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3.2 INTERNAL WIRING DIAGRAM CLASS UNIT
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Operation and maintenance
instructions – CLASS UNIT TAC5
4.0 Functions
4.1 OPERATING MODE
There are five main operating modes. The operating
mode determines how the airflow or the fan torque
is modulated. The default operating mode is Airflow
control. Exceptions if Constant Torque mode has been
selected in the product setup menu, in his cases it is the
fan torque that will be controlled and modulated.
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1 - Airflow control:
Flow control involves operating the air handling unit to keep the pre-set airflow constant. The speed of the
fans is automatically regulated to provide correct airflow even if the filters begin to become clogged, air
terminals are blocked, etc. Airflow control mode is advantageous, since the airflow always is exactly as it was
from the beginning. It should however be noted that everything that increases the pressure drop in the
ventilation system, such as blocking of air terminals and dust accumulating in filters, causes the fans to run at
a higher speed. This results in higher power consumption and may also cause discomfort in the form of noise.
There are three airflow setpoints to be configured by the user (m³h K1, m³h K2, m³h K3).
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2 - Demand control 0-10V:
The airflow is controlled by a 0-10 V signal. The control signal is connected to terminals K2&GND. The assigned
supply airflow is set as a percentage of a linear 0-10 V signal. The user defines the link with 4 parameters: Vmin,
Vmax, m³h Vmin and m³h Vmax, applied to the following diagram. The demand control mode is also
available for modulating fan torque instead of airflow (relevant for backwards fans units without Kit CA).
The principle is identical to the demand control mode operation with the difference that Vmin and Vmax are
connected to a %TQ instead of m³/h.
A CO 2 sensor option is available for selection when ordering. Once this option is selected, the sensors are
prewired and pre-configured to be ready for use.
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3 - Pressure control:
The airflow automatically varies to provide constant pressure in the ducting system. This type of control is
also called VAV control (Variable Air Volume).
Pressure on supply: the airflow of the supply fan(s) is modulated to maintain a certain pressure Setting
constant. The pressure is measured by a pressure sensor located in the supply air duct.
Pressure on exhaust: the airflow of the exhaust fan(s) is modulated to maintain a certain pressure Setting
constant. The pressure is measured by a pressure sensor located in the extract air duct.
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4 - Mode OFF :
This stops the AHU
Operation and maintenance
instructions – CLASS UNIT TAC5
In all the operating modes, the supply fan(s) will operate
as per the assigned mode and parameters. The exhaust
fan(s) will operate according to the chosen percentage
of the supply fan (%EXH/SUP ratio). The four main ope-
rating modes are:
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