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4.7 Air system
4.7.1
Internal air fans
Depending on the configurations, there may be only supply fans or also return fans in the units.
The fans are radial fans with reverse blades, with external rotor motor directly coupled to the impeller.
The radial fans are called "EC", with electronically commutated brushless motor. The fan is powered by mains AC
voltage, and speed control is obtained via DC 0-10V control signal coming from the microprocessor installed on the
unit. This makes it possible to set the air flow rate through the parameter being displayed.
The motors have alarm signalling, which includes thermal overload protection, overcurrent, undervoltage, absence
of one or more phases and seized rotor.
The EC fans are not provided with a contactor and are constantly live as soon as the main disconnect
switch of the unit is closed.
4.7.2
Flow rate sensor for fans
Units with "EC" fans are provided with a differential pressure transducer that detects the pressure difference between
the inside and the outside (upstream) of the intake nozzle. The air flow rate is proportional, for each fan/nozzle pair,
to the square root of the pressure difference according to the equation:
where
- Q = total air flow [m3 / h]
- n = number of fans in the unit
- k = constant according to the fan nozzle
- ΔP = pressure difference measured on the nozzle [Pa]
The characteristic constant "K" for the nozzles used is:
- Fan of diameter 450: k = 217
- Fan of diameter 500: k = 281
- Fan of diameter 560: k = 350
The differential pressure value and the air flow rate can be shown directly on the display of the microprocessor that
carries out automatic control of the air flow rate.
4.7.3 Air flow sensor
This device prevents the unit operating in the absence of air flow. The control is carried out by a differential pressure
switch that measures the pressure difference between upstream and downstream of the evaporating coil and the air
filter. The microprocessor alarm comes on later than intervention of the sensor.
To check their operation, open the automatic circuit breakers of the compressors, from the microprocessor card
remove the terminal with the control signal for the EC fan (for identification, refer to the wiring diagram), and then
switch on the unit. The microprocessor alarm should appear within a few tens of seconds.
Translation from original instructions
Installation manual
18
We reserve the right to make changes without any prior notice.
UATYQ*Y1
Packaged Rooftop
4P522680-1
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