The Air Movement and Control Association International (AMCA) developed an energy efficiency classification for fans, which is called AMCA Standard 205. It describes how a fan manufacturer defines fan efficiency grades (more commonly referred to as FEGs). FEGs are a numerical value intended to give the user an indication of the relative efficiency of a product. The higher the number, the more efficient the fan.
AMCA Standard 205 defines FEG based on the peak total efficiency of a manufacturer's fan product design. If a fan is AMCA Certified, that means that the manufacturer's claim of an FEG for that particular fan product has been reviewed and validated by AMCA. AMCA then licenses the manufacturer to certify to the public that the fan meets those FEG specifications.
Fan manufacturers now provide a report card-like number grade that indicates the relative efficiency of a fan product. What's the value in having access to that information? It leads to two outcomes:
1. Designers need to select an efficient fan.
To comply with ASHRAE Standard 90.1 (published in 2013), fans used in buildings must now have a minimum FEG of 67, with a few minor exceptions. The exceptions are PRVs and fans with 5 horsepower or less. All other fans, including induced flow fans, must adhere to the minimum FEG of 67.
2. Fans need to be sized and selected properly.
Compliance with ASHRAE Standard 90.1 also requires fans to be selected within 15 percentage points of its peak total efficiency. To comply with ASHRAE Standard 189, the tighter selection range requires that fans are selected within 10 percentage points of peak efficiency in addition to the minimum FEG of 67.
Remember, ASHRAE requirements do apply to induced flow fans. The total efficiency of an induced flow fan (among other criteria) is an indication of how much discharge or exhaust velocity that the fan can generate for a given amount of power invested in the fan shaft. The higher the discharge or exhaust velocity of an induced flow fan at a given low horsepower, the more efficient that fan may be and the higher the FEG number.
In application, this means that if you have a high velocity exhaust fan with low relative power consumption, that tends to build in a broad safe turndown range, adjusting the fan performance downward with a VFD while still maintaining safe discharge velocities. Those factors greatly influence the product's overall energy savings.