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The prevention or authorisation of free cooling mode
operation can be controlled by the local interface or
remotely by customer contact 4 or by the CCN network.
If pre-cooling is prohibited, free cooling starts if:
• the outside temperature is lower than the
programmed threshold value (USER2 menu, item 15)
• the difference between outside temperature and
control point is higher than the minimum operating
threshold value (4°C)
If pre-cooling is authorised, free cooling starts if:
• the outside temperature is lower than the programmed
threshold value (USER2 menu, item 15)
• the difference between outside temperature and leaving
water temperature is higher than the minimum
operating threshold value (4°C)
To stop the free cooling, a hysteresis of 0.5 K has been applied
to these temperatures. When free cooling is stopped, a new
session is prohibited for one hour.
Free cooling change-over procedure:
• The compressors stop (if the unit was operating)
• The high/low pressure is equalised by opening the EXV
• The three-way valve receives the command to open
Procedure to start up one circuit in free cooling:
• Wait for the complete opening of the three-way valve
• Draw a vacuum and transfer the residual compressor
charge to the free-cooling circuit by starting up a
compressor (“pump-down”),
• Start up the fans
• Cycle the pump (rotation for 10 seconds, shut-down
for 4 seconds)
• Verify that a differential pressure is established at the
pump terminals.
During free cooling operation all fans are activated except
when the differential between the outside temperature and
the leaving water temperature reaches a certain threshold
value. In this case only half of the fans are energised.
Expansion valve (EXV) control is based on the difference
between the outside temperature and the leaving water
temperature to prevent disengaging or cavitation of the
refrigerant pump.
The same pump stability logic can activate a pump-down
cycle, based on the pressure level detected in the compressors
at shut-down (up to three times in a free-cooling cycle) to
make the full refrigerant charge in the free-cooling circuit
available.
The Pro-Dialog Plus control system has many fault tracing
aid functions. The local interface and its various menus
give access to all unit operating conditions. If an operating
fault is detected, an alarm is activated and an alarm code is
stored in the Alarm menu.
The alarm LEDs on the summary interface (see section
4.1) give a quick display of the status of each circuit and
the unit as a whole.
• A flashing LED shows that the circuit is operating but
there is an alarm.
• A steady LED shows that the circuit has been shut
down due to a fault.
The Alarm menu on the main interface displays up to 5
fault codes that are active on the unit.
When the cause of the alarm has been corrected the alarm
can be reset, depending on the type, either automatically on
return to normal, or manually when action has been taken
on the unit. Alarms can be reset even if the unit is running.
This means that an alarm can be reset without stopping the
machine. In the event of a power supply interrupt, the unit
restarts automatically without the need for an external
command. However, any faults active when the supply is
interrupted are saved and may in certain cases prevent a
circuit or a unit from restarting.
A manual reset must be run from the main interface using
the following procedure:
Hold down the MENU
button until the LED for
alarms lights. The 4-digit
display shows the number
of active alarms (2 in this
example).
0
0 2 ALArM
Press the Enter button until
“rESEt ALARrM” is shown
in the 4-digit display.
0 rESEt ALArM
Press the Enter button
again to validate the reset.
“Good” is displayed for 2
seconds then, “2 ALArM”
and then, “no ALArM”.
0 Good then,
2 AL then,
no ALArM
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