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When entering the Neutral zone, the pRack PR300T software calculates
how the request needs to change in order to exit the Neutral zone at
minimum or maximum output, and applies one of the two values
according to the trend in variation in the control variable. For example, at
point P1 in the fi gure, the trend of the two requests is represented by the
segments with thin lines, and the request 'reverses' because at that point
the control variable has started increasing in value again.
Note: When exiting the Neutral zone, it is possible that the request
is not at the minimum or maximum value, where limitation is enabled for
of the modulating device variation speed.
6.3.4
Control with backup probes and/or probes not
working
pRack PR300T can use backup control probes that are activated when the
normal control probes are not working.
The backup probes must be enabled in main menu branch C.a.g/C.b.g
or D.a.g/D.b.g.
When diff erent pRack boards are used to manage the suction and
condenser lines, the backup suction pressure probe must be connected
to the board that manages the suction line, while the backup condensing
pressure probe can be connected either to the board that manages the
suction line or the board that manages the condenser line.
If the main control probes are not working and no backup probes are
fi tted, or the backup probes are also not working, or the corresponding
temperature probes are also not working, fi xed values are used for the
control request, set in main menu branch C.a.g/C.b.g or D.a.g/D.b.g.
6.4 Compressors
pRack PR300T can manage up to 2 suction lines with diff erent types of
compressors and capacity modulation devices, applying common types
of device rotation and controlling both the start mode and the safety
times for each type of compressor, as well as a number of accessory
functions. The compressor functions and related parameter settings are
enabled from main menu branch C.a/C.b. These features and functions
are described in detail in the following paragraphs.
6.4.1
Possible compressor confi gurations
pRack PR300T can manage diff erent types of compressors:
•
Reciprocating
•
Scroll
Moreover, a capacity modulation device is allowed for each suction line,
which may be one of the following, according to the type of compressor:
Compressors and modulation devices
Compressors
Reciprocating
Scroll
Note: The same modulation device is used on each line.
The maximum number of compressors and load stages per line varied
according to the type of compressor:
Compressors and modulation devices
Compressors
Maximum No.
Reciprocating
12
Scroll
12
Copyright HPL March 2021
modulation devices
Inverter
Inverter
Digital Scroll™
Tab. 6.a
Load stages
24 total
24 total
Tab. 6.b
The compressor size refers to its capacity and number of load stages or
to the inverter presence, therefore diff erent sizes need to be defi ned
for compressors with the same capacity yet a diff erent number of load
stages. The inverter is always associated to size 1.
Tutorial: below is one example of some possible confi gurations:
•
One line, 4 reciprocating compressors with the same capacity, the fi rst
with inverter (2 sizes).
•
One line, 4 scroll compressors with the same capacity, the fi rst Digital
Scroll™ (1 sizes).
•
One line, 4 reciprocating compressors with the same capacity, the fi rst
two with 4 load stages, the other two not capacity-controlled (2 sizes).
•
One line, 4 reciprocating compressors with the same capacity and 4
load stages each (1 size).
•
Two lines, line 1 with 4 scroll compressors, the fi rst Digital Scroll™, line
2 with 4 reciprocating compressors, the fi rst with inverter (1 size line 1,
2 sizes line 2).
6.4.2
Rotation
pRack PR300T can manage 4 diff erent types of device rotation:
•
FIFO (First In First Out): the fi rst device to start is also the fi rst to stop
•
LIFO (Last In First Out): the last device to start is the fi rst to stop
•
By time: the device with the least number of operating hours starts and
the device with highest number of operating hours stops
•
Custom: the on/off sequences are defi ned by the user
NB: Diff erent Sizes of compressors can only be managed with
Custom rotation.
The type of rotation is selected and the corresponding parameters set
during the start-up procedure or in main menu branch C.a.f/C.b.f.
The activation thresholds are calculated diff erently depending on
whether FIFO, LIFO, time or Custom rotation is used:
Device activation threshold calculation
Rotation
Threshold calculation
FIFO
Static: the range of variation of the control request is divided
LIFO
equally between the number of stages available
By time
Dynamic: the thresholds are calculated depending on the
Custom
capacity eff ectively available
Example 1: FIFO rotation, 4 compressors of the same capacity
without load stages.
The activation thresholds are 25, 50, 75 and 100 %.
C1
C2
25%
50%
Example 2: Custom rotation, 4 compressors with capacities of 10,
20, 30 and 40 kW. The activation thresholds with all the compressors
available are 10, 30, 60, 100 %.
C1
C2
C3
10%
30%
35
Page 84 of 172
C3
C4
75%
100%
Regulation request
Fig. 6.m
C4
60%
100%
Regulation request
Fig. 6.n
P4114S Rev 03
pRack PR300T +0300018EN rel. 1.5 - 02.05.2017
ENG
Tab. 6.c
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