Carel Hecu CO2, Руководство пользователя

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26
ENG
Hecu
C O
2
+0300085EN rel. 2.2 - 07.05.2019
With propor integral control, the integral time is summed to
the eff ect of proportional control, giving a null control error in steady
operation. This type of control is illustrated in the following fi gure:
Regulation
variable
P+I
P
Setpoint
time
Fig. 6.g
The integral action depends on time and the deviation from the set point.
The integral time represents how fast integral control is implemented:
•
Low values bring fast actions yet more instability
•
High values bring slower actions and more stability
The values should not be set too low, to avoid system instability.
Two types of control can be set, in loop
C
ompressors
Æ
Control
Æ
screen Cab01
•
Fixed set point
•
Floating set point
Floating set point
This software function is available by exploiting serial communication
with the evaporators. Serial communication allows information to be
exchanged in real time between the main Hecu CO2 controller and the
MPXPRO devices.
Note : the MPXPRO controllers installed on the evaporators
implement the Smooth Lines function (see MPXPRO 0300055).
This function signifi cantly reduces the number of ON-OFF cycles in
traditional control by modulating the evaporator temperature using an
electronic expansion valve and adapting the superheat set point using
appropriate PI control based on the eff ective control temperature.
This function can be enabled and confi gured manually or automatically.
•
The automatic procedure involves the Fast Commissioning operation
described in chapter 7, which automatically confi gures the control
parameters on both the condensing unit and the evaporators, using
the default values optimised by CAREL, yet amply modifi able.
•
To confi gure the function manually, make sure that there is a serial
connection with the MPXPRO controllers on the evaporators, and
choose the type of control on
screen Cab01 . The Smooth Lines
function will then need to be confi gured on the MPXPRO controllers,
as described in the next chapter.
The unit fl oating suction pressure set point can vary between a settable
minimum and maximum value. The minimum and maximum limits for
the fl oating set point are shown on
screen Cab04 , in line with the limits
set on screen Cab02.
Hecu CO2 uses an advanced algorithm to adapt the condensing unit
suction pressure set point based on the request from each evaporator,
then weighing it according to evaporator capacity. Signifi cant variations
in request due to certain evaporator operating states, such as defrost, are
managed by Hecu, maintaining fi ne, stable control.
Min Set point
energy efficiency
Max Set point
time
Suction
pressure
Fig. 6.h
The fl oating set point will then be managed using propor integral
control, the parameters of which can be set on
screen Cab14 .
Pumpdown
The compressor OFF function by pumpdown can be enabled on screen
Cag03. This function keeps the compressor on until the pumpdown
pressure threshold is reached, within the maximum time set on the same
screen.
Low ambient (outside) temperature prevention:
This function prevents the unit from stopping due to low outside
temperatures.
The function can be activated if all of the following conditions are true:
1.
Enabling selected
2. The evaporator request is greater than 0% (MPXPRO or ULTRACELLA
connected) or "Enable compressor from DI" is ACTIVE or the
diff erential pressure threshold (Prec - Psuc) is less than the set value
(default 2 bars).
3. The outside temperature is less than the value set (default -18°C)
4.
The compressor request is = 0% and the compressor speed is = 0 for
longer than the set time (default 30 minutes)
The settings are made on the following screen
When the function is activated:
1.
The compressor set point is decreased by a settable value (default 8
bars) within the time set on the same screen