Greenheck Fan Mixed Flow Fans Belt and Direct Drive QEI-L - Manual (Page 6)

6
Design & Performance
Mixed Flow: Axial/Centrifugal Hybrid
A mixed flow wheel is a hybrid between an axial propeller and a
centrifugal wheel. The result is a design that combines the best axial
and centrifugal properties: highly efficient air movement, increased
pressure capabilities, extremely low sound levels, and a steep fan
performance curve. To further enhance the fan’s performance,
straightening vanes are incorporated in the housing. These serve
to convert swirling airflow into a straight axial flow with a resulting
static pressure rise and energy savings.
60
70
80
90
100
62 125 250 500 1000 2000 4000 8000
Frequency, Hz
Sound Power
, dB
30
40
50
60
70
80
14000 16000 18000 20000 22000 24000
CFM
SE
QEI
Typical Vane Axial
Typical Centrifugal
QEI-L, QEI-I/II
Typical Vane Axial
Typical Tubular Centrifugal
Typical Typical QEI-L
Tubular Centrifugal Vane Axial QEI-I/II
Sound power levels shown at each frequency:
Static Pr
essur
e
CFM
Centrifugal
Mixed Flow
Axial
Lower Sound Power, Better Sound Quality
The sound quality of the belt-driven mixed flow fan line is
as beneficial to low sound design as is the reduced overall
sound power. The sound chart compares units of similar
outer tube diameters at an operating point of 20,000 cfm with
1.5 inches wg of static pressure (Ps). Tubular centrifugals
(green) have dominant tones in the 63 Hz through 250 Hz
octave bands, while vane axials (red) have more mid to high
frequency sound. The mixed flow fan (blue) does not have a
dominant tone. A bystander would hear a more bland sound
that is quieter than a tubular centrifugal or vane axial.
Sound and Efficiency
Sound power levels and fan efficiency are two very important factors when selecting a fan. There is a noticeable
difference between impeller types. The table and chart below compare the sound power (L
w
A) and the static
efficiency of the belt-driven mixed flow fan wheel versus tubular centrifugal and vane axial inline fans. Over a
wide range of operating points, the mixed flow fan provides the quietest and most efficient selection.
Model comparisons based on similar outer tube diameters.
Performance
Mixed Flow
Fan Size
Sound Power (LwA) Static Efficiency
Mixed Flow
(QEI-L, QEI-I/II)
Inline
Centrifugal
Vane Axial
Mixed Flow
(QEI-L, QEI-I/II)
Inline
Centrifugal
Vane Axial
15,000 cfm
@ 1.0 in. wg
24 90 dB 100 dB 103 dB 43% 17% 34%
25,000 cfm
@ 2.0 in. wg
36 86 dB 93 dB 102 dB 68% 45% 56%
50,000 cfm
@ 4.0 in. wg
49 92 dB 98 dB 111 dB 71% 60% 59%
Axial Fans : Straight through
nearly linear airflow.
Centrifugal Fans: Two 90°
deflections, before airflow
exits the fan.
Mixed Flow Fans: Slight
airflow deflection from
straight through.
Airflow Profiles
Axial Centrifugal Mixed Flow