Table of Contents
Advertisement
ENG
The activation screen resembles the one shown in the fi gure and is used
to override the outputs relating to the operation of the selected device,
e.g. compressor 1:
Manual mng.
Digital output board1
Compressor 1
Force to:
The output test is used to activate or deactivate the outputs (where
necessary setting an output percentage for the analogue outputs),
without observing any type of safety feature.
The activation screen resembles the one shown in the fi gure and is used
to override the outputs on the pRack boards, in the order they physically
appear on the board (without links to the devices):
Test DO
Digital output board1
D01
D02
Important:
manual mode and the output test can only be
activated with the unit off .
Both manual mode and above all the output test must be used with
special care and by expert personnel to avoid damage to the devices.
Digital Scroll™ compressors
pRack PR300T can use a Digital Scroll™ compressorä as the modulating
device for suction lines (one for each line). This type of compressor
features special operation, and is controlled by pRack PR300T as follows.
The related parameters can be set in main menu branch C.a.f/C.b.f. The
capacity is modulated by opening/closing a valve with PWM; when the
valve is ON the compressor delivers minimum capacity, while when the
valve is off the compressor delivers maximum capacity. In the following
description and fi gure, ON and OFF refer to the status of the compressor,
while operation of the valve is the exact opposite:
Compressor power request
Compressor PWM
modulation
ON
OFF
2s
13s
15s
Variable cycle time
ON
OFF
2s
18s
20s
The following data are provided by the manufacturer of the compressor:
•
minimum ON time 2 s
•
maximum cycle time 20 s
•
optimum cycle time 12 s
There are three possible operating modes:
•
Fixed cycle time
•
Variable cycle time
•
Optimised cycle time
Based on the operating mode selected, pRack PR300T calculates the
valve activation percentage that satisfi es the required capacity.
Copyright HPL March 2021
pRack PR300T +0300018EN rel. 1.5 - 02.05.2017
Bba02
OFF
Fig. 6.u
Bca10
NO
OFF
NO
OFF
Fig. 6.v
10% 67%
Fixed cycle time
10s
5s
15s
8s
5s
4s
12s
Fig. 6.w
Fixed cycle time
The compressor ON time is calculated as the percentage of the cycle time
corresponding to the required capacity:
T
= % Richiesta * Tempo di ciclo
ON
The cycle time can be set to the optimum value suggested by the
manufacturer to achieve maximum COP, or to a higher value to increase
resolution of the capacity delivered (a higher cycle time implies greater
continuity in the eff ective capacity that can be delivered).
Variable cycle time
The compressor ON time is set to 2 s and the cycle time is calculated
based on the required capacity:
T
CICLO
Optimised cycle time
The compressor ON time is set to 2 s and the cycle time is calculated
based on the required capacity for capacities less than 17 %, after which
the cycle time is set to 12 s and the ON time varies. In essence, this mode
is a combination of the previous two. This guarantees the maximum
possible COP and control rate (obtained with the 12 s cycle time) and the
maximum control range (starting from 10 %).
Note: the minimum capacity that can be delivered by Digital
Scroll™ compressors is Minimum ON time/Maximum cycle time = 2/30 =
6.7 %, which also depends on the selected control mode (for example, in
the fi rst case shown in the fi gure the minimum capacity delivered is
Minimum ON time/Cycle time = 2/15 = 13%).
Note: if high pressure prevention is enabled with activation/
deactivation of the devices, the Digital Scroll™ compressor delivers the
minimum possible capacity.
Starting procedure
pRack PR300T can manage the specifi c starting procedure for Digital
Scroll™ compressors, as represented as in the following fi gure:
4s
Request
Valve
Compressor
There are three stages:
1.
balance: the PWM valve is activated for 4 s, so that the compressor
delivers minimum capacity;
2.
compressor activation with 50 % capacity for 3 minutes;
3.
forced operation at 100 % for 1 minute.
During the starting procedure, the request sent by the controller is
ignored and only at the end of the procedure does the capacity delivered
start refl ecting the request. If the request is cancelled during the starting
procedure, the compressor stops at the end, then the minimum ON time
for these types of compressors is set to 244 s.
The starting procedure is performed when the compressor is started, while
it can be disabled for a set time by parameter for subsequent starts, if the
compressor has not remained off for a minimum set time. After this time
has elapsed the procedure is performed again during the following start.
Note: the safety times for Digital Scroll™
established by the manufacturer, and are as follows:
•
Minimum ON time: 244 s (starting procedure)
•
Minimum OFF time: 180 s
•
Minimum time between restarts: 360 s
38
Page 87 of 172
= T
/% Richiesta
ON
180s
60s
50s
100s
Startup
Fig. 6.x
compressors are
P4114S Rev 03
time
Advertisement
Chapters
Table of Contents
