Carel Hecu handleiding
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Hecu +0300023EN rel. 1.2 - 14.12.2021
MPXPRO/Ultracella control
For example, once the MPXPRO controllers have been connected to
Hecu, the control parameters will relate to the fi rst evaporator on screens
Ec01-02-03-04.
Electronic valve control
The superheat control function calculates the valve position based on
the current superheat reading and set point. PID control (Proportional,
Integral, Derivative) is the sum of three distinct actions:
Proportional action (P) parameter K=proportional gain:
The proportional action opens or closes the valve by K steps when
superheat increases or decreases by 1°C. Thus the greater the K the
higher the response speed of the valve to variations in superheat. The
proportional action is fundamental as it aff ects the speed of the valve in
general.
However it only considers variations in superheat and not the variation
in relation to the set point. If superheat does not vary signifi cantly, the
valve will remain stable and the superheat set point may not be reached.
Integral action (I) parameter Ti=integral time (sec):
The integral action is linked to time and moves the valve in proportion to
the deviation of the superheat value from the set point. The greater the
deviations, the more intense the integral action; in addition, the lower
the value of the integral time (Ti), the more intense the action will be.
The integral action is necessary to ensure that superheat reaches the set
point.
Derivative action (I) parameter Td=derivative time (sec):
The derivative action is linked to the speed of variation of the superheat
value, that is, the gradient at which the superheat changes from instant
to instant. It tends to react to any sudden variations, and has greater
eff ect the higher the values of Td.
Selecting the superheat set point and control parameters
The superheat set point needs to be defi ned based on the design
specifi cations of the controlled unit. Despite this, based on actual system
conditions, this may be changed at any time. A low set point ensures
better evaporator effi ciency and a low air temperature can be reached
more easily. In contrast, instability can be created in the system, with
greater variations in superheat and liquid returning to the compressor.
A high set point ensures high system stability and lower variations
in superheat. However evaporator effi ciency is penalised and the air
temperature set point may not be reached.
As regards the control parameters, the following can be used as a guide:
Proportional gain (from 3 to 30)
Increasing the proportional gain K increases valve response speed and
is recommended if the system is particularly perturbed or to make
superheat control faster. If greater than 20, it may cause swings and
instability.
Integral time (from 40 to 400 sec)
Increasing the integral time Ti improves stability but makes the valve
slower to respond in reaching the set point. If less than 40 sec, it may
cause swings and instability. If the system is already perturbed, high
values (greater than 150 sec) are recommended to avoid creating further
disturbance.
Derivative time (from 0 to 10 sec)
Increasing the derivative time Td improves valve response, in particular in
perturbed systems, and reduced the amplitude of swings in superheat.
If greater than 10 sec it may cause excessively fast response and
consequently instability.
Smooth lines function
The smooth lines function optimises evaporator capacity based on
actual cooling demand, allowing more eff ective and stable control of the
showcase. The function completely eliminates traditional on/off control
cycles, modulating the temperature exclusively using the electronic valve;
superheat set point is controlled through a precise PI control algorithm
based on the actual control temperature. The main features are:
• The superheat set point for managing the electronic expansion valve
can vary between a minimum (traditional set point P3) and maximum
limit (P3+PHS: maximum off set) using PI control (pre-confi gured),
based on the control temperature and how far this is from the
corresponding set point St
• The temperature inside the cabinet can fall slightly below the set point
St, without stopping the main control, however simply closing the
electronic valve.
• Temperature control (and consequently the solenoid valve relay)
therefore remains active at all times, while the electronic expansion
valve stops the fl ow of refrigerant into the evaporator.
• It is easy to use, as it is the controller itself that automatically adapts
control based on current operation, without requiring special
parameter settings.
The main eff ects are:
• No swings in temperature and superheat due to the set point being
reached
• Stable temperature and superheat control
• Maximum energy savings due to load stabilisation
t
Temp. set
SH set
Max
Min
Fig. 7.o
Par Description Def Min Max UoM
PSM Smooth lines - enable function 0 0 1
PLt Smooth lines - off set to stop control below
set point
2.0 0.0 10.0 °C/°F
PHS Smooth lines - max superheat off set 15.0 0.0 50.0 K
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Productinformatie
| Merk | Carel |
| Model | Hecu |
| Categorie | Niet gecategoriseerd |
| Taal | Nederlands |
| Grootte | 10743 MB |
