Technical Manual Cold Storage Controller EVP 3150-1 and EVP 3150-2
Page 11
Intelligent Defrost (adaptive defrost) for Walk-In Coolers
Main Characteristics
This defrost control method, developed in co-
operation with the ‘
GÜNTNER
’ company, fits
especially for
cold stores
and freezers which
are closed (like walk-ins).
It is
less efficient
in applications where
the limitation sensor is located in the
airflow (e.g. open chest freezers).
This technique
reduces significantly the
amount of energy
the refrigeration plant
needs.
Especially while
difficult situations
(like high
air-humidity, in cool-down chambers, while long
opening times of the door of the cold storage
room, uneven feeding of the cold storage
room, etc.) the adaptive method protects the
evaporator from glaciation safely.
Dynamic ‘room-feeding’ situations engage
the controller to adapt itself to the new
situation, without expensive adjustment
by technical personnel.
Specialized sensors or additional probes
are not required.
Parameterization is very easy:
●
set parameter "
d02
" to value "
AdA
"
(adaptive)
●
set parameter "
d05
" (Defrost Page)
to a value which is 2 or 3 times the
normal defrost interval.
Within this period the algorithm
decides independly about the point
in time to defrost. After the end of this
period defrost starts in all cases.
●
parameter "
d04
" (Defrost Page)
shows the time up to the next defrost.
● parameters "
d34
"
and
"
d31
" define the range the heater will
be pulsed within.
Process Sequence
1
. If [se hysteresis > 2,5°C] the
controller uses the fan to reduce icing.
2
. In the time period set by „
d05
“ the controller
decides itself if and at which moment a
defrost cycle is necessary. If icing is
detected, the controller prepares defrost
and begins either immediately or at the
next allowed defrost time.
3.
Cooling stops, the fan goes on turning a
certain time
4.
The fan stops and the defrost heater starts
5.
If several evaporators are installed,
each one has its own defrost sensor and
heater relay, so it is individually heated.
6.
After achieving a defined evaporator
temperature, the heater will be cut on/
off in calculated periods. The period lenghts
depend on evaporator temperature.
7.
Defrost heater cut off, limit temp. is reached.
8.
Cooling and fan remain still off (drain time).
9.
After the end of „
d35
“ cooling starts, but the
fan remains still off.
10.
After end of „
r22
“ the fan starts and normal
refrigeration goes on.
Refrigeration
Even during normal operation the fan stays on after
cut-off of cooling to reduce icing.
Recognition of icing
The more ice on the fins the more increases the
difference of temperature between the roomsensor
and evaporator sensor. The controller uses the value
of these sensors, their difference, the historic curves
of these values as well as curves and duration of
the past defrostings to calculate the necessity of
defrosting.
Use of latent energy by airflow
We recommend to use "
d03
" (defrost forerun, defrost
page) to switch on the fan several minutes ahead
the defrost cycle, while cooling stops and the heater
is not yet on.
Additionally, the fan is switched on automatically at a
certain difference between the sensors. By this, the
„cooling-energy“ is brought out of the evaporator and
stored in the chamber. This helps also to reduce the
amount of heat energy necessary to defrost.
Defrost start
If all six parameters release times are set to Off, the
controller decides itself when it starts defrost.
●
Further time influence
If you want to prevent that defrost starts at
certain day-times use all the defrost release
times and set them to points in time where
defrost is allowed. If no icing is detected,
these times will be ignored.
On the other hand, once icing detected, the
controller will wait for the next defrost release
time before starting a defrost cycle.
●
External command
Assign one of the digital inputs to "
deF
". By
applying voltage to that input it is possible to
start defrosting at every moment.
Defrost heating
When „
d34
“ is achieved, the heater will be cut off.
The heat energy of the resistances will dissipate
slowly and melt the ice. The length of the cut-off is
calculated by the controller and as soon as some
criteria are fulfilled, it will switch on the heater again.
The heater will be pulsed until the temperature of
the evaporator sensor reaches the defrost limitation
temperature "
d31
".
This procedure fits in the same way for the case of
several evaporators in the chamber.
By this way defrost period will take longer, but
will be more efficient.
Several evaporators in one chamber
For certain plants it is necessary to use several
evaporators in one chamber. The controller is able
to control up to 3 evaporators in one chamber. Even
in this case one unique room sensor is sufficient.
E.g. for a chamber with 3 evaporators you need
only 4 sensors:
● one controlsensor
● three defrost sensors (one for each evaporator)
If a defrost cycle is necessary, all evaporators will start
defrost at the same time to avoid short circuit of air,
when one is heating and the fan of another is turning.
The one with the highest rate of icing determines the
start of the defrost cycle. The EVP controller units are
capable to
determine just this evaporator
and
even to adapt it when conditions change.
Thus always the evaporator with the most ice
initiates defrost start, nevertheless the quantity of
energy which is necessary to defrost will be calculated
for each evaporator separately.
To finish defrost cycle all evaporators must have
reached the defrost limitation temperature.
Emergency Operation Mode
In cases the controller recognizes that it would be
incapable or to slow to control the process, or when
it gets not enough information, e.g.:
● charge of unusual very humid goods
● freezer door was open a very long time
● the evaporator is sprinkled with water
● sensor broken or shortened
● defrost terminated by the max. defrost time
the emergency operation starts.
To detect malfunction of the defrost control the unit
uses the increasing of "
d05
".
If a defrost cycle is terminated by this time, the
controller starts several defrost events with the in-
terval corresponding to (¼) one quarter of the time
programmed by "
d05
".
Therefore be careful in choosing the time for
this parameter.
After the end of the disturbance the controller works
on normally.
Example
Max time to defrost is set to 24 hours. If defrost
is not terminated by the evaporator sensor,
the controller will start defrost cycle every
24 / 4 = 6 hours until a cycle will be finished by
the evaporator sensor and not by timer.
Independent from this procedure, a failure
message will be initiated.
End of defrost
When the defrost sensor has reached the defrost
limitation temperature "
d31
", the heater stops and
the controller waits until "
d35
" has expired, to allow
the melted water drop to the drainage.
While the following 'drain-on' time ("
r22
", Setpoint
Page) cooling starts, but the fan still stay OFF to
prevent that the fans blow warm and humid air or
water drops into the chamber.
Further information about possibilities to use
latency heat you can find under "Evaporator
Fan Control"
