Technical Manual Cold Storage Controllers TKP / TKC x130 - x140
Page 13
Intelligent Defrost (adaptive defrost) for walk-ins
(TKP/TKC x140 only)
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), but 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.
Parameterisation is very easy:
• set parameter „
defrost mode
“ (defrost
page) to „adaptive“
• set parameter „
max time to defr
“ (defrost
page) to a value which is 2 or 3 times the
normal defrost interval. Within this period
the device decides independently about the
point in time to defrost.
• parameter „
time to defr
“ (defrost page)
shows the time up to the next defrost.
• parameters „
pulse defr limit
“ and „
defr
temp limit
“ define the range within the
heater will be pulsed.
• set parameter „
defrost forerun
“ to
several minutes, so the fan will be
started before defrost heater starts.
• set parameter „
fan off delay
“ (setpoint
page) to the time that the fan will continue
running after cut-off of the cooling relay.
Process Sequence
1
. In the time period set by „
max time to
defr
“ 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.
2.
The fan runs while cooling is stopped and
while the defrost heater is not yet switched on
3.
The fan stops and the heater starts
4.
Each evaporator is individually heated.
The
leading evaporator
will be recognized
automatically.
5
. With working temperatures of [se
hysteresis >= 2,5°C] the controller is able to
save energy by increases using of the fan
(
more circulating air
).
6.
When the „
pulse defrost limit
“ is achieved,
the heater will be switched off/on in calculated
periods (optimal heat distribution).
7.
Defrost heater cut off, limit temp. is reached.
8.
Cooling and fan remain still off (drain time).
9.
Cooling starts, fan still off.
10.
After end of „
fan start delay
“ the fan
restarts 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 room sensor
and the 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 „
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 „
defrost time ..
“ 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 time..
“
parameters 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 time
“
before starting defrost.
●
External command
Assign one of the digital inputs to „
manual
defrost
“. By applying voltage to that input it is
possible to start defrosting at every moment.
Defrost heater
After the end of the "Fan OFF Delay", the defrost
heater switches on up to the temperatur has been
readed the value „
pulse defrost limit
“. The heat energy
of the heater 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 value of „
defrost temp. limit
“.
This procedure fits in the same way for the case of
several evaporators in the chamber.
By this way a defrost period will take longer,
but will be more efficient.
Special mode for roomtemperatures > 2,5°C
Evaporators can be de-iced already at temperatures
from 2°C by forced air. When cooling stops, fans are
turning on until ice and frost are melted.
Thus humidity stays in the chamber which will improve
the quality of certain goods like meat or vegetables.
Additonally to the compulsatory "
fan off delay
" (fan is
forced to continue turning after cooling reached the
setpoint and stopped), the fan will turn from a specific
temperature [se hysteresis => +2,5°C] until the
evaporator sensor has reached a certain value.
● At room temperatures [shysteresis =>
+2,5°C] notify to set parameter „
max time to
defr
“ to a higher value, because a defrost start
is forced if this time is past.
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 4 evaporators in one chamber. Even
in this case one unique roomsensor 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 the other
is turning. So the one with the highest rate of icing
determines the start of the defrost cycle.
The controller is able to
determine just this evapo-
rator
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 in case of bad conditions
In case recognizing extreme conditions, 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
the emergency operation starts.
To detect malfunction of the defrost control the unit
uses the increasing of "
max. defrost time
".
If a defrost cycle is terminated by this time, the con-
troller starts several defrosts with the interval which
corresponds to one quarter (¼) of the time which is
programmed by „
max time to defr
“.
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, the heater stops and the con-
troller waits until "
pause after defrost
" has expired, to
allow the melted water to flow to the drainage. Then
cooling starts now, but the fans still stay OFF until the
"
fan start delay
" has expired to allow the evaporator
to cool down and to prevent that the fans blow warm
and humid air or water drops into the chamber.
