EN
Functioning of Exhaust Fans in Large-Scale Cooking Facilities
The role of at rest pressure and capture velocity in dynamic air exchange made possible by exhaust fans
In commercial kitchens, exhaust fans create and sustain a controlled pressure differential that extracts 'dirty' air from the facility. For all types of cooking, fans create negative static pressure and draw 'dirty' hot air and grease from the food preparation areas through the exhaust hoods at the capture velocities of 100-150 feet per minute (fpm). Pressure differential and static pressure negative lead the air in prescribed engineered pathways that alleviates air contamination to diners. When properly balanced, air supply and exhaust systems in the cooking areas, at the maximum operating condition, can provide 15-20 ACH (air changes per hour) at the contaminated air source. When that is the condition, the air concentration of the contaminant is at or near the source and is reasonably controlled. At the capture velocities (less than 100 fpm) in the hot cooking zones, they behave in a manner that results in the increased contamination to the air by dispersion of particulates that increases at a rate of 60%, causes damage to the cooking equipment, and shortens the service life of the equipment, and contaminates the air in the kitchen.
Evidence of effectiveness: Variable exhaust fans deployed in a New York Bistro decrease maximum downtime from kitchen exhaust-related to cooking to 37%
Intelligent exhaust fans were deployed in the New York Bistro. Since deployment of the fans, the length of time for closure of cooking in the kitchen due to excessive heat from the cooking appliances was reduced to less than one-third the time. Variable-speed, real-time load sensing fans provided the control. Variable-speed, real-time load sensing fans provided the control. Variable-speed fans, variable from 30-100%, provided the real-time control. Variable-speed fans, load sensing, provided the real-time control. variable-speed fans, provided the control. Variable-speed, real-time load sensing fans provided the control. load sensing, variable-speed fans provided the control. Variable-speed fans, variable from 30-100%, provided the real-time control. Variable-speed, real-time load sensing fans provided the control. Variable-speed fans, variable from 30 to 100%, provided the variable control. Variable-speed fans, real-time load sensing, provided the control. Variable-speed, load sensing, provided the control. Variable-speed, variable, real-time control fans, real-time speed sensing, provided the control. Variable-speed, load sensing, variable and real-time control, provided the control. Variable, load sensing, variable and real-time control, provided the control. Variable-load, variable-speed, variable-control, provided the control. Variable, load sensing, variable-speed variable control, provided the control. Variable-load, variable-control, provided the control. Variable-speed, variable and load sensing, variable control.
Exhaust Fans for Peak Load Air Quality and Grease Control
NFPA 96 exhaust fans and real-time control of grease laden air
Exhaust fans in commercial kitchens must comply with NFPA 96 to handle grease-laden air during peak operations. Correctly designed exhaust fans produce the capture velocity needed for the continuous removal of airborne grease. Gathering grease leads to the accumulation of thicker layers of grease on the ductwork and surfaces of commercial kitchens and is the leading cause of fire in commercial kitchens. NFPA96 (2024 Edition) Section 7.8.2 mentions rooftop exhaust discharges must have integrated grease containment devices to preserve the integrity of the airstream and the grease residue. Without adequate exhaust capabilities grease capture can occur at a rate exceeding 2.5 g/m² per hour at peak conditions, contributing to a sharply elevated fire risk.
High velocity exhaust with dual-stage filtration to achieve exhaust concentration of less than 0.5 mg/m³
When dual-stage filtration is used with high-static pressure exhaust fans (≥1.5 inches of water gauge) exhaust concentrations are maintained below 0.5 mg/m³, which is superior to the majority of the current indoor air quality standards. First to achieve a metal grease removal (stage 1) followed by secondary treatment (stage 2) electrostatic fields, the high velocity exhaust (1,500 – 2,000 fpm) is designed to prevent assisted removal of the air back into the kitchen. This system maintains a high velocity and a continuous air quality control in the kitchen and also keeps the kitchen continuous without impacting the functions of the kitchen during peak hours.
Controlling Odor, Smoke, and Fumes using Changeable Exhaust Fans
Connecting exhaust fan capacity with odor molecules, volatility, and required ACH of 60
Optimizing odor removal hinges on exhaust fan potency designed specifically for cooking odor volatility and emissions. Searing and frying are good examples of volatile odor compounds that quickly disperse and require ACH rates of 60 or higher to avoid odor dispersion to other areas. Variable speed exhaust systems are designed for the cooking intensity and provide capture velocity and variable loads to the systems. With the right systems in place, the protective quality of the air ensures that the smoke and fumes are eliminated from the area.
The Role of Exhaust Fans in the Control of Heat and Humidity
Exhaust fans reduce the positive build-up of heat and humidity in kitchens designed for high-volume food preparation by removing the heat emanating from the cooking surfaces and deep fryer wells. When employees work extended shifts the hot air build-up may exceed the safe working limits. Exhaust fans work for the employees and reduce the temperatures to safe levels. During food prep, boiling pots and the subsequent vapors and steam created may exceed the safe working humidity limits. A properly designed exhaust fan may provide between 15 and 20 air changes per hour. A properly designed exhaust fan may provide between 15 and 20 air changes per hour. Keeping the environment steadier allows the restaurants to relieve the HVAC system of food spoilage and not cause heat stress on the employees. During peak hours, customer serving time is maximized.
Fire Safety Integration: Exhaust Fans and Grease Mitigation Systems
Balancing fan efficiency and hood design to avoid localized grease deposition
Engineered exhaust fans effectively work with hood configurations to reduce fire safety hazards. If fan airflow velocity and hood capture design fail to align, grease escape containment zones and deposition surfaces increase the risk of grease fires. Industry standards specify grease reduction systems. Exhaust fans contain gutter systems to funnel grease into a container that is sealed and flame resistant. This is especially important for rooftop grease deposition, a significant contributor to 74% of grease fires in commercial kitchens, per NFPA. For safety and code compliance, the fan to hood to hood airflow trade-off is designed to capture grease particles and reduce CF by more than 60%. Fans are in systems. Our approach converts exhaust to systems from fans to systems that enhance fire protection.
FAQ
What is capture velocity?
Capture velocity determines the airflow needed in the hood to ensure that the grease particles are caught and contained on the hood and exhaust, and do not spread into the environment.
What are the benefits of variable speed exhaust fans on kitchens?
Variable speed exhaust fans optimize the fans to create a more efficient kitchen. Fans are able to modulate to the amount of cooking, thereby creating quicker cooking times and less downtime of the kitchen.
What role does nfpa 96 play as it pertains to the safety of the kitchen?
Compliance with the NFPA 96 and the grease laden air: exhaust system is essential to make sure that the exhaust system of the kitchen is safe and compliant, and to avoid grease build up in the kitchen. Grease builds up on the exhaust system of the kitchen, which means that it is inherently unsafe and not compliant.