47
ENG
UltraCella +0300083EN - rel. 1.5 - 07.02.2015
Example: in case of failure for example at RTC the scheduled defrost by
td3 (= dd3, hh3, nn3) is not made, after the safety time dI starts a new
defrost.
DEF
t
OFF
ON
dl
dd3
dd2
dd1
Fig. 6.m
Key
dI Maximum interval of time between consecutive defrosts
dd1…dd3 Scheduled defrosts
DEF Defrost
t Time
Note:
• if the interval dI expires when the controller is OFF, when it is started
again a defrost is performed;
• to ensure regular defrosts, the interval between defrosts must be
greater than the maximum defrost duration, plus the dripping time
and post-dripping time;
• if setting dl=0 the defrost is performed only if activated from keyboard
or by setting the scheduled defrosts (ddi).
6.8.2 Other defrost parameters
Par. Description Def Min Max U.M.
d3 Defrost activation delay 0 0 250 min
d4 Defrost at start-up
0/1=No/Yes
001-
d5 Defrost delay at start-up 0 0 250 min
d8 High temperature alarm delay after
defrost (and door open)
1 0 250 hour
dpr Defrost priority over continuos cycle
0/1=No/Yes
001-
• d3 determines the time that must elapse, when the defrost is activated,
between the stopping of the compressor (electric heater defrost) or
the starting of the compressor (hot gas defrost), and the activation of
the defrost relays on the main and auxiliary evaporators. In the hot gas
defrost, the delay d3 is useful for ensuring a suffi cient amount of hot
gas before activation of the hot gas valve;
• d4 determines whether to activate or not the defrost at the controller
start-up. The defrost at start-up request has priority over the activation
of the compressor and the continuous cycle. Force a defrost at
controller start-up may be useful in special situations.
Example: frequent power drops inside the plant. In case of lack of voltage
the tool resets the inner clock that calculates the period of time between
two defrosts, starting from zero. If, in an extreme case, the frequency of
the power failure were greater than the defrost frequency (e.g. a power
failure every 8 hours, against a defrost every 10 hours) the controller
would never perform a defrost. In a situation of this type, it is preferable
to activate defrost on start-up, above all if the defrost is controlled by
temperature (probe on the evaporator), therefore avoiding unnecessary
defrosts or at least reducing the running times. In the case of systems
with a large number of units, if selecting defrosts at start-up, after a power
failure all the units will start defrosting, thus causing a voltage overload.
This can cause power overload. To overcome this, the parameter d5 can
be used. It adds a delay before the defrost, and this delay must obviously
be diff erent for each unit.
• d5 represents the time that elapses between the start of the controller
and the start of the defrost at start-up;
• dd is used to force the stop of the compressor and the evaporator fan
after a defrost cycle in order to facilitate the evaporator dripping;
• d8 indicates the time of exclusion of the high temperature alarm
signalling from the end of a defrost;
• if dpr = 0, the defrost and the cycle have the same priority; if dpr = 1,
if the continuous cycle is in progress and a defrost request intervenes,
the continuous cycle ends and the defrost starts.
6.9 Evaporator Fans
6.9.1 Fixed speed fans
The status of the fans depends on the compressor status.
When the compressor is:
• on: the fan can also be on (F0=0) or activated based on the evaporator
temperature, virtual probe Sv, based on the formula:
if Sd ≤ (Sv - F1) -Frd --> FAN = ON
if Sd ≥ (Sv - F1) --> FAN = OFF
• off : the fan is controlled by a PWM that has duty cycle with a fi xed
period of 60 minutes.
duty_cycle =
60
F2
Par. Description Def Min Max U.M.
F0 Evaporator fan management
0 = always on with compressor on
1= activation depends on Sd, Sv
002-
F1 Fan activation temperature 5 -50 200 °C/°F
F2 Fan activation time with CMP off 30 0 60 min
HO1 Output Y1 confi guration
0 = not active
002-
Evap. fan
Evap. fan
CMP
Sd
t
F0=0
F0=1
(*)= PWM mod.
PWM mod.
OFF
ON
ON
ON
Sv-F1
(Sv-F1)-Frd
(*) (*) (*)
Fig. 6.n
Key
CMP Compressor
PWM mod. PWM modulation
F1 Fan activation threshold
Frd Fan activation diff erential
Evap.fan Evaporator fan
t Time
Sv Virtual probe
Sd Defrost probe
The fan can be stopped:
• when the compressor is off (parameter F2);
• during defrost (parameter F3).
6.9.2 Variable speed fans
The installation of variable speed fans may be useful to optimise energy
consumption. In this case, the fans are powered by the mains, while the
control signal is provided by UltraCella by analogue output Y1 0…10 Vdc.
The maximum and minimum fan speed can be set using F6 and F7
parameters (in percentage respect range 0…10V). If using the fan speed
controller, F5 represents the temperature below which the fans are
activated, with a fi x hysteresis of 1°C.
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