24
ENG
Hecu CO
2
+0300085EN rel. 2.2 - 07.05.2019
time
rps
Req
Start-up
speed
Req = min rps
min rps
min ON
time
Fig. 6.e
If after 15 seconds from when the compressor starts the pressure
diff erential is less than 0.2 barg above the value measured on starting,
Hecu CO2 stops the compressor and generates a "No compressor start-
up” alarm. This alarm is automatically reset and Hecu CO2 tries to start the
compressor fi ve times after a 30 second delay. After the fi fth attempt the
alarm is no longer automatically reset.
The corresponding parameters are found under Compressors Æ
Advanced Æ screens Cag50, Cag51:
Pressure di erential during start-up
The BLDC compressor cannot start if the pressure diff erential is greater
than a threshold defi ned by the compressor manufacturer. This limit
depends on the maximum current delivered by the inverter. As soon
as the pressure diff erential falls below the minimum threshold, the
compressor can start.
The corresponding parameters are found under Compressors Æ
Advanced Æ screen Cag49:
When the pressure diff erential is below 1 barg – 0.5 barg (fi xed value), the
compressor is ready to start.
Equalisation
Hecu CO2 makes it possible to equalise the pressure across the
compressor, simplifying condensing unit start-up. The equalisation mode
can be selected on screen Caf18: either "DELTA PRESSURE" or "TIME".
If equalisation is based on the pressure diff erential (delta), the controller
measures the DeltaP between compressor suction and discharge
pressure. When the diff erential is below the value set on screen Cag49,
the compressor is enabled to start.
In the event of timed equalisation, the controller will not measure the
pressure diff erential but rather will enable the compressor to start after
a fi xed equalisation time, equal to the minimum compressor off time,
which can be set on screen Caf35.
The valves used for equalisation and the percentage of opening to be
maintained during the procedure can be set on screen Caf19. For Hecu
CO2, the following valves can be selected: HPV, RPRV and bypass solenoid.
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