ebm-papst Fans, Blowers and Technology

Four Questions to Choose The Right Fan

Posted on Wed, Oct 01, 2014
describe the imageBy Scott Beauchemin, Vice President – Engineering

Customers often ask what they believe to be a simple question: what is the most efficient fan?

Their logical goal? To identify the most efficient fan type, then select that type for all uses.

The simple answer? Backward curved impellers have the highest peak static efficiency. But if you’re seeking the best match for your specific heating, cooling or ventilation needs, it’s not that simple.

Here’s what we ask to make sure customers get the right fan for the right application:

describe the imageWhat’s your operating point? The operating point (or duty point) is the target air flow rate in cubic feet per minute and a system resistance (or impedance) in inches of water. The target flow rate is usually a known value. The system resistance or impedance is not always available, but it’s essential in selecting the correct fan.

Here’s the experiment I conducted that illustrates the flaw in a “one fan type fits all” approach. I chose two operating points with the same flow rate but with system resistances that differed by a factor of two. I looked at backward curved impellers and axial fan solutions for both operating points.

The backward curved impeller provided lower power consumption and noise for the higher system resistance level. But the axial fan consumed less power and generated less noise for the lower system resistance. Keep in mind: the flow rate didn’t change.

What’s your flow path? Selecting a fan based solely on the operating point will not necessarily lead to the best results. The path that the air must take through the system must be factored into the selection as well.

The impact that the air flow path has on a fan’s selection can be dramatic – it can make a very efficient fan perform very poorly. Changes of direction or sudden contractions in the flow path that could choke off the flow.

For example, if the air must follow a right angle, a centrifugal fan with a backward curved impeller or a forward curved blower might be a better solution than an axial fan since the centrifugal fan naturally turns the air 90 degrees.

What are your design goals? While the operating point defines the most important variable, power consumption and noise reduction are huge drivers. When noise is a critical factor, the best solution is typically a larger fan running at the lowest possible speed.  

What are your space constraints? Selection of the right fan must consider the available space within the application. The most efficient or quietest fan may not fit within the available space.

Fan selection can’t be viewed as a one-size-fits-all approach. It’s really a compromise between variables. The key to success in finding the right fan is to identify which model results in the fewest compromises.

What fan selection challenges have you struggled with? What solutions have you found? Join the conversation — leave a comment below!

About Scott Beauchemin
Scott Beauchemin began his ebm-papst career 15 years ago as an applications engineer. Now Vice President of Engineering, he puts his two decades’ experience in airflow and acoustic testing to work in exceeding customer expectations with fans and blowers that meet their applications’ efficiency and low-noise requirements. Scott earned his M.S. in Mechanical Engineering at Rensselaer Polytechnic Institute and his B.S. in Mechanical Engineering at Worcester Polytechnic Institute. In his free time, he enjoys golf and running.