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In case no probe is present, fans are enabled simultaneously with the compressors; in case of single coil,
fans are enabled when at least one compressor is on; in case of separated coils, each compressor controls
the fans of its own circuit.
2.5.3 Prevent function
High pressure alarm prevention with compressors stopped. Normally, the condensing fans turn on only if
compressors are enabled, but in this case they are forced so as to decrease pressure and try to prevent the
high pressure alarm, which would cause unit shutdown. Pressure increase with compressors stopped may
be due to radiance on the coil. In case of 0-10V modulating fans, modulation is by-passed.
2.5.4 Speed-up function
To overcome inertia at high-power modulating fans peak, they may be started at maximum speed for some
seconds, then speed decreases to the required value and modulation starts.
2.5.5 Pressure
–
temperature conversion
Both pressure and temperature probes can be selected. In case of pressure probes, branch I/O screens
display the temperature value corresponding to the pressure of each probe, based on the coolant type (to be
selected in the Manufacturer branch).
2.6 Temperature set point compensation
The temperature set point can be “compensated” automatically for comfort reasons; for example, think about
a commercial concern in which people frequently enter and go out: if internal temperature is 10°C lower than
the external one, the thermal rush may annoy people and could be prejudicial to their health. The maximum
difference between internal and external temperatures should not exceed 6°C in order to obtain optimum
comfort. In this case, the compensation function increases the set point by 4°C, consequently increasing the
ambient temperature; this function prevents the difference between internal and external temperature from
exceeding 6°C.
Compensation requires a temperature probe to be installed at the exterior. The function is managed based
on the values of compensation set point, differential and offset parameters, as shown in the following
diagram:
Compensation set
2°C
Compensation
offset
25.0 28.0
3°C
External
Compensation proportional band temp. (°C)
25.0°C
23.0°C
Temperature
set-point (°C)