McQuay AGS 225D, Руководство по эксплуатации

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OM AGSD-1 43
At the end of the low OAT start, the evaporator pressure is checked. If the pressure is
greater than or equal to the low evaporator pressure unload setpoint, the start is considered
successful. If the pressure is less than the unload setpoint, the start is not successful and the
compressor will stop. Three start attempts are allowed before tripping on the restart alarm,
so if on the third attempt the start is not successful the restart alarm is triggered.
Capacity Overrides – Limits of Operation
The following conditions override the automatic slide control when the chiller is in COOL
mode. These overrides keep the circuit from entering a condition in which it is not
designed to run. Any compressor running with capacity limits because of these conditions
may be considered to be at full load in the compressor staging logic.
Low Evaporator Pressure
If the evaporator pressure drops below the Low Evaporator Pressure Hold setpoint while the
compressor is running, the Low Evaporator Pressure Inhibit event is triggered. When
triggered, the compressor will not be allowed to increase in capacity.
If the evaporator pressure drops below the Low Evaporator Pressure Unload setpoint while
the compressor is running, the Low Evaporator Pressure Unload event is triggered. When
triggered, the compressor will begin reducing capacity. The maximum allowed slide target
will be adjusted down 5% every 5 seconds until the evaporator pressure rises above the Low
Evaporator Pressure-Unload setpoint.
These events are logged to an event log when they occur. Both remain active until the
evaporator pressure rises above the hold setpoint plus 2 psi or the circuit goes to a state
other than Run.
High Lift Pressure
If the compressor is running and the condenser pressure rises above the High Lift Pressure
Hold setpoint, the High Lift Pressure Inhibit event is triggered. When this happens, the
compressor will not be allowed to increase capacity. This event is active until the condenser
pressure drops 10 psi below the hold setpoint.
If the compressor is running above minimum load capacity and the condenser pressure rises
above the High Lift Pressure Unload setpoint, the High Lift Pressure Unload event is
triggered. When this happens, the compressor will begin reducing capacity. The maximum
allowed slide target will be adjusted down 5% every 5 seconds until the condenser pressure
drops below the High Condenser Pressure Unload setpoint. The compressor will not be
allowed to increase in capacity until the condenser pressure drops to 10 psi below the unload
setpoint.
Low Discharge Superheat Unload
If the circuit is running and the low pressure inhibit event is active, the compressor will
unload when the discharge superheat drops below 20 degrees. The unloading will occur by
adjusting the slide target down by 2% every 10 seconds.
Maximum LWT Pulldown Rate
The maximum rate at which the leaving water temperature can drop is limited by the
Maximum Rate setpoint, only when the LWT is less than 60
°
F. A slope unload factor is
used to reduce the slide target if the pulldown rate exceeds the Maximum Rate setpoint.
Slope Unload Factor: Maximum Rate + LWT slope
If the pulldown rate is too fast, then the slide adjustment made will be equal to the slope
unload factor.