Carel Heos, User Manual

Page: 21 / 60

21
ENG
Heos +0300078EN - rel. 1.6 - 23.11.2017
During the day most of the load of the showcase is due to the warm
air that enters from the outside and mixes with the cool air inside.
Control based on the intake probe, due to high temperature outside
the showcase and the mixing of the air, may not manage to reach the
set point. Displaying the intake temperature would show a temperature
that is too high. Setting a set point that is too low for the intake probe Sr
may cause the food to freeze. On the other hand, displaying the outlet
temperature would show a temperature that is too low. Consequently,
the display (on the PLD) of the control probe, set point or virtual probe
can be confi gured using parameter /t2.
ON-OFF P+I
time
Temp.
Setpoint
Setpoint
Fig. 6.b
Temperature control of the refrigeration unit is managed using a
propor integral (P+I) algorithm. Based on the diff erence between
control temperature and set point (proportional error) and the trend in
this diff erence over time (integral error), the controller varies the request
for cooling capacity on a scale from 0 to 100%. Depending on the model
of compressor installed, this percentage is converted to an operating
speed, expressed in revolutions per second (rps).
To adapt control to the characteristics of the refrigeration unit, the
proportional gain (Kp) and integral time (tI) can be adjusted.
Kp represents the percentage of increase in cooling request according to
the deviation from the set point [%/°C], tI represents the time interval to
evaluate the variation and the trend in the integral error. High values of
Kp lead to higher variations in request for the same variation in control
temperature (Treg), high values of tI lead to smaller variations in request
over time.
Par. Description Def U.M. Min Max
Kp Temperature control diff erential 10 %/°C 1 200
tI Compressor control integral time 500 s 0 999
Night-time operation
During night-time operation, the curtain on the showcase is closed and
consequently less cold inside air is mixed with warm outside air. The
thermal load decreases. The temperature of the air that cools the produce
is near the outlet temperature, and therefore to avoid excessively low
temperatures and reduce energy consumption, the set point needs to be
increased at night, by setting parameter r4. Parameter r6 can then be used
to assign the virtual probe Sv or intake probe Sr as the control probe.
The change to night-time operation must be signalled externally. This is
done using the curtain switch (set using the parameters relating to the
digital inputs) or by setting time bands (S1…S3), or from the supervisor,
or using a command from the Master via the Master/Slave network. Night-
time status is activated by the transition of the assigned digital input from
“Not active” to “Active”. Vice-versa, a transition from “Active” to “Not active”
changes back to daytime status. If, when the digital input is active, the
signal is sent to change to daytime status by the supervisor or one of the
other possible sources, the controller switches to daytime status. In other
words, none of the sources has higher priority than the others, rather the
status depends on the most recent command.
Par. Description Def U.M. Min Max
r4 Set point off set in night mode 3.0
(5.4) °C (°F) -50.0
(-90.0)
50.0
(90.0)
r6
Enable night-time control on intake probe (Sr) 0 -- 0 1
hS1/mS1 Start time band 1 (hours/minutes) - - - -
hE1/mE1 End time band 1 (hours/minutes) - - - -
During daytime status: Set point= St
light on
control on virtual probe Sv (Treg)
During night-time status: Set point= St + r4
light
off
control on Sr (se r6= 1) or Sv (if r6= 0)
Minimum and maximum set point value (parameters r1 and r2)
A parameter can be used to defi ne the minimum and maximum possible
values for the set point.
Par. Description Def U.M. Min Max
r1 Minimum control set point limit -50.0
(-58.0) °C
(°F) -50.0
(-58.0) max
r2 Maximum control set point limit 50.0
(122.0) °C
(°F) min 50.0
(122.0)
ON/OFF
Parameter O/F is used to switch the controller ON/OFF. Any digital input
confi gured as the remote ON/OFF signal has higher priority than the
signal from the supervisor or the parameter.
Par. Description Def U.M. Min Max
O/F Select unit status 0 -- 0 1
If more than one digital input is selected as ON/OFF, ON status will be
activated when all the digital inputs are inactive. The unit is OFF even if
just one of the contacts is activated. When switching from ON to OFF and
vice-versa, the compressor protector times are observed.
When OFF, the following are possible:
•
access all the confi guration parameters;
•
activate remote ON/OFF.
When OFF, the following alarms are reset:
•
high and low temperature;
•
open door (dor);
•
expansion valve alarms LSA, LowSH, MOP).
Control off set with probe error (parameter r0)
By default, Heos uses the virtual probe Sv for control, that is, the weighted
average of the outlet and intake probe (see parameter /4). If one of
the two probes making up the virtual probe is broken or has an error,
parameter r0 is used to continue normal control in controlled conditions,
without the need for an immediate response by maintenance personnel.
Par. Description Def U.M. Min Max
r0 Control off set with probe error 5.0
(9.0) °C
(°F) 0.0
(0.0) 20.0
(36.0)
The recommended value of r0 is the temperature diff erence between
the outlet probe and intake probe reading in steady refrigeration unit
operating conditions:
r0 = Sr-Sm
The following two cases may occur:
outlet probe Sm error: starts control based on the intake probe Sr alone,
considering a new set point (St*) determined by the formula:
St* = St + r0 •
(100 - /4)
100
intake probe Sr error: Heos starts control based on the outlet probe Sm
alone, considering a new set point (St*) determined by the formula:
St* = St - r0 •
(100 - /4)
100
If night-time operation has been set with the intake probe as the control
probe, the controller considers /4=100 and uses the outlet probe. The
new set point becomes:
St* = St-r0
Note:
•
if an error occurs on both probes, the controller switches to duty
setting operation, see below.
Example: Sm fault in daytime operation, with /4=50, St=-4, Sr=0, Sm=-8,
r0 (recommended) = 0-(-8) =8. Then the new control probe will be Sr with:
St*= -4+8 •(100-50)/100=0
If the fault is on Sr, the new control probe will be Sm with:
St*= -4-8 •50/100=-8.