Daikin WGZ030DW Installation, Operation And Maintenance Manual page 67

Figure 36: Staging in Cool and Glycol Mode
Description Occurs When:
Stage #1 ON Lvg Evap T > Evap LWT SP +
(DB/2) +
(See Notes
Below) Startup Delta T
Stage #2 ON After Stage Up Delay times out
then, LVG
Evap T > Evap LWT SP + (DB/2)
Stage #3 ON After Stage Up Delay times out,
then LVG
Evap T > Evap LWT SP + (DB/2)
Stage #4 ON After Stage Up Delay times out
then, LVG
Evap T > Evap LWT SP + (DB/2)
Stage #4 After Stage Down Delay times out
OFF then, LVG
Evap T < Evap LWT SP – (CB/2)
Stage #3 After Stage Down Delay times out
OFF then, LVG
Evap T < Evap LWT SP – (DB/2)
Stage #2 After Stage Down Delay times out
OFF then, LVG
Evap T < Evap LWT SP – (DB/2)
Stage #1 After Stage Down Delay times out
OFF then, LVG
Evap T < Evap LWT SP – (DB/2)-
StopDelta T
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 offline 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 Off
Automatic Pump Down
WGZ units are equipped with single pumpdown control. When
the last compressor running on either circuit is ready to shut
off, the liquid line solenoid valve (LLSV) is closed first and the
compressor continues to run until the pump down pressure is
reached, at which time the compressor shuts off. The shut off
pressure is set at 15 psi below the Low Evaporator pressure
Unload set point.
When the first compressor on a circuit starts, the LLSV opens
simultaneously
www.DaikinApplied.com
Manual Pump Down
When the Pump Down Switch is in the pump down position,
Action Taken
all compressors except #1 and #2 will shut off. Then the Liquid
Available compressor
Line and Hot Gas Bypass Valves will close. The operating
with least starts,
compressor will pump out the refrigerant. When the Suction
ON
Pressure is at 40 psig, the compressors will stop.
Available compressor
Chilled Water and Condenser Water Pumps
on the other circuit with
least starts, ON
The chiller MicroTech II controller can be programmed to start
Available compressor
and stop the system chilled water and condenser water pumps.
on either circuit with
They may also be controlled by the BAS or manually.
least starts, ON
Cooling Tower Control
Remaining compressor,
ON
The cooling tower fans and/or the tower bypass valve can be
controlled by the MicroTech II controller. This provides a simple
Compressor with most and direct method to control the unit's discharge pressure.
run hours, OFF
Some means of discharge pressure control must be installed if
the condenser water temperature can fall below 60°F (16°C).
Compressor on the
ICE Mode
other circuit with most
run hours, OFF
In ICE mode, the compressors stage to 100% load until the
LWT is less than the ICE LWT SP. Then Compressors #3 and
Compressor on either
circuit with most run
#4 shut down. Following that, Compressors #1 and #2 shut
hours, OFF
down after going through normal pumpdown on both circuits.
There is a programmable, start-to-start, Ice Mode Start Delay
Remaining compressor,
that limits the frequency of starts when in the ice mode. The
OFF
timer can be manually cleared to force a restart.
67
Sequence of Operation
IOM 1322-1 • WATER-COOLED SCROLL COMPRESSOR