McQuay AGS 225D, Руководство по эксплуатации

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44 OM AGSD-1
High Water Temperature Capacity Limit
If the evaporator LWT exceeds 65
°
F, compressor slide position is limited to a maximum of
75%. Compressors unload to 75% or less if running at greater than 75% slide position when
the LWT exceeds the limit. This feature is to keep the circuit running within the capacity of
the condenser coil.
Unit Capacity Overrides
Unit capacity limits override the automatic slide control when the chiller is in COOL mode
only. The active capacity limit, as well as the estimated unit capacity, will be calculated in
the unit controller and sent to all circuits.
If the unit capacity is greater than the active capacity limit, then no circuit will increase slide
position. If the unit capacity is greater than the active limit plus 1%, the circuits will unload
until the unit capacity is less than 1% greater than the active limit.
Pumpdown
When a circuit reaches a condition where the compressor needs to shut down normally, a
pumpdown will be performed. The slide target will automatically go to 0 while pumping
down, and the compressor will run until the pumpdown pressure has been reached, or the
pumpdown time has been exceeded.
Service Pumpdown
If the option for a service pumpdown is enabled, then on the next pumpdown the pressure
setpoint will be 5 psi. The circuit will pump down to this pressure and shut off. When the
compressor has completed the service pumpdown, the setpoint is reset to no.
Slide Positioning
Slide Position Indicator
Each compressor estimates its slide load percentage from the present value of the slide
position indicator. The percentage is based on the mA signal from the slide load indicator
as shown in the following table.
Compressor Size mA at 0% Slide Indicator mA at 100% Slide Indicator
205 4.94 14.6
220 4.62 17.0
235 4.32 19.4
Load/Unload
The load output will remain on when all of the following conditions are true:
•
Compressor state is not Off
•
The slide position target = 100%
The unload output will remain on when all of the following conditions are true:
•
Compressor state is not Off
•
Slide position target = 0%
If the slide position target is more than 0% and less than 100% while compressor state is not
off, the load and unload outputs will pulse as needed. Pulses take place every 6 seconds.
Slide Upper Limit = Slide Position 3%
Slide Lower Limit = Slide Position Target – 3%
Slide Change = Slide Position – Slide Position 1 second back