STXC2 User’s guide
Version 2.0
26 of 30
3. Control strategy.
3.1 Ventilation.
When all the safety components (frost, fire and fan failures) are in ON-position and the ventilation
unit is turned ON, the fresh air damper and the exhaust air damper opens. After 30 seconds the fans
start. The fans will then run with the settings input in the control system.
3.1.1 Fresh air reduction at low outside temperatures.
The supply fan speed is reduced gradually to 2/3rds of the set point value, when the supply
temperature has reached a minimum temperature.
The function can be selected in the configuration menu.
3.1.2 Filter surveillance.
The control system has an automatic surveillance of dirty filters.
The control system accelerates the fan motors up to the selected ”filter check value”.
350 seconds after the fan motors are accelerated up to their maximum speed they run for a further
50 seconds. Data for the ventilation unit is then recorded.
When the control signal is increased by 10% (to reach the same air volume pressure) alarm for dirty
filter is given and the indication LED on the MMI STCU shifts to yellow.
3.2 Temperature control.
On the MMI STCU the desired room or supply temperature is selected between 15 and 35°C. The
control system keeps the room or supply temperature constant by controlling the reheater coil,
bypass damper (air-to-air plate heat exchanger) or speed control of the heat wheel.
The heat requirement is split into 1/100 (0-100%). The temperature P-band setting (5 to 50°C) is
made on the control circuit board STXC2 in the ventilation unit.
Reheat (HTS)
Extra cool (ECS)
0 35 40 50 55 75 85 100 Pb-band %
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Energy
recovery
(ERS)
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