IOM 1322 • WATER-COOLED SCROLL COMPRESSOR 98 www.DaikinApplied.com
Figure 52: Staging in Cool and Glycol Mode
Description Occurs When: Action Taken
Stage #1 ON
(See Notes
Below)
Lvg Evap T > Evap LWT SP +
(DB/2) +
Startup Delta T
Available compressor with
least starts,
ON
Stage #2 ON After Stage Up Delay times out
then, LVG
Evap T > Evap LWT SP + (DB/2)
Available compressor on
the other
circuit with least starts, ON
Stage #3 ON After Stage Up Delay times out,
then LVG
Evap T > Evap LWT SP + (DB/2)
Available compressor on
either circuit
with least starts, ON
Stage #4 ON After Stage Up Delay times out
then, LVG
Evap T > Evap LWT SP + (DB/2)
Remaining compressor,
ON
Stage #4
OFF
After Stage Down Delay times out
then, LVG
Evap T < Evap LWT SP – (CB/2)
Compressor with most run
hours, OFF
Stage #3
OFF
After Stage Down Delay times out
then, LVG
Evap T < Evap LWT SP – (DB/2)
Compressor on the other
circuit with
most run hours, OFF
Stage #2
OFF
After Stage Down Delay times out
then, LVG
Evap T < Evap LWT SP – (DB/2)
Compressor on either
circuit with most
run hours, OFF
Stage #1
OFF
After Stage Down Delay times out
then, LVG
Evap T < Evap LWT SP – (DB/2)-
StopDelta T
Remaining compressor,
OFF
NOTE: DB (Dead Band) = Evap Water Delta T x .3
Manual Compressor Disable Logic
Logic is available that allows the operator to manually enable
and disable compressors. When a compressor is disabled, it is
considered unavailable to start in the staging logic. This allows
a damaged compressor to be taken oine while the remaining
compressor can still provide some cooling
• The Compressor Disable set points are found on
Compressor Set Points screens three and four.
• A running compressor cannot be disabled until it has
been shutdown.
• If all of the compressors on a circuit are disabled, then
the circuit will be disabled.
• If both circuits have all of their compressors disabled,
then the Unit State will remain O
Automatic Pump Down
WGZ units are equipped with single pumpdown control. When
the last compressor running on either circuit is ready to shut
o, the liquid line solenoid valve (LLSV) is closed rst and the
compressor continues to run until the pump down pressure is
reached, at which time the compressor shuts o. The shut o
pressure is set at 15 psi below the Low Evaporator pressure
Unload setpoint.
When the rst compressor on a circuit starts, the LLSV opens
simultaneously
Manual Pump Down
When the Pump Down Switch is in the pump down position,
all compressors except #1 and #2 will shut o. Then the Liquid
Line and Hot Gas Bypass Valves will close. The operating
compressor will pump out the refrigerant. When the Suction
Pressure is at 40 psig, the compressors will stop.
Chilled Water and Condenser Water Pumps
The chiller MicroTech II controller can be programmed to start
and stop the system chilled water and condenser water pumps.
They may also be controlled by the BAS or manually.
Cooling Tower Control
The cooling tower fans and/or the tower bypass valve can be
controlled by the MicroTech II controller. This provides a simple
and direct method to control the unit’s discharge pressure.
Some means of discharge pressure control must be installed if
the condenser water temperature can fall below 60°F (16°C).
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