Pergamon, London, U.K.

Goodfellow, H. D. (1985). Advanced Design of Ventilation Systems forContaminant Control, Elsevier, Amsterdam.

Heinsohn, R. J. (1990). Industrial Ventilation: Engineering Principles,John Wiley & Sons, New York.

Goodfellow, H. D., and Tahti, E. (2000). Handbook of Industrial AirTechnology (DGB), Academic Press, San Diego.

Ventilation, IndustrialGlossaryVentilation Design MethodologyBackgroundDesign MethodologyTarget Levels

Ventilation EquipmentBackgroundLouversRoof Ventilators (Gravity or Powered)

Design Equations for Industrial VentilationHeat Release CalculationsAir Set-in-Motion CalculationsGravity or Powered VentilationDilution Ventilation

Ventilation Modeling using ComputersVentilation Modeling using Fluid DynamicsSee also the Following ArticlesReferences

industrial ventilation cap

Documents