Stulz Tel-Air-2 Series, Operating Instructions Manual

Page: 19 / 72

E/0618/35A/19
3.2 Operating method
Cooling
The shelter air is taken in by the radial fan, filtered and then cooled as it crosses the evaporator
coil. The treated air is then returned to the shelter through the supply air opening. The
compressor operates in order to cool the air.
Free-cooling
There is a damper equipped with servomotor which directs internal and external air flows. The
damper is located in the central part of the conditioner. External air is taken in through an
opening near the damper while the internal air is discharged by overpressure through an opening
located above (TLF/TLD) or below (TLU) the other one.
This damper is proportionally controlled by a modulating signal from the C2020 controller. Its
position can be adjusted from 0 to 100% of fresh air, to regulate free-cooling capacity.
Assisted free-cooling
When the temperature of the external air is low enough to enable the free-cooling mode, but the
effect of this operating mode is not sufficient to keep the internal temperature within the required
range, the compressor is switched on while the free-cooling damper remains open. In this way,
the evaporator cools the external air rather than the internal re-circulating air, combining the
benefits of the free-cooling and the cooling modes.
Emergency ventilation (optional)
When there is a power failure, part of the unit (evaporator fans, control components and the free-
cooling damper motor) is powered by an emergency 48 VDC power supply. In this way,
continuous circulation of air inside the shelter is always assured. This circulation of air is
combined with free-cooling when the conditions required to enable this mode are satisfied.
Units with direct current emergency ventilation always require an external direct
current power line even when mains power is present.
Heating (optional)
With the heating elements option, the units include an electric heating element. When the
temperature is low, the heating coil turns on (compressor off) and the free-cooling damper is in
complete re-circulation position, in order to heat internal air. This mode is controlled by the
C2020 microprocessor.