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10 SysAer
3.3.2. COMPRESSOR CYCLING
3.4. DEFROST MODE
The 2 circuits can not defrost at the same time.
If both circuits are requested to defrost at the same time, one circuit will be kept waiting.
NB.: During defrost, the main fan stays on.
When one circuit is defrosting, the second is forced to full heat capacity (one or two compressors ON,
depending on the unit configuration) and maintained 3 minutes after the end of defrost, to attenuate the
effect of defrost on supply air temperature. Moreover, the second circuit is not allowed to defrost during the
5 minutes after the defrost of the first circuit.
3.5. MAIN FAN
The main fan is the first device that starts up within 10 seconds when the unit is switched on. When the unit
is switched off, the main fan continues to operate for about 50 seconds according to the options:
a post-ventilation period of 30 seconds occurs for electric or gas auxiliary heating.
In normal operation (unit ON), the main fan is always ON. But it can be switched OFF depending of the
configuration of the scheduling (see the related part).
For the purpose of saving energy, the fan speed can be reduced when the temperature setpoint is reached
in the room (option to enable via the P9 screen of the service menu)
The main fan, as all the other electric components of the unit, can be started by the digital output test procedure
(Maintenance menu) if there are no alarms to inhibit it.
3.6. TEMPERATURE-BASED FREECOOLING AND FREEHEATING CONTROL
With the unit working in FREECOOLING or FREEHEATING mode, external air can be exploited when its
temperature conditions are favourable with respect to the temperature of the room air.
This control is not
available without the ECONOMIZER (2 or 3 dampers) Temperature control option.
The compressor cycling is driven by different delays:
²
Compressor start-up delay after main blower has been started: the compressor will switch ON only
when the blower is ON for about 10 seconds.
²
Minimum compressor OFF-time: it makes sure that the compressor stays OFF for a while before it is
switched ON again.
²
Minimum compressor ON-time: this time makes sure that the compressor, once switched ON, stays
ON for a while before it is switched OFF again (should any alarm be activated, the compressor will
switch OFF immediately regardless of the above-mentioned delays ).
²
Time lag between starts of a compressor: this time ensures that, once a compressor has been
started, the said time is taken before this compressor starts again (limits demands per hour).
²
Time lag between the starts of different compressors: this time ensures that the said time is taken
before other compressors can switch ON (limits current peaks).
The circuit must be de-frosted if one of the following conditions is fulfilled:
²
Air temperature (RAT) – the de-frosting temperature (OCT) is greater than or equal to a difference
(12°C by default) for a defined period (30 s by default)
²
The evaporation pressure is less than 1.8 bar for 5 s.
Preventive de-frosting can be used according to the outdoor temperature or if a circuit can be stopped due
to icing.
During de-frosting, the flaps of the saver close to use the building's heat to de-frost the batteries.
The de-frosting phase ends if the de-frosting temperature (OCT) is greater than the value set (18°C by
default).
For de-frosting that is too frequent (>3/h) or too long (10 min), an alarm is displayed.
