Technical data

Technical Manual Cold Storage Controllers TKP / TKC x130 - x140Page 16
Defrost
The controller allows several, different defrost
methods. This methods are available for each of
the 4 possible control circuits, that means it is
possible to assign 4 defrost relays. This relay
output(s) then control an electric heater or fan for
defrosting the evaporator(s).
A defrost cycle can be initiated by different ways.
Normally the internal clock is used, but there are
also possibilities to start manual defrost or to use
advanced functions to save energy.
Each evaporator with electric heater is monitored
by a defrost sensor.
According to the application, choose if the fan
stops or turns during defrost (parameter „ defrost
type “ on or off).
•„ defrost mode “ (defrost page) determines how
defrost starts:
- extern
defrost starts only when the digital input (OC-
input) is activated
- extern+intern
defrost start by digital input or by the internal
clock
- difference method
defrost on demand method which uses two
supplementary sensors to measure the
temperature difference across the evaporator
- dem defr by opti (mization)
defrost on demand method, defrost is started by
the clock, but the pauses between the defrost
cycles will be calculated
- adaptive
defrost control by the intelligent, adaptive function
(only TKP/TKC x140, c.f. next pages)
An electric defrost heater is run from the N/O-
contact of the defrost relay independent from the
application (refrigeration/freezing).
Cooling is disabled during defrost automatically.
" last defr cycle 1 " thru " last defr cycle 4 " (defrost
page) show the expired defrost time of each
circuit.
Defrost start by clock
A built-in timer allows you to set up to six (6)
different times for defrosting within 24 hours
(„ defrost time 1 “ to „ defrost time 6 “, defrost-page).
To disable these parameters, set them to „OFF“.
The defrost cycle starts only, if the temperature at
one of the evaporator sensors is below the limitation
setpoint " defr temp limit X ".
If parameter „ defrost mode “ on the mode page is
set to „external“, the timer function is disabled.
Please note that this function differs
with 'adaptive' defrost
Remote Defrost Initiation
To start defrost by digital input, note that mains
phase has to be applied for 2 seconds minimum
and last not longer than the shortest possible
defrost cycle.
Pause ahead defrost
The parameter ' pause ahead defr ' (Defrost Page)
causes that the defrost heaters will switch on
delayed at the beginning of a defrost cycle. This
gives a chance to pumpdown the evaporators
before heating. So the defrost heaters need less
energy, because the evaporator is already warmed
up.
Defrost termination by temperature
Defrost will be terminated (individually for each
output) by the corresponding defrost (evaporator)
sensor. This sensors must be placed at a position
where, by experience, ice remains the longest
time. If the temperature rises at that position, the
ice in the evaporator is probably melted completely.
A defrost cycle ends as soon as all defrost sensors
have reached the defrost limitation temperatures
„ defr temp limit X “ (defrost page) or the safety time
„ max defr Time “ (defrost page) has been expired.
If 2 defrost sensors are assigned to one circuit,
both sensors must reach the limitation temperature
to terminate defrost.
Defrost termination by time
In case that no defrost sensors are assigned or if
they are out of order, the defrost cycle will be
terminated if „ max defr Time “ (defrost page) is
achieved. Parameter „ remain defr time “ (actual
page) shows the time until expiration of this timer.
Defrost termination monitoring
Normally, a defrost period should be terminated if
the temperature in the evaporator reaches the
limitation temperature. In case of bad working
conditions like sensor slack or similar, defrost is
terminated by „ max defr time “. If the number of
defrost periods terminated by timer exceeds the
number programmed by parameter „ n/o .def
evnt>alm “, a failure will be indicated.
In case of defrost by airflow without
evaporator sensor, this function has to be
disabled („OFF“), because here every
defrost cycle is terminated by the timer.
Cooling Delay (drain time)
With „ pause aft defr “ (defrost page) you can set a
duration where the solenoid valve(s) are disabled
after defrost termination. See the remaining time
at „ remain defr pause x “ (actual values page).
Manual Defrost
A manual defrost initiation via keypad is possible
at any time.
Start : Select „ manual defrost “ (defrost page).
Confirm „ start “
Stop: Confirm „ finish “.
Pulsed Defrost
To save energy and to avoid creating too much
moisture it’s possible to work with a pulsed
(switched in intervals) defrost function.
If the evaporator temperature is between „ pulse
def limit “ (defrost page) and the limitation
temperature (the value of „ pulse def limit “ must be
lower than limitation temperature), the controller
determines about the optimal heat distribution in
the evaporator depending on the gradients of the
temperature. If the evaporator temperature reaches
„ pulse def limit “, the heater is not longer heating
continually but will be switched on and off by the
controller in calculated periods until the defrost
limitation temperature is reached.
As a result of this procedure
• heat energy in the evaporator dissipates better
• the defrost limit temperature can be set lower
• less of humidity in the chamber
• save of energy
To disable this function, set „ pulse defr limit “ to a
very high value.
Defrost on demand - Standard methods
Optimiziation Method (for walk-ins)
With every requested defrost cycle the controller
detects the actual period of time needed for melting
the icing at the evaporator around freezing point
(between -2°C and +2°C). This time has a
dependent relationship on the number of defrosts
needed per day or, with other words, how many of
the programmed defrost cycles can be skipped.
The result of this calculation is displayed under
parameter „ n/o defr ignored “ (defrost page).
Defrost start will be initiated by the internal clock or
a digital (OC)-input.
A manually initiated defrost cycle clears the 'skip'
memory and starts a new calculation.
Defrost Demand by Differential Method
This defrost method uses two (2) additional sensors
which sense the differential temperature across
the evaporator. This differential increases with
increased icing.
At a preset amount of icing (temperature differen-
tial) which is set by parameter „ demand defr diff “
(defrost page), the controller starts a measuring
cycle for a certain amount of time which is set by
parameter „ dem defr period “.
If, during this period, the differential reading keeps
its value above setting, the controller stores the
need of defrost (displayed by „ dem defr stored “).
Any stored defrost demand results in initiating a
defrost cycle at the next available defrost time
(timer) or upon activating the defrost signal input.
For achieving good results with this demand defrost
method, the two additional sensors must be placed
carefully as explained in drawing.
eva
p
sensor
M
sensor
warm
sensor
cold
control
sensor
Melting- < 1> 1> 2> 3> 4> 5> 10
time min min min min min min min
Defrosts 654321no-
to be ne
skipped