Evaluating and selecting energy-efficient fans with fan energy index
Fan energy index (FEI) is a useful tool for engineers looking to compare the energy efficiency of fan system
Learning Objectives
- Understand how FEI can be used to measure and optimize energy consumption.
- Compare FEI metrics to traditional BHP measurements for fan systems.
- Identify codes and standards related to FEI.
FEI insights
- FEI offers a comprehensive “wire-to-air” metric that provides a more accurate assessment of energy efficiency than traditional brake horsepower measurements.
- Integrating FEI into fan system selection allows engineers to optimize energy consumption, reduce operating costs, and ensure compliance with evolving energy codes.
For many years, brake horsepower (BHP) has been used as the primary fan energy metric to compare fan power requirements and schedule fans. However, BHP is an incomplete measurement of the total energy consumed by a fan system. It accounts for the aerodynamic and bearing losses of the fan system, but it ignores other components such as belts, pulleys, motors and variable frequency drives (VFDs).
In 2017 the Air Movement and Control Association International (AMCA) introduced the fan energy index (FEI) in ANSI/AMCA Standard 208 to provide a comprehensive fan system energy metric. In 2021, ANSI/AMCA Standard 214 was released, providing a test procedure for FEI calculations that could be incorporated by regulating bodies and energy codes. FEI provides a single energy metric that describes the full fan system, including the impact of any belts, pulleys, motors or VFDs. Anything between incoming power and outgoing air power affects the FEI value (see Figure 1).
What is FEI?
FEI is referred to as a “wire-to-air” metric because it considers the efficiency from the input power to the output power of a fan and converts it into a simple ratio. This ratio compares the electrical input power of a reference fan against the actual input power required by a selected fan at a specified duty point. AMCA 214 defines the calculation of the reference fan’s electrical input power as well as the testing and calculation of a fan’s actual electrical input power. Fan manufacturers calculate and present FEI values in their product data. The baseline input power is uniform for comparable fans at a given duty point, making FEI an excellent comparison of a fan’s wire-to-energy consumption across manufacturers. It also provides a more comprehensive energy metric that better describes the fan system on equipment schedules. A fan system with an FEI of 1.10 will use 10% less energy than the baseline fan or any fan with an FEI of 1.00.
FEI in fan system selection
While fan type is determined by the application, duty point and space constraints, FEI can be used to optimize the energy consumption of the fan system once the model has been determined. FEI allows the engineer to evaluate the energy impact of several fan system characteristics including impeller type, motor type and fan size. In general, a higher FEI value indicates a better overall selection.
Figure 2 is a sample fan equipment selection showing three similar inline fans at 3,500 cubic feet per minute and 1.5 inch static pressure, all with 1.35 bhp. The larger FEI value differentiates which fan uses the least energy. In this case, it is EF2, which uses an electronically commutated (EC) motor. EF1 and EF3 use traditional induction motors and incur losses due to VFDs. In addition, EF1 and EF3 feature different synchronous motor speeds, with one being a 4-pole and the other a 6-pole. FEI considers the input power of these different motor types to determine which fan uses the least energy. FEI quickly highlights inferior fan systems during the submittal review. Without FEI, these selections would appear the same if only BHP were compared.
Using FEI in fan system selection
Higher FEI offers additional advantages for evaluating and selecting the optimal fan system for the application including:
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Higher FEI values equate to lower energy consumption, which means lower operating costs and carbon emissions.
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Higher FEI fans may have a more forgiving selection point. By optimizing FEI, the fan selection likely becomes more central in the fan curve, as shown in Figure 3. This provides more forgiveness against unforeseen static pressure impacts in the field.
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Higher FEI fans are usually quieter. FEI can be increased by upsizing the fan and reducing the fan speed, resulting in quieter operation.
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FEI quickly highlights inferior fan systems during the submittal review. A small difference in FEI can indicate a significant difference between comparable fan systems. If there is a noticeable difference between FEI values in seemingly similar fan systems, check the following:
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Are both fans using the same drive type (direct versus belt)?
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Are both systems using the same motor technologies (EC versus induction)?
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Are the motor voltage, phase, horsepower (hp) or poles different?
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Are all fan controls, like VFDs, being included?
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Did the sound increase?
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Is there a difference in impeller technology (mixed flow versus centrifugal)?
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Are the fans the same type?
FEI in codes and standards
FEI is currently included in energy codes and standards. FEI was incorporated into the 2019 version of ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings. In 2021, FEI was included in the International Energy Conservation Code (IECC-21). Both ASHRAE 90.1-2019 and IECC-21 set minimum FEI values for compliance. Many states have already adopted 90.1-2019 and IECC-21, and several others are in the process of doing so.
There are exceptions to FEI requirements in the ASHRAE Energy Standard code for out-of-scope cases or where other considerations apply, including:
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Non embedded fans with a motor nameplate horsepower of less than 1.0 hp (0.75 kW) or with a fan nameplate electrical input power of less than 0.89 kW.
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Embedded fans and fan arrays with a combined motor nameplate horsepower of 5 hp or less or with a fan system electrical input power of 4.1 kW or less.
Embedded fans that are part of the equipment listed under Section 6.4.1.1. of ASHRAE 90.1-2022.
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Embedded fans included in equipment bearing a third-party-certified seal for air or energy performance of the equipment package.
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Ceiling fans, i.e., nonportable devices suspended from a ceiling or overhead structure for circulating air via the rotation of fan blades.
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Fans used for moving gases at temperatures above 482 F (250 C).
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Fans used for operation in explosive atmospheres.
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Reversible fans used for tunnel ventilation.
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Fans outside the scope of AMCA 208.
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Fans when operating during emergency conditions.
The Department of Energy (DOE) is expected to federally regulate fan products using FEI in 2029. The DOE may require minimum FEI values above those established in ASHRAE 90.1-2019 and they may be unique for each fan type. The DOE will also have FEI requirements for fans embedded in nonregulated equipment.
FEI recommendations
FEI is a powerful engineering tool for designing energy-efficient, code-compliant ventilation systems.
The following are suggested to keep up with rapidly changing codes around FEI:
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Even if your state has not yet adopted a code that requires FEI, update equipment schedules to include FEI. This will keep you ahead of code and regulatory requirements and ensure optimal fan performance on your projects.
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Schedule duty point FEI values by using up-to-date manufacturer fan selection tools to optimize FEI and ensure compliance.
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Use caution when presented with value-engineered alternatives with lower FEI values as this may indicate a significant change.
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Schedule and hold duty point FEI values to prevent inferior fans from making their way into your design.
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IECC mandates third-party certification to comply with code requirements. Specify AMCA-certified FEI values to ensure the fans selected will perform as advertised.
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