Page 6 / 14 Ausgabe SIEMENS-E oA 03 11 04
4 Operation
4.1 Function cooling / heating and dehumidify
The unit operation is completely automatic; all parameters are controlled by the integrated
microprocessor controller type Microface. The sensor installed inside the unit reads permanently the
return air conditions and passes the information on to the Microface controller. The controller compares
the values received (Actual) with the values required (Set Point) and operates the unit components as
required in order to keep the air conditions inside the required limits. Functions to be activated or
deactivated are Cooling, Heating and Dehumidification.
Cooling:
The compressor gets started up if the temperature of the return air into the unit exceeds the preset value.
After entry into the unit the air passes first the return air filter and than the evaporator coil where the air
gets cooled down. Afterwards the conditioned air gets discharged back into the room via supply air grills.
The heat of the air coming from the room loads and the heat of the compressor-motor get transferred first
into the refrigerant and than via the condenser to the ambient. The capacity of the condenser depends
on the condenser fan speed and is controlled by the Variex-device. This ensures a constant and
sufficient condensing pressure even at low ambient temperatures and a permanent and sufficient supply
of liquid refrigerant to the thermostatic expansion valve (TEV).
An appropriate metal made pre-filter protects the condenser-coil from rough dirt. It is possible to remove
and clean it from the front of the unit by opening the front panel and remove the cover panel from the
condensing section.
Heating:
The electrical heater is located inside the air conditioning unit. The heater gets activated if the
temperature of the return air into the unit drops below the preset value. The cooling compressor is
switched off. The heater is protected by a thermal safety switch with manual reset.
Dehumidification:
For dehumidification the compressor gets started up if the humidity of the return air into the unit exceeds
the preset value. After entry into the unit the air passes first the return air filter and than the evaporator
coil where the air gets cooled down and the moisture contained in the air gets removed. Afterwards the
conditioned air gets discharged back into the room via supply air grills.
If the air temperature during this operation drops 0.1 K below the temperature setpoint the electr. heater
heats up the air prior to its discharge back into the room.
4.2 Fan speed control for condenser (VARIEX)
This device ensures the correct unit operation even at low ambient temperatures (down to –25°C). A
pressure sensor is positioned so as to detect permanently the condensing pressure of the refrigerant
circuit. Depending on the actual condensing pressure an electronic fan speed controller (VARIEX)
adjusts the fan speed in order to keep the condensing pressure within the defined limits. In this way,
besides optimising the compressor operation, a significant reduction of the sound pressure level (during
the night) is achieved. Furthermore this device ensures an reliable start up of the compressor at very low
ambient temperature.
5 Microprocessor control
5.1 Cooling/Heating and Dehumidification
The control algorithm of the microprocessor control type Microface is focused on the individual control of
either the cooling OR the heating operation of the unit. The Microface controls any activation and de-
activation of the individual components of the unit and ensures a reliable and long-term operation of the
unit.
