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Contents

Introduction

Humans have been cooking for many millennia using fire to provide the heat with natural ventilation. The chimney first appeared in the 12th century as an early form of controlling cooking emissions in kitchens large and small. In the second half of the 19th century institutional kitchens (including restaurants, schools, hospitals, prisons, etc.) began using hoods with forced ventilation to remove the heat, smoke, water vapor and food emissions from cooking exhaust. (include a Schlieren image?)

Description

Cooking food requires heat and produces water vapor, smoke, and emissions of food constituents. A ventilation system functions to remove heat, smoke, water and food emissions and any combustion products from kitchens and exhaust it outdoors. Figure 1 illustrates major ventilation components, namely the hood, followed by a fire-stop/filter, ducting, and a fan. To balance airflows, makeup air must be furnished in an amount approximately equal to the total exhaust flow. Food emissions, particularly greasy ones, collect as contaminant deposits on all surfaces in the ventilation system. They are fire and health hazards and a major concern for kitchen operators, building owners, safety, health and environmental officials, code authorities, and equipment manufacturers. Addressing the risks and costs of collected contaminants is an ongoing campaign and has been the major driver of both regulation and innovation in the field.

Ventilation Choices

The type of food and the cooking appliance are the key factors determining the required ventilation system. The amount of heat and quantity and types of food constituents emitted from cooking vary widely. Boiling vegetables on an electric range requires a very simple system while grilling fatty meat on a solid-fuel appliance requires a complex system. Typically building codes are the major determinant and will require a minimum level of kitchen ventilation for a new or substantially modified facility. The type of institution doing the cooking will play a role as well. A school kitchen will be allowed a relatively simple system while a chargrilling steak restaurant will require a more complex, and expensive, system. An increasing challenge is the trend of solid fuel cooking and the need for enhanced detection and suppression of fires caused by ignition of highly combustible creosote that’s added to grease in exhaust ducts with solid fuel cooking. Fortunately, there are many new equipment developments and installation techniques in response to challenges. It’s also important to emphasize that periodic preventive maintenance must be provided to enhance the safety of buildings that host commercial kitchens

System Components

Exhaust Hoods

Exhaust hoods are classified as either a Type I or Type II hood per IMC Section 507. Type I hoods are designed for removing grease and smoke effluents, as vapors, liquid droplets, and solid particles produced by the cooking process and combustion of foods and fuels. Type I hoods must include grease filters or extractors classfied to UL Standard 1046 – Grease Filters for Exhaust Ducts, and a fire suppression system listed to UL Standard 300. Type II hoods are used for heat and condensate applications, without requirements for filters or fire suppression systems. In the US, Type I hoods can be listed by a testing agency to UL 710 – Standard for Safety Exhaust Hoods for Commercial Kitchen Cooking Equipment. Listed hoods are constructed in accordance with the terms of the manufacturer’s listing and are required to be installed in accordance with NFPA 96 or applicable local codes. The International and Uniform Mechanical codes allow Type I hoods to be exempt from code-specified exhaust rates if listed to UL 710. Type II hoods are typically used for two different applications: condensate hood or as a heat and fume hood. Condensate hoods are used in applications with high-moisture exhausts, such as from dish-washing appliances. Hoods for these applications are designed to direct the condensate, which forms on the interior surfaces of the hood, toward a gutter located on the perimeter of the hood. The gutter allows for collection and drainage of the condensate instead of dripping down onto the cooking surface. Exhaust rates for Type II hoods are generally in the ranges of 100-150 CFM per foot of the hood length. Unfortunately, exhaust hoods for dishwashers are often undersized in many applications, allowing heat and moisture to escape from hoods, which contributes to discomfort from heat and humidity in kitchens. Based on experience and testing, large overhangs are recommended for hoods over conveyor dishwashers, such as 12 inches in front and 24” at inlet and discharge ends. Another use of Type II hoods is exhausting equipment producing only heat and water vapor, such as steamers. Typically, exhaust rates for these applications are in the range of 100-300 CFM per foot, depending on the application. Per the IMC and NFPA 96, the use of Type II hoods over ovens and other appliances is allowed; subject to verification that grease effluent discharge is less than 5mg/m3 per cubic meter when tested at 500 cfm, per UL 710B.

Listed and Unlisted Hoods

An adjacent chart shows the minimum exhaust flow rates required by the International Mechanical Code (IMC) for unlisted hoods. Backshelf and wall canopy hoods are shown below.

(do as table, combined with table below to better illustrate difference )

                         TYPE OF HOOD	CFM PER LINEAR (or FRONT) FOOT OF HOOD

LIGHT-DUTY MEDIUM-DUTY HEAVY-DUTY EXTRA-HEAVY-DUTY Unlisted, Wall-Mounted Canopy 200 300 400 550 Unlisted, Backshelf 250 300 400 Not allowed

Listed hoods are recommended to be used in all applications because of the lower exhaust rates per foot. Typical minimum exhaust rates for listed wall canopy and backshelf hoods are shown in the table below. NOTE: Specific manufacturer listed minimum exhaust rates could vary.

(do as table) TYPE OF HOOD CFM PER LINEAR FOOT OF HOOD LIGHT-DUTY MEDIUM-DUTY HEAVY-DUTY EXTRA-HEAVY-DUTY Listed, Wall-Mounted Canopy 150-200 200- 300 200-400 350+ Unlisted, Backshelf 100-200 200- 300 300-400 Not Recommended

Grease Filtration

Grease Filtration Removing grease deposits from exhaust hoods, filters, plenums, ducts, and fans is well known requirement of commercial kitchen operation. Grease anywhere in the exhaust system is literally fuel waiting to burn. And with solid fuel cooking creosote is added to the fire risk. With increasing attention of local jurisdictions, pollution and odor emissions are additional concerns. Type I hoods are required by mechanical codes to have grease filters, baffles, or extractors listed to UL Standard 1046 –Grease Filters for Exhaust Ducts. Filters listed or classified under UL1046 are tested to ensure their ability to remove grease, drain the collected grease to a collection device. Additoinallly filters are tested for compliance with maximum the projection of flames beyond the filters. Grease extraction performance can be evaluated by ASTM F-2519, as described below. Devices used in Type I hoods for the removal of grease include baffle filters, cartridge filters, extractors used in water wash hoods and multi-stage filtration. Filters work on the same basic principle - air being exhausted passes through a series of baffles or stages, and centrifugal force causes grease particles to be removed from the airstream and drained to a required trough or other collection device. The amount of grease removed varies based on the type of cooking (appliances and foods), filter efficiency related to particle sizes, air velocity through the filters. Other requipment might also be applied to reduce emissions.

Grease Particle Capture Efficiency

Testing grease filters to UL Standard 1046 does not measure grease filter performance. ASTM F 2519 – Standard Test Method for Grease Particle Capture Efficiency of Commercial Kitchen Filters and Extractors, provides a realistic, reliable, and repeatable means of measuring the grease removal performance of kitchen hood filters. Kitchen exhausts includes grease vapor and small particles. Typically, higher temperature appliances, such as charbroilers and woks, l generate smaller sized grease particles and more grease vapor than those produced by lower temperature appliances, such as ovens and fryers. The ASTM F 2519 Standard generates a challenge aerosol using oleic acid to create emissions having similar particle size and distribution characteristics of real-world cooking between 0.3 and 10 microns in diameter. An optical particle counter is used to measure the particulate, by size, passing through the filter. The result is a capture efficiency percentage graph across a particle size range up to 10 microns. Manufacturers genenerally test submit their filters for independent testing under ASTM F-2519 and publish ticle removal efficiency relative to particle size from 0.3 to 10 microns. The adjacent graph compares grease collection efficiencies of three different filter options. In the sample chart, the gray line in the graph above shows that between about 8 and 10 microns, the sample baffle filter captured approximately 20 to 30 percent and at 5 microns, efficiency was only 6 percent. In comparison, the 2-stage filter (dark green line between 8 and 10 microns, captured 100 percent. Because more efficient filters have a greater static pressure or resistance to flow, exhaust fan size might need to be increased.

Fire Suppression Systems

With high temperatures, open flames, and grease, commercial kitchens fires are common. Codes and standards provide requirements to prevent fires, such as required clearances from appliances, hoods, ducts, and exhaust fans, to combustible construction elements, but commercial kitchen fires ignite from many causes other than clearance issues, and accordingly, codes and standards require fire suppression systems over cooking appliances that produce grease and smoke. In-hood fire suppression systems were developed in the early 1960’s, with ammonium sulfate powder as the suppressant. After detection and actuation, the systems discharged the powder suppressant for about one minute through pipes and nozzles over the appliances, and in the hood plenum and lower exhaust duct. Through the years, manufacturers added features, such as connecting suppression systems with alarm systems and shutting off natural gas and electric power to cooking appliances when fire is detected. In response to issues with re-ignition of fires after suppression, particularly with deep fat fryers, a wet chemical suppressant was developed in the early 1980’s, though detection and system operation was unchanged. In the U.S., UL standard 300 required replacement of powder suppressant systems with wet chemical systems. Under UL 300, applicable suppressant nozzles are piped and mounted over each appliance, or optionally, in an overlapping configuration. Typical fire detectors in conventional fire suppression systems are fusible links – two small pieces of brass held together by solder that fuses (melts) at a specified temperature, such as 360°F (182°C). In accordance with applicable codes and standards, sets of fusible links are placed over cooking appliances and/or in exhaust duct entrances. The fusible links are connected to a small diameter cable, under tension, and when any set of fusible links separate; the cable slackens, which actuates the suppression system. Power for common suppression systems is provided by an industrial strength spring, which, when the system is actuated, pushes a knife blade downward to pierces a gas canister. The gas pressure is controlled to discharge the suppressant from one or more storage cylinders for about one minute. Multple cylinders can be installed for longer hoods with more appliances, but the suppression discharge time remains about one minute. Because of instances of fusible links not always detecting cooking fires, manual actuation stations are required to be placed in the paths of usual egress from kitchens. In response to kitchen fires, typical instructions require that workers manually actuate suppression systems prior to optional use of portable fire extinguishers before evacuation. Type K extinguishers are required by UL 300 for cooking operations producing grease and smoke.

References for this section are: “60 Years of Commercial Kitchen Fire Suppression.” by B. Griffin and M. Morgan. ASHRAE Journal, June 2014, pp 48-58. Ansul History: https://www.ansul.com/en/us/Pages/OurHistory.aspx?value=Our%20History UL 300?

Duct Systems

As part of the exhaust system, the grease duct conveys effluent from the exhaust hood and filters to the outside. Effective ductwork must be grease-tight, clear of combustibles and sized properly to convey the exhaust airstream to the exhaust fan. Ducts used in Type I applications must also contain products of combustion in fire situations to prevent fire spread. Ducts used in commercial kitchen ventilation systems can be either round or rectangular. Rectangular duct is typically fabricated by sheet metal contractors and welded onsite. Round ductwork is factory built and listed to UL Standard 1978: Grease Ducts. Testing and listing cover modular grease duct assemblies, unwelded connections between adjoining duct parts, fittings, access doors, and other accessories. Ducts for Type I hoods must be installed in with listings, and comply with NFPA 96 and applicable mechanical and fire codes.

Exhaust Fans

Centrifugal Upblast

These are the most popular fans for light and medium duty applications because of their relative lower cost than other fan types. The outer shells of these fans are constructed of aluminum.

Utility Set

This type fan is usually constructed of steel, mounted outdoors and used for high static pressure, high temperature, and high exhaust rate applications. Both curb mounted and side inlet utility set models are available. When selecting utility set fans, it is recommended to keep the discharge velocity at less than 1800 FPM.

Inline fans

are used in applications where an exterior installation or rooftop installation is not possible. These fans are located in the duct run inside of a building and are constructed of steel, Motors for this hood type must placed out of the exhaust stream.As with hoods, manuracturer’s sales engineers can suggest fan types and sizes for particular applications.

Fan Drives

Belt drive fans can handle higher static pressure and exhaust rates than direct drive fans and are generally a better choice when using with a variable speed exhaust systems, but belt drive fans usually have more maintenance associated with belts, pulleys and, bearings. Direct drive fans have less friction while operating, with speed by varible frequency drives and associated controls. The reduction is friction increases operating efficiency and lowers operating costs by eliminating periodic belt and bearing replacement.

Fan-location Terminations

Rooftop terminations are preferred because the discharge can be directed away from buildings and fan are more accessible for cleaning.

Fan Actions

Exhaust systems must be designed and installed to prevent a fire starting in the grease exhaust system from damaging the building and to prevent the spread of the fire through the grease exhaust system. Exhaust fans, in fire conditions, typically are required by codes to remain on while the supply fan turns off. The exhaust fan remains on to carry the fire suppressant liquid through the duct and the supply turns off to avoid feeding the fire. NFPA 96 calls for the exhaust fan to continue to run in a fire condition.

Fan Laws & Energy Savings

(reference: https://fishnick.com/ventilation/oalc/oac.ph & https://en.wikipedia.org/wiki/Affinity_laws)

Pollution Control Unit

Concerns about air quality have led to increasingly stringent standards for commercial kitchen exhausts. In many cities, with increasing numbers of multi-use buildings, additional air treatment might be required. Various types of pollution control equipment are available, with technologies that include a multi-stage filtration, electrostatic precipitators, and water mist or scrubbers. Multi-stage pollution control units employ a series of mechanical filters to remove grease and smoke from kitchen exhaust. An example includes a high efficiency filter for the removal of smaller grease particles, followed by a HEPA filter for the removal of smoke, and optionally, odor removal with filter beds of activated charcoal and/or potassium permanganate, such as shown in the adjacent picture. Pollution control units are tested to UL Standard 710, ULC710 and ULCS-646 and must include fire suppression systems listed to UL Standard 300. Regular maintenance of these systems is an important. An initial mechanical filter is usually cleanable, while following stages are disposable and must be replaced periodically, subject to inspection. Cleaning and replacement intervals are , of course, dependent on the cooking appliances, cooking processes, and foods. The better the grease filters in hoods, the less pollution control units must be serviced.

Electrical Control Packages

Electrical control panels are available in single phase, three phase and mixed voltage configurations. They typically include starters to operate makeup and exhaust air fans, and switches to control those starters in conjunction with the hood fire suppresion system. Spare terminals controlled by the fire system are also included. Electrical control panels are typically factory pre-wired to shut down supply fans in a fire condition, to turn on exhaust fans in a fire condition.

Automatic Fan Operation

International Mechanical Code (IMC) section 507.2.1.1, requires that Type I hood systems be designed and installed to automatically activate the exhaust fan whenever cooking operations occur. Several methods are indicated in the code to achieve this operation, such as heat sensors in the hood hood or lower to activate the exhaust system. When the sensor temperature is higher than the kitchen temperature by a number of degrees, exhaust fans are operation is initiated. Forms of variable-speed exhaust systems are also used to meet this code requirement.

Electrical Control Panel

Electrical control panels are available in single phase, three phase and mixed voltage configurations. They typically include starters to operate Supply and Exhaust fans, and switches to control those starters in conjunction with the hood fire system. Spare terminals controlled by the fire system micro switch are also included. Electrical control panels are typically factory pre-wired to shut down supply fans in a fire condition, to turn on exhaust fans in a fire condition if required and to turn off lights in a fire condition.

Makeup Air Unit

A goal of dedicated makeup air is to introduce close to the hood, so that partial tempering is sufficient and without negatively affecting hood performance. Many designs have been tried in the industry throughout the years to bring in makeup air including short-circuit hoods, front face discharge, front air curtain back-wall makeup and most recently perforated perimeter supply. Limitations of some designs described below.

Front Face Discharge

Supply makeup air outward through the upper front of the hood, through louvers or perforated metal. Since the air is directed outward into the space, much of air can become heating and cooling load on the HVAC system. In addition, if speed and direction of the air is not considered, face discharge can reduce hood performance

Air Curtain

Introduce makeup air in a downward direction at the front edge of the hood. Typically the discharge velocity of the air supplied is too high and effectively creates a barrier for capture and containment. The higher discharge velocity can also cause the effluent to spill out into the kitchen. Makeup air being supplied by this method is recommended to 20% of the exhaust flow, according to the CKV Design Guide 2, Improving Commercial Kitchen Ventilation System Performance.

Backwall Supply

Can be an effective strategy for applications that cannot use a perforated perimeter because of space constraints. This application can be used to bring in a maximum of about sixty percent of the exhaust air and the discharge area should be at least 12 inches below the cooking surface of the appliances. If these guidelines are not followed, the makeup air could interfere with the cooking equipment, including pilot lights, as well as becoming cooling or heating load.

Perforated Perimeter Makeup

Lab testing and field experience indicate that this method is a relatively efficient means of providing makeup air, with the least effect on hood operation, and minimal load on the HVAC system. About 70-80 percent of the exhaust rate can be provided by this method. Perforated perimeter supply directs the air downward, from about 18” above the front lip of the hood, on available outside hood surfaces, downward toward the capture area of the hood. Velocity and temperature of the air delivered by this means is an important part installation and performance. For proper hood performance with one manufacturer’s product, the lower, perforated supply should be mounted 18 inches above the front lip of the hood for best results, and discharge airspeeds should be in the range of 140-160 fpm when used with wall mounted canopy hoods. For this application, the makeup air supply is typically heated to 55 °F and the first stage of cooling of the makeup air is initiated when the outdoor temperature is 85°F or higher. The perforated supply devices can also be placed on ends of wall canopy hoods or on all sides of island hoods. A variation of perimeter supply is available with dual plenums. With this concept, partially tempered dedicated make-up air is directed to the inner plenum as usual. Fully tempered outdoor or recirculating from one or more rooftop heating and cooling units is provided to the outer plenum, instead of customary 4-way diffusers in front of the hood, which have been found as a result of laboratory testing to interfere with hood performance. Both single and double perimeter supplies evenly distribute air along the length of the hood, discharging downward through adjustable perforated stainless steel diffuser plates. One manufacturer offers an LED light option to provide lighting along the length of the perimeter supply.

Tempered Makeup Air

The IMC requires makeup air to be conditioned to within 10°F the kitchen space, except where the replacement air does not decrease the comfort of the kitchen. This requirement can be met by having all replacement air come directly from HVAC units, with makeup the air tempered to a range of 68 to 75 degrees F. However, since much of this air is immediately exhausted, many restaurants are furnished with dedicated makeup air can be heated to about to 55 degrees F and cooled when the incoming air is above 85 degrees F. Tempering methods of makeup air can include indirect and direct fired gas heat, heat pumps, evaporative coolers, most predominantly, direct expansion cooling. Heating is recommended for locations in cold climates. Direct-fired natural gas heating is generally the most efficient and economical means of dedicated make-up air heating. These products can typically be modulated to maintain the set temperature, instead of on/off heating operation. Direct-fired heating refers to heating equipment that burns gas directly in the fresh air stream resulting in the most efficient method of heat transfer. Direct-fired heaters generate the lowest cost per BTU of heating when compared to indirect-fired and electric strip heaters. Below are some of the benefits to the using direct fired units: •Direct fired heating is a more thermally efficient process than indirect fired units. Typically direct fired heaters are over 90% efficient, while indirect heaters are around 70% efficient. •Direct fired heating is environmentally clean and equipment is listed to the ANSI Z83.4a and CSA 3.7a safety standards, which set maximum concentrations of carbon monoxide and nitrogen dioxide (CO and NO2) potentially generated by these heaters. •Direct fired heaters can operate on either natural or propane gas and achieve high temperature rises.

System Design Recommendations

Hood Overhangs for Complete Capture

Determining the Appropriate Hood Style. There are many considerations when determining the appropriate hood model. It is important to review local code requirements before specifying a hood style. Also, location of the job site, kitchen layout (walls, doors, pass through and drive through windows, etc.), and building and HVAC design, including exhaust air volume, are important factors to know in advance. Other considerations are cooking equipment sizes, types, locations under hoods, equipment use, and food products cooked. Below is a list of the various hood styles: (pictures of each?)

• Wall Mounted Canopy - covers cooking equipment located against a wall
• Backshelf, Proximity or Low Profile - covers counter height equipment
• Single Island Canopy - covers cooking equipment in a single island configuration
• Double Island Canopy - covers cooking equipment that is in a back to back configuration
• Eyebrow - mounts on top fronts of appliances such as ovens and steamers
• Recirculating - covers electric appliances without grease effluents, generally discharging heat and moisture into the kitchen space
• Type II Hood - condensate or heat and moisture applications

Determining Hood Size

EQUIPMENT RECOMENED OVERHANGS FRONT SIDE Charbroiler* 18”-24” 12” Fryer or Griddle 12” 6”-12” Conveyor Oven 12” 12” beyond conveyor ends Convection Oven** 24” 6” Upright Broilers 18”-24” 12” Solid Fuel 24” 24” Woks 24” 24

When determining the appropriate hood length, the following must be considered: hood length = overall equipment length, plus spaces between sides of appliances, plus side overhangs. Side overhang is defined as the distance from outside edge of the cooking equipment, to the internal end of the hood canopy. Experience and testing have shown that increased side and front overhang can improve system performance, in terms of improved capture, containment, and removal of heat, grease and water vapors, and other cooking effluents (Ref.). Recommended side and front overhang are shown in the table below: For upright, open flame, and solid fuel broilers, with heavy cooking loads, 18” minimum front and side overhangs are recommend, if possible. The additional overhang will ensure that the rapidly rising and expanding effluents are captured and contained by the hood. From experience and testing, 18” minimum overhang is recommended on all sides of single island exhaust hoods. Most hoods from North American manufacturers are available in one piece up to 16 feet long. If the total length of the hood needed is greater than 16 feet, then the hoods are supplied in multiple sections. Two exhaust risers are recommended on hoods greater than 12 feet, especially those with heavy cooking loads.

Cooking Surface Temperature Determination

Though exhaust hoods have customarily been tested and listed to UL Standard 710, with estimated cooking temperatures, there is movement toward classifying by the light, medium, heavy, and extra heavy duty ratings defined by appliance type in the International Mechanical and similar model codes. General practice is to group appliances by their duty rating. If multiple duties are under the hood, then the exhaust rate will be based on the highest duty rating for the entire hood length. The adjacent chart will help determine the cooking temperature of some common types of equipment.

Ducting Sizing

Duct Materials and Construction

Applicable codes and standards provide minimum specifications for the materials, thickness, and constructions of of duct systems. For example, joints, seams and penetrations of grease ducts must be made with a continuous external liquid-tight weld or braze on the external surface of the duct, with exceptions in applicable codes and standards.

Clearance to Combustibles

Grease duct exhaust fires can generate very high temperatures, which without proper clearance, can ignite combustible materials near the duct. Accordingly, codes and standards specifiy required clearance to combustible constructions, such as 18 inches, or protection by external application of listed non-combustible materials, as described below”.

Listed Duct Systems

Factory-built grease duct systems are an alternative to code-prescribed welded or brazed systems. Listed ductwork can be installed with reduced clearance to combustibles in accordance with the listing and the manufacturer’s instructions. Available materials, such as duct wrap, can also be applied directly to the ductwork fore clearance reduction to combustibles. These materials are tested to ASTM Standard E2336, “Standard Test Methods for Fire Resistive Grease Duct Enclosure Systems.” The test standard is now written into IMC 2006 Edition and the 2008 Edition of NFPA Standard 96. These materials are tested to five separate and distinct tests to verify the effectiveness of the enclosure. The flexible wrap type enclosure systems available on the market today that meet all five criteria of ASTM E2336 are all applied in a minimum of two insulation layers. It is important to find materials that have met all the requirements of ASTM E2336; moreover are thinner, lighter, flexible, and offer installation advantages. Duct enclosures are used when grease ducts penetrate a fire-resistance-rated wall or floor-ceiling assembly; the duct must be continuously enclosed from the point the duct penetrates the first fire barrier until the duct leaves the building. Both listed and welded ductwork are subject to the enclosure requirements laid forth by codes. Clearance must be maintained between the duct and the shaft when the duct is in the rated enclosure; NFPA Standard 96 and IMC require minimum of 6-inch clearance. The enclosure can also only contain one ductwork assembly. Some listed ductwork, which is tested to UL Standard 2221, is manufactured to be used without the shaft enclosure. Usually this ductwork is a double wall construction and has fire-resistant insulation material between the two walls. This product must be installed in compliance with the terms of the manufacturer’s listing. Exhaust Airspeed. IMC and NFPA Standard 96 have set the minimum velocity for exhaust ductwork to be at 500 fpm. This is a change from the earlier requirement of 1500 fpm and allows for greater flexibility in design and the use of variable-speed exhaust systems. Helping the change was ASHRAE sponsored research which revealed that velocities below 1500 fpm caused less grease deposit on horizontal duct runs (Ref).

Exhaust Airspeed

IMC and NFPA Standard 96 have set the minimum velocity for exhaust ductwork to be at 500 fpm. This is a change from the earlier requirement of 1500 fpm and allows for greater flexibility in design and the use of variable-speed exhaust systems. Helping the change was ASHRAE sponsored research which revealed that velocities below 1500 fpm caused less grease deposit on horizontal duct runs (Ref). Recommendations for Design and Installation. When designing duct system for an application, the most ideal installation would be a straight duct run from the hood upwards to the exhaust fan above. If the situation described above is unavailable, change of direction, offsets, or elbows, or fittings too close to each other will lead to increased static pressure for the exhaust fan to overcome. To avoid increased system effect and added static, the following recommendations are suggested:

• Run exhaust ductwork straight up to the inlet of the exhaust fan;
• First elbow should be least 18” above the hood;
• Allow for minimum of 4 feet between elbows;
• Use radius back elbows instead of mitered elbows; and
• Avoid placing an elbow directly before the exhaust fan inlet.

Makeup Air Unit Selection and Outlet Location

XXX Needs material relocated or written

Recent Kitchen Ventilation Innovations

Flow Visualization

Schlieren flow visualization is a thermal imaging technology that allows observation of heat and effluents generated by the cooking process, otherwise ‘invisible’ to the naked eye, and usually in a laboratory testing process. Smoke and sometimes steam may be visible. Other effluents including convective heat, water vapor, grease vapor, and combustion by-products are all invisible. A schlieren system aid can aid visualization of effluents by illuminating the refraction of light with changes in air temperature and density. The result is a well-defined, real-time image illustrating the heat and effluent generated and associated flow patterns. Many of the concepts described below have been verified by laboratory use of schlieren systems. The accompanying schlieren images show different exhaust rates for a hood directly above a range top. On the image on the top, the thermal plume is escaping the hood with 165 CFM per linear foot of hood. The same hood, with an exhaust rate of 220 CFM per linear foot, shows that the hood completely capturing and containing the buoyant thermal plume.

Enhanced fire safety

Improved Fire Suppression Systems Hybrid Systems. In response to reliability issues with conventional fire suppression systems, especially with solid fuel cooking, manufacturers are adding features to improve conventional systems. Two U.S. manufacturers offer optional electronic detection in place of detection with fusible links, though these systems retain fixed amounts of suppressant and limited discharge times. A European manufacturer system offers a fully electronic system for detection, operation, and monitoring, with a fixed amount of wet chemical suppressant. Notably, to overcome limitations on the shipment of gas cylinders, this system “employs defence technology ‘Gas Generators’, similar to the technology used in life safety applications such as car airbags…” (ref. http://nobel-fire-systems.com/fire-detection-and-suppression-products/kitchen-fire-suppression-systems/ Another improved system adds unlimited potable water for suppression after actuation and wet chemical agent discharge, though this system continues to use fusible links for detection. This manufacturer also offers an option to monitor whether a propellant cartridge is properly installed, though it does not verify that the cartridge is new and unused. (https://www.ansul.com/en/us/pages/ProductDetail.aspx?productdetail=PIRANHA+Dual+Agent+Restaurant+Fire+Suppression+System Advanced Fire Suppression Systems. Newer systems are emerging, and one new fire suppression system includes fully electronic detection, operation, monitoring, and communications, with battery backup. Electronic detectors sense either a set temperature or a significant rate of temperature rise, and detectors are “rate compensated” to minimize false alarms. Unlike conventional systems, detector distance is not limited, so detectors can be placed in upper duct locations in addition to conventional locations in duct entrances and over appliances. Water suppressant dispersion is powered by building water pressure, with liquid surfactant added for up to 30 minutes for reducing surface tension to improve wetting of fire surfaces. Additionally with new systems, misting nozzles and associated piping provide overlapping coverage of cooking appliances. Suppressant dispersion time is unlimited, though timers are usually set to minimize water limit suppressant discharge times for appliances, hood plenums, and exhaust ducts. These systems can also be employed in pollution control units. Continuous monitoring is provided, with local annunciation and optional communications to building management systems and Internet devices. One advanced technology suppression system also provides automatic daily cleaning with hot water and surfactant of the hood plenum, backs of filters, lower duct surfaces, and electronic detectors. The cleaning cycle is actuated by turning off the related exhaust fan at daily closing, with wash water drained to the kitchen grease trap. Though views are slightly different, comparitive photos show hood plenums in two sister restaurants, three months after opening, with and without automated cleaning. (2 photos?)

Refs: 

National Fire Protection Association NFPA Journal, July/August 2015: http://www.nfpa.org/News-and-Research/Publications/NFPA-Journal/2015/July-August-2015/Features/Fuel-to-Fire Engineered Systems, January 2017: https://www.esmagazine.com/articles/98107-fire-suppression-for-solid-fuel-cooking-in-commercial-kitchens https://www.captiveaire.com/CatalogContent/FireSuppression/Core/index.asp?catid=343 (Photos available for this section)

Automated hood cleaning

Insert info about early & modern (CORE-like) options

Dedicated Outdoor Air Supply

DOAS units are increasingly being used in areas with high humidity conditions, compared to temperatures. For example, the U.S. areas of Atlanta, Georgia, and Miami, Florida, on an annual basis, experience latent (humidity) load that is 6.7 times greater then the annual sensible (temperature) load (Ref Harriman et al or ASHRAE handbook). Recent breakthroughs in sensors, controls, and modulating equipment are contribiting tohat is, controls. DOAS units are often paired with standard rooftop units (RTUs), whereby the RTU is focused on controling temperature and the DOAS controls humidity.

Demand Control Ventilation

Another means of meeting IMC section 507.2.1.1 code requirements, and saving energy, is the use of demand control ventilation system, which controls exhaust and supply airflow quantities while still completely capturing and containing effluents produced by the cooking appliances. The demand ventilation controls are activated through sensors, including temperature, optical, and/or infrared technologies. Instead of the exhaust system running at 100 percent all hours of kitchen operation, the exhaust rate is modulated in relation to the cooking load, often with a preset reduction for periods where there is little or no cooking. If the demand control system is also linked to the makeup air fan(s), there are added savings for space heating and cooling costs, as well as fan operating costs. The modulation of the fans between low and high speeds is typically controled by variable frequency drives and sensors that indicate the intensity of cooking operations. The purple line in the adjacent chart shows the variation of fan energy controlled by a demand control ventilation system over a 12 hour period..

Best Practices

The concept of sustainability is quite profound and is the driver for a design for a fully integrated system. Commercial kitchen use more energy per area than many other building spaces.Owners and operators of modern commercial kitchens can expect to have efficient operations for sustainability, including cooking, space heating and cooling, and fire protectioned. Described in this article are several design principles that will increase efficiancy and safty:

• Aerodynamic hoods, tested and listed to UL Standard 710, are the centerpiece of the kitchen ventilation system. Lower CFM rates can be achieved with listed hoods, compared to unlisted hoods that must meet code specified airflows.
• Determine the appropriate exhaust rate by grouping equipment by duty cycle, use hood end panels to increase hood efficiency, ensure correct placement of equipment particularly charbroilers and using correct overhang for both the side and fronts of hoods.
• Use advanced technology grease filters to remove more grease at the hood and use a pollution control unit if necessary for final grease, smoke and odor control if needed.
• Use direct drive fans where applicable, for energy efficiency and lower operating costs
• Include a variable speed and makeup air , with. exhaust and supply airflow based on the cooking load, to avoid operating at full capacity during operating hours.
• Utilize of dedicated, partially tempered makeup that is discharged close hoods to avoid completely cooking and heating air that will be immediately exhausted. energy and operating costs.
• Employ direct fired gas heating for dedicated make air, as possible. In areas of especially high humidity, pair standard rooftop heating and cooling units with dedicated outdoor air systems (DOAS)
• For enhanced fire safely, install listed ductwork and an electronically detecting and operated fire suppression system, especially with solid-fuel cooking, and multi-story and multi-tenant buildings.

References

• ASHRAE
• ASTM
• IMC
• NFPA
• NSF
• UL

Light(400-450)	Medium(400-450)	Heavy(600)	Extra-Heavy(700+)
Ovens	Griddles	Open-Burner Ranges	Appliances using Solid Fuel (Wood, Charcoal, Briquettes and Mesquite) to provide all or part of the heat source
Cheesemelters	Fryers	Electric/Gas Underfired Broilers
Rethermalizers	Tilting Skillets	Salamander (Upright) Broilers	Example
Steam-Jacketed Kettles	Braising Pans	Chain Broilers	Example
Compartment Steamers	Pasta Cookers	Wok Ranges	Example
Example	Rotisseries	Example	Example
Example	Conveyor (Pizza) Ovens	Example	Example