McQuay AGZ026BS, Инструкция по установке, эксплуатации и обслуживанию

Страница: 63 / 106

IOMM AGZ-5 AGZ 026B through 130B 63
Stage Up
For 2 compressors/circuit:
Control band = Evap Delta T x .3
For 3 compressors/circuit:
Control band = Evap Delta T x .2
IF
[LWT Error > Startup_Delt 0.5(Control band)
AND Number Comps Running = 0
AND Ice Timer Expired]
THEN Stage_Up_Now = YES
ELSE IF
[LWT Error > 0
AND Number Comps Running > 0
AND Stage Up Timer Expired]
THEN Stage_Up_Now = YES
Stage Down
IF LWT Error < 0
THEN Stage_Down_Now = YES
Leaving Water Reset
The leaving water reset input uses a 4-to-20mA signal to reset the leaving water
setpoint to a higher value. The adjustment varies linearly from 0 degrees F to 10
degrees F, with a reset of 0 for a 4mA signal and a reset of 10 for a 20mA signal.
At all times, the active leaving water setpoint is limited to a maximum of 60
°
F. The
reset remains proportional within the 10 degree band, but the setpoint will simply stop
resetting when it reaches the maximum.
Circuit Capacity Overrides – Limits of Operation
The following conditions override the automatic capacity control when the chiller is in
COOL mode or ICE mode. These overrides keep a circuit from entering a condition in
which it is not designed to run.
Low Evaporator Pressure
If a circuit is running, and the evaporator pressure drops below the Low Evaporator
Pressure-Hold setpoint, no more compressors will be allowed to start on that circuit.
This limit is active until the evaporator pressure reaches the hold setpoint plus 8 psi.
If a circuit is running with two or three compressors on, and the evaporator pressure
drops below the Low Evaporator Pressure-Unload setpoint, the circuit will begin
reducing capacity. If two compressors are running, one of the running compressors
will be stopped. If three compressors are running, then one compressor will be stopped
initially. Ten seconds later, if the pressure has not risen above the unload setpoint,
another compressor will be stopped. The last compressor on a circuit will not stop due
to the unload condition.