This document provides information about kitchen ventilation systems. It discusses the types of buildings that require kitchen ventilation such as hotels, restaurants, hospitals, etc. It covers the design of kitchen ventilation systems including components like exhaust hoods, exhaust fans, ductwork, filters and makeup air systems. The document provides guidelines for calculating exhaust air flow rates based on the type of cooking equipment. It also discusses best practices for installation and maintenance of kitchen ventilation systems for effective capture and removal of heat, effluents and grease from commercial kitchens.

1. Kitchen Ventilation
Revac Systems
83, PadmaNagar Phase II
Chintal
Hyderabad 500054
Mobile No +91- 9246 377 652
1

2. Buildings with Kitchens
 Hotels
 Restaurants
 Hospitals
 Canteens
 Retail Malls
 Residences
 Jails
2

3. System Design for Kitchens
 Air Conditioning
 Ventilation
 Fire Safety
 Building Pressurization
 Refrigeration
 Air Distribution
 Food Service Equipment
3

4. Basic Purpose of Kitchen Ventilation
 To provide a comfortable environment in the kitchen
 To ensure the safety of the people working in the
kitchen and other building occupants by:
-Effective Removal of Effluents which may
include gaseous, liquid and solid
contaminants produced by the cooking
process and products of fuel & food
combustion.
Effluents can be life threatening and flammable
4

5. Effluent Generation in Kitchens
 Heat is a primary ingredient of kitchen
effluents
 50% to 90% of the appliance energy input is
released in the form of a rising thermal plume
(convective). Balance is released into
surrounding space through radiation.
 This plume also contains most of the food
and fuel generated effluents.
5

6.  Primary objective of kitchen ventilation is to
capture and remove the air and effluents that
constitute the plume through an effective
exhaust system.
 Heat radiated into space form the appliance
must be addressed by the space airconditioning system.
6

7. A Commercial Kitchen
7

8. Typical Kitchen Exhaust System
600x600
5600 CFM
1500 FPM
VCD
VCD
600x400
600x400
HOOD (8'x4'6") with Baffle Filter
Velocity Across Hood - 150 FPM
ESP
ESP
TRION Air Cleaner
Model T2002
Velocity Across
Air Cleaner 450 FPM
Centrifugal Fan (Exhaust)
6000 CFM 60mm SP 5hp motor
Kitchen Exhaust System
Schematic Diagram
8

9. Grease Emissions
 Amount of grease in vapour phase varies
from 30 to 90% by mass. This is an important
factor in designing the grease removal
system.
 CO, CO2 and NOx emissions are present in
gas and not electrical appliances.
9

10. Spaghetti
Sauce
Range
Pizza
(Sausage)
Oven
Potatoes
Fryer
Broiler
Electric
Gas
Vapour
Particulates
Electric
Gas
Electric
Gas
Electric
Broiler
Gas
Electric
Gas
Griddle
Hamburger Hamburger
Chicken
Grease Emissions by Cooking Appliances & Food Products
Electric
Gas
0
10
20
30
40
Grease (kg per ton of Food)
50
60
10

11. Behavior of Hot Effluent Plume
 In the absence of cross-drafts, a heated plume rises
vertically, entraining the ambient air which enlarges
the plume, cools it and slows it down.
 An Exhaust Hood, generally located above the
appliance, guides this plume into a ducted exhaust
system.
 The exhaust system flow rate must be slightly higher
than the plume volume rate. Extra exhaust capacity
may be required to resist cross-drafts.
 The concept of capture velocity is not applicable to
kitchen exhaust if a hood of sufficient size is placed
at the correct height.
 If the appliance and hood are placed against a
backwall, the plume is drawn towards the wall by the
“Coanda effect”.
11

12. Spaghetti
Sauce
Range
Pizza
(Sausage)
Oven
Potatoes
Fryer
Broiler
Electric
Gas
Electric
Gas
Electric
Gas
Electric
Broiler
Gas
Electric
Gas
Griddle
Hamburger Hamburger
Chicken
Effluent Plume Flow Rates
Electric
Gas
0
200
400
600
CFM
800
1000
1200
1400
12

13. An Exhaust Hood
 The Centre Piece of any Kitchen Ventilation
System (KVS)
 Not just a sheet metal box but a critical
component of a well engineered system
 Much greater awareness today about the
need for an effective KVS
 Issues are health, safety, efficiency and
energy savings
13

14. Hot Air Plume
14

15. Exhaust Hoods
 Type I – for removing grease & smoke : used
for cooking appliances
 Type II – for steam, vapour, heat & odour
when grease is not present : used for
dishwashers, steam tables, etc.
15

16. Basic Styles of Type I Hoods
 Wall Mounted Canopy
 Single Island
 Double Island
 Back Shelf or Proximity
 Pass Over
 Eyebrow
16

17. Hood Styles
17

18. Wall Mounted Canopy Hood
(With Baffle Filter)
18

19. Schematic of an Exhaust Hood
EXHAUST
CHAMBER
EXHAUST
HOOD
LIGHT
BAFFLE
FILTER
GREASE
TROUGH
Hanging
Brackets
19

20. Wall Canopy Hood
 Cooking appliance placed against
a wall
 Minimum air flow requirement
 3” built in gap between hood &
wall
 Three finished sides
 Less susceptible to cross drafts
 Minimum overhang requirement:
6” on sides and 6”-12” in front for
full capture
20

21. Single Island Hood
 Cooking appliance/s (row)
placed in the middle (not
against a wall)
 Four finished sides
 More susceptible to cross
drafts
 Recommended overhang: 12”
on all 4 sides
 Baffle filters in „V‟ configuration
21

22. Double Island Hood
 Double row of
appliances placed
back to back
 Two wall canopy
hoods placed back to
back
 Recommended
overhang : 6”-12” on
all 4 sides
22

23. Basic Styles of Type II hoods
Oven Hoods
Condensate Hoods
23

24. Type II Hood – OVEN Hood
 Removal of Heat & Odour
 Canopy hood with no filters
 Hood size determined with oven door open
24

25. Type II Hood – Condensate Hood
 Removal of heat, odour & moisture
 Condensate baffle and gutter to condense moist air & drain
the water
 Used over dishwashers
Removable
Condensate
Baffles
Condensate Gutter
25

26. Hood Overhang
Minimum Hood Overhang Requirements
(mm)
Hood Type
End
Front
Wall Mounted Canopy
150
150
Single Island
150
150
Double Island (per side)
150
150
Eyebrow
150
Back Shelf
150
250*
Pass Over
150
250*
Rear
150
-
* Maximum Setback
26

27. Exhaust Flow Rate
 Calculation of proper exhaust flow rate very
critical for effective operation of a KVS
 The upward velocity of the effluent thermal
currents is mainly a function of the
temperature of the cooking surface and
varies from 16 FPM over steam equipment to
160 FPM over charcoal broilers.
 Appliances categorized in 4 groups by
cooking duty
27

28. Appliance Duty Category
Light
200
- Ovens
o
- Steamers
- Cheese
Melters
Medium
Heavy
o
o
200
315
- Hot Top/Element - Open Burner
Ranges
Gas Ranges
Extra Heavy
o
370
- Appliance using
solid fuels e.g.
- Griddles
- Broilers
wood, charcoal,
- Fryers
- Wok Ranges
briquettes
- Pasta Cookers
- Conveyor Ovens
(Pizza)
- Rotisseries
50 FPM
85 FPM
150 FPM
185 FPM
28

29. Minimum Exhaust Flow Rates by Equipment Category
CFM per Linear Meter of Hood
Equipment Duty =>
Light
Medium
Heavy Extra Heavy
Wall Mounted Canopy
660
990
1315
1800
Single Island
1315
1645
1975
2300
Double Island (per side)
830
990
1315
1800
Eyebrow
830
830
Back Shelf
990
990
1315
Pass Over
990
990
1315
-
 For a combination of appliances in a row under a single hood,
the flow rate is based on the heaviest duty appliance unless
the hood design permits different rates over different sections
of the hood.
29

30. Schlieren Optical Imaging
 Shows an optical image of the heat and flow
pattern
 Very useful tool in kitchen ventilation
research
30

31. Exhaust Flow Rate - 2750 CFM (Spillage)
31

32. Exhaust Flow Rates- 3600 CFM (Full Capture)
32

33. Baffle Filter
 The primary device for grease removal
 Series of vertical baffles designed to capture
and drain the grease into a container
 Made of stainless steel or aluminium
 Air stream is made to rotate and centrifugal
force throws the heavier grease particles out
of the exhaust air stream.
 Filters are normally removable and are
cleaned by hot water.
33

34. A Baffle Filter - Schematic
34

35. Hood Pressure Drop
Pressure Drop across a Hood with Baffle Filters
A General Guide
Exhaust Flow Rate per Linear Meter
Ps
(CFM)
(mm)
530 - 850
6 - 12
850 - 1150
12 - 19
1150 - 1500
19 - 26
>1500
>26
35

36. More Effective Grease Removal
 Clean air considerations have led to the need
for higher efficiency (HE) grease extraction
systems.
 Mechanical filters (e.g. baffle) are not
effective in removing small grease particles or
grease in vapour form.
 More effective devices reduce grease buildup
downstream of the hood, lowering duct
cleaning frequency and improving fire safety.
36

37. Electrostatic Precipitators (ESPs)
 Used in the exhaust stream downstream of
the hood and the most common HE device.
 By high voltage ionization, particles are
collected on flat electrostatic plates.
 Efficiency may drop as the ionizer section
becomes dirty and effective surface area is
reduced.
 Under heavy loading condition, unit may shut
down because of voltage drop.
37

38. High Efficiency ESP System
38

39. A Dirty Electronic Filter
39

40. Cleaning of a Dirty Filter
40

41. A Cleaned Filter
41

42. Ultra-Violet (UV) Destruction
 UV light chemically converts grease into an inert
substance.
 Adequate exposure time for chemical reaction is
required.
 High intensity UV lamps must be shielded from
eyes.
 Some forms of UV may generate ozone . It is
imperative to have the exhaust on while UV
lights are on.
 UV lamps need to be replaced periodically.
42

43. Water Mist Scrubber and Water Bath
 Passing the effluent through water entraps
particulates and condenses grease vapour
 Static pressure drops are high
 Grease laden water tends to clog drains.
 Water hardness a consideration in spray
nozzle system
43

44. Exhaust Duct Design
Kitchen exhaust ductwork carry hot grease laden air.
The following general guidelines should be followed in their design:
 Ducts can be Round or Rectangular
 Must be grease tight : should be free of traps that can hold
grease.
 Min. sheet gauge should be 16g steel or 18g ss.
 Horizontal dust runs should pitch towards the hood for
continuous drainage. The slope should be 2% for runs under 75‟.
For higher runs, refer to local codes.
 NFPA Standard F96 (US) sets minimum duct velocity of 7.5 m/s
(1500 FPM) for exhaust ducts.
 Maximum velocities are limited by pressure drop & noise and
normally do not exceed 12.5 m/s (2500 FPM).
44

45. Duct Design Considerations
 ASHRAE research finds no evidence to support the NFPA
minimum of 7.5 m/s, but recommends it be reduced to 2.5
m/s (500 FPM). This allows flexibility in design of variable
speed exhaust systems and retrofitting.
 For new single speed systems, a design velocity of 7.5
m/s (1500 FPM) is appropriate. Duct velocities above 2000
FPM cause noise and at less than 1000 FPM, ducts become
large and expensive.
 Straight GI ducts, at duct velocity of 1500 FPM, will have a
pressure loss of about 0.15 mm per meter length. This
pressure loss is proportional to square of duct velocity.
 The total pressure loss is the sum of the loss across the
hood, Y/T connections, bends, straight duct length &
convergent/divergent sections
45

46. Fans for Kitchen Exhaust
 Kitchen exhaust consists of hot, grease laden
air with some solid particulate matter also.
 Fan must be capable of handling this air.
 Motor must be kept outside the air-stream.
 The recommended kitchen exhaust fan is a
SISW centrifugal fan with backward incline
wheel.
46

47. Condition of a FC Impeller used in Kitchen Exhaust
47

48. Advantages of Backward Inclined Fans
 Self cleaning properties
 Higher efficiency
 Limit load characteristics
 Can work without scroll housing
(Plug/Plenum Fan)
48

49. Types of Kitchen Exhaust Fans
49

50. Plug Type Kitchen Exhaust Fan
50

51. SISW BI Impeller
51

52. Plug Type Exhaust Fan – Suction End
52

53. Plug Type Exhaust Fan – Drive End
53

54. Roof Top Centrifugal Fan with Vertical Discharge
54

55. Terminations of Kitchen Exhaust Systems
 Roof Top
 Outside Wall
55

56. Roof Top Terminations
Preferred choice
 Fan at the end of termination
 Accessibility
 Discharge directed away from building
Precautions
 Discharge direction such to minimize re-entry into
fresh air intake. Knowledge of prevailing winds.
 Grease to be collected and drained to a closed
container : a fire safety precaution
 Rainwater to be kept out of the grease container
56

57. Outside Wall Termination
 Fan may or may not be at the terminal
 Precautions
- Discharge direction such to minimize reentry into fresh air intake.
- Away from combustibles
- Horizontal duct sections to pitch towards
the hood for grease collection
- Discharge not to be directed downward
or towards pedestrian areas.
57

58. Makeup Air Considerations
 Exhaust air volume must be replaced with
clean outside air.
 Negative pressure in the kitchen to prevent
odours migrating to outside. Not to exceed 5
Pa as per NFPA Standard 96. Excessive
negative pressure prevents proper drafting of
direct vent appliances.
 Proper design of make up air system ensures
hoods operate as per design.
 IAQ and thermal comfort are also important
considerations in designing a make up air
system.
58

59. IAQ : ASHRAE Standard 62
Outside Air per Person
(CFM)
1. Restaurant Dining Area
(max. 75 persons/100 sq.m)
2. Cafeteria/Fast Food Dining Area
(max. 108 persons/100 sq.m)
3. Bars/ Cocktail Lounges
(Max.108 persons/100 sq.m)
4. Kitchens
(Max. 22 persons/100 sq.m)
21
21
30
15
59

60. Replacement Air Categories
Makeup air for kitchen ventilation must integrate into
the total building fresh air system design
There are three sources of makeup air:
Supply Air : Outside air brought in by the HVAC system
dedicated to comfort conditioning of kitchen space.
Make up Air : Outside air brought in to provide
replacement air specifically for the hood. May or may not
be conditioned & is typically delivered close to the hood.
Transfer Air :Outside air brought into the kitchen but
introduced in the building by the HVAC system dedicated
to the space adjacent to the kitchen.
60

61. Replacement Air Distribution
 Design to eliminate high velocities, eddies, swirls & crossdrafts that can interfere with the natural vertical rising of the
effluent plume.
 Deliver replacement air to the hood
- At proper velocity
- Uniformly from all directions
 For conditioned air, non-directional perforated ceiling diffusers
are the best option. They can distribute large mount of air
throughout the kitchen at low discharge velocities.
 Four-way ceiling diffusers near the hood are not
recommended.
61

62. Compensating Hoods
Hoods with built in (integral) replacement air supply
 Air Curtain (Down Discharge)
 Back Wall Discharge
 Front Face Discharge
 External Supply Plenum
 Combination of above
62

63. Compensating Hoods
63

64. Air Curtain (Down Discharge)




Used for spot cooling of cooking staff
Along the perimeter of the hood (front and/or side)
Uses conditioned air
Can be used to keep un-conditioned air close to the hood at
the cost of comfort.
 Replacement air supply – 10% to 50%
 Discharge velocity a critical factor affecting hood
performance – at too low a value, air enters the hood
directly & at too high a value, it will entrain the exhaust
plume and spill it in the room.
 Recommended design supply rate is 65 cfm per foot. Max.
can be 125 cfm/ft. under ideal conditions.
64

65. Back Wall Discharge
 Makeup air plenum between back wall and hood (about 6”
deep).
 Extends about 6” below cooking surface.
 Runs along the entire length of the hood.
 Very effective way of supplying un-conditioned make-up air
near the hood.
 Recommended design supply rate @ 150 cfm/ft, although
max. can be up to 250 cfm/ft.
65

66. Front Face Discharge
 To throw supply air across the room.
 Used to supply conditioned air in a conditioned kitchen or
conversely for non-conditioned air into a non-conditioned
kitchen.
 Replacement air supply – 40% to 80%.
 Not recommended for conditioned hot air in cold climates.
 Face velocity at discharge should be less than 150 fpm.
 Recommended design rate @150 cfm/ft. Max. can be 250
cfm/ft.
66

67. External Supply Plenum
 Plenum mounted at the ceiling
or the top front edge of the
hood along its full length.
 Supplies air close to the hood.
 Can be used for conditioned or
un-conditioned air.
 Advantages over air curtain
hood – permits higher
discharge velocity.
 Max. supply rate can be 180
cfm/ft. Recommended rate 110
cfm/ft.
67

68. Effect of Four Way Diffuser on Hood Capture
68

69. Exhaust Flow Rate 2750 CFM – 1800 CFM Makeup Air (Spillage)
69

70. Exhaust Flow Rate 3600 CFM – No Makeup Air (Full Capture)
70

71. Makeup Air – Conditioned or Unconditioned?
 If the objective is comfort, use conditioned air.
 If the objective is low cost, use un-conditioned
air.
 Both can be used, provided their distribution
is designed to minimize cost, maximize
comfort and optimize hood performance.
71

72. Makeup Air Distribution – Conditioned Air
For conditioned air, select the system that will
distribute the air throughout the kitchen to
improve comfort - (listed in decreasing
preference):
1. Perforated ceiling
2. Front face discharge
3. Back wall discharge
4. External supply plenum
5. 4-way diffuser
6. Air curtain
72

73. Makeup Air Distribution – Unconditioned Air
For un-conditioned air, the supply system should deliver
the air as close to the hood as possible without
adversely impacting hood performance and without
mixing with room air – (Listed in decreasing
preference):
1. Back wall discharge
2. External supply plenum
3. Front face discharge
4. Perforated ceiling
5. Air curtain
6. 4-way diffuser
73

74. Integration and Balance
 Supply air system must integrate & balance with the
exhaust system
 Balancing using controls and flow adjustments
optimizes system performance
 Every kitchen should be slightly negatively
pressurized compared to surrounding area to contain
the grease vapors, odors and hotter kitchen air within
the kitchen
 In a stand alone restaurant, the overall building
should be at slightly positive pressure compared to
outside to prevent infiltration of heat, dirt, dust and
insects.
74

75. Thank You
75