Kitchen Exhaust Systems — An Overview
The primary objective of a kitchen exhaust system is to effectively remove smoke, grease, and cooking odors generated during the culinary process. The necessity for such systems arises from the inherent byproducts of cooking, particularly in commercial kitchens, where large volumes of food are prepared regularly. The accumulation of smoke and airborne grease particles not only compromises the air quality within the kitchen but also poses a significant fire hazard. Efficient ventilation is crucial to maintaining a safe, comfortable, and compliant working environment for kitchen staff while ensuring the longevity of kitchen equipment and preventing potential fire incidents.
The concept of kitchen exhaust systems traces back to the late 19th century when the advent of gas-powered stoves and commercial kitchens led to the realization of the need for effective ventilation. The first kitchen exhaust systems were rudimentary, often relying on natural airflow through windows or strategically placed vents. As cooking technology evolved, so did the complexity of kitchen exhaust systems. The introduction of electric and gas-powered appliances in the 20th century propelled the development of more sophisticated ventilation solutions to cope with increased cooking activity and diverse cooking methods.
Modern kitchen exhaust systems typically consist of several key components working together cohesively. The process begins with the capture of pollutants at the source, usually above cooking equipment, through the installation of canopy hoods. These hoods are designed to capture and contain airborne particles, directing them toward the ductwork. The ductwork acts as a conduit, transporting the contaminated air to the exhaust fan or fans. The fans, positioned either within the kitchen or on the building's exterior, create negative pressure, drawing the polluted air through the ducts and expelling it outside.
Crucial to the effectiveness of the system is the inclusion of filters, often positioned within the ductwork, to trap grease particles and prevent them from entering the exhaust fan and ducts. This not only ensures the system's efficiency but also reduces the risk of fire hazards associated with the accumulation of flammable grease. Additionally, some advanced kitchen exhaust systems incorporate variable speed controls and sensors to optimize fan performance based on cooking activity, minimizing energy consumption during periods of lower demand. Some also employ UV light to help minimize the grease that sticks to ductwork and fans.
A well-designed kitchen exhaust system acts as a critical component in maintaining a safe, healthy, and efficient kitchen environment. It addresses not only the immediate concerns of smoke and odors but also plays a vital role in fire prevention and overall kitchen safety. The continuous evolution of kitchen exhaust systems reflects the ongoing commitment to improving air quality and safety standards in culinary spaces.
Key components of the kitchen exhaust system include the following:
Hood: The range hood is the metal canopy that hangs over the stovetop. It collects smoke, grease, and other airborne particles from cooking. There are two types of hoods. Type I hoods are equipped with grease filtration and extraction devices and are designed for cooking equipment generating grease-leaden vapors, fumes, and smoke. Type II hoods are designed to for dishwasher, steamers and general kitchen space — areas that do not generate grease-laden vapors, fumes, and smoke.
Grease filters: The grease filter is a metal mesh that traps grease particles before they can enter the ductwork. Grease generated by commercial cooking equipment has a size of 10 microns and more. The grease extraction efficiency of the exhaust hood and filters plays a key role in the removal of grease particles before they reach smoke and odor control equipment. Types of grease filters and extractors that fit into the hood and are in use today include: the baffle filter, and dry-cartridge filter. Ultra-violet (UV) lights are also being incorporated into new hood designs. UV lighting breaks down grease molecules into smaller harmless compounds of carbon dioxide and water vapor, which are carried out with the exhaust airflow.
Ductwork: The ductwork is a network of metal conduits that carries the smoke, grease, and other airborne particles from the range hood to the outside. Depending on their construction, the ducts may have access panels.
Exhaust Fans: The exhaust fan is a powerful fan that draws the smoke, grease, and other airborne particles through the ductwork and to the outside.
Damper: The damper is a valve that opens and closes to regulate the airflow through the ductwork.
Makeup Air: Makeup air is fresh air that is brought into the kitchen to replace the air that is exhausted by the exhaust fan. This is important to prevent negative pressure from building up in the kitchen.
Also of note is the fire suppression system. A fire suppression system in a kitchen hood comprises several key components designed to swiftly detect and suppress fires, minimizing potential damage and ensuring the safety of the kitchen environment. The system typically includes a detection mechanism, commonly a heat or flame detector, strategically placed in proximity to cooking appliances. Upon detecting a fire, the suppression system activates a series of nozzles located under the kitchen hood, releasing a fire-suppressant agent, often a liquid chemical such as wet chemical or a clean agent like FM-200. This agent rapidly covers the surfaces within the hood, effectively extinguishing the flames and preventing reignition. The system may also incorporate a manual activation feature, allowing personnel to initiate the suppression process in the event of an emergency. Overall, a kitchen hood fire suppression system acts as a critical safety measure, swiftly responding to fire incidents and safeguarding against the potential escalation of kitchen fires.
The maintenance of fire suppression systems is outside of the scope of this handbook and typically attended to by licensed professionals. However, it is important for field technicians to be aware of the presence of fire suppression systems in kitchen hoods so as not to damage or inadvertently cause a system to discharge.