Can I Verify the Flow Rate of an Exhaust Fan Based on Specifications?

Click For Summary
SUMMARY

The discussion centers on verifying the flow rate of an exhaust fan rated at 10,900 CFM based on provided specifications. It emphasizes the importance of the fan curve, which illustrates the relationship between pressure and flow, as a critical tool for assessing performance. The single CFM figure is deemed insufficient for design purposes, as actual flow rates will vary depending on system conditions, including ducting and enclosure. Understanding the intersection of the system curve with the fan curve is essential for accurate flow rate verification.

PREREQUISITES
  • Understanding of fan curves and their significance in airflow calculations
  • Knowledge of system curves related to airflow and pressure
  • Familiarity with ducting and enclosure design principles
  • Basic electrical specifications related to exhaust fans
NEXT STEPS
  • Research how to read and interpret fan curves from manufacturer data sheets
  • Learn to calculate system curves for specific ducting configurations
  • Explore methods for measuring actual airflow rates in ventilation systems
  • Investigate the impact of back pressure on fan performance
USEFUL FOR

Engineers, HVAC professionals, and facility managers involved in the selection and installation of exhaust fans will benefit from this discussion.

JoshDeM
Messages
1
Reaction score
1
I've been given some specifications by a company for an exhaust fan that I am looking at purchasing for my company. They tell me it is 10,900 cfm. Then given some specs on the electrical requirements. I am wondering with the information given could I check their given flow rate?

I imagine that I will need to make a few assumptions along the way. I want to make sure they aren't out to lunch.
Below are the specs

243675
 
Engineering news on Phys.org
No.
The actual volume for the fan will depend on inlet and outlet conditions. The manufacturer will have (or you may not want to do business with them) a fan curve showing the relationship between pressure and flow. unless you're using it with no ducts and no restrictions, you'll need to figure out where your system curve intersects their fan curve. Figuring out your system curve can be a real PITA.
 
  • Like
Likes   Reactions: ChemAir, JoshDeM, DaveE and 2 others
Dullard said:
you'll need to figure out where your system curve intersects their fan curve.
Yes! The single published CFM number isn't very useful in design, it's really for sorting fans to consider more carefully. Start by finding the "fan curve" (CFM vs. pressure) in the data sheet. Notice that for almost every fan you will actually get much lower CFM than that single number at most pressures. Systems are usually designed to operate in the middle, flatter part of the fan curve, where the flow is less sensitive to back pressure. It is your system (enclosure, ducting, etc.) that will determine the pressure that the fan will experience. As Dullard said, your system has its own flow vs. pressure curve.
 
  • Like
Likes   Reactions: JoshDeM

Similar threads

Replies
6
Views
5K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
Replies
1
Views
2K
  • · Replies 15 ·
Replies
15
Views
4K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
Replies
6
Views
4K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 3 ·
Replies
3
Views
5K