Sharp JX-9400 Informations techniques Page 121

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The two ports of this manometer are connected to pressure taps located on
both sides of the fan (see Figure 5.13). Care should be taken to avoid too much
dynamic pressure on these taps. It is advisable to install the pressure taps
perpendicular to the airflow, preferably close to the air duct wall, and at
locations where the air velocity is about the same on both sides of the fan so
that the dynamic pressure, if any, is the same on both sides. If the pressure
varies significantly when moving one of the pressure taps, this means that the
dynamic pressure has an effect.
On most air handling units, a differential pressure switch is installed to
check the function of the fan. This switch is connected by two pipes to taps
installed in the ducts before and after the fan. These taps can be used to connect
the differential manometer, but the safety switch should be either disabled or
short-circuited. Otherwise, the fan motor will stop as soon as the pipes of the
pressure switch are disconnected.
Measurement of electric power
The electric power used by the fan motor is measured with a wattmeter, which
should be wired to the fan according to Figure 5.14. This instrument measures
265 Pa
Dp
q
Figure 5.13 Installation of the differential manometer to measure the
pressure differential across the fan
R
S
T
U
V
W
Voltage
inputs
U
V
W
Current
inputs
13.3 kW
Figure 5.14 Schematics of electric power measurement on a
three-phase motor
100 Ventilation and Airflow in Buildings
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