Technical data

Technical Manual Cold Storage Controllers TKP / TKC x130 - x140Page 18
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 „ 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 heating
When „ pulse defrost limit “ is achieved, the heater
is 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 value of „ defrost
temp. limit “.
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.
Intelligent Defrost (adaptive defrost) for walk-ins (TKP/TKC x140 only)
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 [setpoint+hysteresis =>
+2,5°C] until the evaporator sensor has reached a
certain value.
• At room temperatures [setpoint+hysteresis =>
+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. 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 another
is turning.
The one with the highest rate of icing determines
the start of the defrost cycle. The TKP/TKC
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 for case of bad conditions
In cases if the controller recognizes that it would be
incapable or to slow to control the process, or
when it gets not enough informations, 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 " max. defrost time ".
If a defrost cycle is terminated by this time, the
controller starts several defrosts with the interval
which corresponds to (¼) one quarter 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
controller 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.
Thanks to the ability of the controller
to assign its inputs and outputs
liberally it is able to control up to 4
evaporators in one chamber.