Operating Manual
D-EOMCP00104-14_01EN
EWYD_BZ
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5.17.2
Switching from heating modes to cooling modes
5.17.2.1 Compressor running in heating mode
A compressor running in heating mode (four-way valve energized) is switched off without executing pumpdown, the
four-way valve is de-energized 5 seconds after the compressor has been switched off, than the compressor is switched
on after the minimum time compressor off is expired and the standard prepurge procedure is executed.
5.17.2.2 Compressor stopped in heating mode
If a compressor that was stopped in heating mode (four-way valve energized) is required to start than then four-way
valve is de-energized and the compressor is switched on after the 20 sec.
5.17.3
Additional consideration
The previous procedures relay on the fact that the cooling or heating state is a property of the compressor regardless the
fact it is switched on or off. This meanings that, if a compressor is switched of in heating mode its four-way valve remains
energized (at the same manner a compressor switched off in cooling mode has the four-way valve de-energized). If the
unit power is removed the four-way valves are automatically de-energized (it is an hardware characteristic of the valves);
this meanings that also compressors switched off in heating mode goes in cooling mode. So the heating mode of each
compressor is reset if the unit power is removed.
5.18
Defrost procedure
In units configured as heat pumps running in heating mode a defrost procedure are executed. Two compressors will not
execute the defrost procedure at the same time. A compressor will not execute the defrost procedure unless an adjustable
timer (default 30 min) is expired since its startup and will not execute two defrost time before another adjustable timer
(default 30 min) is expired (if this is required a warning message are generated). The defrost procedure are based on the
measure of ambient temperature (Ta) and the suction temperature measure by the defrost sensors (Ts). When the Ts
remains below Ta by an amount greater than a value, depending from ambient temperature and coil design, for a time
longer than an adjustable (default 5 min) value the defrost will start.
The formula to evaluate needs for defrost is:
Ts < 0.7×Ta
–
T
&
Ssh < 10 °C (adjustable value)
Where
T is the adjustable coil design approach (default=12°C) and Ssh is the suction superheat.
Defrost procedure will never be executed if Ta > 7 °C (adjustable under maintenance password).
Defrost procedure will never be executed if Ts > 0 °C (adjustable under maintenance password).
During defrost the circuit are switched in “cooling mode” for an adjustable time (default 10 min) if Ta < 2 °C (adjustable
under maintenance password), otherwise the compressor are stopped and fans are kept at maximum speed f or another
adjustable time (default 15 min). Defrost procedure are stopped if evaporator outlet temperature fall below a set value or
if discharge pressure reaches a set value.
During defrost procedure “Low pressure switch alarm” and “Low suction pressure
alarm” are disabled. If the switch in “cooling mode” is required, it are executed only if the pressure difference between
compressor discharge and suction exceeds 4 bar; if this isn’t the compressor are loaded to reach such a condition. After
the switching compressor fans are switched off and a pre-purge procedure are executed (at minimum compressor load).
After prepurge the compressor are loaded energizing the loading solenoid with an adjustable number of pulse (default 3).
At the end of defrost pro
cedure executed in “cooling mode” compressor are switched off after its complete download
without execution of pumpdown; than the 4-way valve are deenergized; than the compressor are available for temperature
control system ignoring the start to start timer.
5.19
Liquid injection
Liquid injection in the discharge line is activated both in cooling/ice and heating mode if the discharge temperature exceeds
an adjustable value (default 85°C). Liquid injection in the suction line are activated, only in heating mode, if the discharge
superheat exceeds an adjustable value (default 35°C).
5.20
Heat Recovery procedure
The heat recovery procedure is available only in units configured as chillers (not available for heat pumps). The
manufacturer will select the circuits equipped with heat recovers.
5.20.1
Recovery pump
When heat recovery is activated the control will start the recovery pump (if the second pump is foreseen the pump with low
operating hours is selected, a manual pump sequencing is foreseen); within 30 s ec a recovery flow switch must close
otherwise and “Recovery Flow Alarm” will rise and the heat recovery function is disabled; the alarm is automatically reset
for three times if the evaporator flow switch closes for more than 30 seconds. Starting from t he fourth alarm it has to be
reset manually. No recovery circuit must be activated if a flow switch alarm occurs. In case of a flow switch alarm during
