1. INDUSTRIAL VENTILATION
by
Dr. N.C. Srivastava
1.0 Objectives:
Control of -
Heat and local discomforts
Odours
Hazardous contaminants (dust particles, toxic gases, smoke and fumes etc.)
to achieve - Better health and safety of workers
Increase in work efficiency and production
2.0 Principles:
1. Heat and contaminants should be exhausted at source for better control.
2. Ventilation can be a natural draft or a mechanical system or a combination of both.
A mechanical supply and exhaust system provides best control. It includes
- Inlet/outlet sections
- filters, cooling and heating equipment in supply system
- filters and contaminants eliminating devices in exhaust system
- fan sections
- supply/exhaust duct work
- air distribution terminals
3. Care that neighbourhood (including all living beings, agricultural crop, buildings etc.) are not
adversely affected by exhausted air.
3.0 Control Measures:
3.1. Heat Control
hot-dry areas (heat load on the worker is sensible or radiant; rate of cooling
by evaporation of sweat is not reduced)
warm-moist areas (a wet process giv6s latent heat and increases moisture
content results in serious reduction in heat loss by evaporation of swet; is more
hazardous than hot-dry areas)
Heat stress: is the thermal condition of the environment that in combination with metabolic
heat generation of the body causes deep bod)' temperature to exeed 38°C
WBGT (Wet bulb globe temperature) is recommended index for heat stress in
hot environments (fig. I ) and is determined as follows:
Outdoors with solar load:
WBGT = 0.7 t n w + 0.2 tg + 0.1 td b
Indoors or outdoors without solar load:
where
WBGT = 0.71.nw 0.3 to
t m v = natural wetbulb temp. :
td(, = dry bulb temperature
t 3 = V e r r o n a l o b e
O s o m m «*'»«•)
32
30
iu 28 j-
ui i
CI t
O
13 26
m
24
CONTINUOUS WORK
7 S WORK. 2S%.REST EACH HOUR
5 0 1 WORK. 50". REST EACH HOUR
WORK. 7 5 REST EACH HOUR
— —i I 1 I
100 200
LIGHT
WORK
HEAT EXPOSURE LIMIT, WATTS
300 400 500
MOOERATE WORK HEAVV WOOK
Fig. 1 Heat Stress by WBGT Method

2. -2-
3.2 Local discomfort parameters:
Air Speed: Discomfort from drafts or high air speeds may affect work efficiency and sprains in
body parts. Table I gives recommended air speeds for general ventilation for various working
conditions.
Radiant temperature: Heat radiations form hot roof or sunlit walls may cause discomfort in
the work place and may call for radiation shielding specially in mdustnal sheds.
Temperature & Humidity: Control of temperature and humidity simultaneously is required in
special industrial applications as indicated in table - 2» Thes* Gcwditar>s call for specially
designed air-conditioning system including ventilation.
4.0 General Ventilation:
A general ventilation system supplies and/or exhausts air to provide heat control, dilute
contaminants to acceptable limits and replace exhaust air. by either natural supply or mechanical supply
and'or exhaust systems. In most cases, the objective is to provide tolerable working conditions rather than
total comfort. General ventilation rates should be high enough to dilute the carbon dioxide produced by the
occupants. Out door air may be unsatisfactory or may need pretreatment if it is known to have high
unacceptable contaminants levels. Vent.latum rafes jor cecTairt Hos^taJ ar«<x£ aiegtuen foile-4'
4.1 Natural ventiattion:
Natural ventilation is a controlled flow of air caused by thermal and wind pressures and is effective
in work areas with significant heat release, as shown in fig. 0. . It is not suitable if pretreatment of the
supply air is required.
4.2 Spot cooling:
Convective spot cooling is an effective and efficient way of acceptable working conditions in the
work areas of a large factory building. Workers are exposed to air with increased velocities and desired
temperature as indicated in table 3
4.3 Air distribution
Location: for low level ventilation, the outlets should be at about 3m. for spot coo ling the outlets
should be close to worker at about 2m level. Some air supply design strategies are shown in fig J & L
AIR OUTLET
Fig. 2. Natural Ventilation of Single Bay Building
Table 1 Acceptable Air Speed in Workplace
Activity I-evel Air Speed, m'/s
Continuous exposure
Air-conditioned space
Fixed workstation, general ventilation or spot cooling
Silting
Standing
Intermittent exposure, spot cooling or relief stations
Light heat loads and activity
Moderate heat loads and activity
High heal loads and activity
0.25 to 0.4
0 4 10 0.6
0 5 io 1.0
5 io 10
10 to 15
15 ty 20

3. a. Air is supplied by nonattached horizontally projected jet, b. Air is supplied by horizontally projected jet attached to the ceiling,
and occupied zone is ventilated by reverse flow. and occupied zone is ventilated by reverse flow.
OCCUPIED ZONE
c. Air is supplied by horizontally projected concentrated air jets and vertical and/or horizontal directing jets,
and occupied zone is ventilated by reverse flow and vertical directing jets.
Fig. 3 Concentrated Air Supply Methods
With inclined cooled air jets b. With inclined heated air jets
c. With radial jets attached to
the ceiling
d. With downward projected e With downward projected
conical jets compact jets
OCCUPIED ZONE
f. Through the wall-mounted grille; occupied
zone ventilated by the jet directly
g. Through the wall-mounted grille; occupied zone
ventilated by jet and reverse flow
OCCUPIED ZONE
— V
OCCUPIED ZONE
Fig. 4 Nonconcentrated Air Supply Methods

4. - 4 -
T a b l e d Temperatures and Humidities for Industrial Air Conditioning
Process Dry Bulb (°C) rh ( » )
ABRASIVE
Manufacture 26 50
C E R A M I C S
Refractorv 43 to 66 50 to 90
Molding room 27 60 to 70
Clay storage 16 to 27 35 to 65
Decalcomama production 24 to 27 48
Decorating room 24 to 27 48
Use high-efficiency filtration in decorating room. To minimize the danger
of silicosis in other areas, a dust-collecting system or medium-efficiency
paniculate air filtration may be required.
DISTILLING
General manufacturing 16 to 24 45 to 60
Aging 18 to 22 50 io 60
Low humidity and dust control are important w'here grains are ground.
Use high-efficiency filtration for all areas to prevent mold spore and bacteria
growth Use ultrahigh efficiency filtration where bulk fhsh pasteurization is
performed.
E L E C T R I C A L P R O D U C T S
Electronics and X-ray
Coil and transformer winding 22 15
Semiconductor assembly 20 40 to 50
Electrical instruments
Manufacture and laboratory 21 50 to 55
Thermostat assembly and calibration 24 50 to 55
Humidistat assembly and calibration 24 50 to 55
Small mechanisms
Close tolerance assembly 22* 40 to 45
Meter assembly and test 24 60 to 63
Switchgear
Fuse and cutout assembly 23 50
Capacitor winding 23 50
Paper storage 23 50
Conductor wrapping with yam 24 65 to 70
Lightning arrester assembly 20 20 to 40
Thermal circuit breakers assembly and test 24 30 to 60
High-voltage transformer repair 26 5
Water w heel generators
Thrust runner lapping 21 30 to 50
Rectifiers
Processing selenium and copper oxide plates 23 30 to 40
•Temperature to be held constant
Dust control is essential in these processes Minimum control requires
medium-efficiency filters Degree of filtration depends on the type of func-
tion in the area. Smaller tolerances and miniature components suggest high-
efficiency particulate air filters.
F L O O R C O V E R I N G
Linoleum
Mechanical oxidizing of linseed oil* 32 to 38
Printing 27
Stoving process 70 to 120
• P r e c i s temperature control required
Medium-efficiency particulate air filtration is recommended for the siev-
ing process
Process Dry Bulb <°C> r h ( % )
FOUNDRIES*
Core making 16 to 21
Mold making
Bench woik 16 to 21
Floor work 13 to 18
Pouring 4
Shakeout 4 to 10
Cleaning room 13 io 18
•Winter dressing room temperatures. Spot coolers are sometimes used in larger
installations.
In mold making, provide exhaust hoods at tranter points v.ith wet-
collector dust removal system Use280 to 380 L/s per hood.
in shakeout room, provide exhausi hoods with wet-collector dust removal
system. Exhaustl90 to 240 L/s in grate area. Room ventilatory are generally
not effective.
In cleaning room, provide exhaust hoods for grinders and cleaning equip-
ment with dry cyclones or bag-type collectors. In core making, oven and
adjacent cooling areas require fume exhaust hoods Pouring rooms require
two-speed powered roof ventilators. Design for minimum oflO L/s per
square metre of floor area at low speed. Shielding is required to control radi-
ation from hot surfaces Proper introduction of air minimizes preheat
requirements.
FUR
Drying
Shock treatment
Storage
43
- 8 to - 7
4 i o 10 55 to 65
Shock treatment or eradication of any insect infestations requires lower-
ing the lemperature to -8 to - 7 ° C for 3 to 4 days, then raising it to 16 to
21°C for 2 days, then lowering it again for 2 days and raising it to the stor-
age temperature
Furs remain pliable, oxidation is reduced, and color and luster are pre-
served when stored at 4 to 10°C.
Humidity control is required to present mold growth (which is prevalent
with humidities above SO^t) and hair splitting (uhich is common with
humidities lower than 55<H
G U M
Manufacturing 33
Rolling 20 63
Stripping 53
Breaking 23 47
Wrapping 23 58
L E A T H E R
Drying 20 to 52 75
Storage, winter room temperature 10 to 16 40 to 60
After leather is moistened in preparation for rolling and stretching, it is
placed in an atmosphere held at room temperature with a relative humidity
of 95%.
Leather is usually stored in warehouses without temperature and humidity
control. However, it is necessary to keep humidity sufficiently low to prevent
mildew. Medium-efficiency paniculate air filtration is recommended for fine
finish.
LENSES (OPTICAL)
Fusing
Grinding
24
27
45
80

5. Table 3L Temperatures and Humidities for Industrial Air Conditioning (Concluded)
Process Dry Bulb (°C) rh(S>) Process Dry Bulb (®C) rh
MATCHES
Manufacture
Drying
Storage
22 to.23
21 to 24
16 to 17
50
60
50
Water evaporates with the sening of the glue. The amount of water evapo-
rated is 8 to 9 kg per million matches The match machine turns out about
750,000 matches per hour
PAINT APPLICATION
Lacquers: Baking
Oils paints: Paint spraying
150 to 180
16 to 32 80
The required air filtration efficiency depends on the painting process. On
fine finishes, such as car bodies, high-efficiency particulate air filters are
required for the outdoor air supply. Other products may require only low- or
medium-efficiency filters.
Makeup air must be preheated. Spray booths must have 0.5 m/s face
velocity if spraying is performed by humans: lower air quantities can be
used if robots perform spraying. Ovens must have air exhausted to maintain
fumes below explosive concentration Equipment must be explosion-proof.
Exhaust must be cleaned by filtration and solvents reclaimed or scrubbed.
P H O T O STUDIO
Dressing room 22 to 23 40 to 50
Studio (camera room) 22 to 23 40 to 50
Film darkroom 21 to 22 45 to 55
Print darkroom 21 to 22 45 to 55
Drying room 32 to 38 35 to 45
Finishing room 22 to 24 40 to 55
Storage room (b/w film and paper) 22 to 24 40 to 60
Storage room (color film and paper) 4 to 10 40 to 50
Motion picture studio 22 40 to 55
The above data pertain to average conditions. In some color processes,
elevated temperatures as high as 40°C are used, and a higher room tempera-
ture is required.
Conversely, ideal storage conditions for color materials necessitate refrig-
erated or deep-freeze temperatures to ensure quality and color balance when
long storage times are anticipated.
Heat liberated during printing, enlarging, and drying processes is
removed through an independent exhaust system, which also serves the
lamp houses and dryer hoods. All areas except finished film storage require
a minimum of medium-efficiency particulate air filters.
PLASTICS
Manufacturing areas
Thermosetting molding compounds 27 25
Cellophane wrapping 24 to 27 45
In manufacturing areas where plastic is exposed in the liquid >
molded, high-efficiencv particulate air filters may be required Dust
uon and fume control are essential.
PLYWOOD
Hot pressing (resin) 32
Cold pressing 32 15
RUBBER-DIPPED G O O D S
Manufacture 32
Cementing 27 25
Dipping surgical articles 24 to 27 25
Storage prior to manufacture 16 to 24 40
Laboratory (ASTM Standard) 23.0
"Dew point of air must be belov. evaporation temperature of solvent
Solvents used in manufacturing processes are often explosive an
requiring positive ventilation. Volume manufacturers usually insial
vent-recovery system for area exhaust systems
TEA
Packaging 18
Ideal moisture content is 5 to 69c for quality and mass. Low-lim
ture content for quality is 4*3:.
T O B A C C O
Cigar and cigarette making 21 to 24 55
Softening 32 85
Stemming and stripping 24 to 29 7C
Packing and shipping 23 to 24
Filler tobacco casing and conditioning 24
Filter tobacco storage and preparation 25
Wrapper tobacco storage and conditioning 24
•Relative humidity fairly constant with range as set by cigarette machine.
Before stripping, tobacco undergoes a softening operation.
Table 3 Recommended Spot Cooling Air Speed
and Temperature
Air Speed in Jet,
Average Air Temperature, °C,
in Jet Cross Section
on 0.1 m : Heat Flux Density. W / m 2
Activity I^evel of Workplace 140-350 700 1400 2100 2KOO
Light—1 1 28 24 21 16 —
Light—1
i — 28 26 24 20
3 — 28 26 24
3 5 — - —
~>7 25
Moderate—11 1 27 22 — — -
•> 28 24 21 16 —
3 — 27 24 21 18
3.5 — 28 25 22 19
Heavy—III 2 25 19 16 — —
Heavy—III
3 26 n 20 IS r
3.5 — 23 n 20 19

6. —
Table •A General Pressure Relationships and Ventilation of Certain Hospital Areas
Pressure Minimum Air Minimum Total All Air Air Recirculated
Relationship Io Changes of Out- AirChan&es Exhausted Directly YVithin
Function Space Adjacent Areas door Air per Hour" per Hour" •o Outdoors Room Units
S U R G E R Y A N D C R I T I C A L C A R E
Operating roomfall outdoor air s y s t e m ) P I V 15 Yes N o
(recirculating air s y s t e m ) P s 2 5 Optional N o
Delivery room (all outdoor air s y s t e m ) P 15 15 Optional N o
(recirculating air s y s t e m ) 1' 5 2 5 Optional N o
Recovery room E 6 Optional N o
Nursery suite P s 12 Optional N o
Trauma room11
P 5 12 Optional N o
Anesthesia storage (see c o d e requirements) ± Optional 8 Yes N o
N U R S I N G
Patient r o o m c
i 2 4 Optional Optional
Toilet room' N Optional 10 Yes N o
Intensive care P 2 6 Optional N o
Optional"1'iotective isolation* P 15 Yes
N o
Optional"
Infectious Isolation8
i 6 Yes N o
Isolation alcove or anteroom » -i 10 Yes N o
1 .abor/delivery/recovery/postpartu m ( L DR P) F.
-i 4 Optional Optional
Patient corridor-' E
-i 4 Optional Optional
A N C I L L A R Y
Radiolog X-ray (surgery and critical care) P 3 15 Optional N o
X-ray (diagnostic and treatment) ± 2 6 Optional Optional
Darkroom N
•> 10 Yes' N o
Laboratory, general N 2 6 Yes N o
Laboratory, bacteriology N 2 6 Yes N o
Laboratory, biochemistry P 2 6 Optional N o
1 .uboratory. cyloiogy N 6 Yes N o
laboratory, glasswashing N Optional 10 Yes Optional
Laboratory, histology N i 6 Yet N o
Laboratory, nuclear m e d i c i n e N 2 6 Yes N o
Laboratory , pathology N
->
6 Yes N o
Laboratory, serology P
-t 6 Optional N o
laboratory, sterilizing N Optional 10 Yes N o
Laboratory media transfer P
-i 4 Optional N o
Autopsy N 2 12 Yes N o
Nonrefrigerated b o d y - h o l d i n g room' N Optional 10 Yes N o
Pharmacy P -i 4 Optional Optional
A D M I N I S T R A T I O N
Admitting and Waiting R o o m s N 2 6 Yes O p t i o n a l
D I A G N O S T I C A N D T R E A T M E N T
Bronchoscopy, sputum collection, and pentamidine administration N i 10 Yes Optional1
"'
Examination room0
* 2 6 Optional Optional
Medication room P 4 Optional Optional
Treatment r o o m ' ± •t - Optional Optional
Physical therapy and hydrotherapy N 2 6 Optional Optional
Soiled w o r k r o o m or soiled holding N > 10 Yes N o
Clean w o r k r o o m or clean holding" P 4 Optional Optional
S T E R I L I Z I N G A N D S U P P L Y
Sterilizer equipment r o o m N Optional 10 Yes N o
S o i l e d or decontamination r o o m N
-i 6 Yes N o
Clean w o r k r o o m and sterile storage P 2 4 Optional Optional
Equipment storage ± : i Optional i -i Optional Optional
S E R V I C E
Food preparation c e n t e r s 1
* 2 10 Yes N o
Warew ashing N Optional 10 Yes N o
Dietary day storage ± O p t i o n a l Optional N o
Laundry, general N 10 Yes N o
Soiled linen sorting and storage N Optional 10 Yes N o
Clean linen storage P 2 l O p u o n a l i
~>
Optional Optional
Linen and trash chute room N . Optional 10 Yes N o
Bedpan r o o m N Optional 10 Yes N o
B a t h r o o m N Optional 10 Optional' N o
Janitor's closet N Optional 10 Optional N o
P - Positive N = Negative ± = Continuous directional control not required0
•Ventilation in accordance with ASHRAE Siarulani 62-1989. Ventilation for Acceptable
IikJoot Air Qualits. should be used for area* for which specific ventilaii«Hi rates arc not g n e n
V> here a higher outdoor air requirement is called for in SianJard 62 than in Table 3. the
higher value should be used
'Total air changes indicated should be either supplied or. v.here required, exhausted
T o r operating rooms. 100> outside air should dc used o n h w hen codes require it and o n h if
heat recovery de kcs are used
<>
Thc term trauma room as used here is the first aid room and/or emergencs room used for
general initial treatment of accident victims. The operating room within the trauma center
thai is roulineh used for emergeocs surgery should be treated as an operating room.
Although continuous directionaJ control U not required, variation* >hould be minimized,
and in no case sh.njld a lack of directional control allow- the spread of infection from one area
lo another. Boundaries between functional areas (wards or ocpanment-0 should have dinx-
uonal control Lewi* (1988) describes methods for maintaining directional control b appi> -
ing air tracking controls
For a discussion of design considerations for central toilet exhaust systems, see the section
or. Patient Rooms
-The infectious isolation room* .described in this table are those that might be used. !«>r infec-
tious patients in the average community hospital The rooms are negatieK prvssun/od Some
isolation rooms ma have a separate anteroom. Refer to the discission ir. chapter tor more
detailed information Where highh infectious respirable diseases such a- 'uberculosis arc to be
isolated, increased air change rates should he considered.
Protective isolation rooms arc those used for immu.it'suppressed patient*. ITv room i* po-»i
iivclv pressun/ed to protect the patient Anterooms art' generally required and should be nega-
tivelv pressun/ed with respect to the patient room.
Recirculation is allowed in rooms with possible respirators isolation patient*, if suppU air is
HEPA tlltea^j
'All air need not be exhausted il darkroom equipment has scavenging exhaust duct attached
and meets ventilation standards o| NIOSH. O S H A . and local employee expo-we limits
JThe nt «tre frige rated bod) holding room exists o n h in facilities thai do not pertorm autopsies
on-site and use the space for short periods while waiting lor the KkIn to he transferred
l
Food preparation centers should have an excess of air supph lor positive pressure *hcn
hoods are not in operation The number of air changes mas be reduced or varied for odor con-
trol when the space is not in use Minimum total air changes per hour should he that required to
provide proper makeup air to kitchen exhaust systems. Sec O u p t e r 28. Kitchen Ventilation.

7. 4.4 Exhaust systems:
Industrial exhaust systems should collect and remove air borne contaminants of particulates,
vapours and gases that can create an unsafe, unhealthy or undesired atmosphere both with in the space and
outside surroundings.
Types of systems -
General exhaust for entire work space without local considerations
Local exhaust: comprise of five components namely: hoods, duct system, air cleaning
device, fan andexhaust stack as shown in figs-Si C- Table £ gives the capture velocities
for hoods design under various applications and table gives transport velocities for
various types of contaminants, for duct design purposes.
[ i T Y T T T Y T
Fig. 5 Typical industrial exhaust system
4.5 Evaporative cooling:
Evaporative coolers or air-washers provide an energy efficient way of providing cold working
conditions in hot and dry climatic conditions. Air is cooled by evaporation of water droplets either sprinkled
across the air stream or on wetted porous pads/curtains and in the process the solid contaminants are also
removed from the air. An effective evaporative cooling system employs supply system of evaporatively
cooled air and almost equal amount of air exhust system. Technically the power exhaust should be
controlled so that it increases with the increase in out door air relative humidity.
Indirect evaporative cooling has been effectively used to precool the air entering in the refrigeration
coils of an air-conditioning system, thereby reducing the size of refrigeration plants as well as energy and
operating costs.
Bibliography:
1. ASHRAE Hand Book. 1992 HVAC Systems and Equipment volume
2 -do- ] 993 Fundamentals volume
3 -do- 1995 HVAC Applications volume

8. Table - 6 Range of Hood Capture Velocities
Condition
of
contaminant
dispersion
Examples Capture
velocity
m/s
Released
with no
Evaporation from
tanks,degreasing,
velocity into plating etc.
still air
0.25 to
0.5
Released at Container filling,
low vel. into slow speed
moderate conveyor transfer,
still air welding
0.5 to 1.0
Active
generation
into rapid
air motion
Barrel filling, chute
loading of con v-
eyors,crushing
cold shakeout
1.0 to 2.5
Released at Grinding, abrasive
high vel. blasting, tumbling, 2.5 to 10
into very hot shakeout
rapid air
Typical inflow velocity for hoods is 0.5 m/s for
calculating the hood area.
AEnclosing >od
3tn
Hooper /
ENCLOSING HOOD
But
Hopper 1
NONENCLOSING HOOD
Fig.&a-Enclosing and Nonenclosing Hoods
Fig. 6 b Nonenclosing Hoods
cai .aus!
DOWNDRAFT
UPDRAFT COAXIAL
exhaust
plume
source
SIDEDRA FT
exhaust
convective
plume