KITCHEN
VENTILATION
VENTILATION
• Ventilation is the single most important factor in the design, construction
and operation of kitchens.
• Without adequate ventilation and an ample supply of clean makeup air, no
kitchen will operate efficiently.
• 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.
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.
• 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
OBJECTIVES
• The general ventilation through the kitchen has to introduce sufficient clean, cool air and remove
excess hot air for the occupants to breathe adequately and remain comfortable.
• The general ventilation has to provide sufficient air for complete combustion at burning appliances,
otherwise chronic debilitating carbon monoxide poisoning could occur.
• The general and local ventilation has to dilute and remove products of combustion from gas and oil
fired appliances.
• The general and local ventilation has to dilute and remove odors, vapors and steam from the cooking
processes.
• Local ventilation has to protect against particular hazards to health arising from some cooking fumes,
such as those involving direct application of heat to the food.
OBJECTIVES
• The local ventilation has to be capable of being kept clean from fat residues to avoid loss of efficiency
and fire risks.
• The system has to be quiet and vibration free.
• The amount of ventilation required in a particular cooking area depends on various factors: the type of
• product(s) being cooked, the structure which houses the cooking area, the type of equipment used and
• local code regulations. And, depending on your location, the building heat source may also play a
factor.
• This course will provide basic guidelines to achieve these objectives and facilitate ventilation design
KITCHEN HOODS
There are two types of 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.
TYPE 1-HOODS:
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 .
Single Island Hood
• Cooking appliance/s (row) placed in the middle (not against a wall)
• Four finished sides
• More susceptible to cross drafts.
• For the same equipment single island will take higher exhaust rate as
compared to Single Island Hood
• Recommended overhang: 12” on all 4 sides
• Baffle filters in „V‟ configuration
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
Proximity Hoods (Back shelf)
• Proximity hoods are TYPE I hoods that are shorter in
height and depth than a typical canopy hood.
• The name “Proximity” or “Back shelf ” refers to the close
location of the hood with respect to the cooking equipment.
A note of Caution
• Although a well-engineered proximity hood can be
applied with success at very low exhaust rates
(e.g., 150 cfm per linear foot over medium-duty equipment),
this same style of hood (if specified without performance
data and/or in accordance with maximum height and setback
permit-ted by code) may fail to effectively capture and
contain the cooking effluent at exhaust rates of 300 cfm/ft
or more.
Pass Over Hoods
• The pass-over hood configuration is used over counter-height
equipment where a pass-over capability is required.
• That is, prepared food is passed over from the cooking surfaces
to the serving side.
Eyebrow Hoods
• Eyebrow style hoods are mounted directly to ovens and
dishwashers to catch effluents.
• This hood type can be designed to operate only when appliance
doors are opened or at certain points in the cycle.
TYPE 2-HOODS:
Oven Hood
Condensate Hood
Oven Hood
• The oven hood is an exhaust only canopy hood with an
exhaust duct collar for the removal of heat and vapor.
• These hoods are the simplest of all hoods and are usually
placed over ovens or small appliances only producing heat and odor.
• For complete capture and containment, overhangs should
be measured with the oven door open.
Condensate Hood
• The condensate hood is an exhaust only canopy hood with
U-shaped gutters to capture and direct condensate to a drain.
• It also has an exhaust duct collar for heat, moisture, and
odor-ridden air to exit.
• Condensate hoods are usually found mounted over dishwashers.
HOOD FILTER
HOOD FILTER
• What Is A Hood Filter?
• Hood filters are installed over stoves and are designed to capture and remove smoke, grease,
and debris to prevent them from getting into the ventilation system. Without these hood
filters, grease, particulate matter in smoke and other types of debris would build up in the air
ducts and could become a fire hazard. Kitchen hood filters are very important for homes
and commercial kitchens.
• In order to meet the International Fire Code and National Fire Protection Association
regulations, residential and commercial kitchens are required to have hood filters. These
organizations recognize the importance of having hood filters to improve the kitchen’s air
quality, protect the ventilation system and to help prevent kitchen fires.
HOOD FILTERS
HOOD FILTER
HOOD FILTER
• Cleaning and Maintenance
• It is very important to make sure the hood filter is regularly cleaned and properly maintained.
This is of particular importance with hood filters for commercial kitchens that see a lot of
activity. Dirty hood filters make a kitchen unsafe. It can be a serious fire hazard, cause the kitchen
to have extremely smoky air and excessive heat and strain on the exhaust system leading to
dangerously poor air quality. Keeping the hood filter clean and properly maintained will make it
run more efficiently, reduce utility costs and extend its life.
HOOD FILTER
• How To Clean Hood Filters
• Cleaning the hood filter is simple.
• Hood filters can be washed by hand using non-abrasive sponges and hot soapy water to
remove the grease and grime.
• Do not use harsh chemicals in the hood filter cleaning process, as they can cause corrosion.
• One option for faster, easier cleaning of the hood filter is to put the parts into the
dishwasher.
• To ensure the hood filter is working properly, maintenance service should be performed on
it at regularly scheduled intervals several times each year by a trained professional.
HOOD FILTER
• Disposable Hood Filters
• Some people use disposable grease filters in their kitchen hood. These filters can be installed
in seconds, capture as much as 98% of grease particles and keep them out of the kitchen
hood.
• They do not require cleaning or maintenance from a
professional and can be thrown out and replaced when dirty.
• Made of wool, disposable hood filters are fire retardant and
completely biodegradable. They are used in commercial kitchens
worldwide. Plus, used properly, they meet the National Fire
Protection Association safety requirements.
GREASE FILTERS (NFPA sec:6.2.3)
• 6.2.3.1 Grease filters shall be listed.
• 6.2.3.2 Grease filters shall be constructed of noncombustible material.
• 6.2.3.3 Grease filters shall be of rigid construction that will not distort or crush
under normal operation, handling, and cleaning conditions.
• 6.2.3.4 Grease filters shall be arranged so that all exhaust air passes through the
grease filters.
• 6.2.3.5 Grease filters shall be easily accessible for removal.
• 6.2.3.6 Grease filters shall be installed at an angle not less than 45 degrees from the
horizontal.
NFPA 96 Fire Codes for Spark Arrestor
Filters (Solid Fuel Cooking Systems)
• 14.5.1 – Grease removal devices shall be constructed of steel or stainless
steel or be approved for solid fuel cooking
• 14.5.2 – If airborne sparks and embers can be generated by the solid fuel
cooking operation, spark arrestor devices shall be used prior to using the
grease removal device to minimize the entrance of the sparks and embers
into the grease removal device and into the hood and duct system.
• 14.5.3 – Filters shall be a minimum of 1.2 m (4 ft) above the appliance
cooking surface
NUMBER OF FILTERS REQUIRED
• The minimum required number of filters for a particular hood can be calculated by dividing
the total volume of air to be exhausted, in CFM, by the optimum operating velocity of the
filter, in FPM usually 300 to 400FPM.
• This number is then divided by the actual square footage of the standard size filter
(excluding the frame). The resulting figure represents the minimum number of filters
required to efficiently remove the grease from the exhausted air
EXAMPLE:
Example: Assume an exhaust hood with a minimum required airflow of 4200 CFM. Baffle
type filters with a nominal size of 16" x 20", have an actual filtering surface of 14" x 18".
(Nominal size minus the frame equals the actual filtering area.) Calculate the number of
filters required, considering an optimum operating face velocity of 300 FPM across the filter.
Solution:
Filter Area Needed = Volume of exhaust air / Permissible face velocity
Filter Area Needed = 4200 / 300 = 14 sq-ft
Actual filter surface area (minus frame) = 14” x 18” = 252 sq- in or dividing by 144
(conversion factor for sq-ft to sq-in)
Actual filter surface area = 1.75 sq-ft
Number of filters required = Filter area needed / actual fitter surface area
= 14 / 1.75 = 8 filters.
Therefore, in this example, 8 filters would be required to provide adequate removal of the grease. Any space in the hood
not occupied by a filter should be blanked off with sheet metal. As much as possible, the blanks should be divided equally
between the filters. This will ensure optimum performance and will equalize the air velocity over the entire length of the
hood opening
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
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
WET SCRUBBER
WET SCRUBBER
• Wet scrubbers are used for removal of particles which have a diameter of the
order of 0.2 mm or higher.
• Wet scrubbers work by spraying a stream of fine liquid droplets on the
incoming stream.
• The droplets capture the particles
• The liquid is subsequently removed for treatment.
WET
• Advantages and Disadvantages
• There are advantages and disadvantages to the use of a wet scrubber. First and foremost,
these scrubbers are beneficial as they prevent a wide range of pollutants from entering
the air through the exhaust gas. Second, these units are fairly sturdy and can tolerate a
wide range of temperatures, making them ideal for operation in almost any environment.
Lastly, wet scrubbers can be used to remove a wide range of pollutants from sulfur to acidic
gases that contribute to acid rain.[5]
• Despite the advantages, there are a few drawbacks. These machines require frequent
maintenance, and they can suffer from corrosion quite severely. If maintained and
vented properly, these machines can be used for many years before they require
replacement.
WET SCRUBBER
Advantages of Wet Scrubbers
• Wet Scrubbers can handle incoming streams at high temperature, thus removing the need for temperature
control equipment.
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Wet scrubbers can handle high particle loading.
Loading fluctuations do not affect the removal efficiency.
They can handle explosive gases with little risk.
Gas adsorption and dust collection are handled in one unit.
Corrosive gases and dusts are neutralized.
Disadvantages of Wet Scrubbers
• High potential for corrosive problems
• Effluent scrubbing liquid poses a water pollution problem.
DRY SCRUBBER
• A dry Scrubbing system unlike the wet scrubber does not saturate the flue
gas stream that is being treated with moisture. In some cases no moisture is
added; while in other only the amount of moisture that can be evaporated
in the flue gas without condensing is added. Therefore, dry scrubbers do
generally not have wastewater handling/disposal requirements. Dry
scrubbing systems are used to remove acid gases(such as SO2 and HCl)
primarily from combustion sources
ELECTROSTATIC PRECIPITATOR
ELECTROSTATIC PRECIPITATOR
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Principle:
The particles in a polluted gas stream are charged by passing them through an electric field.
The charged particles are led through collector plates.
The collector plates carry charges opposite to that on the particles.
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.
ELECTROSTATIC PRECIPITATOR
ELECTROSTATIC PRECIPITATOR
Advantages of Electrostatic Precipitators
• Electrostatic precipitators are capable very high collection efficiency, generally of the order of %.
• Since the electrostatic precipitators act on the particles and not on the air, they can handle higher
loads with lower pressure drops.
• They can operate at higher temperatures.
• The operating costs are generally low.
Disadvantages of Electrostatic Precipitators
• The initial capital costs are high.
• Although they can be designed for a variety of operating conditions, they are not very flexible to
changes in the operating conditions, once installed.
• Particulate with high resistivity may go uncollected.
UV LAMPS
UV LAMPS
• Ultraviolet Lights or UV-C lights are a type of bulb that has a very high intensity that allows
it to break down organic compounds. UV has been applied in a variety of sterilization and
water treatment applications for decades. The wavelength varies by application. In the case
kitchen exhaust systems, UV-C light is used to break down grease particles through two
processes: photolysis and ozonolysis. The photolysis process breaks the molecular bond of
grease whereas ozonolysis is a process that oxidizes the grease molecules.
• The primary grease extraction for an exhaust hood is the mechanical grease filters in the
hood. They work to remove grease particles by inertial means. The remaining smaller
particulate and vapor are exposed to ultraviolet lights or UV-C light in the exhaust plenum.
The result of this conversion is to reduce the fire risk by decreasing the grease buildup in
the ductwork. It is important to understand that UV-C systems are not filtration systems.
UV LAMPS
• For a UV installation to be successful, several things are necessary.
• Routine maintenance. Over time the UV bulbs will develop a coating from
the converted grease. The bulbs must be wiped down periodically. Systems
have usage timers that would indicate when routine maintenance is
warranted. Also, one should monitor the initial maintenance cycle to
determine if it should be increased or decreased based on usage.
• UV-C effectiveness diminished when exposed to temperatures above 160° F.
Typical exhaust temperatures are in the range of 100°-120°F
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).
STATIC PRESSURE GUIDLINES
EXHAUST FANS
EXHAUST FANS
• 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.
EXHAUST FANS
Advantages of Backward Inclined Fans
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Self cleaning properties
Higher efficiency
Limit load characteristics
Can work without scroll housing (Plug/Plenum Fan)
EXHAUST TERMINATIONS
• Terminations of kitchen exhaust system:
1. Roof Top
2. Out Side Wall
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
Outside Wall Termination
• Fan may or may not be at the terminal
Precautions -
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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.
IAQ : ASHRAE Standard 62
• Outside Air per Person (CFM)
1. Restaurant Dining Area (max. 75 persons/100 sq.m)
21
2. Cafeteria/Fast Food Dining Area (max. 108 persons/100 sq.m) 21
3. Bars/ Cocktail Lounges (Max.108 persons/100 sq.m)
30
4. Kitchens (Max. 22 persons/100 sq.m)
15
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.
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.
Replacement Air Distribution
• Replacement air quantity shall be adequate to prevent negative pressures in
the commercial cooking area(s) from exceeding 4.98 Pa (0.02 in. water
column). “NFPA 96 sec 8.3.1”
• International Mechanical code :
Replacement Air Distribution
• Design to eliminate high velocities, eddies, swirls & cross drafts 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.
Compensating Hoods
Hoods with built in (integral) replacement air supply
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Air Curtain (Down Discharge)
Back Wall Discharge
Front Face Discharge
External Supply Plenum
Combination of above
Air Curtain (Down Discharge)
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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.
Back Wall Discharge
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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.
Front Face Discharge
• To throw supply air across the room.
• Used to supply conditioned air in a conditioned kitchen or
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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.
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.
Makeup Air –
Conditioned or Unconditioned?
• Air that is heated or conditioned before it is brought in from the outdoors is called
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tempered air.
If the goal is to make the kitchen comfortable, then utilize tempered air. If the goal is low
cost, then use untempered air.
Both tempered and untempered can be introduced, however, selecting the proper supply
types will affect comfort and economic efficiency. Once this decision has been made a type
of make-up air system can be selected, but always keep two things in mind.
When tempering the air, use a source that will distribute the air throughout the kitchen to
increase employee comfort.
When using untempered air, use a source that will keep the air near the hood so it can be
exhausted quickly without mixing in the space causing discomfort and increased
heating/cooling loads.
Makeup Air DistributionConditioned Air
• For conditioned air, select the system that will distribute the air throughout the
kitchen to improve comfort - (listed in decreasing preference):
1.
2.
3.
4.
5.
6.
Perforated ceiling
Front face discharge
Back wall discharge
External supply plenum
4-way diffuser
Air curtain
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
AIR CURTAIN SUPPLY
4 WAY DIFFUSER
FRONT FACE DISCHARGE
REAR DISCHARGE
PERFORATED PERIMETER
SUPPLY
Recommendations
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Do not use short-circuit hoods
Avoid air curtain strategies
Do not spec 4-way diffusers near hoods
Minimize MUA velocity near hood
Maximize transfer air – minimize local
MUA
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.
Energy Management
Considerations
• Hood exhaust flows can result in twenty or more air changes per hour. Installing a variable
volume system is the first step towards energy conservation to allow for the exhaust and
supply units to ramp up and down depending on the cooking load. Varying both the exhaust
and the supply will vary the amount of air that needs to be conditioned. In some cases, a
variable system can reduce the costs associated with conditioning make-up air by up to
50 percent. Exhaust and supply air flow rates should be controlled by installing variable
frequency drives (VFD) on the fan motors. The VFDs are controlled by a temperature
sensor mounted in duct collar. The control system varies the frequency of the motor drives
and thus fan speed, according to the temperature seen in the duct collar.
• The VFD system varies the flow continuously as per the cooking requirement, as opposed
to the high, medium and low speed settings on the motor controlled manually. The energy
savings using VFDs result from the fact that the fan power, W is proportional to the third
power of speed, N, that is,W directly proportional to the cube of N.
FIRE EXTINGUISHING
SYSTEMS
National codes require automatic fixed type fire protection systems to protect ducts, plenums, and
cooking surfaces whenever the cooking process releases grease vapors. The respective NFPA standards
which cover the application are as follows:
• Exhaust systems used to remove smoke and grease-laden vapors generated by commercial cooking
equipment must comply with the State Fire Prevention Code and the latest edition of ANSI/NFPA96.
• Electrical wiring shall conform to the requirements of the National Electrical Code -NFPA #70
• NFPA 10 also encompasses requirements for portable hand type extinguishers in addition to fixed
systems.
• Wet chemical system - NFPA 17A
• Water sprinkler system - NFPA 13