Technical data

Technical Manual Cold Storage Controllers TKP / TKC x130 - x140 Page 17
Intelligent Defrost (adaptive defrost) for walk-ins (TKP/TKC x140 only)
Targets
Defrost too soon will squander energy by
using too much heat-energy and
defrosted too late will squander energy
by decreasing the power factor of the
refrigeration plant.
The main attribute of this ice detecting
system, which is developed in co-
operation with the company ‘
GÜNTNER
Heat Exchangers ’, is to recognize safely
the rate of icing in the evaporator which
can just be admitted and to start defrost
when icing increases either immediately
or in certain allowed periods.
The controller adapts itself to a changed
situation and optimizes the control
process, which we call the autoadaptive
defrost method.
It is particularly suitable for cold storage
chambers and enables the user to
decrease the energy expenditure during
the defrost process and increases the
operational safety of the refrigeration
unit.
Defrost itself should be made completely,
using the less energy as possible.
The procedure should be suitable even
for more than one evaporator and should
not require special sensors, but use
standard sensors.
Main Features
This defrost procedure 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 procedure 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.
Using this new defrost method 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 decides about the
point in time to defrost independly.
• 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. If [setpoint + hysteresis > 2,5°C] the
controller uses the fan to reduce icing.
2. 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.
3. Cooling stops, the fan goes on turning a
certain time
4. The fan stops and the heater starts
5. If several evaporators are installed,
each one has its own defrost sensor and
heater relay, so it is individually heated.
6. When the „ pulse defrost limit “ is achieved,
the heater will be cut off and on in
calculated periods. The time spacing
depends on the evaporator temperature.
7. Defrost heater is cut off completely when
„ def temp limit X “ is reached.
8. Cooling and fan remain still off
(drain time).
9. After the end of „ pause aft defrost “ cooling
starts, but the fan remains still off.
10. After end of „ fan start delay “ the fan
starts and normal refrigeration goes on.
standard-
control sensor
standard-
evap sensor
defrost-
heater
self monitoring
emergency operation
pulsed heating
• delta-t across the evaporator
during refrigeration
• breakpoint duration and defrost duration
of the last defrost events
• middle value calculations and
disturbance value filtering
• use of latency heat
• use of refrigeration breaks
• use of informations about former defrost courses