Models 14.4 - 26.4, controller pCO
2
Blue Box - Page 74
8.2.8 Evaporator low temperature chilled water protection
If the evaporator leaving water temperature is lower than the limit value programmed in the low temperature
chilled water protection set-point, the controller will stop all the compressors and activate the low temperature
water alarm.
This alarm must be reset manually and the compressor restarted only when the evaporator leaving water tempe-
rature is equal to or higher than the alarm trip value, increased by the low temperature water differential.
The low temperature water alarm can only appear when the unit is switched on (in stand-by conditions the freeze
alarm is not operational).
8.2.9 Evaporator anti-freeze protection electric heater (optional)
In conditions that lead to tripping the freeze alarm, the controller energises the heater.
The heater remains powered for the entire time that the conditions for the freeze alarm continue.
Unlike the low water temperature alarm, which is enabled only when the unit is powered on, the anti-freeze
heater can be energised when the machine is on stand-by.
8.2.10 Compressor operation
When the unit is running correctly and no general alarms are present, the microprocessor controller starts the
compressors in accordance with the water temperature reading.
Compressor starts are staggered in accordance with preset delay intervals, thus avoiding excess input current
surges.
Before starting a compressor, the microprocessor checks the value of the delivery pressure by means of the
relevant transducer, the status of the high pressure switch and the compressor motor windings temperature by
checking the thermal protection.
When the compressor has been started, tripping of any of the safety devices will cause the compressor to stop
immediately and an alarm will be displayed.
While the compressor is running, discharge pressure and suction pressure are monitored constantly by means of
the relevant sensors.
On unit start-up the first compressor is started with a delay, set on the microprocessor controller, after the start of
the hydraulic system circulating pump.
Once started, each compressor must run for a minimum operating period, unless a critical alarm should trip in the
meantime.
The critical alarms which can stop the compressor during the minimum operating time are the high pressure
alarm and the compressor thermal cut-out alarm. Once stopped each compressor can be restarted only after a
minimum idle time or after a minimum time interval between two consecutive starts has elapsed.
The consecutive starting of two compressors or the consecutive starting of one compressor, is executed with
minimum delay intervals equal to the capacity step activation time.
Stopping compressors is also performed with a minimum programmed delay interval.
8.2.7 Heat pump mode operation
In heat pump operation, the controller increases the water temperature value, maintaining it as close as possible
to the programmed set-point.
Management of compressor operation is performed in the same way as already illustrated for chiller mode
operation.
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