ASHRAE Journal - December 2021 - 15

TECHNICAL FEATURE
fan system to move conditioned air through the
occupied space.
Electric motors that power fan systems have
been identifi ed as the one of the biggest energy
consumers in buildings. Fans used in HVAC systems
are among the largest consumers of electrical
power, consuming more than 22% of the
all the electricity used in the European Union.1,2
It is estimated that 18% of electricity consumed
by motors is consumed in fan applications.2 In
the U.S., commercial buildings account for 35%
of electricity consumption, and HVAC&R applications
account for nearly 46% of the total electricity
consumed by buildings.3 Thus, reducing
fan power consumption can have a signifi cant
impact on building energy use.
The fan system effi ciency, i.e., the ability to convert
electrical power to air power, is a function of the fan's
aerodynamics and the motor, transmission and controller
effi ciencies, with the primary factor being the aerodynamic
effi ciency of the fan. Though the fan system
consists of other components such as motors (AC induction
or electronically commutated [EC]), variable speed
drives (VSD), and transmission components (belts, pulleys
and bearings) to transmit the power from the motor
to the fan impeller, the effi ciency losses in these devices
are signifi cantly less than the aerodynamic losses of the
fan impeller in full-load conditions. However, in partload
conditions (for example, less than 50% of maximum
load) these effi ciencies can be more similar.
Background
Currently, fans used in commercial HVAC applications
are typically ranked based on fan effi ciency grade (FEG)
and fan motor effi ciency grade (FMEG) as described in
AMCA Standard 2054 and ISO 12759.5 FEG is published
as a single number rating that classifi es fans by their
maximum aerodynamic ability to convert mechanical
shaft power to air power. Higher FEG translates to
a more effi cient fan. FEG ratings can be used as a valuable
design guide to compare various fans available
in the marketplace. FEG ratings are applicable to fans
only, excluding other components from the calculation
such as motors, VSDs, bearings and other transmission
components.
Using FEG as a design guideline is a positive start to
understand the effi ciency of a fan system. However, it is
Controller Loss
(~5% to 15%)
(Heat)
Motor Loss
Power In
(~5% to 15%) (Heat, Noise)
Pcontroller
Electrical Power (Pe )
Air Power
Airfl ow (cfm) × Pressure (Ps or Pt )
FIGURE 2 Power losses from a plenum fan with direct-drive motor.
Impeller Loss
Controller Loss (~5% to 10%)
(Heat)
Pcontroller
Power In
Electrical Power (Pe )
Motor Loss
(~5% to 15%)
(Heat, Noise)
Power Out
Air Power
Airfl ow (cfm) × Pressure (Ps or Pt)
FIGURE 3 Power losses from an integrated controller electronically controlled
motor (motorized impeller).
Controller Loss (~5% to 10%)
(Heat)
Bearing Loss (~3% to 7%)
(Heat, Noise)
Power In
Electrical Power (Pe )
Motor Loss (~5% to 15%)
(Heat, Noise)
Power Out
Air Power
Airfl ow (cfm) × Pressure (Ps or Pt )
Impeller Loss (Aerodynamic) (~25% to 40%)
(Heat, Noise)
not suffi cient to predict the overall energy consumption.
As explained previously, FEG ratings only account for
fan aerodynamic losses, ignoring all other losses in the
system. The motor may have 5% to 10% losses; the controller
may have losses of 3% to 10%; mechanical components
in the systems (bearing, belt, etc.) will have losses
D E C E M B E R 2 0 2 1 ashrae.o rg ASHRAE JOURNAL
15
(Aerodynamic) (~25% to 40%)
(Heat, Noise)
Power Out
FIGURE 1 Power losses from a traditional belt-driven housed centrifugal fan.
Impeller Loss (Aerodynamic)
(~25% to 40%) (Heat, Noise)
Bearing, Pulley Loss
(~2% to 5%) (Heat, Noise)
Belt Loss
(~2% to 6%) (Heat, Noise)
Mechanical Loss
(~5% to 10%)
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ASHRAE Journal - December 2021

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