ASHRAE Journal Supplement - AMCA inmotion - Fall 2017 - 4

2 in. wg
FEI

BHP

the baseline FEP (FEPstd ), as shown in Equation 3. Note that
FEP has engineering units of kW, which cancel out when FEI
is calculated.

Equation 3:

FEPstd
FEI = FEP rating

Table 1 shows how FEI can be used for regulations and
voluntary incentive programs.2
A useful characteristic of this metric is that for FEI ratings
greater than one, the amount of energy savings over the baseline
is FEI minus 1.0 on a percentage basis. So a fan rated FEI =
1.1 uses 10 percent less energy than the baseline requirement.
This makes FEI useful for calculating relative energy savings
between any two fans or between a fan and the FEI threshold
in a fan code, standard or regulation provision.
Possible
FEI Requirement

U.S. Department of Energy

FEI ≥ 1.0 at design point

ASHRAE Standard 90.1 or
International Energy
Conservation Code

FEI ≥ 1.0 at design point

ASHRAE Standard 189.1

FEI ≥ 1.1 at design point

RPM

BHP

APPLYING FEI

Instead of specifying a minimum peak efficiency level for
each of the various fan types, the FEI establishes a baseline
efficiency and resulting baseline power that varies with both
airflow and pressure, universally applied to all fan categories.2
FEI defines a "compliant range of operation" instead of a
single compliant efficiency threshold. For a single-speed fan
curve, the compliant range is a subsection of the total fan
curve (Figure 1).6
On multiple-speed fan curves, as would be used with a
variable frequency drive, these compliant zones look like
bubbles. Bubble sizes are proportional to fan efficiency. Generally, the more efficient the fan, the larger the compliance
bubble (Figure 2, Figure 3).1 In some cases, however, fans
can be very efficient over a small operating range. The shaded
regions in the figures indicate compliance FEI 1.0. Bubbles
are defined within the compliance zone to indicate higher FEI
levels where applicable and outside the compliance zone where
FEI is less than zero. In Figure 3, a label indicates the maximum speed at which the fan can be operated to have compliance.
This gives operators and engineers an opportunity to set up
variable speed drives and belts to restrict fan speed.
Manufacturers will include such diagrams, or their tabular
equivalents, in product literature and sizing/selection software
to help consumers make good purchasing decisions for their
applications.
THE SUPERIORITY OF FEI AS A METRIC

The ratio of fan power to baseline power at design conditions
Utility Incentive Programs
FEI ≥ 1.1 at design point
makes FEI easy to use for customers, owners, regulatory bodies and creators of utility rebate programs. The baseline
Table 1: How FEI can be applied in regulatory and
represents a reasonable efficiency level that is common to all
voluntary programs.
fan types as they are normally applied.
Also, there is much potential for
2.0
Pressure
Compliant Range of Fan
an upcoming DOE regulation based
on FEI. Regulations can be written
around FEPstd , as documented in the
ASRAC term sheet.3 However, a
1.0
regulation, program or written FEI
of 1.0 could serve as an optimal FEI
requirement. When FEI is less than
FEI
1.0, allowable exceptions could
include fans used for variable air
volume (VAV) systems to encourage
0
Airflow
more use of these systems.1 Fans
used infrequently, such as emergency
Figure 1: Compliant range of operation for a single-speed fan.
fans or fans used for material hanImages courtesy of AMCA International.
Fan Energy Index - FEI

Pressure

Fan Regulatory or
Voluntary Program Body

3 in. wg

Fall 2017

A M C A I N T E R NAT I O NA L

inmotion

W W W. A M C A . O R G

http://WWW.AMCA.ORG

Table of Contents for the Digital Edition of ASHRAE Journal Supplement - AMCA inmotion - Fall 2017