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ENG
Disable simultaneous starts
Disabling simultaneous compressor starts may be useful for all
system confi gurations with two separate lines and in cascade system
confi gurations. The function to avoid simultaneous starts can be enabled,
setting a delay time between the starts of compressors on diff erent lines.
Forcing the medium temperature line
Forcing the medium temperature line may be useful for cascade
system confi gurations and involves, once enabled, forcing at least
one compressor on medium temperature line L1 to start at minimum
capacity, if at least one compressor on low temperature line L2 is running.
This means that before the low temperature line starts, the DSS function
forces at least one of the compressors on medium temperature line L1
to start. The low temperature line L2 thus has higher priority than the
control request for medium temperature line L1.
Shutdown the low temperature line
The low temperature line is shutdown by the DSS function if a serious
alarm is activated on the medium temperature line, or, in general, if the
medium temperature line is OFF.
Enable pump-down medium temperature line
During normal compressor rack operation, when at least one compressor
on the low temperature line is running, the medium temperature
compressor control will enable pump-down. If there is demand on
the low temperature line, the minimum capacity step for medium
temperature line will be guaranteed if MT suction pressure is not lower
the set threshold.
Note: in the event of pLAN network faults, DSS is disabled.
6.6.7
Electronic valve synchronisation (EVS)
For confi guration of the DRIVER or DRIVERS, where there are two heat
exchangers, access OTHER FUNCTIONS EVS; iwhich comprises the
following submenus:
a. Temperature control
b. Manual management
c. I/O status
d. Control
e. Valve confi guration
f. Driver confi guration
Temp. control:
Information relating superheat is shown
Manual management:
The valve can be moved to a certain number of steps
I/O status:
Display and confi guration of the probes connected
to the 4 analogue inputs on the driver
Control:
Valve opening, PID parameters, alarm limits/delays
Valve confi guration:
Minimum/maximum number of steps, nominal
frequencies
Driver confi guration:
Enable driver, defaults
For branches a, b, c, d, e, f refer directly to the parameter table in chapter
7, while for a more detailed explanation of the DRIVER EVD EVO functions,
see the technical manual: +0300005EN
Note: one DRIVER is needed for each valve; if a Twin Driver is used,
this will be managed as a single driver; also the connection must be
made on the fi rst valve (EXV1-J27 in the case of built-in drivers).
Enable driver:
The driver can be enabled in the confi guration menu (E.i.f ) and once
enabled, the number of valves and corresponding addresses of the two
drivers can be entered.
The Driver is enabled automatically when the system selected in the
Wizard is either "Cascade" or "Pumped".
pRack +0300025EN rel. 1.3 - 17.12.2015
Fig. 6.as
Note:
•
make sure that Fieldbus driver management refl ects the logic of the
generic functions, i.e. up to 2 drivers per suction line can be enabled,
with a limit of 2 drivers per board in the pLAN (L1&L2 on single board,
maximum 2 drivers);
•
on the supervisor, L1, L2 management on separate boards requires the
use of two single line templates;
•
a Fieldbus driver cannot be connected to boards 3 and 4 in pLAN.
Screen Eif02 contains the commands to set the defaults for the Driver,
after which the parameters are updated (pRack Driver), ); in addition,
the line of compressors used for the pre-positioning logic can be selected.
Note:
•
Control based on line 1 is only possible on pLAN board with address 1.
While control based on the compressors on line 2 is only possible on
boards where the low temperature compressors are confi gured (pLAN
1 for double suction on single board and pLAN2 for double suction on
separate boards);
•
important, if the line is not managed o the current board, the Driver
function is disabled.
COMMON varying cooling capacity
Pre-positioning/start control: if switching from standby to control, before
actual control starts the valve is moved to a specifi c initial position. The pre-
positioning time is the time in which the valve is kept in a fi xed position,
according to the parameter "Valve opening at start-up".
Parameter/Description
CONTROL
Pre-positioning time
Valve opening at start-up
(evaporator /valve capacity ratio)
The valve opening parameter should be set based on the ratio between
rated evaporator and valve cooling capacity (e.g. rated evaporator
cooling capacity: 3 kW, rated valve cooling capacity: 10 kW, valve opening
= 3/10 = 33%).
•
If 100% capacity is required: Opening (%)= (Valve opening at start-up);
•
If capacity required is less than 100% (capacity control): Opening (%)=
(Valve opening at start-up) • (Current unit cooling capacity), where the
current unit cooling capacity is sent to the driver via pLAN by the pCO
controller. For stand-alone drivers this is always equal to 100%.
Note:
•
this procedure is used to anticipate valve movement and bring it much
closer to working position immediately after the unit is powered on;
•
if there are problems with liquid return after the start of the refrigeration
unit, or there are frequent unit on-off cycles, valve opening at start-up
must be decreased. If there are low pressure problems after starting
the refrigeration unit, the valve opening must be increased.
Positioning (change cooling capacity)
In practice, the valve is re-positioned starting from the current position
in proportion to how much the unit cooling capacity has increased or
decreased, in percentage terms. On reaching the calculated position,
irrespective of how long it takes (variable according to the type of valve
and the actual position), there will be a constant 5 second delay, after
which control resumes.
48
Fig. 6.at
Def.
Min.
Max.
UOM
6
0
18000
s
50
0
100
%
Tab. 6.i
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