Carel Heos - Page 28

28
ENG
Heos +0300078EN - rel. 1.6 - 23.11.2017
Pump Down
With a heater defrost, the pump down cycle is always performed, in
which the evaporator is emptied of liquid refrigerant immediately before
the defrost starts. When starting the defrost, the expansion valve is
immediately closed, and the compressor stops with a deceleration ramp
lasting a few seconds. In this stage, the refrigerant is pumped to the high
pressure section of the unit.
Other defrost management parameters concern the activation delays,
synchronisation between Master and Slave, defrost stages such as pump
down and dripping, and advanced functions, including
• Running time;
• Sequential stops;
• Skip defrost;
• Power defrost.
End defrost synchronised by Master (parameter d2)
This parameter determines whether or not, in a local network, at the end
of the defrost Heos waits for an end defrost signal from the Master before
restarting the cooling cycle.
Par. Description Def U.M.
Min Max
d2 End defrost synchronised by Master
0 = local only;
1 = start;
2 = start and end.
1--02
In the event of synchronised end defrosts (d2=1), after the post-dripping
time (if set), control resumes when the last unit has ended defrosting. The
units that end the defrost before the last wait in the dripping stage (see
the following fi gure); in this case parameter dd (dripping time) must be
≠ 0.
time
DEF
MasterSlave 1Slave 2
CMP
speed
DEF
CMP
speed
DEF
CMP
speed
Normal
reg.
Normal
reg.
Defrost state Drip
Drip
Drip
Post drip
Fig. 6.t
Defrost ended by timeout signal (parameter r3)
For defrosts that end at a set temperature, this enables an alarm to signal
the end of the defrost by timeout.
Par. Description Def U.M.
Min Max
r3 Enable end defrost signal for maximum time
0: disabled (NO); 1: enabled (YES)
0--01
Running time defrost (parameters d10, d11, dA1)
Running time is a special function that determines when the refrigeration
unit needs defrosting. In particular, it is assumed that if the evaporator
temperature measured by probe Sd remains continuously below a
certain set threshold (d11) for a certain time (d10), the evaporator may
be frozen and a defrost is activated. The time is reset if the temperature
returns above the threshold. The probe used is set by parameter dA1. In
addition, at start-up the time dA2 must elapse before the running time
procedure is activated.
Par. Description Def U.M.
Min Max
d11
Defrost Running Time temperature threshold
-4.0
(24.8)
°C
(°F)
-50.0
(-58.0)
30.0
(86.0)
d10
Defrost time in Running Time mode
0 = function disabled
0 min 0 240
dt1
End defrost temperature (read by Sd)
8.0
(46.4)
°C
(°F)
-50.0
(-58.0)
50.0
(122.0)
dA1
Select probe for activation (Sd or Tsat)
0--01
dA2
Delay at start-up before activating Running
Time
30 min 0 480
time
Temp.
DEF
ON
OFF
T
sat
/Sd
dt1
d11
d10dA2
Fig. 6.u
Key
Sd Defrost probe DEF Defrost
Tsat Saturation temperature converted from suction
pressure
Running time defrost in a Master/Slave system
The defrost is activated, based on the selected probe reading, on the
individual unit, independently of the others; if the Master starts a defrost
in running time mode, this will be a network defrost, otherwise it will be
local.
Sequential stops (parameters dS1, dS2)
Par. Description Def U.M.
Min Max
dS0
Enable defrost by Sequential Stops
0--01
dS1
Compressor operating time for Sequential
Stops defrost
180 min 0 999
dS2
Compressor off time for Sequential Stops
defrost”
10 min 0 999
Sequential stop mode is especially useful for high-normal temperature
refrigeration units, and is based on intelligently stopping control to
allow the evaporator to defrost naturally by the fl ow of ambient air only,
without activating the defrost output.
If the function is enabled (parameter dS0), during normal control two
countdown timers are started:
• OFFTIME: counts down when control has stopped and paused during
control;
• ONTIME: counts down during control and paused when control has
stopped.
Two events may occur, with reference to the following fi gure:
• OFFTIME reaches zero (instant C): OFFTIME and ONTIME are reset with
the values of dS1 and dS2 and the defrost is considered as having
already been completed. Control resumes;
• ONTIME reaches zero (instant A): OFFTIME is reset with the value of dS1
and the natural defrost cycle starts, which lasts for the time dS1. At the
end of the defrost (instant B), OFFTIME and ONTIME are reset with the
values of dS1 and dS2 and control resumes.