Datasheet

MEASUREMENT of AIRFLOW and STATIC PRESSURE
Technical Information
It is very difficult to measure airflow and
static pressure, and there are cases
where measured values vary depending
on measuring devices. There are two
kinds of measuring methods; double
chamber method provided by JIS and
AMCA (Air Moving and Conditioning
Association) and wind tunnel method.
Our company adopted the double
chamber method, and therefore we will
explain it hereinafter.
The auxiliary blower (fan) adjusts an
inner pressure by sucking out air. At this
moment, as airflow and static pressure
are varied by opening or closing the
damper, each value is read on the
manometer.
Maximum airflow:
The damper opens, and the auxiliary
blower sucks out air so that static
pressure becomes zero. At this moment,
the pressure differential (airflow
differential pressure: Pn) in chambers A
and B becomes maximum. The airflow
whose Pn is measured and which is
determined by using the equation shown
at right is called the maximum airflow.
Maximum static pressure:
When the damper is completely closed,
the pressure in chamber A becomes
maximum. At this moment, the pressure
differential (static pressure: Ps) in
chambers A against atmospheric
pressure is called the maximum static
pressure.
Double chamber measuring device
Ps Pn
Measured fan
Static pressure
manometer Airflow manometer
Airflow adjusting damper
Auxiliary blower
Nozzle
Chamber BChamber A
1. Equation
Airflow Q =
In the above equation,
C: Flow coefficient of nozzle
D: Nozzle diameter (m)
γ: Air density =
t: Temperature(°C)
P: Atmospheric pressure(Pa)
g: 9.8(m/s
2
)
Pn: Airflow differential pressure (Pa)
Ps: Static pressure (Pa)
2. Unit conversion table
1) Airflow
2) Static pressure
m
3
/min. l/s
CFM
(ft
3
/min.)
1 16.678 35.334
0.06 1 2.1186
0.0283 0.472 1
Pa mmH2O (mmAq)
1 0.10197
9.80665 1
NOISE MEASUREMENT
Operation noise is measured by hanging
the fan in midair. For the DC fan, noise is
measured in dB(A) 1 m from the front of
the air-intake side. For the AC fan, noise
is measured in dB(A) 1 m from the front
of the air-intake side and the side of the
fan.
The background noise complies with the
section in JIS B8346 that states that it
should be at least 10 dB lower than the
target noise reading.
Our measurements were made in an
anechoic chamber with a background
noise of approximately 15 dB.
Fan motor
Microphone
DC FAN MOTOR 1 m 3.281 ft
(AC FAN MOTOR 1 m 3.281 ft)
Fan motor
Microphone
AC FAN MOTOR 1 m 3.281 ft
COUNTERMEASURES
AGAINST MOISE
Our fan motors are designed placing
great importance on low noise. However,
take into consideration the following
points because noise is influenced
depending on the mechanism design
used.
1) Leave a space between the rear side
of the fan suction opening and the cooled
object.
2) When using two or more fan motors,
leave a space between the fans.
3) According to the mounting hole
dimensions (page 22), design so that the
mounting face and blades are not
crossed.
4) Grease in the bearings will deteriorate
and noise will gradually increase as the
fan is used. The replacement period will
differ depending on the conditions of use
and allowable sound level. We
recommend periodic replacement.
02/2006
16