26
ENG
Heos +0300078EN - rel. 1.6 - 23.11.2017
6.7 Defrost
Scheduling
Screens Dcb01-Dcb04 can be used to set up to 8 defrost events managed
by the clock (RTC) on the controller, and activate Power Defrost. The
screen for setting the fi rst two events is shown below:
Heos can manage the following types of defrost, depending on the
setting of parameter d0: electric heater, hot gas, reverse cycle. The defrost
can end based on temperature, in which case the defrost probe Sd needs
to be installed, or after a set time. In the fi rst case, the defrost ends when
the defrost probe Sd reading exceeds the end defrost value dt1 or the
time dP1 has elapsed, while in the second case, only when the time dP1
has elapsed. If end defrost by temperature is selected, an alarm can be
activated if the defrost ends when exceeding the maximum time. At
the end of the defrost, a dripping stage can be activated (if the dripping
time dd is greater than 0), in which the cooling cycle is not active and
the fans are off , and then a further post-dripping stage, if the time Fd
(screen Dd02) is greater than 0, during which the cooling cycle restarts
with the fans off . Parameter d6 (screen Ec02) can be used to select what
is displayed on the PLD during the defrost.
Par. Description Def U.M.
Min Max
d0 Type of defrost/end defrost
0: electric/ temp-timeout
1: reverse cycle/ temp-timeout
2: electric/ timeout only
3: reverse cycle/ timeout only
4: electric/ time with temp. control
5: hot gas bypass/ temp-timeout
6: hot gas bypass/ timeout only
0--0 6
dt1 End defrost temperature 8.0
(46.4)
°C
(°F)
-50.0
(-58.0)
50.0
(122.0)
dP1 Maximum defrost duration 40 min 1 240
dd Dripping time after defrost (fans off )
0 = no dripping
120 s 0 600
d9 Disable evaporation pressure alarm in defrost 0 -- 0 1
Fd Fan off time in post-dripping 60 s 0 240
Dripping time after defrost (param. dd)
This parameter is used to stop the compressor and the evaporator fans
following a defrost so as to allow the evaporator to drip. The value of the
parameter indicates the off time in minutes. If dd=0 no dripping time is
enabled, and at the end of the defrost control resumes immediately, without
stopping the compressor and the fan, if active.
The standard defrost cycle is illustrated below.
time
DEF
FAN
EEV
CMP
speed
Normal
reg.
Normal
reg.
Defrost state Drip Post drip
Fig. 6.l
Key
CMP Compressor Drip Dripping time
EEV Expansion valve Post drip Post-dripping time
FAN Fan
DEF Defrost
For Master/Slave networks with synchronised end defrost, control resumes
on all units when the last of these reaches dt1 or the time dP1 has elapsed.
The units in standby remain in the dripping stage: fans off and cooling
deactivated (or at minimum capacity without heater defrost).
Heater defrost (d0 = 0, 2, 4):
Waterloop
Fig. 6.m
When starting the defrost, the compressor stops, following the stopping
ramp. The heaters are activated, the fans switch off and the expansion
valve closes. At the end of the defrost, the heaters are deactivated, and
the dripping time elapses with the compressor, valve and fans off . This
is followed by the post-dripping stage, with the compressor and valve
reactivated while the fans remain off . At the end of the post-dripping
stage, normal control resumes.
time
DEF
FAN
EEV
CMP
speed
Normal
reg.
Normal
reg.
Defrost state Drip Post drip
Fig. 6.n
Key
CMP Compressor Drip Dripping time
EEV Expansion valve Post drip Post-dripping time
FAN Fan
DEF Defrost
The heater defrost by time with temperature control (d0=4) activates the
defrost output only if the evaporator temperature (Sd) is less than the value
of parameter dt1, and ends after the time defi ned by dP1. This function is
useful for energy saving.
Hot gas defrost (d0 = 5, 6)
Waterloop
Fig. 6.o
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