Kitchen Exhaust Hood Design involves several considerations to ensure effective removal of heat, grease, smoke, and odors. This includes determining the appropriate size, airflow rate, ductwork, and filtration system. Here’s a comprehensive guide to kitchen exhaust hood design:
1. Determine Hood Type and Configuration
- Type I Hoods: Used for appliances producing grease and smoke (e.g., fryers, grills).
- Type II Hoods: Used for appliances producing heat and steam but no grease (e.g., ovens, dishwashers).
2. Calculate Exhaust Airflow Rate
The required exhaust airflow rate depends on the type of cooking equipment and the hood configuration.
General Formula:
𝑄=𝐴×𝑉Q=A×V
Where:
- 𝑄Q = Exhaust airflow rate (CFM)
- 𝐴A = Hood capture area (square feet)
- 𝑉V = Face velocity (FPM)
Typical Face Velocities:
- Light-duty: 150-200 FPM (e.g., ovens, steamers)
- Medium-duty: 200-250 FPM (e.g., griddles, ranges)
- Heavy-duty: 250-300 FPM (e.g., fryers, charbroilers)
Example Calculation for Kitchen Exhaust Hood Design
For a heavy-duty cooking line with a hood measuring 10 feet long by 4 feet deep:
- Hood capture area: 10×4=4010×4=40 square feet
- Recommended face velocity: 300 FPM
𝑄=40×300=12,000 CFMQ=40×300=12,000 CFM
3. Select Hood Size
Ensure the hood extends beyond the cooking surface:
- Wall-mounted hoods: Extend at least 6 inches beyond the cooking equipment.
- Island hoods: Extend at least 12 inches beyond the cooking equipment.
4. Ductwork Design
Proper ductwork design is crucial for maintaining efficiency and safety.
- Material: Use stainless steel or galvanized steel ducts.
- Diameter: Sized based on airflow and duct length, typically 6-12 inches for small systems and up to 24 inches for large systems.
- Velocity: Maintain 1500-2500 FPM in ducts to prevent grease deposition.
- Layout: Minimize bends and keep duct runs as straight and short as possible.
5. Filtration System
- Grease Filters: Baffle or mesh filters to trap grease particles.
- Additional Filters: High-efficiency particulate air (HEPA) filters or activated carbon filters for odor control.
6. Exhaust Fan Selection
Choose a fan that can handle the calculated airflow rate with appropriate static pressure.
- Type: Upblast or utility set fans are common for kitchen exhaust systems.
- Capacity: Ensure the fan can handle the CFM and static pressure requirements.
7. Make-up Air System
Provide make-up air to replace the exhausted air, maintaining kitchen pressure balance.
- Volume: Typically, 80-90% of the exhaust air volume.
- Location: Introduce make-up air away from the hood to prevent short-circuiting.
8. Compliance with Codes and Standards
Ensure the design complies with local building codes and standards such as:
- NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations.
- ASHRAE Standard 154: Ventilation for Commercial Cooking Operations.
Example Design Process
Step-by-Step Design Example
1: Determine Hood Type and Configuration
- Type I hood for a commercial kitchen with heavy-duty equipment.
2: Calculate Exhaust Airflow Rate
- Hood size: 12 feet long by 5 feet deep.
- Hood capture area: 12×5=6012×5=60 square feet.
- Face velocity: 300 FPM.
𝑄=60×300=18,000 CFMQ=60×300=18,000 CFM
3: Select Hood Size
- Hood extends 6 inches beyond the cooking equipment on the wall-mounted setup.
4: Ductwork Design
- Duct diameter: 18 inches to handle 18,000 CFM.
- Duct velocity: 2000 FPM.
5: Filtration System
- Grease filters: Stainless steel baffle filters.
- Additional filters: None needed for heavy-duty grease applications.
6: Exhaust Fan Selection
- Upblast fan with a capacity of 18,000 CFM at 1.5 inches of static pressure.
7: Make-up Air System
- Make-up air volume: 15,000 to 16,200 CFM.
- Introduce make-up air through ceiling diffusers away from the hood.
8: Compliance with Codes and Standards
- Ensure design meets NFPA 96 and local building codes.
Conclusion
Designing a kitchen exhaust hood involves careful consideration of airflow rates, hood size, ductwork, filtration systems, and compliance with standards. Following these steps will help create an efficient and safe exhaust system tailored to the specific needs of the kitchen.
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