D-EOMCP00104-14_01EN
Operating Manual
20/35
EWYD_BZ
Where:
DischTemp is the compressor discharge temperature
TOilPress is the saturated temperature at the oil pressure
5.13 Energy Saving mode
The energy saving function reduces the power consumption deactivating the compressors crankcase heater, when the
chiller is Disabled. This mode implies that the time needed to start the compressors, after an Off period, could be delayed
until a maximum of 90 minutes.
For time critical application, the energy saving function can be disabled by the user to ensure the compressor start within
1 minute from unit On command.
5.14 Pumpdown
As a compressor stop request is recorded (and if the request doesn’t originate from an alarm), before to proceed, the
compressor is fully discharged and operated for a certain amount of time with a closed expansion valve (in the case of
electronic expansion valve) or closed liquid line valve (in the case of thermostatic expansion valve).
This operation, known as “pumpdown”, is used to evacuate the evaporator avoiding that in a following restart the
compressor will such liquid.
Pumpdown procedure will end after a user defined timer is expired (adjustable, default 30 sec.) or the saturated
temperature at the evaporator pressure reaches the value of
–10°C (adjustable in the range –12
-4 °C (10.4
24.8 F) ).
After compressor stop the unloading solenoid valve are energized for a time equal to the minimum compressor off time to
assure the complete unloading also in case of non-normal stop procedure completion.
5.15 Low ambient temperature start
Units working in cooling, cooling/glycol or ice mode has to manage start -up with low outside ambient temperature.
A low OAT start is initiated if, at the compressor start up, the condenser saturated temperature is less than 15.5 °C (60 F).
Once this happens, 3 seconds after the end compressor startup procedure (end of prepurge cycles) low pressure events
are disabled for a time equal to the low OAT time (setpoint has an adjustable range from 20 to 120seconds, defaults 120
sec.).
The absolute low pressure limit (the threshold which has no time delay) is still enforced. If this limit pressure is reached a
Low Ambient Start-Up low pressure alarm is issued.
At the end of the low OAT start, the evaporator pressure is checked. If the pressure is greater than or equal to the
evaporator pressure stage down setpoint, the start is considered successful. If the pressure is less than this, the start i s
not successful and the compressor shall stop. Three start attempts are allowed before tripping on the restart alarm.
The restart counter should be reset when either a start is successful or the circuit is off on an alarm.
5.16 Economizer valve
If the option is present (expansion board 1) and enabled under manufacturer password, when the compressor’s load
percentage is greater than an adjustable threshold (default is 90%) and if the saturated condensing temperature is lesser
than an adjustable setpoint (default is 65.0°C ) the economizer valve is energized. The valve is deenergized if either the
compressor’s load percentage falls below another adjustable threshold (default is 75%) or if the saturated condensing
temperature falls below the setpoint minus an adjustable differential (default is 5.0 °C).
5.17 Switch between cooling and heating mode
Any time the switching of a compressor between cooling (or cooling/glycol or ice) and heating mode is require, either if this
is required by unit switching form one mode to other or to start defrost or to end defrost, the following procedures are
followed.
5.17.1
Switching from cooling modes to eating mode
5.17.1.1 Compressor running in cooling mode
A compressor running in cooling mode (four-way valve de-energized) is switched off without executing pumpdown, the
four-way valve is 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.
5.17.1.2 Compressor stopped in cooling mode
If a compressor that was stopped in cooling mode is required to start in heating mode it is switched on in standard cooling
mode (with four-way valve de-energized and executing the standard prepurge procedure), it is kept running for 120
seconds in cooling mode and than is switched off without pumpdown, the four-way valve is energized 5 seconds after the
compressor has been switched off, than the compressor is switched on after the minimum time compressor off is expired .
