SystemAir HHFlex C, Operating Instructions Manual, Page: 22 / 47

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4.3 Fan speed control
Different options for ventilation control can be selected:
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Fixed fan speed control (low or high speed)
•
Air flow control (low or high airflow)
•
Supply duct pressure control
•
Supply and exhaust duct pressure control
•
Indoor air quality control
4.3.1 Fixed Fan Speed Control
To activate this function, set Fan control to Fixed (on/off) or Fixed (high/low) in the configuration menu.
Setpoints for this function are available in the menu Actual/Setpoint.
Supply and extract fan are ‘On’ or ‘Off’. Supply and extract air volumes or pressures are not closed loop controlled and
vary with airside resistance.
This setting is mainly intended for commissioning, inspection and maintenance, but can also be selected in the fan speed
control menu.
In the frequency inverter the maximum motor speed limit is set on the design fan speed x 1.05. To run the unit on design
duty, the setpoints for fixed fan speed are set to 95%.
4.3.2 High / low speed operation
For certain applications two different setpoints fixed speed operation can be selected within the controller. The setpoints
for high/low speed will be the rated speed of the fans in the air handling unit. The setpoints for low speed shall be entered
as a percentage of the design speed performances of the supply and extract fan. For each fan a different percentage can be
inputted.
High and low speed operation can be programmed in the internal clocktimer (See Time Program menu). To activate this
function, set Runmode to Internal clock
As an option low speed operation can also be selected with a remote contact on a digital input of the controller! To
activate this function, set Runmode to Contacts
4.3.3 Air Flow Control
To activate this function, set Fan control to Flow or Flow (high/low) in the configuration menu.
Setpoints for this function are available in the menu Actual/Setpoint, flow supply fan and flow extract fan.
Supply and extract air are maintained at the desired airflow rate independent of the actual airside resistance. Supply fan
and extract fan are controlled by separate setpoints.
4.3.4 High / low air flow operation
For certain applications two different setpoints for fixed flow operation can be selected within the controller. One
setpoints for normal operation and one setpoint for low speed. For each fan a different air volume can be inputted.
Normal and low speed operation can be programmed in the internal clocktimer (See Time Program menu). To activate this
function, set Runmode to Internal clock
As an option high/low speed operation can also be selected with remote contacts on digital inputs of the controller To
activate this function, set Runmode to Contacts.
4.3.5 Supply Duct Pressure Control
To activate this function, set Fan control to Constant pressure in the configuration menu.
Setpoint for this function is available in the menu Actual/Setpoint, Static duct pressure.
The actual supply airflow rate is measured, while the pressure in the supply duct is controlled at the required setpoint. The
extract airflow is controlled in order to maintain the correct flow ratio between supply and extract air flow.
The pressure sensor is not pre-assembled, but delivered in a cardboard box in the unit and has to be mounted at an
appropriate location in the ductwork.