Daikin RDT Installation And Maintenance Manual page 83

Condenser Fan Operation for Variable Speed
Compressor Option
Daikin's head pressure control operates by modulating the
motor speed of all the condenser fans in each refrigeration
circuit in response to the condenser pressure. Each refrigerant
circuit also contains a solenoid valve that blocks refrigerant
flow to the upper half of the condenser coil, which effectively
removes 50% of the condenser surface from the circuit for low
load/low ambient conditions.
This option allows for mechanical cooling operation down to 0F
(-18C). The VFD option senses refrigerant head pressure and
varies the fan speed accordingly. When the pressure rises, the
SpeedTrol increases the speed of the fans, when the pressure
falls. SpeedTrol decreases the speed of the fans.
The VFD throttling range is 250 to 400 psig, fixed, with a
corresponding fan speed range of 10Hz to 60Hz. The fan
motor is a three-phase motor, identical to the unit voltage
(208V to 460V) and is controlled by a variable frequency
drive. The variable frequency drive receives a signal from a
pressure transducer and varies the speed of the condenser
fans accordingly.
The SpeedTrol arrangement for VFD compressors is also
employing "Start-Stop control by Speed reference Level"
in which the VFD will stop the condenser fan motors under
certain conditions. If the head pressure were to fall below 250
PSIG with the condenser fans operating at minimum speed of
10Hz (possibly due to a low ambient or high wind condition)
the VFD will shut down the condenser fans. The VFD will
restart the condenser fans at 20 Hz if head pressure rises to
a level above 250 PSIG. In addition to modulating fan speed,
refrigerant solenoid valves are included in each refrigerant
circuit. Operation of the solenoid valves is based on head
pressure. If the average condensing pressure falls below 250
PSIG (83F sat) for 60 seconds, the condenser solenoid valve
closes, effectively removing 50% of the condensing surface.
If the averaging condensing pressure rises above 350 PSIG
(105F sat) for 60 seconds, the condenser solenoid valve is
opened, activating the entire condenser surface. The solenoid
valves are disabled above an outdoor ambient of 80F. The
solenoid valves are in a normally open configuration.
Refer to Figure 80 for wiring schematics of SpeedTrol.
Refer to Figure 82 and Figure 82
characteristics.
www.DaikinApplied.com
for SpeedTrol operating
Figure 82: Speedtrol Operating Characteristics (for
Variable Speed Inverter Compressor Unit)
60 Hz
10 Hz
Figure 83: Speedtrol Operating Characteristics (for
Variable Speed Inverter Compressor Unit with Start-Stop
Control)
60 Hz
20 Hz
10 Hz
83 IM 893-10 • ROOFPAK SINGLEZONE UNITS
u
250 psig 400 psig
(83°) (116°)
Condensing Pressure
Stop Start Max Speed (100%)
Speed Reference
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nIT PTIons