ASHRAE Journal - December 2021 - 18

TECHNICAL FEATURE
TABLE 1 The motor and impeller combinations used for wire-to-air efficiency study.
FAN SYSTEM
MOTOR
1 AC Induction
ECM
2
3
4
Technology 1
ECM
Technology 2
ECM
Technology 2
SPEED
CONTROLLER
Integrated
Controller
Integrated
Controller
Integrated
Controller
IMPELLER
BLADE SHAPE
VFD Airfoil Blade 1
Airfoil Blade 1
Backward
Curved
Airfoil Blade 2
FIGURE 4 Fan curves and wire-to-air efficiency curves for Fan System 1 and Fan
System 2 at 2,500 rpm.
IMPELLER SIZE
18 in.
18 in.
12.2 in.
12.2 in.
In direct-drive induction motor systems, the controller
and motor efficiencies could be measured or
calculated separately. AMCA 207 provides a means to
calculate part-load motor and controller efficiencies for
induction motors and pulse width modulated (PWM)
variable frequency drives.
The Test Setup
Airflow tests per AMCA Standard 210 were carried out
to study the influence of various components of the fan
system on the wire-to-air efficiency. A total of four fan
systems with three different motor technologies and
three different impeller blade shapes were used for this
study. The four fan systems are given in Table 1. Air performance
tests were carried out in an AMCA-accredited
lab and test chamber. Electrical power measurements
were taken using a power analyzer capable of measuring
three-phase pulse width modulation (PWM) signals.
Fan shaft rotational speed was measured with an optical
tachometer.
Influence of Motor Technologies on Wire-to-Air Efficiency
Fan System 1 and Fan System 2 (Table 1) were used to
study the impact of different motor technologies on the
wire-to-air efficiency of a system. The induction and EC
motor (ECM) used in this study were operated within
motor name plate limits: no over speeding and they
were operated up to maximum current. Both systems
were tested with the same airfoil blade impeller: two
identical impellers preinstalled with these two different
motors. Fan System 1 was driven by a NEMA frame ac
induction motor controlled by a VFD. Fan System 2 was
driven by an ECM with an integrated controller.
Airflow and electrical input power were collected at
four different fan shaft operating speeds. Fan System
1 operated at 2,650 rpm, 2,500 rpm, 1,750 rpm and
1,250 rpm, and Fan System 2 was operated at 2,925 rpm,
18
ASHRAE JOURNAL ashrae.o rg D ECEM BER 2 0 2 1
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Fan System 1: Wire-to-Air Efficiency
Fan System 2:
Wire-to-Air
Efficiency
Stall/Surge Region
Fan System 1: Fan Curve
Fan System 2: Fan Curve
Outside of Typical Fan Operating Range
80
70
60
50
40
30
20
10
1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000
Airflow (cfm)
2,500 rpm, 1,750 rpm and 1,250 rpm.
The measured airflow (cfm) and static pressure
(in. w.c.), for a given speed were used to calculate the air
power (Pout). The measured input electrical power (Pe)
and the measured air power (Pout) were used to calculate
wire-to-air efficiency of the fan systems (Equation 1). The
fan curves (airflow vs. static pressure) and wire-to-air
efficiency curves for Fan System 1 and Fan System 2 are
shown in Figure 4 for 2,500 rpm. The similar behavior are
observed for other speed lines as well. Figure 5 shows this
observation for three different speed lines.
It is clear from Figure 4 that the wire-to-air efficiency of
the two fan systems are similar even though two different
motor systems were used to operate the same model
(type and size) impellers. This shows that the efficiency
of the ECM with integrated controller and the AC motor
with VFD are roughly the same across a wide range of fan
system operating points.
Influence of Impeller Types on the Wire-to-Air Efficiency
Fan System 3 and Fan System 4 (Table 1) were used
to study the influence of different impeller designs
on wire-to-air efficiency. Both systems used ECM
Technology 2 to drive the two different impellers. An
impeller with backward curve blades was used in Fan
System 3, and an impeller with airfoil blades was used in
Fan System 4.
Airflow and power data were collected for seven different
fan speeds. Fan System 3 was operated at 3,550 rpm,
3,200 rpm, 2,800 rpm, 2,500 rpm, 2,100 rpm, 1,700 rpm
and 1,400 rpm. Fan System 4 was operated at 3,635 rpm,
Static Pressure (in. w.c.)
Efficiency (%)
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ASHRAE Journal - December 2021

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