What is an EC Plug Fan?

Airflow for EC Plug Fan
Airflow for EC Plug Fan

Why are EC Plug Fans getting so much hype?

EC plug fans provide  a new means of airflow through a CRAC or CRAH unit more efficiently, more evenly, and with significantly less energy than the currently adopted scroll fans.  In what seems to be the latest toy for data center operators, plug fans are being adopted quickly and enthusiastically. This post describes how these fans work and why they are so much better.

First let’s define what ‘EC’ and ‘Plug Fan’ actually mean.

  • EC stands for ‘Electrically Commutated’ and refers to the type of motor used to drive the fan.  Electrically commutated motors have been around for a long time. They are driven using direct current as opposed to the three-phase current that is ubiquitous in the HVAC industry (more info on EC motors from Wikipedia).
  • Plug Fan refers to the type of fan and how it is mounted.  Unlike typical scroll fans which are found inside the CRAC or CRAH units, plug fans are mounted under the raised floor as shown below

CRAC/CRAH with Scroll Fan

CRAC/CRAH with EC Plug Fan


EC Plug fans are mounted in this fashion  because they use a different method to move air than the more commonly used scroll fans.  Scroll fans have many tiny airfoils that ‘bite’ into the air forcing it downward.  The airfoils, or blades, are called “forward inclined blades” which are not very efficient (more scroll fan info here).   Plug fans use backward inclined blades (as seen here). This blade design allows plug fans to draw air through the middle of the fans and ‘throw’ the air out horizontally.  The backward inclined fan design for plug fans is inherently more efficient than forward inclined fans which is one reason why these plug fans are so attractive.

Another benefit of the plug fan design is that air is delivered horizontally under the floor allowing a more even air distribution compared to the scroll fans which force air directly downward against the slab floor.  The path of the air flowing through a CRAC/CRAH unit with plug fans is much smoother incurring less resistance than with scroll fans as shown below.


Airflow for Typical Scroll Fan

Airflow for EC Plug Fan

Speed control

EC plug fans are all equipped with speed control inputs which means they are compatible with an intelligent cooling control system that can modulate their speed based on load.  This not only saves energy but results in a data center that is dynamic and thus more efficient and reliable.  Since EC plug fans can be mounted below the floor, retrofitting these units simply involves removing the existing scroll fans and mounting the plug fans.  The existing CRAC/CRAH units do not need to be replaced.  Most of the large data center HVAC vendors are selling EC plug fans and retrofit packages.  As data centers continue to grow and become more and more complex and dynamic, the benefits of energy efficiency, improved airflow, and intelligent control from plug fans is more than worth their investment.

Here is a youtube video that provides some more information on EC plug fans:


More Interesting Information

  • Introduction to data centers – Data Center 101
  • EC Plug Fans can save even more energy by reducing their fan speed.  Learn the physics behind this phenomenon here: The Fan Affinity Law
  • Do you know the difference between a CRAC unit and CRAH unit?  If you don’t, find out here: CRAC vs CRAH


  1. Very interesting. For how long have these been on the market? Are they expected to be widely and quickly adopted?

    • Dan Mascola says:

      I first heard about them 2 years ago but in the last year I’ve noticed the major HVAC vendors marketing them heavily. I believe they will be widely adopted, but as with anything in the data center industry, it will take a while because everyone will be skeptical at first.

  2. Colin Pratt says:

    I was a Product Manager with Stulz in the UK, I left that business 8 years ago shortly before Stulz were about to introduce EC Fans into the European market. I remember the first samples being available. That would have been around 2004. Further efficiencies can be achieved by using chilled water units on free cooling chillers – although I appreciate that water and Data Centres don’t usually mix! The majour advantage is fully proportional cooling, most DX systems are on / off or at best feature staged cooling rather than fully proportional.

    Proportional cooling can be very useful in hosted sites where the loads can be very variable. In end user application this is less so as loads tend to be stable and designs accurate.


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