Wheel Characteristics; Belt Drive: Fan Class; Direct Drive: Percent Wheel Width; Sound Power Versus Sound Pressure - Greenheck QEI-L Manual

Wheel Characteristics

Belt Drive: Fan Class

Class I and II fans have different wheel designs with different performance characteristics.
Class I mixed flow wheels are optimized for performances involving low pressures and high volumes. Class II
wheels are designed for a steeper fan curve with higher pressure capabilities. This is illustrated in the graph
with the two different class wheels plotted at identical fan RPMs.
When selecting a mixed flow fan, it cannot be assumed that moving into a Class II fan will produce the same
results as a Class I mixed flow fans. Model QEI-L utilizes a Class I wheel.

Direct Drive: Percent Wheel Width

Direct drive mixed flow fans are optimized for performance requirements by the use of partial width wheels. This
is necessary because the fan RPM is commonly fixed and identical to the motor RPM. A reduction in the width
of the wheel (or the air passage) results in reduced airflow capacity and a steeper fan curve. This is similar to
the effect of a reduced pitch in a direct drive vane axial fan. QEID wheels are available in 5% increments from
50 - 100% wheel width.
QEID fans can be used in conjunction with variable frequency drives (VFD's) for variable air volume (VAV)
systems. In these applications, the wheel width is optimized to ensure efficient operation and stable
performance throughout the turndown range. VFD's are also used for final system balancing and to reduce the
airflow when building requirements are reduced. In this case, the fan and wheel width are selected using the
final design CFM and static pressure.
50% Wheel Width
50% Wheel Width

Sound Power versus Sound Pressure

The sound values displayed on the performance pages are in terms of inlet sound power (
power (L ). These values are the acoustic power radiating from the inlet and outlet of the fan, respectively.
A
W
o
Sound pressure, expressed as dBA, is the acoustic pressure at a point in space which can be measured with a
microphone or can be heard. To convert sound power (L
are applied for a hemispherical free field.
100% Wheel Width
100% Wheel Width
dBA = L A - correction
w
Note: Refer to AMCA Publication 303, Application of Sound Power Level Ratings for additional information on calculating typical sound pressure levels for fan installation.
Class II
Class I
CFM
Intermediate
50%
Wheel
Wheel
Widths
Width
Intermediate
50%
Wheel
Wheel
Widths
Width
CFM
CFM
A) into sound pressure (dBA), the following corrections
w
Distance from Fan
Correction
50% Wheel Width
100%
Wheel
Width
100%
Wheel
Width
100% Wheel Width
A) and outlet sound
L
i
W
3 ft. (0.9 m) 5 ft. (1.5 m)
7 db 11.5 db
Inter
50%
W
Wheel
W
Width
CFM
10 ft. (3.0 m)
17.5 db
7