ASHRAE Method for Kitchen Ventilation

The ASHRAE method for kitchen ventilation is a widely recognized approach for ensuring that commercial kitchens maintain optimal air quality and safety. This guide will walk you through the steps to calculate kitchen ventilation using the ASHRAE method, including determining the exhaust flow rate, fresh air supply, and hood size.

Step 1: Calculating the Exhaust Flow Rate

The exhaust flow rate is crucial for removing heat, smoke, and grease-laden vapors from the kitchen. The ASHRAE method provides specific formulas to calculate this rate based on the type of cooking equipment and hood.

Formula

The basic formula for calculating the exhaust flow rate (Q) is:

Q = A x V

Where:

Q = Exhaust flow rate (cubic feet per minute, CFM)
A = Hood area (square feet)
V = Capture velocity (feet per minute, FPM)

Example Calculation

For a hood with an area of 10 square feet and a capture velocity of 150 FPM:

Q = 10 x 150 = 1500 CFM

Step 2: Determining Fresh Air Supply

Fresh air supply is essential to replace the exhausted air and maintain a balanced kitchen environment. The ASHRAE method recommends that the fresh air supply should be approximately 80-90% of the exhaust flow rate.

Formula

The formula for calculating the fresh air supply (F) is:

F = Q x (0.8 to 0.9)

Example Calculation

Using the exhaust flow rate from the previous example (1500 CFM):

F = 1500 x 0.85 = 1275 CFM

Step 3: Sizing the Hood

The size of the hood is determined by the dimensions of the cooking equipment and the required capture area. The ASHRAE method provides guidelines for hood overhang and height.

Guidelines

Overhang: The hood should overhang the cooking equipment by at least 6 inches on all sides.
Height: The hood should be installed at a height of 6 to 7 feet above the cooking surface.

Example Calculation

For a cooking equipment area of 8 feet by 4 feet:

Overhang: Add 6 inches to each dimension:
- Width: 8 + 0.5 = 8.5 feet
- Depth: 4 + 0.5 = 4.5 feet
Hood Area: Multiply the adjusted dimensions:

A = 8.5 x 4.5 = 38.25 square feet

Conclusion

By following these steps, you can effectively use the ASHRAE method to calculate the necessary kitchen ventilation requirements. This ensures a safe and comfortable working environment for kitchen staff. For more detailed comparisons, you can refer to our Comparison of ASHRAE and SMACNA Methods page.

For further insights on different hood types, check out our Common Hood Types in Kitchen Ventilation page.