Step-by-Step Guide to Calculate Fresh Air CFM

Calculating Fresh Air CFM (Cubic Feet per Minute) is essential for maintaining indoor air quality and ensuring proper ventilation. This guide will walk you through the process step-by-step, using the formula from ISHRAE's book and providing an example calculation for a restaurant.

Step 1: Understand the Formula

The formula to calculate Fresh Air CFM is:

Fresh Air CFM = (CFM per person * Number of persons) + (CFM per square feet * Area in square feet)

Step 2: Gather Necessary Values

To use the formula, you'll need the following values:

1. CFM per person: This value is typically provided in standards or guidelines. For example, ISHRAE recommends a certain CFM per person depending on the type of space.
2. Number of persons: The total number of people expected to occupy the space.
3. CFM per square feet: This value is also provided in standards or guidelines and varies based on the type of space.
4. Area in square feet: The total area of the space in square feet.

Step 3: Apply the Values to the Formula

Let's go through an example calculation for a restaurant.

Example Calculation for a Restaurant

1. CFM per person: According to ISHRAE, the recommended CFM per person for a restaurant is 10 CFM.
2. Number of persons: The restaurant is expected to accommodate 50 people.
3. CFM per square feet: The recommended CFM per square feet for a restaurant is 0.12 CFM.
4. Area in square feet: The total area of the restaurant is 2,000 square feet.

Now, apply these values to the formula:

Fresh Air CFM = (10 CFM/person * 50 persons) + (0.12 CFM/sq ft * 2000 sq ft)

Step 4: Perform the Calculation

1. Calculate the first part of the formula (CFM per person * Number of persons):

10 CFM/person * 50 persons = 500 CFM

2. Calculate the second part of the formula (CFM per square feet * Area in square feet):

0.12 CFM/sq ft * 2000 sq ft = 240 CFM

3. Add the two parts together to get the total Fresh Air CFM:

Fresh Air CFM = 500 CFM + 240 CFM = 740 CFM

Step 5: Verify and Adjust if Necessary

Ensure that the calculated Fresh Air CFM meets the ventilation requirements for the specific type of space. Adjust the values if needed based on updated standards or specific requirements.

Conclusion

By following these steps, you can accurately calculate the Fresh Air CFM required for any space. This ensures proper ventilation and maintains indoor air quality, contributing to a healthier and more comfortable environment.

For more detailed examples and common values, refer to our Example Calculation for a Restaurant and Common Values and Tables for Fresh Air CFM pages.