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6.4.4
Starting
pRack PR300T can manage diff erent types of compressor starting:
•
Direct
•
Part-winding
•
Star/delta
The type of starting can be selected and the related parameters set in
main menu branch C.a.f/C.b.f.
For part-winding starting, the delay in activating the digital output that
controls the second winding needs to be set:
Compressor request
Line
Part-winding
Delay
For star/delta starting, the star time, the delay between the activation of
the line and star digital input, and between the delta and star digital input
all need to be set, as shown in the fi gure:
Compressor request
Line
Part-winding
Delta
Star-line delay
Delay
6.4.5
Safety times
pRack PR300T can manage common safety times for each compressor:
•
Minimum on time
•
Minimum off time
•
Minimum time between consecutive starts
The related parameters can be set in main menu branch C.a.f/C.b.f.
Note: for two lines, a further delay can be set between starts of the
compressors on diff erent lines, so as to avoid Simultaneous starts. See
paragraph 6.6.6 for the detailed description of the synchronisation
function for two lines (DSS).
6.4.6
Balancing
pRack PR300T can control any balance valves in parallel with the
compressors.
This function can be used to activate a communicating solenoid valve
between compressor suction and discharge, for a set time, before each
individual compressor starts. In this way, the suction and discharge
pressure can be balanced and the compressor can be started in more
favourable conditions.
The balancing function can be enabled and the related activation time
set in main menu branch C.a.f/C.b.f.
Copyright HPL March 2021
Fig. 6.s
Start-delta
delay
Fig. 6.t
6.4.7
Economizer
pRack PR300T can activate the economizer function to boost compressor
effi ciency by injecting vapour. Some of the liquid is taken from the
condenser, expanded through a valve and then sent to a heat exchanger
to cool the liquid leaving the condenser. The resulting superheated
vapour is injected into a special section of the compressor.
The function can be enabled and the related parameters set in main
menu branch E.c.a.b.
The economizer is only effi cient for high compressor activation capacities,
typically over 75 %, therefore the economizer function control valve is
only activated when exceeding a set threshold.
As the economizer tends to increase the condensing pressure, this needs
to be controlled to ensure the high condensing pressure alarm is not
generated. In addition, the injection of vapour decreases the discharge
temperature and so this value also needs to be monitored.
Consequently, the three conditions for activation of the economizer
function are:
•
Capacity above a set threshold
•
Condensing pressure below a set threshold (with reset diff erential)
•
Discharge temperature above a set threshold (with reset diff erential)
Note: the function can be activated on a maximum of 6
compressors.
6.4.8
Liquid injection
As an alternativ e to the economizer, pRack PR300T can manage the
injection of liquid into the compressors (the two functions are alternative,
as the point of vapour injection into the compressor is the same).
The function can be enabled and the related parameters set in main
menu branch E.d.a.b/E.d.b.b.
Liquid injection is used to protect the compressor, and in fact decreases
the discharge temperature. Operation is Similar to the economizer
function, with the diff erence that the expanded liquid is not sent to a
heat exchanger, but rather directly into the compressor. The function is
only activated when the compressor is on and the discharge temperature
exceeds a set threshold (with diff erential).
Note: the function can be activated on a maximum of 6
compressors.
6.4.9
Manual operation
pRack PR300T can manage 3 diff erent compressor manual operating
modes:
•
Enabling / disabling
•
Manual management
•
Output test
Enabling / disabling is managed in main menu branch C.a.f/C.b.f., while
manual management and the output test can be activated in main menu
branch B.b or B.c.
Enabling / disabling is used to temporarily exclude the compressors from
operation, to allow, for example, repair or replacement. The disabled
compressors are also excluded from rotation.
Note: enabling is the only compressor manual operating mode
that can be activated when the unit is on.
Both manual management and the output test are enabled by parameter
and remain active for a set time after the last button is pressed, after
which the unit returns to normal operating mode.
Manual management is used to switch the compressors on or off
without observing the control needs, however still considering any safety
devices (alarms, safety times, starting procedures) and respecting the set
confi guration of the inputs/outputs.
37
Page 86 of 172
P4114S Rev 03
pRack PR300T +0300018EN rel. 1.5 - 02.05.2017
ENG
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