27
ENG
Hecu CO
2
+0300085EN rel. 2.2 - 07.05.2019
The function can be deactivated when at least one of the following
conditions is true:
1. Compressor control OFF
2. Active compressor alarms
3. The cut-off threshold has been reached (P suction < cut-off threshold)
4. The evaporator request is equal to 0% (from MPXPRO or ULTRACELLA)
or "Enable compressor from DI" is NOT ACTIVE (OFF due to control)
5. The compressor has been active for longer than a settable timeout
(default 10 minutes)
6. The suction pressure is greater than the operating set point
7. The outside temperature is greater than the set threshold (default
-18°C) + the diff erential (default 8°C) set on the following screen
When the function is deactivated:
The compressor set point is reset to its normal value over a set time
(default 2 min, see time on screen Cad15).
6.4 Compressor management on LT units
(DSS and independent)
Management with DSS1 and DSS3
This involves synchronised management of the compressors. It
is recommended to activate both DSS1 and DSS3 so as to avoid
simultaneous compressor starts and optimise operation of the LT stage
in all operating conditions.
Below is a description of the functions that can be set:
DSS1: screen Fib02
This function prevents the two compressors from starting simultaneously.
Once the required percentage for activation has been reached, the LT
compressor waits for the parallel compressor to start, and then is turn
started after a set delay.
DSS3: screen Fib04
Start the parallel compressor (L1) when starting the LT compressor (L2).
If NO is selected, the parallel compressor cannot start without a request.
When DSS1 is enabled, the following parameters remain hidden on
screen Fib04:
• Switch on period: 180s (hidden). During this period, the parallel
compressor request is forced to 50% to allow it to be started;
• Timeout: 180s (hidden). The LT compressor waits for the parallel
compressor to start, however is switched on in any case after the set
timeout has elapsed;
• Force off line 2 if line 1 is off : YES (hidden). The LT compressor (L2) is
switched off when the parallel compressor (L1) is switched off .
When DSS1 is NOT enabled, the following parameters can be modifi ed
on screen Fib04:
• Switch on period: 0-999s (def 180, this is the time that the parallel
compressor request is forced to 50% to allow it to start);
• Timeout: 0-999s (def. 180s; this is the time that the LT compressor waits
for the parallel compressor to start, after the set timeout it is switched
on in any case);
• Force off line 2 if line 1 is off : NO/YES.
• YES Æ forces the LT compressor off if the parallel compressor cannot
start.
• NO Æ forces the LT compressor off if there is an alarm on the parallel
compressor.
Independent management
Activating independent management on screen Fib05 automatically
disables DSS1 and DSS3, and the compressors can be switched on/off
independently, based on their own request. Some safety logic s also
guaranteed.
Below is a description of the functions that can be set.
By selecting YES, functions DSS1 and DSS3 are automatically disabled
and:
• the LT compressor can start even if activation of the parallel compressor
is NOT requested;
• the LT compressor cannot start if the parallel compressor is off due to
timing or alarms;
• the Parallel compressor is not activated if the LT compressor is not
operating (no LT required, LT compressor off due to timing or alarms).
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