34;Cap" has not been an active member of the Committee for the past eleven years, his presence has been felt at almost every meeting. Occupational Health, Michigan Department of Health, for the contribution of their original field manual which forms the basis of the First Edition was , and to mr.
Previous Members
Density: The ratio of the mass of a sample of a substance to the volume of the sample. Gravity, specifically: The ratio of the mass of a unit volume of a substance to the mass of the same volume of a standard substance at a standard temperature.
GENERAL PRINCIPLES OF VENTILATION
- ACCELERATION OF AIR AND HOOD ENTRY
- AIR FLOW CHARACTERISTICS OF BLOWING
- INTRODUCTION
- SUPPLY SYSTEMS
- EXHAUST SYSTEMS
- BASIC DEFINITIONS
- PRINCIPLES OF AIR FLOW
SP can be positive or negative relative to the local atmospheric pressure, but must be measured perpendicular to the air flow. Velocity pressure (VP) is defined as the pressure required to accelerate air from zero velocity to a certain velocity (V) and is proportional to the kinetic energy of the airflow.
ATMOS'PHE'R1C
- ACCELERATION OF AIR AND HOOD ENTRY LOSSES
- DUCT LOSSES
- MULTIPLE-HOOD EXHAUST SYSTEMS
- AIR FLOW CHARACTERISTICS OF BLOWING AND EXHAUSTING
This equation gives the friction losses, expressed as "wg per 100 feet of pipe, for standard air with a density of 0.075 Ibm/ftl flowing through an average, clean, circular galvanized pipe with approximately 40 slip joints per 100 feet (k = 0.0005 ft ) The later work of Loeffler(l4) presented equations for use in the "velocity pressure" calculation method. Because the static pressure at the end of the duct must be atmospheric (SPs = 0), the energy principle results in
![FIGURE 1~5, Variation of SP, VP, and TP through a ventilation system [1.7]](https://thumb-ap.123doks.com/thumbv2/123dok/10803389.0/24.918.178.674.108.807/figure-1-5-variation-sp-vp-tp-ventilation.webp)
GENERAL INDUSTRIAL VENTILATION
- ADAPTIVE MECHANISM OF THE BODY
- ACUTEHEATDISORDERS .1 Heat Stroke
- ASSESSMENT OF HEAT STRESS AND I-IEAT STRAIN
- VENTILATION SYSTEMS . 2.16 VELOCITY COOUNG
- PROTECTIVE SUITS FOR SHORT EXPOSURES 2.19 RESPIRATORY HEAT EXCHANGERS
- REFRIGERATED SUITS 2.21 ENCLOSURES
- INSULATION REFERENCES
- INTRODUCTION
- DILUTION VENTILATION PRINCIPLES
- DILUTION VENTILATION FOR HEALTH
Dilution ventilation systems typically process large volumes of air using low-pressure fans. The values in the table must be multiplied by the evaporation rate (pts/min) to obtain the effective ventilation rate (Q') (see equation 2.5).
34;K)}Z;'A CTORS
SUGCESTED FOR INLET
AND EXHAUST LOCATIONS
- MIXTURES-DILUTION VENTILATION FOR HEALTH In many cases, the evaporating liquid for which dilution
- FIRE DILUTION VENTILATION FOR MIXTURES It is common practice to regard the entire mixture as
- VENTILATION FOR HEAT CONTROL
- HEAT BALANCE AND EXCHANGE
- ACUTE HEAT DISORDERS
- ASSESSMENT OF HEAT STRESS AND HEAT STRAIN
- WORKER PROTECTION
- VENTILATION CONTROL
- VENTILATION SYSTEMS
- VELOCITY COOLING
- RADIANT HEAT CONTROL
- PROTECTIVE SUITS FOR SHORT EXPOSURES For brief exposures to very high temperatures, insulated
- RESPIRATORY HEAT EXCHANGERS
- REFRIGERATED SUITS
- ENCLOSURES
- INSULATION
In the absence of information to the contrary, the effects of the various hazards should be considered additive. The rate and amount of heat exchange is governed by the basic laws of thermodynamics of heat exchange between objects.
LOCAL EXHAUST HOODS
- INTRODUCTION
- CONTAMINANT CHARACTERISTICS
- HOOD TYPES
- HOOD DESIGN FACTORS
The hood's primary function is to create an air flow field which effectively captures the pollution and transports it into the hood. However, if the pollution contains large particles which are emitted at a significant speed, the hood should be placed in the path of the emission.
CON EENCF
AME:F{ICAN CONF'ERENCE;
LJDe 10
The design of the slot and plenum is such that the pressure loss through the slot is high compared to the pressure loss through the plenum. Thus, all portions of the slot are subjected to essentially equal suction and the slot velocity will be essentially uniform.
FREELY SUSPENDED HOOD
SUSPENDED HOODS
INDUSTHIAL BYG IENISTS DATE
F'LOW/C'AP /
AMERICAN CONFERENCE OF GOVERNMENTAL
INDUSTRIAL HYGIENISTS DATE
HOOD TYPES
4- 96 FIGURE 3-11
DISTRIBUTION BY SLOT RE:S[S'TANC
HOOD LOSSES
The hood entry loss (he) can therefore be expressed in terms of hood loss coefficients (Ff) which, multiplied by the slot or duct velocity pressure (VP), will give the entry loss (he) in inches of water. The hood entry loss represents the energy needed to overcome the losses due to air moving through and into the duct.
INDUSTHIAL HYG NISTS
NOO]) LOS
- MINIMUM DUCT VELOCITY
- SPECIAL HOOD REQUIREMENTS
- PUSH-PULL VENTILATION
- HOT PROCESSES
The opening height of the hood should be the same as the width of the extended beam, if possible. VI = the velocity of the hot air column at the hood, fpm As = area of the heat source, ft2.
AIR CLEANING DEVICES
INTRODUCTION
The degree of removal required, the amount and characteristics of the contaminant to be removed, and the conditions of the air or gas flow will all influence the device selected for a particular application. Air filters are designed to remove low dust concentrations of the magnitude found in atmospheric air.
SELECTION OF DUST COLLECTION EQUIPMENT Dust collection equipment is available in numerous designs
One of the main economies of unit collectors is recycling, for which such equipment may not be suitable. It should be remembered that the visibility of an effluent will be a function of the light-reflecting surface of the effluent material.
DUST COLLECTOR TYPES
An electrostatic precipitator, for example, may be a better choice for a significant initial cost penalty because of the energy savings through its substantially lower pressure drop. Packing and overflow of dry materials in dust pits, floating or sludge-forming characteristics in wet collectors are examples of problems that may be encountered.
DRY TYPE DUST COLLECTORS DUST DISPOSAL
SLIDE GATE
DUST GATE
DRY TYPE DUST COLLECTORS DISCHARGE VALVES
The curtain is held closed by differential pressure until the collected material has built up sufficient height to overcome the pressure.
DOUBU~ DUMP VALVE
DRY TYPE DUST COLLE'CTORS DISCHARGE VAL VES
ELECTROSTATIC PRECIPITATOR HIGH VOLTAGE DESIGN
AMEHICAN CONFEHENCE OF GOVEHNMENTAL
INDUSTHIAL HYG IENISTS DATE
ELECTROSTATIC PRECIPITATOR ,LOW VOLTAGE DESlGN
The efficiency of the cloth as a filter only has significance when the new cloth is put into use for the first time. The combination of dust and collected dust becomes increasingly efficient as the dust cake accumulates on the surface of the fabric.
AMEHICAN CONFEHENCE OF GOVEENMENTAL
INDUSTHIAL HYGIENISTS DATE
PERFORMANCE VS TIME BETWEEN RECONDITIONINGS
FABRIC COLLECTORS 1-88 FIGURE 4-6
Periodically (usually at 3- to 6-hour intervals) the air flow must be stopped to re-condition the fabric. All models collect dust on the outside and have air flow from the outside to the inside of the fabric.
INDUSTRIAL HYG IENISTS DATE
FABRIC COLLECTORS 1-88 FIGURE 4-7
AIR FLOW THROUGH FABRIC COLLECTORS
FABRIC COLLECTORS PULSE JET TYPE
1-88 FIGURE 4-9
EPA-sponsored research(43) has shown that superior performance results from downflow of the contaminated air stream. The flow of water can be driven by the velocity of the air stream or maintained by pumps and channels.
WET TYPE' COLLECTOR
F'OR GASEOUS CONTAMINANT)
WET CENTHIFUGAL
VENTURI SCRUBBER
WET TYPE DUST COLLECTORS (FOR PARTICULATE
CONTAMINANTS)
1-88 FIGURE 4-11
COLLECTING ELEMENTS
TYPICAL WET ORIFICE TYPE COLLECTOR
WET TYPE DUST COLLECTOR (FOR PARTICULATE
1-88 FIGURE 4-12
ADDITIONAL AIDS IN DUST COLLECTOR SELECTION The collection efficiencies of the five basic groups of air
Example: A suitable collector will be selected for a lime kiln to illustrate the use of the scheme. A vertical line from the intersection of the 2.25 grains per cubic feet horizontally and the deviation line to the bottom of the chart will indicate an average wastewater particle size of 6.0 microns.
CONTROL OF MIST, GAS, AND VAPOR CONTAMINANTS
Referring to Figure 4- I 4, the concentration and average particle size of the material leaving the furnace can vary between 3 and 10 grains per cubic foot, with a 5-10 micron range for the mass average particle size. Using the previous deviation line and its horizontal intersection of 0.045 grains per cubic foot gives a vertical line that intersects the average particle size plot at 1.6 microns, the average particle size of the collector wet stream.
LOW PHESSUHE CYCLONE
HIGH EFFICIENCY CENTHIFUGALS
DRY TYPE
CENTRIFUGAL COLLECTORS
RANGE OF PARTICLE SIZE AMERICAN CONFERENCE
OF GOVERNMENTAL
1-88 FIGURE 4-14
- GASEOUS CONTAMINANT COLLECTORS
- UNIT COLLECTORS
- DUST COLLECTING EQUIPMENT COST
- Notew Collector Collector Collector static static Remark No
- SELECTION OF AIR FILTRATION EQUIPMENT Air filtration equipment is available in a wide variety of
In most applications, cleaned air is recirculated, although exhaust ducts can be used if the additional resistance is within the capability of the air eliminator. Recirculation water pumps and/or settling tanks may be required, but not included in the equipment price.
UNIT COLLECTOR (FABRIC-SHAKER TYPE)
COST ESTIMATES OF
DUST COLLECTING EQUIPMENT
- RADIOACTIVE AND HIGH TOXICITY OPERATIONS There are three major requirements for air cleaning equipment
- EXPLOSION VENTING
The contact does not depend on inertia and the particle is retained on the fiber due to the inherent adhesive forces that exist between the particle and the fiber. High efficiency is essential due to the extremely low tolerances for the amount and concentration of the waste water from the stack and the high cost of the materials handled.
This effectively limits the maximum pressure rise to less than the burst pressure of the vessel. In order to select the most reliable, economical and effective means of explosion control, an assessment of the specifics of the exhaust system and the degree of protection required is necessary.
EXHAUST SYSTEM DESIGN PROCEDURE
- DIFFERENT DUCT MATERIAL FRICTION
- FRICTION LOSS FOR NON-CIRCULAR DUCTS .5-13 5.13 CORRECTIONS FOR NONSTANDARD DENSITY 5-15
- CONSTRUCTION GUIDELINES FOR LOCAL
- INTRODUCTION
- PRELIMINARY STEPS
- DESIGN PROCEDURE
- DUCT SEGMENT CALCULATIONS
- DISTRIBUTION OF AIR FLOW
Determine the channel area by dividing the design flow rate by the minimum channel velocity. Multiply the designed duct length by the loss coefficient from the tabulated data of Tables 5-5 or 5-6 (lines 23 through 25.) Use of galvanized sheet duct was assumed throughout this chapter.
HOOD NO
VELOCITY PRESSURE METHOD CALCULATION SHEET
TAPERED DUCT SYSTEM
EXTENDED PLENUM SYSTEM
CONVENTIONAL SYSTEM
Sell cleaning rn,Wl
Hopper duel - with pncurnaLic cleaning
- AIDS TO CALCULATIONS
- PLENUM EXHAUST SYSTEMS
- FAN PRESSURE CALCULATIONS
- CORRECTIONS FOR VELOCITY CHANGES
- SAMPLE SYSTEM DESIGN
- DIFFERENT DUCT MATERIAL FRICTION LOSSES The friction loss table, Table 5-5, provides average values
- FRICTION LOSS FOR NON-CIRCULAR DUCTS Round ducts are preferred for industrial exhaust systems
- CORRECTIONS FOR NONSTANDARD DENSITY Fan tables and exhaust flow rate requirements assume a
An increase or decrease in static pressure would correspond exactly to a decrease or increase in air velocity pressure. This is equal to -4.2 SP because the static pressure on the suction side of the fan is always negative.
PROBLEM 2
1-88 FIGURE 5-8
AIR CLEANING EQUIPMENT
Each exhaust system handling such materials should be provided with a suitable air cleaner as described in Chapter 4. As a general rule, the exhaust fan should be located on the clean air side of such equipment.
EVASE DISCHARGE
Most important is the air pattern as it passes through the building. According to Wilson (5.6), the boundary of the zone of high turbulence (Z2) follows the slope I: I 0 down from the top of the recirculation cavity.
AIR BLEED-INS
CONSTRUCTION GUIDELINES FOR LOCAL EXHAUST SYSTEMS
Unless flanges are used for connections, the duct must be supported near each connection, usually within 2 inches. A straight duct section of at least six equivalent duct diameters should be used when connecting to a fan (see Figure 5-27).
HOOD ENTRY
A composite hood, such as the slot/plenum shown at right, will have 2 losses, one through the slot and the other through the transition to the duct.
LOSS COEEFICIENTS
1-95 IFIGURE 5-13
INDUSTRJAL YGIEN 'TS DATE
UI1ANC,1 EINTR.Y LOSS
OF' GO VEHNMENTAL,
In :::oieolo SF) for expansion or ethroction use ol:jeiJraic W) (+), (mel lIsliolly SP is In discharge channel of fon, and SP is.
AMEHICA CONFERENCE
The typical sheet metal fabricator has patterns for channels in 0.5 inch increments up to 5.5 inches in diameter; 1 inch increments from 6 inches through 20 inches and 2 inch increments from 22 inches and larger diameters.
PSYCHROMETRIC CHART
AVOID ASPECT HATIO (n)
INDUS']" TAL HYGIENISTS
PRINCIPLE'S OF' DUCT' DE'SIGN E'LBOWS
AN CONFERENCE OVE MENTAL
SUDE
PUL OUT CAP
DUCT ENLARGEMENTS
DUCT CONTRACTIONS
SYMMETRICAL WYES
PREFERRED
AVOID
AMERICAN CONFERENCE
PRINCIPLES OF DUCT DESIGN OF GOVERNMENTAL
INDUSTRIAL HYGIENISTS DATE 1-95 FIGURE 5-25
P F'EHHED ACCEPTABLE BHANCF[ EN'I'HY
AMERIC AN CONFERENCE OF GOVERNMEN'TAL
AIRFLOW AROUND BUILDINGS
EFFECTIVE STACK HEIGHT AND WAKE DOWNWASH
4-94 FIGURE 5-29
OFFSET STACK
STACKHEAD
WEATHER CAP
INOT RECOMMENOEOI
STACKHEAD DESIGNS 1-95 FIGURE 5-30
FANS
INTRODUCTION
However, most systems require some powered drive device, such as a fan or an ejector. Selecting an air handling device can be a complex task and the specifier is encouraged to take advantage of all information available from applicable trade associations as well as individual manufacturers.
BASIC DEFINITIONS
Moving air in a ventilation or exhaust system requires energy to overcome system losses. This chapter describes the various air-moving devices used in industrial applications, provides guidelines for selecting the air-moving device for a particular situation, and discusses the proper installation of the air-moving device into the system to achieve the desired performance.
INDUST'RIAL BYG IENISTS DATE
EJE'CT01?S
TERMINOLOGY FOR AXIAL AND TUBULAR CENTRIFUGAL
Reprinted~ from AMCA Publication 201-90, FANS AND SYSTEMS, by permission of the Air Movement and Control Association, Inc.(6.1). Reprinted from AM~A Publication 201-90, FANS AND SYSTEMS, by permission of the Air Movement and Control Association, Inc.(6.1).
TERMINOLOGY FOR CENTRIFUGAL FAN
COMPONENTS
5-92 FIGURE 6-3
FAN SELECTION
Guide rods correct the circular motion imparted to the air by the wheel and improve the pressure characteristics and efficiency of the fan. On larger units, the motor is mounted separately and connected directly to the fan or indirectly through a belt drive.
DRIVE ARRANGEMENTS FOR CENTRIFUGAL
8 SWSI For belt drive or direct connection Arrangement 1 plus extended base for drive motor. 3 SWSI For belt drive or direct connection One bearing on each side and supported by a fan housing.
AMERICAN CONFERENCE OF GOVEHNMENTAL
DRIVE ARRANCEMEWT~C;F'OR
Drive loss is based on the conventional V-belt, which has been the "workhorse" of the drive industry for several decades. Reprinted from AMCA Publication 203-90, FIELD PERFORMANCE MEASUREMENT OF FAN SYSTEMS, by permission of Air Movement and Control Association, Inc.(P.1).
AMERICAN CONFERENCE ESTIMATED BELT OF GOVERNMENTAL DRIVE LOSS
HJGHER BELT SPEEDS TEND TO HAVE HIGHER LOSSES THAN LOWER BELT SPEEDS FOR THE SAME HORSEPOWER.
INDUSTRIAL HYGIENISTS DATE 5-92 FIGURE 6-6
RPM 1 P1
Since these expressions involve relationships between the variables, any appropriate units may be used as long as they are consistent. Size can be represented by any linear dimension, since all must be proportional in homologous series.
ACT[JAL
Care must be taken to apply laws between the same relative points of assessment. So enter the table with the actual volumetric flow at the fan inlet, 1000 acfm and FSP 4 "wg.
PWR =PWR (~)=4.39(0.0375)
FAN INSTALLATION AND MAINTENANCE
LLEL
AMEHICAN CONFERENCE
OF' GO VEENMENTAL
This can result in damage or failure of the fan impeller, housing, bearings or pedestal. The power supply must be shut off and locked in a disconnect near the fan.
