20
ENG
“EVD mini” +0300036EN - rel. 1.2 - 23.04.2018
t
t
t
O
FF
ON
ALA
R
M
O
FF
ON
L
O
P
L
O
P
_TH
T_
EVAP
D
B
Fig. 6.b
Key:
T_EVAP
Evaporation temperature
D
Alarm timeout
LOP_TH
Low evaporation temperature
protection
ALARM
Alarm
LOP
LOP protection
t
Time
B
Automatic alarm reset
M
OP
(high evaporation pressure)
MOP= Maximum Operating Pressure.
The MOP protection threshold is applied as a saturated evaporation
temperature value so that it can be easily compared against the technical
specifications supplied by the manufacturers of the compressors. The
protector is activated so as to prevent too high evaporation temperatures
from causing an excessive workload for the compressor, with consequent
overheating of the motor and possible activation of the thermal protector.
The protector is very useful in self-contained units if starting with a high
refrigerant charge or when there are sudden variations in the load. The
protector is also useful in multiplexed systems (showcases), as allows all
the utilities to be enabled at the same time without causing problems
of high pressure for the compressors. To reduce the evaporation
temperature, the output of the refrigeration unit needs to be decreased.
This can be done by controlled closing of the electronic valve, implying
superheat is no longer controlled, and an increase in the superheat
temperature. The protector will thus have a moderate reaction that tends
to limit the increase in the evaporation temperature, keeping it below the
activation threshold while trying to stop the superheat from increasing
as much as possible. Normal operating conditions will not resume based
on the activation of the protector, but rather on the reduction in the
refrigerant charge that caused the increase in temperature. The system
will therefore remain in the best operating conditions (a little below the
threshold) until the load conditions change.
Par. Description
Def.
Min.
Max. U.M.
C5
MOP protection threshold
50
(122)
Protection LOP:
threshold
200
(392)
C(°F)
C6
MOP protection integration
time
20
0
800
s
The integration time is set automatically based on the type of main
control.
When the evaporation temperature rises above the MOP threshold, the
system enters MOP status, superheat control is interrupted to allow the
pressure to be controlled, and the valve closes slowly, trying to limit the
evaporation temperature.
As the action is integral, it depends directly on the difference between
the evaporation temperature and the activation threshold. The more the
evaporation temperature increases with reference to the MOP threshold,
the more intensely the valve will close. The integration time indicates the
intensity of the action: the lower the value, the more intense the action.
t
t
t
t
O
FF
ON
ALA
R
M
O
FF
ON
P
I
D
O
FF
ON
M
O
P
M
O
P
_TH - 1
M
O
P
_TH
T_
EVAP
D
Fig. 6.c
Key:
T_EVAP Evaporation temperature
MOP_TH MOP threshold
PID
PID superheat control
ALARM
Alarm
MOP
MOP protection
t
Time
D
Alarm timeout
Important:
the MOP threshold must be greater than the rated
evaporation temperature of the unit, otherwise it would be activated
unnecessarily. The MOP threshold is often supplied by the manufacturer
of the compressor. It is usually between 10 °C and 15 °C.
If the closing of the valve also causes an excessive increase in the suction
temperature (S2) above the set threshold – set via parameter (C7), not
on the display - the valve will be stopped to prevent overheating the
compressor windings, awaiting a reduction in the refrigerant charge. If
the MOP protection function is disabled by setting the integral time to
zero, the maximum suction temperature control is also deactivated.
Par. Description
Def.
Min.
Max.
U.M.
C7
MOP protection: disabling threshold
30
(86)
-85
(-121)
200
(392)
°C (°F)
At the end of the MOP protection function, superheat regulation restarts
in a controlled manner to prevent the evaporation temperature from
exceeding the threshold again.
