Operating Manual
D-EOMCP00104-14_01EN
EWYD_BZ
19/35
Table 4 - Compressors shutdown scheme in Ice mode (3 compressors unit)
Evap Lvg Temp
Compressors status
SetP
– SDT/n < Evap Lvg Temp < SetP
All compressors allowed to run
SetP
– 2*SDT/n < Evap Lvg Temp < SetP– SDT/n
(n-1) compressors allowed to run
SetP
– 3*SDT/n < Evap Lvg Temp < SetP – 2*SDT/n (n-2) compressors allowed to run
SetP
– 4*SDT/n < Evap Lvg Temp < SetP – 3*SDT/n No compressor allowed to run
5.6 Compressors timing
Compressors operation will meet four timer requirements:
•
Minimum time between a same compressor starts (start to start timer): it is the minimum time between two starts of
the same compressor
•
Minimum time between different compressor starts: it is the minimum time between two starts of two different
compressors
•
Minimum time compressor on (start to stop timer): it is the minimum time the compressor may run; the compressor
cannot be stopped (unless an alarm occurs) if this timer is not expired
•
Minimum time compressor off (stop to start timer): it is the minimum time the compressor may be stopped; the
compressor cannot be start if this timer is not expired
The minimum time compressor off (stop to start timer) will has two different settings; one applicable to cooling,
cooling/glycol and heating mode and the other one applicable in ice mode.
5.7 Compressors protection
To protect compressor against loss of lubrication, the compressor pressure ratio is continuously c hecked; a minimum value
is set for compressor minimum and maximum load; for intermediate compressor loads a linear interpolation are executed.
The low pressure ratio alarm will occur if pressure ratio remains lower than the minimum value at rated compress or capacity
while a timer expiration.
At the startup the compressor is completely downloaded and its loading will not be enabled up to the pressure ratio exceeds
a set value (default equal to 2).
5.8 Compressors startup procedure
Before to start compressors the unloading solenoid valve is energized up to a timer is expired (default 60 sec).
At compressor startup the control will executed a series of prepurge procedure to evacuate evaporator; the prepurge
procedure will depend on the expansion valve type.
Prepurge procedure will not be executed if the evaporating pressure is below the low pressure alarm setpoint (vacuum
conditions inside the evaporator).
The compressor will not be allowed to load up to the discharge superheat exceeds a set value (default 12.2 °C, 22 F) for
a time longer than a set value (default 30 sec) .
5.9 Fan pre-starting in heating mode
When the unit is operated in heating mode, if the outside ambient temperature is lower than an fixed threshold of 10.0°C
(50.0F) before the compressor is started and the start-up procedure is initiated all fans are started with a constant delay
between each other.
5.10 Prepurge procedure with electronic expansion
At the compressor start the EEXV are completely closed up to the saturated temperature at the evaporator p ressure
reaches the value of
–10 °C (14 F) (adjustable in the range –12
-4 °C (10.4
24.8 F) ), then the valve are opened at a
fixed position (adjustable by the manufacturer with a default value equal to 20%) up to a timer is expired (default 30 sec).
5.11 Prepurge procedure with thermostatic expansion
At the compressor start the liquid line solenoid is completely closed up to the saturated temperature at the evaporator
pressure reaches the value of
–10°C (14 F) (adjustable in the range –12
-4 °C (10.4
24.8 F)), then the valve is opened
up to a timer is expired; this procedure is repeated for a number of times adjustable by the operator (default is 1 time).
5.12 Oil heating
The startup of compressors will not be allowed if the following formula is not respected:
DischTemp
– TOilPress > 5 °C
